Cyclotron safety design rules

The temperature coefficient of gap magnetic field was measured as about -0.07%/0C. Such coefficient is acceptable for normal work of cyclotron.

Antokhin et al., Magnet System for PET Cyclotron Based on Permanent Magnets (2006) — p. 2

Editorial note, tabletop extrapolation: A PM cyclotron in an unheated garage will drift off resonance with the seasons: from the quoted coefficient, a 10 degC swing is a 0.7% field change - orders of magnitude larger than the stability regulated professional machines hold (the dg-027 machine held +/-2.4 parts in 10^4).

It is necessary to add a small weld bead, electrically connecting all the laminations. The core can then be grounded to a single ground point.

Tanabe, Iron Dominated Electromagnets, Lecture 8: Core Fabrication, Assembly, Installation and Alignment (2005) — p. 23

Editorial note, tabletop extrapolation: Single-point grounding of the yoke also matters on a solid-core machine carrying RF and HV nearby - one deliberate ground, no accidental loops.

IV > 150 V-Amperes or I > 30 Amps or V > 130 Volts or when the magnet stored energy is > 5 joules.

Tanabe, Iron Dominated Electromagnets, Lecture 9: Coil Fabrication, Testing and Electrical Safety (2005) — p. 12-13

Editorial note, tabletop extrapolation: The reference machine's magnet exceeds several of these thresholds, so the source's guarding rule applies: a sheet-metal or polycarbonate coil cover including the hot cooling fittings. Guarding is one layer only - protective earthing, overcurrent protection, and stored-energy discharge are separate requirements this rule does not cover.

The velocity of the cooling medium ... should be sufficiently high to guarantee a turbulent flow but low enough (u_avg <= 5 m/s) to avoid erosion and vibration. A maximum permitted temperature of less than 60 C on the coil surfaces was found to be good practice.

Zickler, Basic Design and Engineering of Normal-Conducting, Iron-Dominated Electromagnets — arXiv:1103.1119 (2010) — p. 31

Editorial note, tabletop extrapolation: Hard numbers for a home chilled-water loop as DESIGN limits, not damage cliffs: hold velocity under ~5 m/s (erosion and vibration risk grow beyond it), coil surfaces under 60 C (insulation aging accelerates with temperature), and note the arithmetic - a 30 C inlet plus 30 C rise means up to 60 C outlet water, consistent with the surface limit but tight in a hot garage: derate for your ambient.

Lbs. force on conductor = 1/1750 x kilogauss x amperes x inches length; Lbs. force between pole faces = 1/1.735 (kilogauss)^2 x (inches^2 area)

Wouters, General Recommendations for Design of Small Cyclotrons — UCRL-476 (1949) — p. 13

Editorial note, tabletop extrapolation: Directly applicable: at 5.9 kG on 50 in^2 poles that is ~1000 lb of attraction a next machine's bolts and spacers must carry.

The circulating pumps and heat exchanger are sized to handle a 1000-kw heat load, with the normal operating load being about 300 kw.

Ramler & Parker, The Argonne 60-Inch Cyclotron — ANL-5907 (1959) — p. 6

Editorial note, tabletop extrapolation: For a next machine dissipating 1-5 kW, real margin over normal load is what makes long runs boring - ANL carried about 3x; pick your own factor from duty cycle, ambient conditions and fouling allowance rather than copying the ratio.

Water hoses should be at least one meter long and use nonconducting material to prevent current leakage from the magnet. The water “in” fittings should be smaller than the water “out” fittings ... If a flow interlock (orifice plate) is used, it should be attached to the return manifold.

Tanabe, Iron Dominated Electromagnets, Lecture 9: Coil Fabrication, Testing and Electrical Safety (2005) — p. 3

Editorial note, tabletop extrapolation: The reference machine's water-cooled copper-tubing coil sits at supply potential; a meter of non-conducting hose per lead limits leakage current, and an interlock on the return detects a blocked circuit - cheap practices worth copying at home scale. They reduce specific risks; they are not shock protection as a whole, which still rests on earthing and supply-side protective devices.

The normal set-point of Klixons is about 89 C. It will generally reset at about 70 C ... One thermal interlock is installed on each water circuit ... All the interlocks on one magnet are connected in series. ... The Klixon is preferably mounted on the water return lead of the coil ... always mounted on the current carrying portion of the conductor ... mounted to a block hard-soldered to the conductor.

Tanabe, Iron Dominated Electromagnets, Lecture 9: Coil Fabrication, Testing and Electrical Safety (2005) — p. 5-7

Editorial note, tabletop extrapolation: A thermal snap-switch soldered to the coil exit tube, wired in series with the supply enable, is cheap, high-value protection against cooking a winding on a lost-water event - alongside the flow interlock (dg-202), not instead of it. Set-point and switch rating are the designer's to verify against the winding's own insulation limit.

Water resistivity higher than 0.1x10^6 Ohm m; pH-value between 6 and 6.5; dissolved oxygen below 0.1 ppm

Zickler, Basic Design and Engineering of Normal-Conducting, Iron-Dominated Electromagnets — arXiv:1103.1119 (2010) — p. 34

Editorial note, tabletop extrapolation: If a next machine uses water-cooled coils at supply potential, ordinary tap water misses all three quoted limits. A deionizing cartridge loop is the standard way to hold resistivity, but the spec is three-dimensional - oxygen and pH need their own control - and the source pairs the water spec with filters near the magnet.

The magnet coil circuit must never be broken at high currents, of course, unless adequate surge protection is provided.

Wouters, General Recommendations for Design of Small Cyclotrons — UCRL-476 (1949) — p. 5

Editorial note, tabletop extrapolation: Directly applicable: any magnet coil whose stored energy exceeds a few joules needs a dump path across the winding - freewheel diode, varistor, or resistor - rated for the coil's stored energy, peak current and clamp voltage. Without one, opening the circuit at current can arc the switchgear.

An alarm warns the operator when the coil temperature has reached a predetermined value, usually 70 to 80 C ... one to three hours are required for the temperature to reach equilibrium ... the maximum life of the magnet coil insulation, which the manufacturer estimates will vary with temperature as follows: [table: 79 C, 8-40 years; 87 C, 4-20 years; ... 130 C maximum allowable]

Livingston & Boch, The Oak Ridge 86-Inch Cyclotron — ORNL-1196, OSTI 4357145 (1952) — p. 33

Editorial note, tabletop extrapolation: Directly applicable: put a thermocouple in the next machine's winding and log it; a coil that is fine at 30 minutes can still cook at 2 hours. The 130 C figure is this manufacturer's rating for this insulation - a next machine's ceiling is its own insulation's thermal class.

All circuits connected to tank elements should have adequate choking and bypassing to prevent r.f. from reaching the meters and supply lines.

Wouters, General Recommendations for Design of Small Cyclotrons — UCRL-476 (1949) — p. 9

Editorial note, tabletop extrapolation: Directly applicable: the reference machine's beam-current, bias and gauge lines all deserve feedthrough RC/choke filtering at 9 MHz - with 'adequate' proven by measurement: an RF sniff at the meter terminals with the transmitter running.

The voltages employed on the various cyclotron components are deadly; proper precautions must be taken, even during preliminary testing ... Interlock switches on the power supply covers and grounding hooks

Wouters, General Recommendations for Design of Small Cyclotrons — UCRL-476 (1949) — p. 9

Editorial note, tabletop extrapolation: Directly applicable home-lab safety baseline for the HV systems of a next machine - covers interlocked, hooks in reach, and the full discharge discipline around them (dg-522).

Mammoflex M-1 HV cable has C of 56 pF per foot ... ~20 feet total ~0.4 Joules at 30 kV ... Removed excess cable. Run is now ~ 5 feet total

Ponter, Beam Energy Measurements with a New HV Deflection System and Ion Source Upgrades on the Rutgers 12-Inch Cyclotron (2010) — p. 43-49

Editorial note, tabletop extrapolation: For any HV feed on a next machine (deflector, source bias): keep cable runs short. Stored cable energy is delivered into an arc in the first instant, faster than any supply limiter acts - it adds to what the supply and other capacitances feed the fault, it does not replace them. Series resistance at the load (dg-286) limits the follow-on current.

We've encased the resistor in a grounded shield, and the coax shields go through 68 Ohm, 2 watt resistors ... 150 Meg HV resistor ... 5 Meg HV resistor ... inside an acrylic tube covered with copper mesh.

Ponter, Beam Energy Measurements with a New HV Deflection System and Ion Source Upgrades on the Rutgers 12-Inch Cyclotron (2010) — p. 49 (also 43, 45, 47, 48)

Editorial note, tabletop extrapolation: A staged-resistance pattern for electrostatic HV feeds (deflector, PIG source bias) whose load draws no standing current: series megohms limit arc current at the price of regulation under load, so it does not transfer to circuits that must deliver current. Even with this shielding the arcs stopped only after the cable-energy fix (dg-285) - resistors limit damage, they don't prevent flashover.

A large increase in current occurs only as the local field approaches 10^10 V per meter... After several minutes of current flow at the constant voltage, a remeasurement of the threshold voltage shows that it has increased. This phenomenon is called conditioning.

Miley & Murali, Inertial Electrostatic Confinement (IEC) Fusion: Fundamentals and Applications (2014) — p. 111-113

Editorial note, tabletop extrapolation: Bring the reference machine's dee and extraction voltages up gradually on first pump-down, watching for micro-discharge pulses. Conditioning raised the measured threshold in the source's account; the gain is not permanent capital - re-condition after venting rather than assuming the old ceiling still holds.

I also added a limiting power resistor (20 ohms at 50w) in series with 50v to the TIP102 as a precaution...with this resistor in place, a short on the 12v line will limit the current and prevent a catastrophic failure. ... I used 500v micas but slowly but surely I am changing them to 1000v specs because they are more robust.

Buckler, Solid-State, 2-Decade, 1.25 kW Linear Amplifier — Development Notebook (2015) — p. 31-32

Editorial note, tabletop extrapolation: Cheap fault-tolerance for a homebuilt RF deck, as the source built it. Check the fault arithmetic before copying: 50 V across 20 ohm is 2.5 A and 125 W, above the resistor's continuous rating, so the part rides through brief faults only - pair it with a fuse or fast shutdown rather than treating it as continuous-duty protection. Voltage-derating the filter caps matters more with the reactive load a dee presents.

safety monitoring of temperature, load failure, and diplexer HPF outputs, and ALC feedback for driver

Buckler, A Solid State 1.25 kW Linear Amplifier — QST, January 2015 (2015) — p. 1

Editorial note, tabletop extrapolation: A directional coupler with fast drive-cut on high reflected power is a strong defense when the cyclotron dee arcs or drifts off resonance mid-run - one protection among the source's set (thermal, load-failure), not a complete answer on its own.

In the 'early processing' regime, breakdown is overwhelmingly likely to increase the breakdown field of a cathode site.

Werner, Probing and Modeling Voltage Breakdown in Vacuum — Cornell dissertation (2004) — p. 91-92

Editorial note, tabletop extrapolation: Ramp the next machine's dee voltage slowly and accept the limited, current-limited micro-discharges that come with first processing - that conditioning is what raises the ceiling. Deliberately provoking arcs as 'cleaning' is a different matter: arcs can damage electrodes and insulators, and current limiting does not control the stored-energy delivery into the fault (dg-285). Let conditioning happen; do not manufacture it.

Aluminum=290 kV/inch ... We settled on a minimum radius of R=.1875 inches ... Emax=170 kV/inch

Ponter, Beam Energy Measurements with a New HV Deflection System and Ion Source Upgrades on the Rutgers 12-Inch Cyclotron (2010) — p. 8

Editorial note, tabletop extrapolation: The method transfers to 5-13 kV dees: radius all dee and stem edges and check the enhanced field with the formula. The 290 kV/in is one team's design number, not a material constant - vacuum holdoff moves with gap, finish, contamination and conditioning - so copy their margin practice (peak field well under the adopted figure), not their number.

The peripheral walls of the dees are perforated to permit high pumping speed. Graphite plates are attached to the inside of the dees ... to protect the copper from the stray proton beam.

Livingston & Boch, The Oak Ridge 86-Inch Cyclotron — ORNL-1196, OSTI 4357145 (1952) — p. 50, 7

Editorial note, tabletop extrapolation: Perforation transfers directly - pressure inside an unvented dee can sit far above gauge pressure (the dee interior is a conductance-choked volume). Graphite armor earns its place wherever stray beam dwells, at ANY energy: heating, sputtering and erosion first (dg-426's material lesson), with activation reduction joining the list at higher energies.

Cited in: The Vacuum Budget of a Cyclotron

Not recommended for positive shut-off. If bubble-tight shut-off required, the use of a Series HR Metering Valve is suggested.

Parker Hannifin, Series 20 & 30 Metering Valves (datasheet) — p. 2

Editorial note, tabletop extrapolation: Practical form for the gas panel: give the metering valve an isolation valve between it and the bottle - or specify a metering valve designed for shut-off duty, the HR-class option the sheet names. Forcing a plain tapered stem closed to seal ruins the calibrated taper and still leaks into the vacuum system.

The location of the ammeter in the circuit keeps it essentially at ground potential... CAUTION! This supply is lethal. Allow at least 2 minutes after shutdown before touching any connections. Make sure that the voltmeter reads zero. Do not omit the 10 meg bleeder resistor.

Hull, The Farnsworth/Hirsch Fusor — The Bell Jar, Vol. 6 No. 3/4 (1997) — p. 8

Editorial note, tabletop extrapolation: The ground-leg metering trick lets the builder log arc and extraction currents on the next machine without floating instruments at kilovolts - the meter still needs protection (shunt, series resistance, clamping) against fault transients. On shutdown, the source's voltmeter-zero check is the load-bearing step: the 2-minute wait is a floor that depends on the actual RC of supply and bleeder, and zero on the meter - then a shorting stick - is what proves it.

D-D fusion can occur in an IEC device at voltages as little as 10 kV or less, but detectable fusion generally does not occur until voltages are at least 15 kV

Kovalchick, Deuterium Fusion Using Inertial Electrostatic Confinement (2012) — p. 18

Editorial note, tabletop extrapolation: Calibrates expectations for any sub-threshold nuclear signal at home: being physically above a reaction threshold is not enough - the detectable onset sits well above it, and where it sits depends on geometry, gas pressure and loading, current, and the counting setup.

Cited in: Experiments by Energy Band · Shielding a Small Cyclotron

The amateur is limited to the middle or D-D reaction which yields a split 50:50 reaction D+D to T + Proton, D+D to He3 + neutron

Hull, Fusor: An Easy to Construct Fusion Reactor Based on Inertial Electrostatic Confinement (2009) — p. 19-20

Editorial note, tabletop extrapolation: The reference machine's p-B11 choice sidesteps this entirely. If deuterium ever runs in the cyclotron, D-D is the accessible fusion fuel in the source's US hobbyist-era framing - but licensing attaches by jurisdiction and by what the device produces (see /legal/), so verify locally rather than treating any fuel as license-free. The safety fact is the neutron branch: half of D-D reactions emit a 2.45 MeV neutron.

Pitting primarily in the outline of the electrode - not directly underneath or on top.

Ponter, Beam Energy Measurements with a New HV Deflection System and Ion Source Upgrades on the Rutgers 12-Inch Cyclotron (2010) — p. 45-47

Editorial note, tabletop extrapolation: When the builder opens the chamber after sparking, pit geography is the first CLUE: perimeter concentration is consistent with edge-field enhancement (fix radii - dg-353), scattered pits with contamination or particulates (clean and re-condition). A lead to follow, confirmed by whether the fix actually moves the breakdown voltage.

We coated the HV electrode with Aerodag G dry lubricant, which is also conductive and has low secondary electron emission coefficient. The RU shop machined away the top and bottom plates to gain more of a gap.

Ponter, Beam Energy Measurements with a New HV Deflection System and Ion Source Upgrades on the Rutgers 12-Inch Cyclotron (2010) — p. 50 (cited 53 is off by 3)

Editorial note, tabletop extrapolation: A cheap surface treatment to try if a deflector or dee edge hits breakdown limits near the top of its range - one element of the Rutgers fixes, and their own account credits the cable-energy fix (dg-285) and staged resistance (dg-286) with the decisive difference, so treat the coating as a contributor, not a cure.

The voltage divider allowed use of a low voltage meter by tapping the divider string at a 10,000 part fraction of the total voltage drop.

Kovalchick, Deuterium Fusion Using Inertial Electrostatic Confinement (2012) — p. 18-19

Editorial note, tabletop extrapolation: Reusable for the reference machine's DC monitoring - extraction or supply voltage - with a divider rated for the voltage and power, in a fail-safe enclosure, and calibrated. NOT for the dee: a high-resistance DC divider on an RF resonator capacitively loads and detunes it, reads wrongly, can overheat, and can put RF onto the meter. Measure dee voltage with a calibrated capacitive pickup or an RF-rated probe. [Note revised 2026-08-23: earlier note offered the DC divider for 'dee/extraction HV monitoring' without distinguishing the two.]

One might choose a 12 kV, 60 mA neon sign transformer and use 2 - 12 kV microwave oven diodes... Never apply full voltage immediately to the fusor!

Hull, The Farnsworth/Hirsch Fusor — The Bell Jar, Vol. 6 No. 3/4 (1997) — p. 5-8

Editorial note, tabletop extrapolation: A scrounger-grade current-limited architecture for source-conditioning and glow-cleaning supplies. Current limiting makes faults survivable for the hardware, not the operator - 12 kV at 60 mA is far beyond lethal, so the full HV practice set applies (grounded case, bleeder, voltmeter-zero, shorting stick; dg-522). Check diode ratings against the topology: in a center-tapped full-wave circuit each diode blocks about twice the half-winding peak - around 17 kV here - so single 12 kV parts are marginal; stack diodes in series per leg.

At voltages greater than 20 kV, the resulting x-rays can be hazardous. ... Radiation surveys of the chamber showed the presence of x-ray radiation at voltages exceeding 18 kV.

Kovalchick, Deuterium Fusion Using Inertial Electrostatic Confinement (2012) — p. 14, 25, 45

Editorial note, tabletop extrapolation: The reference machine's dee/extraction voltages sit below this line today, but HV conditioning or a higher-voltage upgrade crosses it. Monitor with an instrument that actually responds at 15-25 keV - a thin-window GM or scintillation survey meter; a standard thick-walled GM tube under-reads soft X-rays - and remember the viewport is one weak point among several (feedthroughs and thin walls count too).

Cited in: Choosing Your Machine · Shielding a Small Cyclotron

currently produces in excess of 600,000 neutrons per second which allows some low level neutron activation work of short lived isotopes. Both light neutron and x-ray shielding are needed beyond this level and the planned fusor V will incorporate these upgrades.

Hull, Fusor: An Easy to Construct Fusion Reactor Based on Inertial Electrostatic Confinement (2009) — p. 39

Editorial note, tabletop extrapolation: One experienced builder's numeric line for when a home device graduates from monitored to shielded - specific to his output, geometry and occupancy, not a universal threshold: dose scales with distance, time and moderation, so a measured survey decides the actual case. p-B11 alpha work produces no comparable neutron source term.

Cited in: Shielding a Small Cyclotron

mainly fast neutrons are generated, and the permissible flux is 30-60 neutrons/cm2 s

Smirnov, The Cyclotron and Its Modeling — Phys. Part. Nuclei 52 (2021) — p. 16

Editorial note, tabletop extrapolation: At <=1 MeV protons the reference machine is below every (p,n) threshold - not only the common structural metals but the light targets too: 7Li 1.88 MeV, 9Be 2.06 MeV, 11B 3.02 MeV, and even deuterium 3.34 MeV (NNDC QCalc, retrieved 2026-08-23) - so these neutron numbers do not set its shielding scale. They start to as soon as the machine accelerates deuterons, because D-D and Be(d,n) are exoenergetic with no threshold at all (dg-1047), or pushes protons past ~1.9 MeV on lithium; dg-1041 and dg-1047 carry the residual channels that keep a neutron survey honest below that. Read this as a scale for the case that applies, not as a clearance for the case that does not. [Corrected 2026-08-22: previously said neutron shielding is "a non-issue" for the machine; the exception clause was there, but the headline was an absolute.] [Corrected 2026-08-23: the exception clause itself was imprecise - it said the neutron channels "open far lower" for Li, Be, B or a deuterated material, but every one of those (p,n) thresholds is above 1 MeV as well; the genuinely thresholdless route is deuterons, per dg-1047. Raised by an upstream review of the source dataset.]

a criterion for the product of electric field E and potential V for a cyclotron deflector in order to avoid electric discharges: VE < 1.5 104 (kV)2/cm. The maximum sustainable voltage in a magnetic field is 20-30% lower.

Botman & Hagedoorn, Extraction from Cyclotrons — CAS, CERN 96-02 (1996) — p. 14

Editorial note, tabletop extrapolation: A 3-5 kV, 5-10 kV/cm tabletop deflector sits orders of magnitude below this bulk-discharge criterion - so at tabletop scale the practical ceiling comes from feedthrough, surface and edge-radius engineering (dg-353, dg-297, dg-295), not from the Smith-Grunder product.

At HV edges, electric field lines become so dense that breakdown becomes a major concern. Aluminum=290 kV/inch ... We settled on a minimum radius of R=.1875 inches ... Emax=170 kV/inch

Ponter, Beam Energy Measurements with a New HV Deflection System and Ion Source Upgrades on the Rutgers 12-Inch Cyclotron (2010) — p. 8

Editorial note, tabletop extrapolation: Direct amateur precedent: a 1 T / 472 keV university tabletop deflector ran at 28-32 kV. A lower-energy machine needs proportionally less deflector voltage (scaling roughly with beam energy at similar geometry - a 150 keV-class machine perhaps a third, not a tenth), and the edge-field formula stays the design check: generous radii reduce peak field, they do not make sparking impossible - finish and conditioning still rule (dg-295, dg-353).

Mammoflex M-1 HV cable has C of 56 pF per foot ... ~0.1 Joules at 30 kV ... ~0.4 Joules at 30 kV ... The bottom plate and deflector electrode - no pitting on the electrode noticed.

Ponter, Beam Energy Measurements with a New HV Deflection System and Ion Source Upgrades on the Rutgers 12-Inch Cyclotron (2010) — p. 43 (stored energy; repeated 45, 49) and 44 (pitting)

Editorial note, tabletop extrapolation: Editorial note, tabletop extrapolation: Rutgers' slide sequence recounts arcing a feedthrough run above its class and rebuilding with the feedthrough inside vacuum plus a corona adapter. The specific numbers, page-image verified 2026-09-06: cable stored energies ~0.1 J (5 ft) and ~0.4 J (20 ft) at 30 kV via 56 pF/ft Mammoflex M-1, and a feedthrough 'rated for 30 kV (we want to run it at 35)' - the overrun plan is the cautionary half of the lesson. Choose feedthrough rating from the manufacturer's figure, the vacuum-side geometry and test history, and never run a feedthrough above its rating. [Note revised 2026-08-23: 'rate 2-3x over operating voltage' was an invented margin.]

A density of 200 pounds per cubic foot was obtained with a 28 day crushing strength of 3,000 pounds per square inch and a water content of 10 percent. ... All removable shielding blocks were stacked in two vertical layers to that no straight-through cracks remained.

Creutz, Design and Construction of Synchro-Cyclotron — NYO-780 (1950) — p. PDF 43 (printed p. 38), Section VIII - SHIELDING

Editorial note, tabletop extrapolation: Transferable - stagger any shielding blocks on a next machine (concrete, water, borated PE) so seams never line up with the beam plane.

Cited in: Shielding a Small Cyclotron

they cannot be opened without turning off the cyclotron oscillator or reducing the magnetic field from its resonance value.

Creutz, Design and Construction of Synchro-Cyclotron — NYO-780 (1950) — p. 44

Editorial note, tabletop extrapolation: Directly applicable: interlocking RF-enable to the enclosure door is the cheap, classic scheme. Prefer the oscillator-off condition as the gate - an off-resonance field reduces acceleration but leaves RF and high voltage energized, so field detuning alone is not a conservative personnel interlock.

Cited in: Shielding a Small Cyclotron

All the adapters on the coil terminals are water cooled and supplied with thermal switches to protect the coil terminals from overheating.

Creutz, Design and Construction of Synchro-Cyclotron — NYO-780 (1950) — p. 56

Editorial note, tabletop extrapolation: Directly applicable - thermal cutouts on a next machine's coil terminals/lugs (and dee stem cooling) are cheap insurance against a loose-joint meltdown.

The valves are automatically operated by compressed air cylinders and are controlled by vacuum gauges so that they will close when a leak occurs which the pump is not able to handle.

Creutz, Design and Construction of Synchro-Cyclotron — NYO-780 (1950) — p. 58

Editorial note, tabletop extrapolation: Directly applicable: an interlocked isolation valve (even a spring-loaded solenoid gate) protects a next machine's diff or turbo pump from a chamber let-up - with closure speed and actuation chosen for the pump being protected.

the inner face, or back, is made of 1/2 in steel ... this house serves as a magnetic shield for the oscillator tube. A crude replica (1/16 size) was tested by the magnetic measurements group ... using the 1/16-scale 184-inch model magnet, and this shielding was found sufficiently effective, the field being cut from 140 Gauss to less than 20 Gauss. This is further reduced at the 9C21 elements by means of a 1/2 in steel sleeve slipped over the cooling jacket. The magnetic force on the oscillator box amounts however to 450 lbs.

MacKenzie et al., Design of the Radio-Frequency System for the 184-inch Cyclotron — UCRL-64 (1948) — p. 20

Editorial note, tabletop extrapolation: LDMOS amplifiers, fans and ferrite-cored parts near a 0.59 T magnet want a steel housing - and the source's method is the transferable part: they verified the shielding on a scale model before committing, and budgeted the large attractive force on the box. Measure the fringe field at the amplifier location and check the housing's effect; do not assume a thickness.

Provision was made for arbitrary amplitude modulation by inserting an 893 triode in series with the power supply lead. As yet it has not been used for this purpose, but as it has a 20 kw plate dissipation, it has been used as an emission limiting device to protect the oscillator tubes when discharges occur in the tank and condenser.

MacKenzie & Waithman, R.F. System for Frequency Modulated Cyclotron — MDDC-1045 (1946) — p. 12

Editorial note, tabletop extrapolation: The principle transfers: fast current limiting or foldback in the LDMOS drain supply, plus a VSWR trip, is the modern form. It reduces fault energy; it is not immunity - reflected-power overvoltage and drain transients are separate failure paths needing their own protection (dg-338).

a high intensity point (21 mr/hr) on the top outside edge of the copper foil holder, another high intensity point (18.5 mr/hr) on the foil just above the median plane

Reyenga, 184″ Cyclotron: Radiation Measurement of Breech Load Probe Head — MDDC-982 (1947) — p. 3

Editorial note, tabletop extrapolation: At nA currents and sub-MeV energies on ordinary holder metals, residual activation of the hardware is small where it occurs at all (thresholdless capture and deuteron operation excepted - the standard scoping). The lesson transfers regardless: check holder edges and apertures for beam strike with film, phosphor, or discoloration, because a large fraction of the beam can miss the target.

Cited in: Shielding a Small Cyclotron

a sharp peak of radioactivity was found on the dee lip at the 82-inch radius, which gave additional evidence that the beam was spreading vertically in this region.

Sewell, Henrich & Vale, Some Operating Phenomena Associated with the 184-inch Cyclotron — MDDC-1092 (1947) — p. 3

Editorial note, tabletop extrapolation: At tabletop energies activation of ordinary structural metals (copper, steel, aluminium) is small and short-lived where it occurs at all - thresholdless (p,gamma) capture and any deuteron operation are the exceptions - so a survey of the dee lip may well find nothing; a cheap wipe survey costs little and settles it. The localization logic transfers regardless: line the dee aperture with removable witness strips (paper, phosphor, anodized Al) and read burn or discoloration marks to find the loss radius. A bombarded target is a separate question and is surveyed on its own terms (dg-1041). [Corrected 2026-08-22: previously 'No activation at tabletop energies', an absolute the site's own safety pages contradict.]

Cited in: Shielding a Small Cyclotron

protected by an interlocked air-cooling system, spark gaps at both ends of the half-wave transmission lines leading to the dee stems, and by an rf-dc fault circuit

Heusinkveld et al., Studies with a Three-Dee Three-Phase Proton Cyclotron — UCRL-3187 (1955) — p. 11

Editorial note, tabletop extrapolation: The rf-dc comparison is the tube-era ancestor of modern output-detect foldback and ports to the LDMOS upgrade: DC applied but no RF developing means something is wrong - an arc, a detune, or a failed stage - so kill drive and investigate. Spark gaps at the feedthroughs remain cheap insurance.

In order to provide an adequate margin for day-to-day operation, a design value of 1.5 X 10^4 should be used.

Smith & Grunder, Electrical Design of Electrostatic Deflectors for Sector-Focused Cyclotrons — UCRL-10654 (1963) — p. 33

Editorial note, tabletop extrapolation: The most quotable deflector design number in the collection: design to VE = 1.5e4 (kV)^2/cm and treat the tested 2.25e4 as commissioning margin - as the source machine practiced. Transfer it as a starting point under the usual conditions (electrode material, finish, conditioning - dg-353, dg-295), and verify on the actual electrodes.

it stores only 2-1/2 joules and, at most, this is distributed among 1200 diodes. ... There is so little energy in a spark from this rectifier that it will not puncture even a piece of 5-mil aluminum foil.

Smith, Deflector Power Supply for Sector-Focused Cyclotrons — UCRL-10655 (1963) — p. 28

Editorial note, tabletop extrapolation: The governing philosophy for a next machine's deflector supply: limit the energy delivered per spark rather than trying to prevent sparks - low stored energy is an equipment-survival property, and a sub-joule store at 50-100 kV is achievable. It is not a personnel-safety property: such a supply remains dangerous to people, and in human contact the supply's follow-on current adds to the stored energy. Personnel protection stays with enclosure, interlocks, grounding and discharge practice (dg-522, dg-654).

typically, it takes a few microseconds ... The recycling time is 1 sec. ... the power supply can be turned off before a spark becomes visible.

Smith, Deflector Power Supply for Sector-Focused Cyclotrons — UCRL-10655 (1963) — p. PDF 28 carries the quoted sentence; the two performance figures are on PDF 19

Editorial note, tabletop extrapolation: The feature to replicate in a modern build: fast drive-kill on spark detection with an operator-adjustable threshold, used deliberately during bake-in (UCRL-10654's practice). A solid-state inverter's gate shutdown gives the fast drive-kill - but killing drive is not a crowbar: energy already stored in the output stack and cable still feeds the spark (dg-285), so pair gate-kill with a dump path or series resistance rated for that stored energy.

the switch must pass a peak current of 5000 amperes per transformer ... 8 in parallel on each transformer or 16 in all and introducing a very small inductance in each plate lead to make the tubes share the load

Kerns et al., High Voltage Pulser for 184-inch Cyclotron Electric Deflector — UCRL-95 (1948) — p. PDF p.13 (printed p.-10-)

Editorial note, tabletop extrapolation: The derating discipline - waveform-specific stress, not catalog rating - transfers to every switching element an amateur uses: MOSFET/IGBT avalanche and dV/dt limits in a Marx or inverter play exactly the role the 5C22's reversal limit played here.

We have not attempted to obtain particle beams for the cases discussed here as we do not plan to accelerate protons until the shielding vault is completed.

Jungerman, Kibbe & Peek, Central Region Studies for Incorporating an Axial Ion Source in the Davis 76-in. Cyclotron — UCD-CNL-49 (1966) — p. 7

Editorial note, tabletop extrapolation: Directly relevant to the plan's shielding gate: species choice is a radiological control. Commissioning on H2+ at the same B*rho halves the total kinetic energy and quarters the per-nucleon energy versus protons - same tuning fields, gentler consequences - and the proton program waits until the vault or survey case is ready. Davis's sequencing is the model; the record itself says only that they deferred protons until shielding was complete.

Cited in: Shielding a Small Cyclotron

They permit, however, the backing of all three diffusion pumps by a combination of any two of the booster pumps, should any one of the booster or mechanical backing pumps become inoperative.

Foss et al., Cyclotron Component Design Technical Reports — TID-454 (1952) — p. 140-142

Editorial note, tabletop extrapolation: Scales down to one gauge and two relays: a foreline-pressure interlock that kills the diff-pump heater and an over-temperature switch on its casing are the two automatics that protect an unattended amateur system's pump and oil - necessary automatics, not a complete unattended-operation case. Setpoints come from the pump's own tolerable forepressure, not the source's 50/160 microns.

Cited in: The Vacuum Budget of a Cyclotron

a careful choice of materials of construction, for example, using as much aluminum as possible and very little stainless steel, should reduce the radiation problem significantly.

Boom, Toth & Zucker, Residual Radiation of the LRL 184-inch Cyclotron — ORNL-3158 (1961) — p. 18

Editorial note, tabletop extrapolation: ENERGY SCOPE: a 730-MeV machine's recommendation. At the reference machine's sub-MeV proton operation the spallation and (p,xn) channels behind it are closed, so bulk structural activation does not drive material choice at that scale - with the standing exceptions: thresholdless capture on some nuclides, light-element targets, and any deuteron operation. The drawing-board principle bites the moment a machine crosses into open-channel territory.

Cited in: Shielding a Small Cyclotron

Aluminum yields no long-lived activities, while Co58 is produced from copper ... Stainless steel produces two long-lived isotopes, Co58 and Mn54, while only Mn54 is induced in iron.

Boom, Toth & Zucker, Residual Radiation of the LRL 184-inch Cyclotron — ORNL-3158 (1961) — p. 18

Editorial note, tabletop extrapolation: ENERGY SCOPE: nuclide-by-material bookkeeping from 730-MeV spallation; these channels are closed at sub-MeV proton energy. The durable pattern is inventory-follows-alloy-content (Ni -> Co58, Cr -> Cr51) - worth knowing when reading other labs' surveys. The report's list is what their instruments saw, not an exhaustive table: modern data adds Be-7 and Na-22 from high-energy aluminum, so treat any such inventory as survey-specific.

Cited in: Shielding a Small Cyclotron

foils of aluminum, copper, iron, and stainless steel were affixed at various positions on the walls of the cyclotron vault and on the cyclotron vacuum tank.

Boom, Toth & Zucker, Residual Radiation of the LRL 184-inch Cyclotron — ORNL-3158 (1961) — p. 15

Editorial note, tabletop extrapolation: The one activation rule that applies at any energy, because it is a measurement, not a prediction: a witness-foil pack plus the next machine's NaI/PIPS counters is a near-zero-cost check. Read a null correctly - it bounds what those foils, positions, counting and cooling times could detect; strong practical evidence, not proof that nothing anywhere activated. Useful for licensing conversations and for catching surprises if beam or species ever changes.

Cited in: Shielding a Small Cyclotron

the ratio of Cu64 activity in the cadmium-wrapped sample (due only to fast particles) to that in the uncovered foil was ~1/1.6.

Boom, Toth & Zucker, Residual Radiation of the LRL 184-inch Cyclotron — ORNL-3158 (1961) — p. 15

Editorial note, tabletop extrapolation: ENERGY SCOPE: relevant only when neutrons exist to be moderated. The Cd-difference technique splits capture activation into below- and above-cutoff parts APPROXIMATELY - epithermal response and the wrapper's spectrum perturbation blur the split, which is why practice reports cadmium ratios rather than clean fractions. Keep it in the toolkit for any future neutron-producing experiment; meaningless for pure sub-MeV proton running.

To reduce the radiation by an order of magnitude one needs only 2 cm of lead - an amount that can readily be made into a portable shield. Shadow shields of 6 cm of lead would reduce even the 100 r/hr radiation field to a quite tolerable 100 mr/hr. The same radiation has a half-thickness of 4 cm for concrete.

Boom, Toth & Zucker, Residual Radiation of the LRL 184-inch Cyclotron — ORNL-3158 (1961) — p. 18

Editorial note, tabletop extrapolation: ENERGY SCOPE: a sub-MeV machine on ordinary structural materials produces no comparable residual gamma fields (light-element targets, thresholdless capture and deuteron operation are the exceptions - see the safety pages). The transferable part is the sizing discipline: identify the actual photon energy first, then buy attenuation in half-thickness units - the same arithmetic sizes the lead around a NaI detector against room background. Note the report's own arithmetic: even 6 cm of lead leaves 100 mr/hr from a 100 r/hr field - reduced is not zero.

Cited in: Shielding a Small Cyclotron

the important source of radiation in the cyclotron comes from the gap and the structures in it, rather than from neutron-induced activities in the magnet yoke.

Boom, Toth & Zucker, Residual Radiation of the LRL 184-inch Cyclotron — ORNL-3158 (1961) — p. 12

Editorial note, tabletop extrapolation: An energy-APPROPRIATE technique: a lead collimator with a removable plug around a next machine's NaI turns it into a pointing instrument for X-ray leak hunting (RF multipactor sites, dee-liner discharge bremsstrahlung) on a running machine. Choose wall thickness for the photon energies in play - soft dee X-rays need little lead; harder sources need more, plus attention to fluorescence and off-axis penetration. The aimed-vs-plugged comparison is the transferable discipline.

Cited in: Shielding a Small Cyclotron

use of a reliable radiation meter in the cyclotron near the targets ... takes much of the guesswork out of the question "How long should the target cool?"

McWalters et al., Radiation Exposures of Personnel at the 60-inch Cyclotron — UCRL-8276 (1958) — p. 16

Editorial note, tabletop extrapolation: ENERGY SCOPE: Crocker's 10-24 MeV/nucleon beams at tens of uA made 100-500 r/hr targets; a sub-MeV proton machine on ordinary targets produces no comparable residual source term (light-element targets and deuteron operation are the exceptions). The instrument discipline transfers exactly: a logged dose-rate channel at the machine - an instrument whose response covers soft X-rays (dg-559) - gives prompt X-ray dose during RF conditioning and a defensible record alongside the beam-current log.

The average time required for setting up a target is usually about 3 minutes ... removing the target assembly from the cyclotron is about 1 minute. The assembly is then dismantled, which takes less than a minute.

McWalters et al., Radiation Exposures of Personnel at the 60-inch Cyclotron — UCRL-8276 (1958) — p. task-time and shield figures on PDF p. 7 (report's opening page); exposure figures on PDF p. 16 as cited

Editorial note, tabletop extrapolation: The practice - rehearse any hands-on task near a radiation hazard until it is quick and sure, and put a bench shield where hot items are worked - is the cheapest safety hardware there is, because dose = rate x time. Do not transfer speed to electrical work: HV and RF tasks are controlled by de-energizing, verifying zero and lockout (dg-522), where hurrying adds risk rather than removing it.

Cited in: Shielding a Small Cyclotron

Finger films show that the hands receive about ten times as much exposure as the body for target operations; i.e., setting up and dismantling.

McWalters et al., Radiation Exposures of Personnel at the 60-inch Cyclotron — UCRL-8276 (1958) — p. 16

Editorial note, tabletop extrapolation: ENERGY SCOPE: measured on multi-MeV activated targets. The geometry lesson transfers: the hands work closest to the source, where rates are highest (inverse-square for a compact source, and higher still in contact geometry, where the simple 1/r^2 picture breaks down) - so tongs that add inches and a ring dosimeter are the response if the machine ever handles activated or tritiated items. For energized circuits the analogue is distance by design - insulated tools and clearances - not speed (dg-871).

Cited in: Shielding a Small Cyclotron

They are run only on Friday evenings and Saturday, and - if demands are high - on Sundays. For these bombardments a longer cooling time is required. A nominal time of 25 to 30 minutes is set

McWalters et al., Radiation Exposures of Personnel at the 60-inch Cyclotron — UCRL-8276 (1958) — p. 10

Editorial note, tabletop extrapolation: ENERGY SCOPE: Crocker's figures are (d,n) activation at tens of uA and ~20 MeV. Sub-MeV deuterons still make neutrons - D(d,n)3He and 9Be(d,n) are exothermic - so the analogue exists the day deuterium enters the machine (dg-121, dg-545). The scheduling pattern transfers either way: batch the nastiest operations (HV conditioning, any future deuteron or neutron work) into planned windows with a defined stand-down, rather than interleaving them with routine bench time.

Targets and their assemblies normally emit about 100 to 500 r/hr 5 minutes after bombardment ... The intensity of radiation by the exit strip averages about 10,000 r/hr, and the deflector about 500 r/hr.

McWalters et al., Radiation Exposures of Personnel at the 60-inch Cyclotron — UCRL-8276 (1958) — p. internal-target and external-target figures on PDF p. 10 as cited; deflector/exit-strip figures on PDF p. 15 (section 'Maintenance')

Editorial note, tabletop extrapolation: ENERGY SCOPE: these are 10-24 MeV activation levels. The design ordering survives: whatever intercepts full beam (probe tip, Faraday cup, target holder) concentrates the consequences. On a sub-MeV machine that is heat and sputtering today - and activation joins the list via thresholdless capture on some materials, light-element targets, or any deuteron operation, growing first at these same components if energy climbs.

Cited in: Shielding a Small Cyclotron

we have designed the shielding so that the limits for general population are observed in the regularly inhabited work areas adjoining the accelerator and experiment rooms.

Oak Ridge National Laboratory, A Proposal for the Mc² Isochronous Cyclotron — ORNL-3540 (1963) — p. 186

Editorial note, tabletop extrapolation: Directly transferable posture for a residential-basement machine: the family upstairs is 'general population', so design to the CURRENT public limit at occupied locations - in the US today 1 mSv (0.1 rem) per year, fifty times below occupational and five times stricter than the source's era ratio - and take the numbers from the jurisdiction's own regulations (/legal/), not from a 1965 report.

Cited in: Shielding a Small Cyclotron

The extreme radioactivity induced in type 304 stainless steel makes its use undesirable, the use of an aluminum alloy is now being investigated.

Howard (ed.), Electromagnetic Research Division Semiannual, period ending 20 March 1953 — ORNL-1531 (1953) — p. 18

Editorial note, tabletop extrapolation: At sub-MeV energies on ordinary structural metals activation is small where it occurs at all - thresholdless capture and deuteron operation are the exceptions - and the selection logic transfers whole: thermal adequacy is not the whole selection. Prefer aluminum or graphite for probes, septa and slits anywhere protons above a few MeV are contemplated, and let the licensing story inherit the same reasoning.

Cited in: Shielding a Small Cyclotron

a beryllium target is bombarded with protons, approximately 1 neutron for 50 protons is obtained.

Howard (ed.), Electromagnetic Research Division Semiannual, period ending 20 March 1953 — ORNL-1531 (1953) — p. 17

Editorial note, tabletop extrapolation: SCALE-SCOPED - this 2% yield is a ~20-MeV number; at the reference machine's and a next machine's energies (0.15-5 MeV) p-Be yields are orders of magnitude lower. Useful as the upper anchor when building the shielding/licensing dose model for any future MeV-class educational machine.

Being mostly below ground level, the room will be easy to shield. Placing the room at the basement floor level will make it convenient to transfer heavy equipment.

Howard (ed.), Electronuclear Research Division Semiannual, period ending 20 March 1955 — ORNL-1884 (1955) — p. 21

Editorial note, tabletop extrapolation: Directly relevant to the facility question for any MeV-class educational machine: below-grade siting was the study's shielding strategy, and siting beside existing utilities and controls was a cost line they weighed as seriously as the magnet. Earth shields in the directions it actually covers, by its actual thickness, density and moisture - it does not blanket-replace engineered shielding, and the uncovered directions, the roof, and every penetration still get the full design treatment (see the shielding deep dive).

Cited in: Choosing Your Machine · Shielding a Small Cyclotron

A considerable amount of undesirable radiation will be produced by that part of the beam intercepted by the slit system. ... it is also desirable that the analyzer image distance be large, in order to reduce the angular spread of the beam at the image point. ... [placing the condenser farther from] the cyclotron port ... required larger condenser pole pieces in order to accommodate the horizontally spreading beam.

Bromley & Bruner, The Design of a Focusing and Analyzing System for the 27-inch Cyclotron Beam — NYO-3823 (1954) — p. 5

Editorial note, tabletop extrapolation: DIRECT and cheap to honor at layout time, nearly impossible later: treat every defining aperture as a place where beam power - and therefore radiation - concentrates. At 150-170 keV the intercepted beam makes mostly heat plus thick-target bremsstrahlung whose X-ray yield climbs steeply with voltage, so the slit belongs with the shielded, surveyed components, wherever the survey ranks it that day.

Cited in: Shielding a Small Cyclotron

The dee voltage must be at least twice the d.c. plate voltage. 2. The oscillator must be stable enough to sustain an arc drawn from the dee face (simulating discharges in that region). ... 4. The phasing capacity, as calculated in MacKenzie's report ..., should be as near [the calculated value] as possible.

Anderson, Half-Scale Model Tests on the Three Quarter Wave R.F. System — UCRL-31 (1947) — p. 12

Editorial note, tabletop extrapolation: The requirement transfers as a criterion, not a procedure: the planned LDMOS amplifier must demonstrably survive dee-side arcs before it is trusted in vacuum, where conditioning sparks are guaranteed. For solid-state that means proving the protection chain - VSWR trip, drain clamping, fast drive-cut (dg-338, dg-679) - against controlled fault tests, not drawing an open arc onto an unprotected amplifier the way the 1947 tube crews could.

Secondary radiations produced as a result of the interaction of the primary beam with a target, portion of the accelerator, or the shielding most often determine the type and magnitude of the shielding.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 22

Editorial note, tabletop extrapolation: For the reference machine and a next machine the primary protons stay inside the chamber in normal operation, so the external radiation field is dominated by secondaries - dee-gap electron bremsstrahlung today; reaction products (the 11B(p,alpha) alphas) and any (p,n)-capable contaminants joining the inventory at a next machine's energies.

The bremsstrahlung is approximately inversally proportional to the M2 where M is the mass of the incident particle. It is therefore usually insignificant for heavy particles.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 30

Editorial note, tabletop extrapolation: Supports the program's standing model that dee-voltage electrons, not the proton beam's own bremsstrahlung, dominate the X-ray hazard on a sub-MeV proton cyclotron. Dominant is not sole: characteristic X-rays and any nuclear gammas from targets keep their own lines in the survey plan.

This radiation is soft and the shielding problem small. It is however important to be remindful of its existance and importance even at low energies of the incident particle. Instruments must be able to detect and measure this soft radiation.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 30

Editorial note, tabletop extrapolation: The reference machine's survey problem in one sentence: a ~10 kV dee makes sub-10-keV photons that ordinary GM/ion-chamber walls partly block — pancake/thin-window instruments are required to even see the hazard (pairs with the Ch. VI 150-keV response rule).

If we assume that the ion current "I" results in a reverse directed electron current of magnitude 0.2*I that is accelerated through 1/3 the terminal voltage we would usually get a very considerable x-ray production.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 31

Editorial note, tabletop extrapolation: Use this only as the lesson that stray-electron X-rays exist wherever there is RF voltage and vacuum, never as a ceiling. For a next machine's hazard analysis, plan around at least the peak-to-peak dee voltage as the electron impact energy - a planning floor, not a physical ceiling, since multi-transit RF processes can exceed single-gap figures - and let the measured X-ray endpoint from the survey be the authority the analysis answers to.

The % of the electron energy that is converted to X-rays upon complete stopping of the electrons ... 0.5 ... 0.265 ... 0.59 ... 1.34 ... 4.77 ... 6.21

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 23

Editorial note, tabletop extrapolation: Sets the scaling logic - conversion efficiency rises with Z and with energy - even though the table starts at 0.5 MeV. At dee-voltage energies the Z-trend persists in direction, but the table's factors do not extrapolate cleanly (characteristic lines and backscatter enter), so the design instinct is what transfers: land stray electrons on LOW-Z surfaces (aluminum, graphite) rather than tungsten or steel, and let the survey measure the actual benefit.

At very low electron energy (few keV), the intrinsic angular distribution is the same as from a radio-antenna, i.e., the intensity is greatest perpendicular to the direction of the electron beam.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 23

Editorial note, tabletop extrapolation: For dee-gap electrons, the INTRINSIC few-keV emission peaks sideways to the electron path - a reason to survey all around the chamber midplane and its windows rather than along any assumed axis. What actually leaks where folds in scattering, multiple electron directions, self-absorption and wall attenuation - so the survey pattern, not the dipole formula, is the finding.

Because of the Coulomb barrier, proton cross sections for nuclear interaction are negligible below about 0.1 MeV. In light nuclei there are some exceptions which are of little interest here.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 48

Editorial note, tabletop extrapolation: Closes the neutron question for the reference machine at ~150 keV-class energies EXCEPT via the light-nuclei exceptions the chapter waves off - and the exceptions differ in kind: the deliberate 11B(p,alpha) target yields charged alphas and gammas, not neutrons directly (the indirect path to check is secondary (alpha,n) on nearby low-Z materials); deuterium contamination is the direct neutron path, D(d,n) being thresholdless (see Ch. IV rule).

For light and low-intermediate nuclei, (p,n) thresholds are of the order of an MeV. Neutron emission becomes the dominant reaction when the incident particle energy exceeds the threshold by about 1 MeV.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 48

Editorial note, tabletop extrapolation: The threshold-audit pattern for every machine energy bump: list materials the beam can strike, look up (p,n) thresholds, and confirm E_beam sits below them. At 170 keV (a next machine) every (p,n) channel on stable nuclei is closed by >600 keV of margin; the audit must be redone if energy ever approaches ~1.9 MeV (7Li(p,n) threshold 1.88 MeV).

H2(gamma,n)H1 ... 2.23 ... C12(gamma,n)C11 ... 18.7 ... O16(gamma,n)O15 ... 16.3

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 47

Editorial note, tabletop extrapolation: At the reference machine's photon energies (keV-class bremsstrahlung) every channel in the table is closed. Two honesty caveats for reuse in hazard analyses: 9Be sits below the deuterium trap (S_n = 1.665 MeV, IAEA NDS/AME, retrieved 2026-08-25), so beryllium joins heavy water on the audit list wherever multi-MeV photons exist; and reaction gammas can exceed the projectile energy - 11B(p,gamma) capture emits ~16 MeV photons at small cross-section, so a p-B11 machine's analysis must bound that two-step channel rather than declare photonuclear reactions impossible.

Two of these reactions, the D(d,n)He3 reaction and the T(d,n)He4 reaction are exoenergetic and can be initiated at very low energies. Thus these two reactions can be produced in small Cockcroft-Walton accelerators.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 78

Editorial note, tabletop extrapolation: THE loophole in the 'sub-MeV machines make no neutrons' argument: natural hydrogen is ~150 ppm deuterium and D accumulates in beam-loaded surfaces, so a D-on-D source term exists in principle on any hydrogen machine - at yields the Coulomb barrier suppresses steeply at low energy, which is why the honest posture is a survey requirement, not alarm.

In the slowing down process ... an insignificant amount of induced activity is produced as compared with the activity produced by thermal neutrons. Therefore the thermal cross section should be used for purposes of calculating the activity produced.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 78

Editorial note, tabletop extrapolation: The correct FIRST bookkeeping if a neutron-capable operation is ever run: inventory surrounding materials against thermal flux (Cu 3.9 b, W 34 b, Au 96 b thermal, per Table IV-2). Capture is the floor of the inventory, not its ceiling - epithermal resonances and fast threshold reactions ((n,p), (n,alpha), (n,2n)) can dominate for some materials and spectra. On today's neutron-free machines there is nothing to activate either way.

Only Na24 and perhaps K42 could present any kind of hazard. Because of the half-lives of these two isotopes, a shut down of three to five days will allow decay to very low levels.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 84

Editorial note, tabletop extrapolation: Cooldown-scheduling logic for any future neutron-producing work, as the report's era assessed its concrete: modern assessments add impurity-driven products (Mn-56, Co-60, Eu-152/154, tritium and others) whose relevance depends on the actual aggregate and spectrum, so a real facility characterizes its own concrete rather than inheriting this list. For the current machines the practical point stands: with no neutron source term there is nothing to activate the basement structure - deuteron operation being the standing exception.

If large quantities of this isotope build up, it will be necessary to physically remove the activated shielding, so plans for this contingency should be made in the design of the walls.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 84

Editorial note, tabletop extrapolation: Scope closed for the machine's photon energies - photoproduction needs multi-MeV photons far beyond any dee. The design principle transfers as prudence rather than prohibition: prefer enclosure designs that could be dismantled selectively (block walls, the sacrificial inner course of dg-1050) over monoliths - cheap to choose now, expensive to regret.

The effective dose called the "Dose Equivalent" in units of rem is given by DE=D*QF*DF.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 110

Editorial note, tabletop extrapolation: The structure survives (modern practice uses operational quantities and wR), applied only where the instrument actually reads absorbed dose: a calibrated rem/Sv survey meter already reports a weighted operational quantity, and re-weighting it double-counts. Log what each instrument reports, record WHICH quantity that is, and weight only raw rad/gray readings before comparison to limits.

QF = 0.8 + 0.16 LET where LET is in keV/u.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 110

Editorial note, tabletop extrapolation: A window into how weighting works, not a generator of modern factors: current practice assigns wR by radiation type (alphas: 20) and the Q(L) relation differs from this 1972 line. The 11B(p,alpha) reaction shares ~8.7 MeV across a broad three-alpha spectrum - not fixed 1.7 MeV lines - and alpha weighting today is simply wR = 20. Flag anywhere it appears as the 1972 formulation of what is now wR.

X-rays, gamma rays, electrons or positrons 1 ... Neutrons, Energy < 10 KeV 3 ... Neutrons, Energy > 10 KeV 10 ... Protons 1 - 10 ... Alpha particles 1 - 20

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 111

Editorial note, tabletop extrapolation: HISTORICAL VALUES - cite for provenance, apply ICRP-103 wR in analysis (photons 1, neutrons 2.5-20 by energy, alphas 20). Where endpoints agree (photon 1, alpha 20) the numerical conclusions survive - re-derive under modern operational quantities all the same (dg-1052's instrument-quantity discipline).

2.5 x 10-8 (thermal) 2 680 ... 5 x 10-1 11 27 ... 1 11 19

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 112

Editorial note, tabletop extrapolation: The conversion pattern for any future neutron survey, used with its conditions: a reading converts only when the energy is known or the instrument already folds the spectrum in (a rem-meter does), and these are 1972 occupational numbers - modern public limits sit far lower. The design fact survives: fast neutrons near 0.5-1 MeV are the most restrictive per unit flux, which is why a D-D contamination field matters at even a few n/cm2-s.

When the whole body is exposed to relatively non-penetrating radiation it may be assumed that the skin is the "critical organ" ... When the whole body is exposed to penetrating radiation the blood-forming tissue is assumed to be the critical organ ... background radiation varies considerably over the earth (approximately 50-175 mrad/year with isolated areas over 1000 mrad/year)

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. PDF 116 (printed 107) for the skin / blood-forming-tissue pairing; PDF 115 (printed 106) for the natural-background range

Editorial note, tabletop extrapolation: Directly relevant to sub-10-keV dee bremsstrahlung, which deposits mostly in shallow tissue: the shallow/skin dose is usually the governing quantity for the machine's leakage fields - established by measurement, not assumption, since photons near 10 keV do reach past the epidermis - which is why survey instruments must be thin-window (Ch. VI) and why whole-body numbers alone can understate the field.

shall not exceed 5 rems multiplied by the number of years beyond 18. The dose in per calendar quarter shall not exceed 3 rems.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 116

Editorial note, tabletop extrapolation: CAUTION — HISTORICAL NUMBERS, superseded by 10 CFR 20 / NCRP 116 (5 rem/yr occupational, 100 mrem/yr public, age-proration abolished). Keep for reading-era context and for the still-valid design pattern: public-tier limits ~10-50x below occupational drive product-machine enclosure design, since customers are "general population."

Cyclotron positive ions 50-200 usec ... Microstructure at RF frequencies

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 123

Editorial note, tabletop extrapolation: The reference machine runs CW-RF but a beam bunched at 9 MHz; any future pulsed-RF operation (LDMOS duty-cycling) puts the machine squarely in this table — recheck every survey instrument's pulse response before trusting it.

the second term in the equation above becomes zero and the number of counts per second, as is expected, becomes the radiation source pulse rate.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 134

Editorial note, tabletop extrapolation: THE classic accelerator-survey trap, and the reason the program's survey doctrine prefers current-mode ion chambers over GM counters for any pulsed operation: a counter reading 60 cps at a 60 Hz pulse rate is reporting its saturation value, not a dose rate. The saturation reading appears when the field is strong; a weak pulsed field reads below the pulse rate, so equality with the pulse rate is the alarm signature.

An approximation to the dose equivalent in a mixed neutron and gamma ray field can then be given by DE = Gamma + 1ON ... 10 = a conservative value for the quality factor

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 127

Editorial note, tabletop extrapolation: The cheapest credible mixed-field method for an amateur program - two chambers and a subtraction - and the fallback if a rem-ball is out of budget for future neutron-capable tests. Two updates travel with it: modern wR for D-D neutrons is ~16-20, so the manual's 10 is no longer conservative - plan with 20; and the subtraction is only as good as each chamber's known gamma and neutron response, so calibration is part of the method, not an extra.

They obtained an accuracy of +-10% in measuring dose equivalent of neutrons over the range 0.04 to 10 MeV.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 127

Editorial note, tabletop extrapolation: Justifies planning on one moderated rem meter as the primary neutron instrument for a D-D-class source term (2.45 MeV sits mid-band). Its band is not everything: moderated and scattered fields extend below 40 keV where response rolls off, so corners and maze mouths get checked against the instrument's stated energy response - and the calibration must be current.

The ICRU has recommended a quality factor of 2 for neutrons between thermal and 10 KeV. This then rises to a peak of about 11 near 500 KeV before falling back to about 6 between 10 and 20 MeV.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 131

Editorial note, tabletop extrapolation: Amateur-scale neutron concerns CENTER on the worst band: D-D neutrons are born at 2.45 MeV and moderate down through the keV-MeV weighting peak, so never average a survey away with a thermal-flux conversion. Modern wR moves the peak to ~20 near 1 MeV - the reasoning got MORE conservative, not less - while fully moderated thermal populations still get their own, lower weight.

At energies below about 150 KeV the principal interaction mechanism is the photoelectric effect. ... In a cavity ionization chamber the relative response falls off at low energies because of the effect of the thickness of the walls. Just above this energy the relative response can rise above unity because the effective atomic number of the walls exceeds that of air.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. PDF 130 (printed 121)

Editorial note, tabletop extrapolation: The measurement-side half of the reference machine's X-ray problem: the machine's photon spectrum ends at the dee voltage - tens of keV at most - squarely inside the misbehavior region, so an uncalibrated chamber reading of dee bremsstrahlung can err in either direction. Use thin-window instruments with a low-energy calibration point (dg-559, dg-1035).

Commercial mu metal shields, if properly used, will normally provide sufficient shielding against magnetic fields. To eliminate the effects of RF fields, aluminum foil or screening can be used.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 128

Editorial note, tabletop extrapolation: Written for exactly such a bench: a scintillator PMT near a 0.6 T magnet's fringe field and a 9 MHz (soon LDMOS) transmitter. 'Properly used' is load-bearing - mu-metal saturates in strong fields and PMT gain moves at millitesla - so position the PMT where the fringe field is already small, shield, and verify gain with a check source in place; confirm RF quieting with the transmitter actually running. The Keithley 617 grounding lore in the reference machine's as-builts is this rule independently rediscovered.

The most common cause of serious radiation exposures associated with accelerators, has been accidental (and sometimes intentional) entrance into the normally shielded target cell.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 144

Editorial note, tabletop extrapolation: The product-machine posture in one line: an educational cyclotron IS the 'small shielded box with an interlocked lid' (Ch. I's phrase). Lid switch + beam-off interlock + machine-on light is the historically identified starting set for this machine class - not a sufficiency proof: fail-safe wiring (opening kills beam; no automatic restart on re-closing), periodic interlock function tests, and the access and bypass rules (dg-654, dg-1074) complete the design.

Naturally no "line of sight" path for radiation would be permitted yet it is also necessary that the scatter path through the maze be considered.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 145

Editorial note, tabletop extrapolation: The audit rule for every feedthrough, window and joint in an enclosure: check sight-lines from the X-ray source point (the dee gap) outward, then bound the one-bounce leakage with the albedo rules (dg-1068). Geometry creates the streaming problem; material still sets what each bounce and wall costs, so both enter the estimate.

it should never be convenient for an operator or an experimentor to remake an open interlock without someone actually going to the position of the break and, if the hazard no longer exists, reestablishing the interlock.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 149

Editorial note, tabletop extrapolation: Design requirement for the product controller: a tripped lid/door input must latch and require a local (at-the-lid) action plus console reset — a firmware-only "clear fault" button recreates the exact failure mode this rule exists to prevent.

only heavy duty industrial type limit switches should be employed, avoiding light duty switches to insure durability and reliability.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 149

Editorial note, tabletop extrapolation: BOM-level guidance for product machines — safety-rated (positive-opening) limit switches on lids/doors, not PCB microswitches, plus an interlock-test line item in the ops checklist (Cyclotron_procedures2 already has the pattern for vacuum; extend to safety chain).

Teflon 5 x 104 ... Phenolic, Glass laminate >1 x 1010 ... Aluminum Oxide 1 x 1012

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 151

Editorial note, tabletop extrapolation: Counterintuitive and worth flagging in the next machine's design notes: PTFE, the amateur's default HV insulator, is the most radiation-fragile common insulator on the table - by four decades against phenolic-glass. At the reference machine's current operation insulators see no significant dose in the first place; the flag matters wherever a future neutron- or target-adjacent position exists - specify ceramic or glass-laminate there, per the table.

a fail-safe design may typically use a complete path or presence of a signal to permit accelerator operation and an open circuit or loss of signal to disable operation.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 152

Editorial note, tabletop extrapolation: The normally-energized interlock-loop architecture: a series loop holding the RF/HV enable relay closed puts breaks, unplugs and power loss on the safe side. One loop is the architecture, not the whole chain - channels that must be independent stay independent (dg-1074), the loop gets exercised periodically (dg-1110), and any trip thresholds (a beam-current ceiling included) come from the machine's own hazard analysis.

For interlocks, however, the loss of operating time must be preferred to the loss of safety.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 153

Editorial note, tabletop extrapolation: Two concrete requirements: (1) an FMEA-style enumeration of interlock failure modes with each shown to land safe; (2) latched annunciation: the controller must remember a mid-run lid opening even if reclosed, until deliberately reset.

This system uses a dual input which prevents the single key from disabling an interlock which affects personnel safety without the additional input provided by the Radiation Safety Officer's key.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 153

Editorial note, tabletop extrapolation: What the two keys buy is INDEPENDENT CUSTODY of the bypass itself: no single person can disable a personnel-safety interlock alone. Restoration is a separate control - the written restore-verification the manual calls for. A school machine can reproduce both (instructor key distinct from the operator credential; signed restore checklist before the next class). A one-person home lab cannot reproduce the independence: a logged bypass record preserves the paper trail, not the custody - which is the argument for designing so bypasses are rarely needed at all.

A person overlooked during the search before lockup must be able to positively defeat the beam instead of ineffectively shutting down some unassociated apparatus.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 153

Editorial note, tabletop extrapolation: In-enclosure e-stop requirement for any walk-in product installation; even for benchtop machines the classroom master kill must cut the actual hazard (RF+HV+source), not merely the controller, and the no-blame-for-pressing norm belongs in the curriculum.

After completion of the lockup procedure the person who has performed the survey should have seen every position capable of hiding a man.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 153

Editorial note, tabletop extrapolation: Trivially satisfied on a benchtop machine, but a REAL checklist line for any walk-in enclosure a customer institution builds (dg-1065's accident mechanism is the reason); it belongs in the product installation manual's commissioning procedure.

Colors of lights should represent constant situations. ... Confusion with meanings of various audible alarms can be avoided by routine test alarms at programmed times. Too frequent tests, however, may do more harm than good (cry wolf).

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 154

Editorial note, tabletop extrapolation: The product HMI spec seed — a "machine on" beacon distinct from "RF enabled", consistent across every unit shipped, with an alarm-test entry in the curriculum's first lab.

Doors should be designed to provide shielding at least equivalent to the adjoining walls ... Travel of these large doors is necessarily slow but the momentum is great ... one must be able to open these doors even after a loss of power. Some manual method of opening the door from inside and outside must be included in the design.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. PDF 145 (printed 136)

Editorial note, tabletop extrapolation: Scale-invariant egress principle: even an interlocked benchtop lid or a walk-in enclosure door must never imprison anyone on power loss. The criterion is manual operability from both sides without power, verified by actually trying it - whatever the mechanism - and the door's own motion is a machinery hazard (pinch points, momentum) to engineer alongside its radiological job.

Human safety should not be entrusted to one or more persons following a written routine. ... Even mechanized systems become routine after a time and hence may lose their effectiveness.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 155

Editorial note, tabletop extrapolation: The strongest possible source endorsement for the program's hardware-interlock- over-procedure stance (procedures complement, never replace, the interlock chain), plus a curriculum idea: occasionally rotate the interlock test scenario so student operators never go through the motions.

The recorded cases in which potentially lethal doses of radiation have been received have all involved highly experienced personnel. This accents the need for continuous education programs.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 17

Editorial note, tabletop extrapolation: Aimed straight at a two-person family lab and at teacher-operators: familiarity is the documented risk factor, and the visitor/helper (the "maintenance worker") is the documented victim class — brief every guest, and rehearse the rules even after years of clean operation.

There can be no substitute for the vigilance of personnel. Automatic devices, interlocks and remote area monitoring systems are essential but insufficient to do the job without personnel training.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 17

Editorial note, tabletop extrapolation: The counterweight to over-trusting the product machines' interlock chains — the curriculum's radiation-safety module is a safety SYSTEM component, not documentation overhead.

if proper safeguards are incorporated into the construction of the accelerator facility the cost of safety will be significantly lower then if such safeguards are superimposed upon already existing facilities.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 17

Editorial note, tabletop extrapolation: Why a hazard analysis belongs at desk phase rather than after first beam: the enclosure, interlocks and monitoring get designed into the machine rather than left to whoever installs it.

Cited in: Choosing Your Machine

The oxygen from the air condensed in the liquid nitrogen, radiolyzed to ozone and left in concentrated form after the evaporation of the nitrogen presents a significant explosion hazard.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 19

Editorial note, tabletop extrapolation: Directly applicable to any LN2 cold trap on the diff-pump line if machine energies ever rise - and worth a procedures line now: a trap that has sat in a radiation-plus-discharge environment gets attended warm-up and venting, because the quoted mechanism concentrates oxidizer exactly at boil-dry. (An editorial precaution drawn from the quoted physics.)

it may be necessary for the operations staff to act as the health physics staff as well. Though less then ideal, this condition will frequently be a "way of life". Under these conditions it is of paramount importance to define responsibilities and priorities.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 19

Editorial note, tabletop extrapolation: A 1972 acknowledgement, with conditions, of the small-facility reality in which one person wears both the operator and radiation-safety hats. The conditions transfer to any teaching installation - the documentation names the RSO-equivalent role and its decision rights - and the arrangement itself must clear the jurisdiction's requirements: registered machines commonly require a named, qualified RSO (/legal/), which written role definitions support but do not replace.

indicate a confident Xray value of 13.8 +- 0.7 molecules of O3/100 e.v. in the radiolysis of oxygen. This value is used here.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 177

Editorial note, tabletop extrapolation: At the reference machine's beam powers the radiolytic term is negligible against the model's other terms - but the same production-vs-exhaust balance covers corona and discharge ozone from the HV and RF systems in a closed basement. Odor (threshold ~0.01-0.05 ppm) tells you ozone exists, not how much, and olfactory fatigue silences it during exposure - so the control is ventilation sized by the model or a measurement, with the era's 0.1 ppm occupational figure replaced by the jurisdiction's current limit.

noted an approximate "half-life" for the ozone in their measurements at Rensselaer and Yale of 35 minutes.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 178

Editorial note, tabletop extrapolation: Practical basement rule of thumb: after an RF/HV session with ozone smell, a ventilated half-hour is one measured half-life - which only halves an unknown starting concentration. The checklist entry is therefore 'ventilate, wait, then confirm by fresh-nose absence of odor at re-entry' - surfaces, humidity and any continued production move the real decay rate, in either direction.

Serious changes in the pressure differential on the up and down stream sides indicate that the filter has either clogged or ruptured.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 176

Editorial note, tabletop extrapolation: The delta-P-as-health-monitor pattern transfers to every filtered exhaust in the lab (pump exhaust filters, fume paths for boron sputtering later): instrument the pressure drop, not the filter's appearance. Delta-P sees gross changes - clog rising, rupture falling - while pinholes and seal bypasses can pass it silently, so where a release would actually matter, periodic sampling still closes the loop.

The threshold for (gamma,n) reactions are of sufficient magnitude to make the production of 13N and 15O of concern only to electron accelerators of energies in excess of 15-20 MeV.

Martin (ed.), Accelerator Radiation Protection — AD-755510 / USA-NLABS-TR-73-7, US Army Natick Laboratories (1972) — p. 176

Editorial note, tabletop extrapolation: Scopes air activation out of every current and planned program machine - all far below even the 10.6 MeV threshold - so the air-handling design concentrates on ozone (dg-1085). When a reviewer asks, cite the actual thresholds alongside the manual's concern line rather than conflating them.

stopping the beam at r < 10 in. radius in graphite targets. This avoids neutron production and induced cyclotron radioactivity

Rainwater et al., The Columbia University Nevis Synchrocyclotron Major Modification — NEVIS-189 / R-774 / CU-295 (1971) — p. 5

Editorial note, tabletop extrapolation: The staging discipline transfers to every machine even where activation does not: low-duty, small-radius-first commissioning also protects septa, collectors, and instruments. Stage one's activation-safety is species- and energy-specific, not automatic - deuterons on carbon make neutrons above ~0.33 MeV via 12C(d,n), and D-on-D in any deuterium-loaded surface is thresholdless - so re-establish the claim whenever species or energy changes.

with all workers averaging below 100 mrad/week, and most below 25 mrad/week for the 10 weeks of this activity

Rainwater et al., The Columbia University Nevis Synchrocyclotron Major Modification — NEVIS-189 / R-774 / CU-295 (1971) — p. 4

Editorial note, tabletop extrapolation: Dose scale is irrelevant to a 150 keV proton machine, but the pattern — cooling time, planned sequence, measured-not-assumed exposure — is the template for any future activated-hardware work and for the plan's licensing narrative.

We expect to use marble pole liners where possible, as in the past, to reduce sector iron, etc., activation

Rainwater et al., The Columbia University Nevis Synchrocyclotron Major Modification — NEVIS-189 / R-774 / CU-295 (1971) — p. 6

Editorial note, tabletop extrapolation: A higher-energy note, with a scale-free idea inside: CHOOSE what lost beam hits. At any scale that choice already governs sputter contamination and outgassing; it becomes activation-relevant the moment a machine crosses into neutron or few-MeV territory - with thresholdless capture the standing exception to 'negligible below a few MeV'.

each wire will have its own thermocouple to sense any rise in the cooling water temperature which will shut off the current in the channel

Rainwater et al., The Columbia University Nevis Synchrocyclotron Major Modification — NEVIS-189 / R-774 / CU-295 (1971) — p. 13

Editorial note, tabletop extrapolation: Per-element thermal interlocks scale down perfectly - the RF amplifier dummy load, water-cooled dee stubs, any powered septum - and match the fail-safe doctrine (dg-1110). A coolant-temperature sensor only responds after heat reaches the water: pair it with a flow interlock (dg-202's return-orifice practice) so loss of flow trips the supply without waiting for temperature to say so.

Since the underground beam stop is aimed away from the experimental areas, this greatly eases shielding, and subsequent background problems

Rainwater et al., The Columbia University Nevis Synchrocyclotron Major Modification — NEVIS-189 / R-774 / CU-295 (1971) — p. 3

Editorial note, tabletop extrapolation: Direction-dependence of secondary radiation is universal even though the 550-MeV numbers are not: orient any future target station and Faraday-cup dump so the forward cone points at mass, not people. The specific takeoff angles and bend counts are per-facility physics rather than constants - lay out first, then let the survey confirm the geometry did what was expected.

all support insulators have been designed so that they can be removed and replaced by remote handling tools.

Rainwater et al., The Columbia University Nevis Synchrocyclotron Major Modification — NEVIS-189 / R-774 / CU-295 (1971) — p. 12

Editorial note, tabletop extrapolation: At tabletop energies the driver is vacuum hygiene and downtime rather than dose, but the same design habit — most-likely-to-fail parts (insulators, filaments, septa) replaceable without major disassembly — is what the reference machine's filament-change experience already argues for.

The trend seems to be toward more elaborate systems which utilize solid state devices, fail-safe circuitry and self-checking circuits.

Ohnesorge & Butler, Recent Trends in Particle Accelerator Radiation Safety — CONF-741040-6, Oak Ridge National Laboratory (1974) — p. 2

Editorial note, tabletop extrapolation: Directly actionable for the next machine and the tiny controls spec: an amateur interlock chain (door, HV, RF-enable, radiation monitor) should be fail-safe and self-testing. Those properties come from the circuit design, not the device family - solid-state parts can fail shorted - so the design proves de-energize-to-safe behavior and exercises each channel periodically. What was state of practice in 1974 is trivially cheap in 2026.

techniques of dealing with problems such as relay races, sneak grounds and power-supply crossties

Ohnesorge & Butler, Recent Trends in Particle Accelerator Radiation Safety — CONF-741040-6, Oak Ridge National Laboratory (1974) — p. 2

Editorial note, tabletop extrapolation: Fully transferable and cheap: a deliberate review pass asking 'what unintended path can energize the HV or open the shutter' on the interlock schematic - a shared ground defeating an enable line is exactly the class it hunts. One pass finds sneak paths on paper; it does not validate the built system, so it complements, never replaces, fail-safe design and periodic function tests (dg-1110, dg-1065).

There is often a safety officer appointed. Many installations have safety review committees.

Ohnesorge & Butler, Recent Trends in Particle Accelerator Radiation Safety — CONF-741040-6, Oak Ridge National Laboratory (1974) — p. 3

Editorial note, tabletop extrapolation: For a one-person program the transfer is external review - the archive's cross-review protocol is exactly this committee function. For the planned educational-accelerator business, whether a named safety officer and a written program are REQUIRED is the jurisdiction's call (/legal/); the survey records the practice, and the practice is worth adopting either way.

the As Low As Practicable philosophy can be adopted and put into practice only where there is a firm commitment by management to do so

Ohnesorge & Butler, Recent Trends in Particle Accelerator Radiation Safety — CONF-741040-6, Oak Ridge National Laboratory (1974) — p. 3

Editorial note, tabletop extrapolation: The governing philosophy any licensing narrative must speak fluently - in its modern wording (ALARA), since the terms are not interchangeable in a regulatory context. For the home program it means shielding and interlock decisions justified as 'as low as reasonably achievable', not 'under the limit'.

Besides the neutron beam cone from the probe there was found to be a general spray of neutrons due to the deuteron beam grazing the interior of the dee.

Moyer, Hildebrand, Knable, Parmley & York, Character of the Radiation Field and Shielding at the 184-Inch Cyclotron — AECD-2149, UC Radiation Laboratory (1947) — p. 2

Editorial note, tabletop extrapolation: Wherever beam is lost - dee edges, septum, probe stalk, chamber wall - is a candidate source, and a survey plan that only looks downstream of the target can miss most of the emission solid angle. Moyer's spray was found by surveying: that is the lesson.

Measurements with a BF3 proportional counter have indicated diffusion of slow neutrons through various access openings from the enclosure.

Moyer, Hildebrand, Knable, Parmley & York, Character of the Radiation Field and Shielding at the 184-Inch Cyclotron — AECD-2149, UC Radiation Laboratory (1947) — p. 2

Editorial note, tabletop extrapolation: Cable ways, viewport lines-of-sight and door gaps are where slow-neutron leakage concentrates ONCE the bulk shield is adequate - penetrations dominate when the walls no longer do, which is the regime a designed enclosure should be in. Thermal-neutron instruments answer a different question than fast-neutron ones; both belong in a survey.

With an ionization reading of 24 r/hr in the center of the neutron beam cone 1 foot outside the tank wall (9 3/4 feet from the probe), the ionization just outside the shielding in the center of the beam is 10 mr/hr, while the general building areas are 0.5 to 1.5 mr/hr. These quoted measurements are made with Al-walled ionization chambers, and correspond to a deuteron beam of about 0.2 x 10-6 amp.

Moyer, Hildebrand, Knable, Parmley & York, Character of the Radiation Field and Shielding at the 184-Inch Cyclotron — AECD-2149, UC Radiation Laboratory (1947) — p. 2

Editorial note, tabletop extrapolation: A survey number without the simultaneous beam current is unusable later: log dose rate, location, instrument, and Faraday-cup current as one record so the map rescales when beam current grows - and re-survey when anything besides current changes (energy, species, tune, loss pattern), because those break the linear rescale.

This may happen before the operator can determine the sensor causing the fault condition. Therefore, a device was needed which could detect and store the location of a large number of possible faults.

Cyclotron Staff, Report of Cyclotron Operation 1 July – 31 December 1969 — NRL Memorandum Report 2103, Naval Research Laboratory (1970) — p. 22

Editorial note, tabletop extrapolation: Any interlock chain needs fault capture - latching relays, or a logged timestamp per sensor; per-sensor timestamps also give first-out ORDERING, which turns a cascade of consequential trips back into its primary cause. Without capture, intermittent faults (thermal, flow, vacuum burps) become undiagnosable ghosts that waste sessions.

One is assigned as priority faults, errors which must be corrected to continue cyclotron operation ... The other is non-priority faults, such as the failure of a mechanical vacuum pump which may be bypassed and operation continued.

Cyclotron Staff, Report of Cyclotron Operation 1 July – 31 December 1969 — NRL Memorandum Report 2103, Naval Research Laboratory (1970) — p. 22

Editorial note, tabletop extrapolation: Hard-wire the chains whose failure is immediately hazardous - radiation monitors, HV enclosure, cooling on powered elements, vacuum-envelope and arc faults, as the machine's own hazard analysis identifies them - so they cannot be acknowledged away, and give genuinely operational faults a bypassable alarm that stays displayed until fixed. The design insight survives: a system where every fault stops the machine trains its operator to defeat interlocks. The tier assignment comes from the hazard analysis, never from a fixed list.

A large portion of the 220Rn gas is created as positive ions which are attracted by the -300 volt collecting potential

Thomas & Karasek (eds.), Proceedings of the Fourth Annual Conference of the Nuclear Target Development Society — ANL/PHY/MSD-76-1, Argonne National Laboratory (1975) — p. 61

Editorial note, tabletop extrapolation: The physics is elegant - the 2.7 MeV spread between the 212Pb lines self-calibrates a spectrometer with no external standard - and the procedure is not an amateur recipe: an open 228Th container means thoron gas, plated-out daughters and removable contamination, and possessing 228Th in usable quantity is licensed activity in most jurisdictions (/legal/). For the program's spectrometer calibration the appropriate form of this idea is a commercial sealed or electroplated check source.

sparks will occur, destroying the parting film and the thin isotope layer by hairline cracks.

Thomas & Karasek (eds.), Proceedings of the Fourth Annual Conference of the Nuclear Target Development Society — ANL/PHY/MSD-76-1, Argonne National Laboratory (1975) — p. 235

Editorial note, tabletop extrapolation: Grounding topology inside the evaporator is part of the recipe - and the same charging physics will bite any deposition or beam system with floating fixtures near keV electrons: bond fixtures deliberately rather than assuming they find ground.

The cleaning process is of utmost importance ... The substrate must first be cleaned with a mild abrasive powder ... The water is removed with Ethyl Alcohol and while still wet with alcohol is immediately placed in the evaporator and pumping started.

Thomas & Karasek (eds.), Proceedings of the Fourth Annual Conference of the Nuclear Target Development Society — ANL/PHY/MSD-76-1, Argonne National Laboratory (1975) — p. PDF p.257 (printed p.240); the pre-warm step and the colour chart are on PDF p.258 (printed p.241)

Editorial note, tabletop extrapolation: Template for any compound that dissociates or splashes: pelletize the charge, chimney the boat, pre-warm the substrate with the source itself - and treat any color-temperature chart as a coarse process indicator only (color-to-temperature conversion is unreliable; a thermocouple wins when the number matters). Valve off the diffusion pump so compound vapor does not load the pump oil.

Iron forms a carbide if a graphite boat is used (Heagney & Heagney, "Reduction Techniques for Isotopic Materials")

Fifth Annual Conference of the International Nuclear Target Development Society — LA-6850-C, Los Alamos Scientific Laboratory (1977) — p. 98

Editorial note, tabletop extrapolation: The route from purchased oxide powder to rollable or evaporable target metal - consult the per-element table before buying any element as oxide. A hot hydrogen furnace is its own hazard class: inert purge before and after H2, flow and flame management, and per-element vapor and hydride toxicity are prerequisites the table assumes rather than teaches; the report's apparatus description is the checklist seed, not the whole checklist.

the reaction with mercury oxide runs into an explosion (Friebel et al., "Preparation of Isotopically Enriched Mercury Targets")

Fifth Annual Conference of the International Nuclear Target Development Society — LA-6850-C, Los Alamos Scientific Laboratory (1977) — p. 127

Editorial note, tabletop extrapolation: Strongest is not best in metallothermic reduction: a controllable reaction that completes in minutes beats a violent one that contaminates the product. Mercury adds its own layer - at these temperatures Hg is mobile, toxic vapor, so the paper's sealed-retort integrity, condensation path and exhaust handling are part of the method, and mercury work sits behind fume containment at any scale.

survived a bombardment of Au ions of an energy of up to 15 MeV/u and intensities of up to 1 uA, rotating with 1333 rpm ... exposed to the full beam intensity while the disc-driving motor was already switched off ... producing zones of molten Au

International Nuclear Target Development Society Workshop — ANL/PHY-84-2, Argonne National Laboratory (1983) — p. PDF p.47 = printed p.38 (Folger, Sec. 3.3 'Improved Rotating Target-Disc for Fragmentation-Reaction Experiments')

Editorial note, tabletop extrapolation: Folger's before/during/after SEM sequence is the reference picture of beam kill on a metal foil. Any moving-target scheme needs a rotation-OK permissive in the beam interlock chain: a stalled wheel concentrates the whole designed-for-distributed load on one spot.

automatically turned on when the oscillator power is on and there is no dee voltage, but which is automatically turned off as soon as dee voltage appears.

Fulbright, The Sparker, a Device to Overcome the Multipactor Difficulty in Starting the Oscillator of a Cyclotron — NYO-9359, University of Rochester (1961) — p. 3

Editorial note, tabletop extrapolation: DIRECT automation pattern: gate the starter on (RF enabled) AND (dee pickup below threshold) - a dee voltage pickup is standard monitoring hardware, and where one exists it is exactly the signal needed. The same gate makes stalls detectable: a starter that keeps refiring means the machine is not coming up, so alarm on repeated firings, with the rate threshold chosen at the machine.

It was concluded from these tests that the force on the Alpha tanks tending to push them out of the gaps lies somewhere between 9.71 and 4.53 tons.

Wakerling & Guthrie (eds.), Magnets and Magnetic Measuring Techniques — TID-5215, Radiation Laboratory, University of California (1949) — p. force bracket on PDF 190 (printed p. 180) as cited; the quoted 2.5-in. creep sentence is on PDF 189 (printed p. 179)

Editorial note, tabletop extrapolation: Anything ferromagnetic sitting in or near the gap on nominal-symmetry grounds - chamber, probe carriages, shim plates, tools - needs positive mechanical retention: the destabilizing force is smallest at the symmetric position and grows as the part displaces, which is exactly when it is hardest to stop.

It is designed so as to take maximum advantage of naturally occurring shielding of a small ravine.

The University of Washington 60-Inch Cyclotron: Progress and Status Report of Design and Construction — AECU-1951, University of Washington (1951) — p. 5

Editorial note, tabletop extrapolation: The siting lesson transfers even if the scale does not: cheap mass - earth berms, water, basement corners - is legitimate shielding MATERIAL for a D-D-capable machine, once treated as engineering rather than slogan: effectiveness depends on composition, thickness, geometry and the capture gammas that moderation produces (hydrogenous media slow neutrons well, then emit 2.2 MeV capture photons), so earth and water get designed and surveyed like any shield (see the shielding deep dive). Spec detail: PDF p.128.

Aluminum was chosen over stainless steel because of its short half-life property.

The University of Washington 60-Inch Cyclotron: Progress and Status Report of Design and Construction — AECU-1951, University of Washington (1951) — p. 46

Editorial note, tabletop extrapolation: DIRECT for any machine that will make neutrons: aluminum's dominant activation products are short-lived compared with stainless steel's cobalt-trace Co-60 (years) - the report's reasoning - though aluminum is not activation-proof: fast neutrons make 24Na (15 h) and alloying elements add their own products, so 'short half-life' is comparative, never absolute. Choose the beam-facing metal for the machine you hope it becomes; TIG-welded aluminum is proven UHV-adequate practice from 1951.

Cited in: Cyclotron Vacuum Chamber Design and Sealing

the plate is operated at d-c ground potential so that no insulation is required in the water lines.

The University of Washington 60-Inch Cyclotron: Progress and Status Report of Design and Construction — AECU-1951, University of Washington (1951) — p. 85

Editorial note, tabletop extrapolation: Solid-state amps moot the HV plumbing, but two doctrines survive: pick the grounding scheme that minimizes what the coolant circuit must insulate - DC-grounding the plate removed the DC insulation requirement, while RF potentials, leakage control and water quality stay on the checklist - and use source impedance (here transformer reactance) as passive inrush protection where a component's own rating allows it.

On the basis of cost it was decided to omit this refinement.

The University of Washington 60-Inch Cyclotron: Progress and Status Report of Design and Construction — AECU-1951, University of Washington (1951) — p. 90

Editorial note, tabletop extrapolation: The decision pattern - name the deleted protection, name what stands in for it, keep a commissioning-only resistor in the drawer - is reusable as an engineered, recorded risk acceptance, not a license: verify the stand-ins actually bound the fault energy for YOUR stored energy and clearing time (a 6-cycle breaker passes ~0.1 s of fault current), and re-examine the acceptance at each upgrade. Contrast ucrl-9435, where the 88-inch - with 20x the stored energy - bought the full hard-tube-modulator protection instead. Scale decides.

it should be completely interlocked in such a manner that serious damage cannot occur due to any failure of the operator or of equipment such as water failure or a vacuum leak.

The University of Washington 60-Inch Cyclotron: Progress and Status Report of Design and Construction — AECU-1951, University of Washington (1951) — p. 95

Editorial note, tabletop extrapolation: A strong SEED for a tabletop control panel or PLC - the quoted requirement (no serious damage from ANY single operator or equipment failure) plus their sequence logic - to be completed rather than copied: the 1951 scheme is equipment protection, and a modern chain adds the personnel-safety layer on top (access, radiation, e-stop: dg-1065, dg-1072, dg-1075).

Vacuum switches connected in the three-phase, 16.6 kv ac lines feeding the rectifier ... open within 10 msec plus the time to the first current zero ... In this service it will open the anode circuit within 10 usec of a fault.

Smith, The RCA 6949 as a Self-Excited Cyclotron Oscillator — UCRL-9435, Lawrence Radiation Laboratory (1960) — p. PDF p. 6 (printed -6-) for the layer arrangement; PDF p. 7 (printed -7-) for the regulation and termination items

Editorial note, tabletop extrapolation: The modern translation, mapped by FUNCTION rather than spec-for-spec: an LDMOS drain supply wants a fast electronic disconnect (the hard-tube modulator's descendant), a slower breaker layer, and snubbing on the dc feed - each layer rated against the actual stored energies and fault modes of the build (dg-330, dg-679, dg-1371).

The rf-dc interlock compares the dee voltage with the amount of oscillator anode dc. If the ratio is too low, indicating the presence of an arc, the fault detector opens the anode circuit and recycles

Smith, The RCA 6949 as a Self-Excited Cyclotron Oscillator — UCRL-9435, Lawrence Radiation Laboratory (1960) — p. 7

Editorial note, tabletop extrapolation: DIRECT and cheap: a comparator on the dee-voltage-to-drive ratio with a drop-and-retry turns dee sparks from session-enders into log entries - the ratio form matters, because absolute thresholds miss arcs that still draw full power. Two amendments for a tabletop copy: cap the retry count and latch out on repeated faults, since an endless auto-recycle would keep re-feeding a failed feedthrough or persistent arc; and if forward power stands in for anode dc, validate the arc signature on the actual amplifier - it is not the same quantity Smith's ratio used.

The signal from the rf-dc interlock is slowed down by an RC circuit, so that the discharge will persist for about a millisecond. ... Experience indicates that 1 msec is about the right delay.

Smith, The RCA 6949 as a Self-Excited Cyclotron Oscillator — UCRL-9435, Lawrence Radiation Laboratory (1960) — p. PDF p. 7 (printed -7-)

Editorial note, tabletop extrapolation: A protection spec you cannot derive from electronics alone: the dwell is chosen so each spark finishes cleaning the spot that caused it. The compromise transfers; the number does not - Smith's ~1 ms suits his machine's stored energy and electrode scale, so a tabletop supply picks its own dwell from its fault energy, starting shorter and lengthening only if conditioning stalls. Amplifier-device faults still trip as fast as the electronics allow: two speeds, two purposes.

the resonator has to be vacuum-tight, automatically making it rf-tight.

Smith, The RCA 6949 as a Self-Excited Cyclotron Oscillator — UCRL-9435, Lawrence Radiation Laboratory (1960) — p. 8

Editorial note, tabletop extrapolation: Comforting for a residential machine, with 'somewhat' doing real work: the metal chamber contains the dee's RF well, and the leakage paths are feedthroughs, viewports, gauge ports and the amplifier chain - gasket and shield those, then VERIFY with a receiver walk-around. Quiet neighbors' radios are a measurement, not a promise.

Mit Spannungen kleiner als 2–3 kV sind wir auf der sicheren Seite [tr.: with voltages below 2-3 kV we are on the safe side]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 41

Editorial note, tabletop extrapolation: Electron energies equal to the dee voltage produce bremsstrahlung with end-point energy of the same value; at 3 keV any metal wall stops it, at 15-30 keV it does not, and stray electron currents in a multipacting dee are not bounded by the beam current. Flashover can also occur below 3 kV with bad geometry, pressure or contamination. Check, do not assume: evaluate the actual electrode potentials, survey with a suitable low-energy detector at operating power, and treat viewports and thin windows as the weak points.

Ein Nachteil ist die relativ hohe Permeation von Wasserstoff durch Schläuche und Kanülen; dies betrifft insbesondere die Ionenquelle [tr.: a drawback is hydrogen permeation through hoses and cannulas]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 30

Editorial note, tabletop extrapolation: Use metal lines with a mass-flow controller rather than elastomer tubing (PEEK is lower-permeation than elastomers, not zero). A small cartridge is still HYDROGEN: even ~10 standard litres forms a flammable mixture in air, so ventilate, leak-check, control ignition sources and handle the pressurized cartridge properly. Runtime: compute from the cartridge's usable standard volume at the actual MFC setting rather than quoting a lifetime.

Im Betrieb müssen die Spulen des Magneten mit Wasser gekühlt werden. Dies geschieht durch ein (von Schülern selbst entwickeltes) Kühlsystem, das mit Hilfe einer Heizungspumpe für den notwendigen Durchfluss von ca. 10 l/min sorgt. Ein Druckausgleichsgefäß stellt den notwendigen Betriebsdruck von ca. 1 bar während des Betriebs her. Sollte das Kühlsystem einmal ausfallen, so wird der Magnet über einen Notschalter abgeschaltet. [tr.: in operation the magnet coils must be water-cooled, by a student-built cooling system whose central-heating circulator provides the necessary ~10 l/min flow; an expansion vessel maintains the ~1 bar operating pressure; should the cooling fail, the magnet is switched off by an emergency switch]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 36

Editorial note, tabletop extrapolation: Size cooling from the measured coil loss, allowable winding temperature and coolant temperature rise - the 10 l/min is this magnet's number. A fail-safe interlock (flow AND winding temperature, arranged so failure trips rather than merely alarms) is cheap against a coil rewind; whether an air-cooled coil set needs duty cycling depends on its thermal design, not its power class.

Die Herausforderung dieses Projekts bestand demnach darin, ein Zyklotron in diesem niedrigen Energiebereich zum Laufen zu bringen [tr.: the challenge was to get a cyclotron running in this low energy range]

Prechtl & Wolf, Das Lehr-Zyklotron COLUMBUS — Mit einem Teilchenbeschleuniger Physik und Technik erleben, Springer (2020) — p. 7-8

Editorial note, tabletop extrapolation: Define the teaching machine's safety envelope explicitly rather than declaring it hazard-free: maximum electrode potential (X-ray endpoint), ion species and energy (reaction thresholds - remembering exothermic channels like D-D have none, so deuterium is a different machine), beam current, target and contaminant composition, plus the ordinary electrical, RF, vacuum and stored-energy hazards that exist at ANY energy. Survey, don't assume; the low-energy regime shrinks the radiological terms, not the list.

an interlock which shuts down the magnetic if less than 2.5 liters per minute of chilled water are supplied

Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 36

Editorial note, tabletop extrapolation: The transferable pattern is the method, not the numbers: independent low-flow and over-temperature interlocks wired to POWER DOWN the load, with trip points derived from the coil's insulation limits or measured thermal performance (including sensor lag) - Houghton's 2.5 L/min floor and their coil ceiling are that machine's settings, not defaults.

In order to avoid sparking in the gaps in the cyclotron chamber, the voltage supplied by the amplifier must be carefully chosen.

Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 45

Editorial note, tabletop extrapolation: With a high-Q resonator the dee voltage is set indirectly, so the spark limit must be designed in rather than discovered: use the measured or modeled loaded transfer function from amplifier to dee, verify with a calibrated pickup (dg-307/dg-1356), and back it with arc detection - the branch-current subtlety is exactly where a naive I*X_C sizing goes wrong.

in a concrete brick room with an interlock control system to prevent the accelerator from being turned on when a person is in the room

Cressman, The Design and Construction of a Small Cyclotron — Houghton College thesis (2006) — p. 29

Editorial note, tabletop extrapolation: The documented access-control arrangement of the source machine - occupancy interlock plus (per its electronics chapter) remote operation - is a COMPONENT of protection, not a certified minimum: shielding calculations, surveys, monitors, fail-safe interlock design and applicable regulatory requirements decide sufficiency for any neutron-capable machine, and the thesis presents no dose analysis.

In non-magnetic assembly, the yoke and pole are first aligned and fixed, and the PM blocks are inserted afterward. In this project, we used the first method, with magnetic force. Because the magnetic attraction during assembly can exceed several hundred kilograms, this process presents engineering and safety challenges. To address this, we developed a systematic and repeatable assembly process using custom-designed fixtures. We also found that applying a reverse magnetic field during the process can help reduce the attractive force and make the assembly smoother. The fixtures include mechanical guides, magnetic shielding, and locking mechanisms to ensure safe, controlled, and staged installation

Hsu, Jan, Chu & Lin, Integrating Permanent Magnets and Electromagnets — A Hybrid Dipole Magnet Design — WEBD3, Proceedings of IPAC2025 (2025) — p. 2

Editorial note, tabletop extrapolation: Editorial note, tabletop extrapolation: methods that transfer at any scale — never free-hand strong magnets toward iron; use guided, locking fixtures that control the approach axis and stage the force; and consider the insert-magnets-last sequence or a bucking field when the full-force path is unmanageable. A reverse field applied to PM material must stay well inside the magnets' coercivity and recoil limits and brings its own stored energy — model the forces and limit the current before relying on it.

Thermal cut-off switches (fully insulated in a screw on housing type), set to open an electrical circuit at 40°±5°C shall be fitted on the external lead (return lead of water circuit) of each pancake ... Suitable thermal switches will be placed on outer terminals of the coils to prevent over-heating of the coils (cut-off value: > 40 oC) by shutting off the power supply ... [spec table:] Thermal sensors (cut-off value) — > 400 C (8 nos. of sensors to be mounted on each coil); Interlocks — overload, high temperature cut-off

IUAC, e-Tender 09/GOR/2024–25 — H-Dipole Water-Cooled DC Electromagnet for the Table-Top Cyclotron: Engineering Specification and Acceptance Tests (2024) — p. 19, 24, 25

Editorial note, tabletop extrapolation: Editorial note, tabletop extrapolation: hardware thermal switches on every pancake's return water lead, dropping the supply through an interlock, is a simple, software-free protection pattern for a water-cooled coil stack — with two cautions. An outlet-mounted switch lags stagnant-water and winding hot spots when flow is lost, so pair it with flow or pressure detection; and the interlock must command the supply's controlled shutdown or energy-dump path, never break magnet current mechanically — an inductive circuit interrupted dry arcs.

[Facility licensing status table — Facility / Status / License valid till:] Table Top Cyclotron — Initiated — NA (listed alongside Running facilities such as the Pelletron-linac, and the HCI facility with design construction approval) ... Civil work for setting up of the cyclotron development laboratory and storage racks.

IUAC, Annual Report 2024–25, Chapter 3 — Research Support Facilities (table-top cyclotron RF system) — p. 23, 37

Editorial note, tabletop extrapolation: Editorial note, tabletop extrapolation: method observation, not a dose rule — the machine sits in the regulator-facing facility-status table from project initiation, so authorization proceeds in parallel with construction rather than gating it at the end. What 'Initiated' commits either party to, the table does not define; the transferable habit is the early appearance itself. Small-accelerator builders in any jurisdiction can copy the early-engagement pattern.

After initial operation, internal arcing between the HV electrode and the grounded housing clearly indicated secondary electron emission. The evidence was in pitting, shown in Figure 4 on the internal surfaces of the top and bottom structural plates - the bulk of which occurred directly above and below the perimeter of the HV electrode. A general rule-of-thumb places the threshold for damage from arcing at 1 Joule. Locations of the closest approach, such as directly below the centerline did not show much pitting, exonerating field emission based brake-down. Further, damage was only noted on the top and bottom plates, not the deflector electrode, suggesting secondary electrons were emitted on the electrode, accelerated away from the HV electrode, tightly following the vertical magnetic field lines.

Koeth, Ponter, Hoffman, Schneider & Krutzler, Rutgers 12-Inch Cyclotron Electrostatic Deflector (2010, rev. 2011) — p. 3

Editorial note, tabletop extrapolation: A post-mortem method for any HV campaign: read the damage map. On this deflector, pitting sat above and below the electrode perimeter — displaced along the vertical field lines — while the closest-approach points and the electrode itself were clean, which the authors read as magnetically guided secondary electrons and against field emission. Treat such patterns as evidence to corroborate (trajectory modeling, polarity tests, conditioning behaviour), not as unique proof — field emission can light a discharge whose energy lands elsewhere. The 1 Joule damage threshold is the authors' quoted rule of thumb. (The source's figure reference appears to be to Figure 5, captioned "Pitting observed from arcing"; "brake-down" is the source's spelling.)

Initially only a constant-voltage regulated 30 kV power supply was available. For safety, the supply required a current limiting series resistor of 75 MΩ in the event of a short or arc. Even though the supply was capable of providing 30 kV, the leakage current from corona reduced the maximum achievable deflector electrode voltage to 28 kV. Even so, 28 kV was sufficient to just bring the beam to the edge of the screen, as seen in Figure 10.

Koeth, Ponter, Hoffman, Schneider & Krutzler, Rutgers 12-Inch Cyclotron Electrostatic Deflector (2010, rev. 2011) — p. 4

Editorial note, tabletop extrapolation: A planning number for tabletop extraction: budget the series resistor's IR drop, because corona current through a 75 megaohm resistor cost these authors ~2 kV out of 30 kV, about 7%. The current-limiting resistor is reported as the authors' own required practice for their supply; the lesson to carry over is that the supply must be specified above the design electrode voltage, not at it.

Subsequently, a surplus Bertan 205A-50N 50 kV power supply was ordered and installed. This supply was also only a constant voltage supply requiring a 150 MΩ current limiting resistor. The resistor was housed in an acrylic tube, capped at both ends, which was then externally covered with a grounded copper mesh. The resistor housing was installed in a relatively inaccessible location at the top and backside of the magnet yoke.

Koeth, Ponter, Hoffman, Schneider & Krutzler, Rutgers 12-Inch Cyclotron Electrostatic Deflector (2010, rev. 2011) — p. 5

Editorial note, tabletop extrapolation: This is the source's own construction practice for a stack of HV resistors on a small machine: an insulating tube for standoff plus an outer grounded screen so the assembly presents a defined, grounded surface rather than a floating one, and physical placement out of casual reach. Reported here as what they did, with their numbers.

The Mammoflex cable is rated for 60 kV and had a capacitance of 56 pF per foot. After installation of the new supply and cable, mysterious behavior was noticed and is still not fully explained. At sufficiently high voltages (~ 30kV) arcing inside the chamber occurred – both light and audible snapping were observed. Coincident with the internal arcing, external arcing was observed between the shield of the Mammoflex cable (of the 6 foot segment between the resistor and chamber) and chassis ground, such as the magnet frame. One such arc terminated on the upper magnet coil, causing the magnet power permanent damage, requiring costly repair. The stored energy in the 6 foot cable at 30 kV is about 0.2 Joules, not much lower than the rule-of-thumb damage threshold of 1 Joule. It is also known that the focusing influence of the magnetic field can enhance the damage of an electrical discharge.

Koeth, Ponter, Hoffman, Schneider & Krutzler, Rutgers 12-Inch Cyclotron Electrostatic Deflector (2010, rev. 2011) — p. 5

Editorial note, tabletop extrapolation: The most expensive lesson in the document, and it scales down unchanged: HV cable capacitance is a stored-energy reservoir whose shield is not automatically at ground everywhere. Computing from the paper's own numbers, 56 pF/ft × 6 ft = 336 pF, and ½CV² at 30 kV is 0.15 J — the source's "about 0.2 J" at the same order (computed here). Neither 0.2 J nor the 1 J rule of thumb is a safety boundary; cable length is the variable a builder controls directly.

After consulting an experienced high voltage engineer, it was suggested that due to the rapid formation of the internal arc, the segment of HV cable between the resistor and chamber was effectively a Blumlein HV pulse generator [5], several steps were taken to suppress the arcing. First, the HV cable length was reduced to the bare minimum required, thereby minimizing the stored energy in the cable. To limit the discharge current, 68 Ω, 2 Watt carbon resistors were placed in series with the cable shield at the resistor box. However, streamers traveling greater than 1 inch in air were still observed bypassing the 68 Ω resistors. The resistors were subsequently tested and found to be undamaged and properly functioning. A 5 MΩ HV resistor was then next installed in series with the center conductor and the chamber just prior to the HV vacuum chamber bushing. This has been found to suppress the arcing. … Finally, to ensure machine safety, the HV coaxial cables have been routed clear of any sensitive electronics in the event of a reoccurrence.

Koeth, Ponter, Hoffman, Schneider & Krutzler, Rutgers 12-Inch Cyclotron Electrostatic Deflector (2010, rev. 2011) — p. 5

Editorial note, tabletop extrapolation: A rare documented failed-fix-then-working-fix sequence at exactly this scale: shorten the cable (less stored energy), try shield-side series resistance (bypassed — streamers jumped more than an inch of air around the 68 Ω resistors, which survived undamaged), then put 5 MΩ in the CENTER CONDUCTOR at the chamber bushing — which suppressed the arcing here, plausibly because that is where series resistance can actually limit the discharge current into the arc. Component values are this installation's; buy any such resistor for working voltage and impulse energy, and route HV cables away from electronics as they finally did.

A Programmable Logic Controller (PLC) based machine-protection system was implemented to allow safe, un-attended operation of the 12-Inch magnet. In the event of high-temperature condition or a coil cooling-water flow loss for more than 10 seconds, the PLC will slowly ramp the magnet down and latch it off, requiring an operator to reset. The PLC safety system was necessary as the scans could take in excess of 24 hours: a standard measurement grid of 129 x 129 points equals 16,641 measurement points, each measurement required ~ 5 seconds totaling an excess of 23 hours scan time.

Koeth, Hine, Hoffman, Krutzler, Ponter, Rosenberg, Ruisard & Schneider, Comparison of Azimuthally Varying with Constant Gradient Magnetic Fields with the Rutgers 12-Inch Cyclotron (2011) — p. 4

Editorial note, tabletop extrapolation: The source's own practice and thresholds, reported as such: 10-second flow-loss window, slow ramp-down rather than a trip, latching off until a human resets. The planning arithmetic transfers directly — points × (dwell + settle + motion) — and this machine's standard 129×129 map at ~5 s/point is a 23-hour job, which is why the protection exists: budget your own scan time honestly, and if it lands unattended, engineer fail-safe interlocks with a shutdown response derived from YOUR coil's thermal time constant and cooling failure modes, not copied from these numbers.

Many nuclear reactions produce neutrons, but perhaps the simplest is d-d reaction, with a broadly peaked cross section at a mere 180 keV. With an incident energy beam, in the regime of 180 keV, the reaction d(d,n)He3 reaction produces 2.45 MeV neutrons quasi-isotropically.

Koeth, Neutron Production with a 12-Inch Cyclotron (2017) — p. 1

Editorial note, tabletop extrapolation: The species distinction is the load-bearing radiological fact: deuterons on a deuterated target make fast neutrons at only ~180 keV, while common stable targets have (p,n) thresholds above 1 MeV (7Li(p,n) at ~1.88 MeV is among the lowest) — so a sub-MeV proton machine's neutron picture hinges on verifying the beam really is protons (deuterium contamination opens the D–D channel), what the beam actually strikes, and the truthful maximum energy; no blanket neutron-free claim follows. The cross-section characterization and the quasi-isotropic 2.45 MeV figure are the source's own: at finite beam energy the neutron energy is angle-dependent, and quantitative cross-section shapes should be taken from evaluated data at design time, not from this description. The source states its laboratory move was what provided the radiological controls to permit fast-neutron generation (abstract, p.1).

While not as sensitive as the other two tubes, the 12-4 was the primary diagnostic as its BF3 tube was unaffected by the magnetic field and could be positioned arbitrarily close to the cyclotron chamber. The second and third detectors were photomultiplier based detectors; one being a Ludlum Model 42-4 LiF(Eu) scintillator, and the third detector a Ludlum Model 42-2 proton recoil detector. When positioned sufficiently far away from the cyclotron magnet, neutrons were detected by both, however, an approach closer than two feet of the magnet gap either greatly reduced or otherwise extinguished the photomultiplier tube signals.

Koeth, Neutron Production with a 12-Inch Cyclotron (2017) — p. 4

Editorial note, tabletop extrapolation: Concrete siting guidance from one instrumented machine: its gas-filled BF3 rem-ball worked arbitrarily close to the chamber, while its two PMT-based instruments (LiF(Eu) scintillator, proton-recoil) lost or degraded signal inside roughly two feet of the magnet gap, and its NaI(Tl) spectrometer failed close-in even with a mu-metal shield (sited ~three feet out; that sentence is on p.6). The pattern — gas tubes tolerate fringe field, PMTs suffer — is a sound prior, not a law: test each complete detector-plus-electronics assembly in the actual fringe field before committing to a layout. (The companion 2020 draft ran a 3He tube close-in, its own separate data point.)

With an RF duty factor of 25% (RF on for 125 ms twice a second) an average dose rate of 20 mrem/hour was measured. Using the health physics standard of 8.2 n/sec/cm2/mrem/hour for 2.45 MeV neutrons, a peak isotropic neutron production of 10 million neutrons per second can be inferred. The average dose rate increased linearly with the RF pulse repetition rate. The duty factor was briefly raised to 100% where the measured average dose rate reached 80 mrem/hr.

Koeth, Neutron Production with a 12-Inch Cyclotron (2017) — p. 5

Editorial note, tabletop extrapolation: The source's measured and inferred numbers for its own machine and detector placement — not a dose limit or a shielding recommendation. The methodological transfer, stated correctly: local fluence rate = dose rate × the 8.2 (n/s/cm² per mrem/h) factor for 2.45 MeV neutrons; isotropic source strength S_avg = fluence × 4πr²; peak S = S_avg / duty factor. Worked with the source's numbers at its 29.5 cm detector radius: 20 × 8.2 = 164 n/s/cm²; × 10,935 cm² = 1.79e6 n/s average; ÷ 0.25 duty = 7.2e6 n/s peak — the source's ~1e7 on rounding. (Starting from raw counts instead, divide by intrinsic efficiency × A/(4πr²).) Dose scaling linearly with duty factor held at fixed pulse amplitude and tune. Verified against the rendered page image (all radiological numbers re-read from the 150 dpi render).

Several tests were performed to ensure the detectors' response were to neutrons. First, the target was inserted so as to only intercept the low energy deuterons – the detectors ceased their counting. Second, with the target the position of greatest production rate, the ion source was gas starved, beam current decreased as well as the measured neutron dose rate. Finally, the cyclotron's magnetic field was slightly adjusted to break the optimized magnetic resonance acceleration condition, and again the neutron fluence followed the diminishing beam current. … All three detectors responded in unison for the duration of each pulse when operating in RF pulse mode.

Koeth, Neutron Production with a 12-Inch Cyclotron (2017) — p. 4

Editorial note, tabletop extrapolation: A reusable falsification protocol: every claimed detection should switch off with a beam parameter, three independent ways here. It demonstrates beam correlation — strong support, not proof, since RF pickup can also track tune and beam loading; the remaining discriminators are a calibrated-source response check, an RF-only background run, and moderator/absorber tests. For a machine surrounded by kilowatt RF, this discipline is what separates a count from pickup.

The energetic neutrons of the d-d reaction must be moderated to thermal energies to before the can be absorbed by the target nuclei. The foils were taped to a 45 mm thick polyethylene moderator and placed directly outside of the glass view port which was the nearest to the Ti:D target. ... The half-life of Ag110 is 24.6 seconds; the half-life of Ag108 is 2.42 minutes. Their short half-lives quickly bring them to equilibrium during irradiation, however, they make the subsequent decay measurements challenging. Indium is also commonly used for activation analysis. In115 à In116m is a metastable state with a 54.2 minute half-life, thus requiring a longer irradiation time, and of course, improving the decay measurement. … The irradiation time of the indium foil was approximately 6.5 minutes, a fraction of the time needed to achieve activation saturation; yet, the peak-induced activity was at an order of magnitude above background. … The theoretical curve is a single exponential decay constant, with a half-life of 54.2 minutes, with initial count rate of 153 counts per minute above a background of 24 counts per minute.

Koeth, Neutron Production with a 12-Inch Cyclotron (2017) — p. 5

Editorial note, tabletop extrapolation: Practical foil selection for a setup with only a Geiger counter: indium's 54.2-minute half-life is forgiving of a slow walk from machine to counter; silver's 24.6 seconds is not. The 45 mm polyethylene block is what THIS setup used to raise the thermal component at its geometry — thermalizing 2.45 MeV neutrons takes many hydrogen collisions and the emerging spectrum depends on geometry and surroundings, so size a moderator by transport estimate or test, not by copying 45 mm. On the signal: the source calls its indium activity 'an order of magnitude above background'; the printed fit values give 153 cpm net over 24 cpm background — 6.4× net, 7.4× gross — its own rounding, worth knowing when planning counting statistics. (The indium numbers are on p.6.)

Again, the 847keV and 2.22MeV lines are the prominent peaks, the additional gamma ray lines originate in the cyclotron's construction materials, such as 472, 1015keV lines from the aluminum chamber lid, and the 962keV line of copper, from the copper magnet coils. Several gammas lines, i.e. 140, 198, 596keV originate in the germanium of the gamma ray detector itself.

Koeth, Neutron Production with a 12-Inch Cyclotron (2017) — p. 7

Editorial note, tabletop extrapolation: A useful line list for anyone who puts a gamma detector near a small neutron-producing machine: the machine's own aluminium chamber and copper coils show up in the spectrum, so a background-subtracted, beam-gated run is needed to attribute anything. The 847 keV iron line doubles as evidence that fast neutrons are reaching the magnet steel. The Fig. 15 in-figure labels give 598 keV and 1014 keV and 2223 keV where the body text says 596, 1015 and 2.22 MeV; minor internal rounding differences. (The 847 keV +/-10% measurement and the 2.22 MeV proton-capture explanation are on p.6; the HPGe line list is on p.7.)

The fission chamber used was a spare Westinghouse WL6376A, HEU 235U lined tube intended for reactor nuclear instrumentation. Approximately 1 gram of 235U lined an argon-filled proportional tube. The detector bias and signal are split with a preamp, the HV bias was +1100 V, the signal was conditioned with a pulse shaping spectroscopy amplifier, and distributed to an oscilloscope for observation and scalar/timer for counting. ... These occurred at a rate of approximately 1 fission event per RF pulse.

Koeth, Neutron Production with a 12-Inch Cyclotron (2017) — p. 8

Editorial note, tabletop extrapolation: Reported as the source's own experiment and instrumentation, with no recommendation attached: an HEU-lined legacy fission chamber is specialized regulated material — possession, transfer and disposal rules must be verified for any such device, whatever its surplus provenance. What transfers is the method (optimize with the sensitive detector first, then bring in the insensitive instrument) and the calibrated fact that this complete configuration — this beam charge per pulse, target, moderator and ~1 g chamber — produced about one fission event per RF pulse; the rate belongs to the whole configuration, not to 150 keV alone.

After being positioned, the 3He detector was calibrated by placing a NIST calibrated 252Cf sealed neutron source at the face of the deuterated target, thus giving the ability to quantify peak neutron production from the cyclotron during operation. Care was taken not to disturb the 3He detector geometry to maintain the calibration. During a 5 second CW run of the RF at full operating power, the DEE voltage and ion source production rate were adjusted for an average neutron production of 500,000 neutrons per second, which were considered to be isotropic.

Koeth, Gilde & Moroch, Measurement of Neutron Diffusion Time from Fast Pulsed Systems (draft, 2020) — p. 3

Editorial note, tabletop extrapolation: An in-situ absolute-efficiency calibration: a calibrated source at the target face, the detector geometry then left undisturbed. This is the source's own practice and its own reported yield, not a general dose statement — and a ²⁵²Cf spectrum is not a 2.45 MeV D–D spectrum, the source and beam spot are not spatially identical, and D–D emission at finite deuteron energy is not exactly isotropic, so a quantitative D–D yield still needs response and geometry corrections. Draft report.

Additionally, the response of the NIM electronics to the detection of a genuine nuclear event results in a deadtime on the order of 10us or longer. … Although the neutron production window may be short (10us or less), the neutron transportation time from the source to the detector is relatively long, with a characteristic time of 100us, which affords the pulsed plasma experimenter the opportunity to "look" for neutrons in a quiescent period after the pulsed event. … 5 minutes of neutron events were collected with all cyclotron systems operational, including the pulsed RF, except the Ion Source Discharge power supply was shut off and no neutrons were detected during that time.

Koeth, Gilde & Moroch, Measurement of Neutron Diffusion Time from Fast Pulsed Systems (draft, 2020) — p. 1

Editorial note, tabletop extrapolation: The draft's transferable conclusion: moderator transport delays neutrons past the transient-and-deadtime window, so NIM-based counting survives pulsed operation. The everything-on-but-the-ion-source background run is a clean, cheap control — but it is one partial control (removing the discharge also removes discharge-borne transients), so a per-installation timing spectrum and a pulser/deadtime check still belong in the plan. Draft report.

the HV electrode’s corners were rounded so as to limit the maximum E field to a conservative 170 kV/inch.

Koeth, Rosenberg, Krutzler, Ponter, Schneider & Hoffman, Rutgers 12-Inch Cyclotron: Dedicated to Training Through Research and Development — WEPPT024, Proceedings of Cyclotrons2013 (2013) — p. 3

Editorial note, tabletop extrapolation: PDF p.3 = printed p.368. Read the numbers as design practice, not as an allowance: Rutgers rounded and polished the electrode so the peak local field stayed at their chosen conservative 170 kV/inch (6.7 MV/m) while the channel ran 4.2 MV/m — the ratio is the geometric peak-enhancement they permitted themselves, not a demonstrated breakdown margin. What transfers: control the peak-to-working field ratio by geometry, polish, and seat the feedthrough conductor directly in the electrode; then condition and test at the actual gap, pressure and surfaces, and put a current-limiting series resistor in the HV line (here 75 MΩ) so the inevitable arc is survivable.

Pitting, Fig. 6, on the internal surfaces of the top and bottom lids only occurred directly above and below the perimeter of the electrode … Evidence suggested the internal arcing was initiated by secondary electron emission. … however, locations of highest E-field, such as directly below the electrode’s centerline did not show pitting, exonerating field emission based brake-down. Further, no damage was observed on the deflector electrode.

Koeth, Rosenberg, Krutzler, Ponter, Schneider & Hoffman, Rutgers 12-Inch Cyclotron: Dedicated to Training Through Research and Development — WEPPT024, Proceedings of Cyclotrons2013 (2013) — p. 3

Editorial note, tabletop extrapolation: PDF p.3 = printed p.368. A transferable diagnostic method, reported with the source's own interpretation: they read the pitting pattern — under the electrode perimeter, absent at the highest-field centerline, electrode itself undamaged — as evidence for secondary-electron-driven breakdown and against field emission. The pattern is evidence, not proof (field-emitted electrons also strike remotely); the practical takeaway is to read the chamber lids after any HV campaign, and to expect onset at whatever voltage YOUR gap and surfaces condition to — 30 kV was this channel's.

One such arc terminated on the upper magnet coil, causing costly damage to the magnet power supply.

Koeth, Rosenberg, Krutzler, Ponter, Schneider & Hoffman, Rutgers 12-Inch Cyclotron: Dedicated to Training Through Research and Development — WEPPT024, Proceedings of Cyclotrons2013 (2013) — p. 3

Editorial note, tabletop extrapolation: PDF p.3 = printed p.368. A concrete, expensive failure chain for anyone adding HV to an existing machine — and it is two-stage: the internal deflector discharge excited the charged cable (the Blumlein mechanism, dg-1826), and the resulting EXTERNAL arc terminated on the magnet coil and took out the magnet supply. The warning that transfers: HV transients couple into unrelated subsystems through cabling, grounds and stray capacitance, so an HV fault must be analyzed as a whole-machine event, not a deflector event.

the segment of HV cable between the series resistor and chamber formed a Blumlein HV pulse generator explaining the apparent ground-to-ground arcing … A 5 MΩ HV resistor was also installed in series with the coaxial center conductor and the chamber just prior to the HV vacuum chamber bushing. This suppressed all arcing and deflector operation at full potential is routine.

Koeth, Rosenberg, Krutzler, Ponter, Schneider & Hoffman, Rutgers 12-Inch Cyclotron: Dedicated to Training Through Research and Development — WEPPT024, Proceedings of Cyclotrons2013 (2013) — p. 3

Editorial note, tabletop extrapolation: PDF p.3 = printed p.368. The craft lesson: a protective series resistor at the supply end leaves the cable beyond it as a charged transmission line that dumps into any internal arc. The fix that worked here — a second resistor at the chamber bushing — is cheap and retrofittable; 5 MΩ is the value that worked in THIS installation. Size yours from the downstream cable's capacitance and stored energy at your voltage, and buy the resistor for the job: working-voltage, impulse-energy and creepage ratings, or the protective part becomes the next flashover.

reaching a maximum energy of 1.2 MeV protons, the Rutgers Cyclotron is not a radiological hazard and is easily approachable while operating.

Koeth, Beam Physics Demonstrations with the Rutgers 12-Inch Cyclotron — WEPPT025, Proceedings of Cyclotrons2013 (2013) — p. 1

Editorial note, tabletop extrapolation: PDF p.1 = printed p.369; the companion non-activation statement is we1pb02 PDF p.1 / printed p.291. Reported strictly as the authors' assessment of their own machine and setting — neither paper reports survey data, shielding or a licensing basis. Two physics limits on transferring it: a 1.2 MeV proton ceiling is not a universal no-activation threshold (thresholdless capture reactions such as 12C(p,γ)13N and light-element targets produce prompt gammas and activation below it), and the assessment assumes proton beams — deuteron contamination opens neutron channels. A builder in this class should read it as evidence such machines are operated in classrooms, and still do their own commissioning survey, species verification and regulatory review.