Cyclotron detectors design rules

Alpha resolution measurements should be made with a detector source spacing equal to 1.5 to 2 times the detector diameter and under good vacuum (< 100 microns HG or 10 Pa).

Canberra, PIPS Detector Instruction Sheet (2012) — p. 1

Editorial note, tabletop extrapolation: For his ~8 mm active-diameter PIPS, that is 12-16 mm standoff; closer spacing degrades resolution through wide-angle entrance-window losses.

Cited in: Experiments by Energy Band

the ion gauge is not turned on until the tank pressure is less than 0.5 microns ... In this position the conductance from the diffusion pumps around the gate valves to the ion gauge has been estimated to be approximately the same as the conductance from the diffusion pumps to the tank proper. ... the wall of the manifold provides the tube filament with some protection from the magnetic field

Livingston & Boch, The Oak Ridge 86-Inch Cyclotron — ORNL-1196, OSTI 4357145 (1952) — p. 45

Editorial note, tabletop extrapolation: Directly applicable gauge practice near a stray-field-rich H-frame magnet: place the gauge to read the pressure you care about (conductance gradients bias a badly placed gauge under gas flow), and verify the shielding by comparing readings with the field on and off.

Cited in: The Vacuum Budget of a Cyclotron

far more rugged than the triode ion gauge and sensitive to small changes in pressure; but it is probably not as accurate in reading absolute pressure.

Livingston & Boch, The Oak Ridge 86-Inch Cyclotron — ORNL-1196, OSTI 4357145 (1952) — p. 46

Editorial note, tabletop extrapolation: A cheap Penning head earns its keep as a trend and gas-flow indicator, with the ion gauge kept for absolute readings. For protection interlocks use fail-safe, manufacturer-approved instrumentation - Penning cells can ignite late and drift with contamination - and commercial heads carry their own magnet: mount and shield per the head's specification rather than borrowing the cyclotron's field.

It is seen that particles are detected at about 70 kv. and the numbers increase more rapidly with increase of bombarding energy than with the lithium film.

Oliphant & Rutherford, Experiments on the Transmutation of Elements by Protons (1933) — p. 266-270

Editorial note, tabletop extrapolation: Proof that p-B11 alphas are observable far below the 675 keV resonance: the 1933 apparatus saw them at 60-70 kV using tens of microamps and large solid angle, so a lower-current machine compensates with integration time and geometry. Their alphas stopped in under 5 cm of air, hence the vacuum path to a PIPS detector.

Cited in: Experiments by Energy Band

0.15 0.91 +/- 0.015... 0.65 218.42 +/- 0.55

Spraker et al., The 11B(p,α)8Be → α+α and the 11B(α,α)11B Reactions at Energies Below 5.4 MeV (2012) — p. 360

Editorial note, tabletop extrapolation: The master rate table for the reference machine's PIPS window (150-675 keV) - as fitted A0 coefficients: a count-rate prediction folds in the angular terms, solid angle, target thickness and integration time (the experiments-by-energy arithmetic). What the table quantifies exactly is what reaching the resonance is worth: ~240x in A0 from 150 to 650 keV.

Cited in: Experiments by Energy Band

Voltage -kV dc / Current milliamps / Pressure millitorr / Neutrons cpm: 16, 11, 18, 10 ... 25, 8.1, 14, 60 ... 31, 10.8, 13, 130. Figure 25 - Neutron readings versus other chamber parameters.

Kovalchick, Deuterium Fusion Using Inertial Electrostatic Confinement (2012) — p. PDF p.46 = printed p.46 (Kovalchick, 'Experiment 7 - Observations', Figure 25)

Editorial note, tabletop extrapolation: The same lesson as the p-B11 cross-section curves: sub-barrier yield rises steeply with particle energy, so extra beam energy buys far more counts than the same fractional increase in current. The specific sweep numbers are one fusor's; the steepness is the physics.

Cited in: Experiments by Energy Band

It was limited to low level output by its 22kv internal supply. 103 n/sec... a 33 kilovolt supply. 105 n/sec... currently produces in excess of 600,000 neutrons per second

Hull, Fusor: An Easy to Construct Fusion Reactor Based on Inertial Electrostatic Confinement (2009) — p. 36-39

Editorial note, tabletop extrapolation: Reinforces energy-over-current for the builder: sub-Coulomb-barrier reaction rates reward every extra keV steeply - though not by a fixed orders-per-10-kV law; Hull's own steps differ between jumps.

Cited in: Experiments by Energy Band

a mica window W, 1 cm in diameter and supported on a grid which subtends the smallest possible area... The solid angle obtained in this way is approximately 0.7.

Oliphant & Rutherford, Experiments on the Transmutation of Elements by Protons (1933) — p. 262-265

Editorial note, tabletop extrapolation: The close-geometry, calibrate-with-a-known-alpha-source method is how the builder should commission the PIPS geometry before hunting p-B11 alphas - an analogous procedure, with a traceable sealed source, the PIPS dead layer in the accounting, and the solid angle computed for the actual geometry.

Cited in: Experiments by Energy Band

Pulser line width should be about 5 keV (FWHM) narrower than Alpha Resolution ... the noise level which is approximately 3 times the pulser line width (FWHM).

Canberra, PIPS Detector Instruction Sheet (2012) — p. 1-3

Editorial note, tabletop extrapolation: A pulser check exercises the whole electronic chain and baseline - including grounding, 9 MHz RF pickup, and detector leakage/capacitance contributions while connected - without risking source contamination; isolating charge-collection or detector-response degradation still needs a real particle peak for comparison.

Cited in: Experiments by Energy Band

The target probe must show a high resistance to ground; of course, a sensitive galvanometer (protected by r.f. chokes and bypasses) may be used initially for detecting the beam current ... The six-inch cyclotron has indicated a 7 microampere beam

Wouters, General Recommendations for Design of Small Cyclotrons — UCRL-476 (1949) — p. PDF p.11 (printed -12-)

Editorial note, tabletop extrapolation: The choke-protected, well-insulated probe is the right pickup design. Treat the 7 uA as one historical machine's result, not an expectation: beam current rides on source, vacuum, RF voltage and capture, and tabletop machines have commissioned at picoamps.

a convenient target substance would be LiF which, when bombarded with protons, will emit gammas from Li ... The target may be prepared by simply fusing a small amount of LiF onto a small stainless steel block

Wouters, General Recommendations for Design of Small Cyclotrons — UCRL-476 (1949) — p. 11

Editorial note, tabletop extrapolation: Partially applicable: 7Li(p,gamma)8Be is exothermic - there is no threshold - but its prominent resonance near Ep = 441 keV is what makes the signal jump, so at the reference machine's ~150 keV the yield is far down the tail. A next machine near 0.5 MeV could use exactly this check; estimate thick-target yield and detector response first, and remember LiF adds fluorine channels (19F(p,alpha-gamma) with its own strong resonances).

Cited in: Experiments by Energy Band

At these energies beam intensities varied from 0.5 to 10 nA on target ... detected by eight silicon surface barrier detectors ... each detector subtending a solid angle of approximately 2.5 x 10^-4 sr.

Spraker et al., The 11B(p,α)8Be → α+α and the 11B(α,α)11B Reactions at Energies Below 5.4 MeV (2012) — p. PDF 3 (printed 359), continuing on PDF 4 (printed 360)

Editorial note, tabletop extrapolation: The single most encouraging number in the batch: professional low-energy p-B11 data at exactly the reference machine's nA beam scale. Whether nA suffices for a given measurement follows from the rate arithmetic - cross-section, solid angle, integration time (the experiments-by-energy worked examples) - not from precedent alone.

Cited in: Experiments by Energy Band

simulations show that out of the three emitted a-particles, on average 2.1 a-particles contribute to this peak at the 0.675 MeV resonance

Spraker et al., The 11B(p,α)8Be → α+α and the 11B(α,α)11B Reactions at Energies Below 5.4 MeV (2012) — p. 359-360

Editorial note, tabletop extrapolation: When the builder converts PIPS counts, publish counts-per-luminosity as this paper does. Extracting a cross section needs more than dividing by ~2: detector efficiency, angular acceptance, the alphas' angular/energy distributions and window effects all enter, and the multiplicity itself changes with beam energy and analysis window.

Cited in: Experiments by Energy Band

The relative solid angles for each detector were measured using low energy Rutherford scattering on gold as well as a known 241Am source.

Spraker et al., The 11B(p,α)8Be → α+α and the 11B(α,α)11B Reactions at Energies Below 5.4 MeV (2012) — p. 360

Editorial note, tabletop extrapolation: The builder already owns the pieces: an Am-241 check source exercises the PIPS geometry and energy scale in practice, and the Faraday cup/Keithley 617 integrates charge for yield normalization - noting that ABSOLUTE calibration needs certified source activity, controlled geometry and live-time accounting, and a single alpha line is a one-point energy check.

Cited in: Experiments by Energy Band

A +9 V bias can be applied to the target using a battery to reduce the effect of secondary electrons on beam current measurements ... secondary electrons are created in significant numbers on the target.

Yuly, The Houghton College Cyclotron: a Tool for Educating Undergraduates — Cyclotrons 2013, WE1PB01 (2013) — p. 4-5

Editorial note, tabletop extrapolation: One battery attacks the main systematic in the builder's main diagnostic, and the biased/unbiased comparison sizes the secondary contribution - verify the suppression is sufficient by stepping the bias and looking for a current plateau; energetic secondaries and backscatter can survive +9 V.

Cited in: Experiments by Energy Band

This is of steel and has three faces at 45 deg to the axis, which form a sort of truncated pyramid with a circular base. Each face bears a recess, 1.2 cm. in diameter and about 1 mm. deep. The metal or powder to be bombarded is pressed or hammered into these spaces and the beam strikes the surface which is uppermost. The target is carried on a water-cooled stem M which rotates in a ground joint and can be set so as to bring any one of the three faces into the beam. By having only three faces any one face is completely shielded from the material sputtered from that which is in the beam, and at the same time it is possible to make very rapid comparisons between various targets

Oliphant & Rutherford, Experiments on the Transmutation of Elements by Protons (1933) — p. 262

Editorial note, tabletop extrapolation: A boron target plus a blank plus a calibration face on one rotatable holder would let the builder switch targets and measure background without venting.

it is a good idea to evacuate the chamber for 10 to 15 minutes before applying bias. This will remove excess surface moisture ... It is recommended to wait 30 seconds to stabilise the detector.

Canberra, PIPS Detector Instruction Sheet (2012) — p. 1

Editorial note, tabletop extrapolation: Build the pump-first-then-bias order into the beam-diagnostics routine as a TIMED permissive (vacuum reached plus 10-15 min), not a bare pressure interlock, and keep the 30 s post-bias stabilization; moisture raises initial leakage current, which is reason enough for the discipline.

Cited in: Experiments by Energy Band

PIPS detectors have an ion implanted entrance window of about 500 A thickness. ... To clean standard PIPS detectors first blow dry air or N2 gas on the surface to remove particles that might cause scratches ... use a cotton ball dampened with a good quality isopropyl alcohol; Do not use methyl alcohol ... put under vacuum for 15 minutes or heat to 50 C for an hour to remove residual moisture before applying bias.

Canberra, PIPS Detector Instruction Sheet (2012) — p. 1

Editorial note, tabletop extrapolation: The ~500-angstrom implanted window (the manual's figure) scratches easily; in a chamber with pump oil and target debris, stick to the manual's procedure.

Remember that leakage current doubles for about 5 C rise in temperature and take this into account when you compare your measurement to that of the factory.

Canberra, PIPS Detector Instruction Sheet (2012) — p. 1-3

Editorial note, tabletop extrapolation: A detector near warm cyclotron hardware can legitimately read several times its certificate value. Before blaming radiation damage or contamination, walk the checklist: temperature, bias setting, light leaks, humidity, cabling and connectors, microdischarge - the doubling rule is an approximation, not a diagnosis.

Recommended bias voltage +130 Volts ... Full depletion bias voltage +110 Volts ... Maximum bias voltage +150 Volts

Canberra, PIPS Detector Instruction Sheet (2012) — p. 2-3

Editorial note, tabletop extrapolation: The reference machine's two detectors (S/N 98343/98344) have only 20 V of headroom above recommended bias; a supply glitch to 150+ V risks breakdown, so use a current-limited, capped supply.

(10 ... 300 um thick): 100ps-30ns. Thick (~cm) Si or Ge detector: 1-10us

Spieler, Semiconductor Detectors Part 2 — SLUO Lectures on Detector Techniques, Lecture 7 (1998) — p. 2

Editorial note, tabletop extrapolation: The reference machine's ~500 um PIPS sits above the quoted 10-300 um range - its collection time should still be tens of ns (verify from the datasheet or a rise-time measurement) - and shaping time is then chosen for noise TOGETHER WITH count rate, pile-up and pulse-height stability, not noise alone.

S/N cannot be improved by feedback. This result is generally valid, i.e. it also holds for active integrators (charge-sensitive amplifiers).

Spieler, Semiconductor Detectors Part 2 — SLUO Lectures on Detector Techniques, Lecture 7 (1998) — p. 24

Editorial note, tabletop extrapolation: For the builder: mount the preamp on the vacuum feedthrough, not at the far end of a coax run. Cable capacitance raises the series-noise term, and at alpha-spectroscopy resolutions it competes with detector leakage and shaping-time choices for the noise budget - short cable is the cheapest term to fix.

Detector capacitance may vary within a system or change with bias voltage (partially depleted semiconductor diode)... Amplifier output directly determined by signal charge, insensitive to detector capacitance

Spieler, Semiconductor Detectors Part 2 — SLUO Lectures on Detector Techniques, Lecture 7 (1998) — p. 3-8

Editorial note, tabletop extrapolation: Confirms the standard PIPS chain for the p-B11 experiment: a charge-sensitive preamp at the feedthrough - the spectroscopy-grade choice, since a plain voltage amplifier's gain rides on the diode's bias-dependent capacitance. Voltage readout keeps niche uses (fast timing, very high rate) that energy spectroscopy is not.

en2 = 12 tau IB + 6e5 tau/RP + 3.6e4 vn2 C2/tau [rms electrons]

Spieler, Semiconductor Detectors Part 2 — SLUO Lectures on Detector Techniques, Lecture 7 (1998) — p. 42

Editorial note, tabletop extrapolation: Computes the expected electronic FWHM of the PIPS chain from datasheet numbers before buying a shaping amplifier, and says how tau should move if leakage rises - combine electronic, statistical and charge-collection terms in quadrature for the total resolution.

a 1 MeV neutron transfers about 60 to 70 keV to the Si recoil atom, which in turn displaces roughly 1000 additional atoms in a region of about 0.1 um size.

Spieler, Semiconductor Detectors Part 2 — SLUO Lectures on Detector Techniques, Lecture 7 (1998) — p. 49

Editorial note, tabletop extrapolation: The reference machine's PIPS detectors tolerate its X-ray background as far as displacement damage goes (ionizing/surface effects are a separate, slower concern), but shield or retract them during any neutron-producing run - deuterium work above all - and budget by estimated neutron fluence at the detector, not just by whether the reaction label says neutrons.

For 650 MeV protons alpha = 3e-17 A/cm, 1 MeV neutrons alpha = 2e-17 A/cm.

Spieler, Semiconductor Detectors Part 2 — SLUO Lectures on Detector Techniques, Lecture 7 (1998) — p. 51-52

Editorial note, tabletop extrapolation: Track the PIPS bias current on the Keithley 617 as a damage INDICATOR: an unexplained, temperature-corrected secular rise warrants investigating beam or neutron exposure - after ruling out temperature (leakage roughly doubles per ~7 C), humidity/surface leakage and annealing history; raw current is not a calibrated dosimeter.

Cooling to 0 C typically reduces the reverse bias current to 1/6 of its value at room temperature.

Spieler, Semiconductor Detectors Part 2 — SLUO Lectures on Detector Techniques, Lecture 7 (1998) — p. 52

Editorial note, tabletop extrapolation: A Peltier or cold-finger on the PIPS mount is a cheap resolution upgrade WHEN leakage-current shot noise dominates the noise budget - verify that first, control condensation and temperature stability, and remember cooling does not repair irradiation-induced charge-trapping losses.

the common mode of disintegration is into two [alpha] particles which proceed at angles of 150 to 180 relatively to one another, the third particle receiving very little energy

Spraker et al., The 11B(p,α)8Be → α+α and the 11B(α,α)11B Reactions at Energies Below 5.4 MeV (2012) — p. 357-358

Editorial note, tabletop extrapolation: Two PIPS detectors in near-back-to-back coincidence would give the builder a background-crushing p-B11 signature even at very low count rates.

Cited in: Experiments by Energy Band

While the resonance at 0.675 MeV exhibits isotropy, anisotropy can be seen for the resonance at 2.64 MeV

Spraker et al., The 11B(p,α)8Be → α+α and the 11B(α,α)11B Reactions at Energies Below 5.4 MeV (2012) — p. 358-360

Editorial note, tabletop extrapolation: For yield measurements NEAR the 675 keV resonance, detector angle costs only a few percent, so geometry and shielding can drive PIPS placement - at other beam energies get angular-distribution data or carry an anisotropy uncertainty, and remember angle still affects kinematic acceptance and scattered-particle background.

Cited in: Experiments by Energy Band

The detectors were located 16.5 cm from the target ... 60, 75, 90, 115, 135, and 160 [degrees], with each detector subtending a solid angle of approximately 2.5 x 10-4 sr. ... The large peak just below 1 MeV is produced by elastically scattered protons

Spraker et al., The 11B(p,α)8Be → α+α and the 11B(α,α)11B Reactions at Energies Below 5.4 MeV (2012) — p. 358-360

Editorial note, tabletop extrapolation: Expect the PIPS spectra to carry a scattered-proton peak wherever two-body kinematics puts it for the actual beam energy and detector angle - compute that first, then set the alpha window or choose an absorber; a proton-stopping foil also costs the alphas energy and straggling, so evaluate it with stopping-power numbers before committing.

Cited in: Experiments by Energy Band

the target, which was composed of 56 +/- 2 ug/cm2 of isotopically pure 11B deposited on a 9 ug/cm2 carbon backing. Target thickness was measured using elastically scattered a-particles at 4.86 MeV, where the ratio of the elastic scattering cross section to the purely electromagnetic Rutherford cross section is known at a scattering angle of 165 deg. This measurement provided two independent measures of the target thickness via the known cross section and via the energy loss as measured by the broadening of the elastic peak. Analyses of both results agree and provide a target thickness of 56 +/- 2 ug/cm2 leading to a 3.6% systematic uncertainty in our yields.

Spraker et al., The 11B(p,α)8Be → α+α and the 11B(α,α)11B Reactions at Energies Below 5.4 MeV (2012) — p. 360

Editorial note, tabletop extrapolation: Defines 'thin' for the reference machine's boron target (tens of ug/cm2) and gives two thickness checks performable with their own detectors - reproducing the alpha-scattering one requires the stated alpha energy and angle where the ratio to Rutherford is known, plus calibrated fluence and solid angle.

Cited in: Experiments by Energy Band

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

a peak capture rate is obtained with a 3.89 cm layer of HDPE. This detection method involves positioning the HDPE as close to the neutron source as possible ... A piece of silver ... and its subsequent radioactive decay can be measured. An activation chamber was made HDPE with another layer behind the silver

Kovalchick, Deuterium Fusion Using Inertial Electrostatic Confinement (2012) — p. 23-24

Editorial note, tabletop extrapolation: If the builder cross-checks PIPS counting with activation or a moderated tube (e.g., for D-D work), start from the cited thickness but optimize for the actual geometry - a thickness scan or transport estimate - since the optimum moves with source spectrum and arrangement. Ag-108 (t1/2 2.37 min) remains the classic activation target.

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.

Fast neutron bubble detector acts as backup to electronic detection

Hull, Fusor: An Easy to Construct Fusion Reactor Based on Inertial Electrostatic Confinement (2009) — p. 43

Editorial note, tabletop extrapolation: Same philosophy for p-B11: pair the PIPS/electronics chain with a passive detector (e.g., CR-39 track plastic) immune to the cyclotron's RF pickup.

Cited in: Experiments by Energy Band

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

The best detection of the beam deflection was made by mounting X-ray film on the probe and exposing it to both the undeflected and deflected beam.

Sewell, 184″ Cyclotron: Vertical D.C. Electrostatic Deflector — MDDC-1051 (1947) — p. 2

Editorial note, tabletop extrapolation: Start extraction commissioning with on/off comparison images - film or a scintillator-plus-camera at the channel exit - alongside a shielded Faraday collector: integrating detectors trade time for sensitivity and ignore RF pickup, while a well-guarded electrometer is also capable of picoamps when the noise is managed. Use both; agreement is the commissioning signal.

Cited in: Experiments by Energy Band

Since the singly-ionized nitrogen ions at this radius have an energy of only 2 1/2 Mev, it may be concluded that the burst of radiation observed was indeed due to triply-charged nitrogen ions.

Howard (ed.), Electromagnetic Research Division Quarterly, period ending 30 June 1952 — ORNL-1345 (1952) — p. 9

Editorial note, tabletop extrapolation: The evidentiary pattern transfers - an observed nuclear signature whose energetics disfavor the alternative species is strong evidence - but treat it as evidence, not proof: identify the radiation, use modern Q-values and cross-sections, run detector controls, and exclude electron-induced X-rays, contaminants and other q/m candidates (and remember radiative capture has no threshold, only Coulomb suppression). The reference machine's 5.6x-background best-beam sits in this tradition as supporting evidence for acceleration, with species claims needing their own case.

When nitrogen was bombarded in the form of TaN, 2-minute, 10-minute, 112-minute, and 15-hour activities were observed ... it is difficult to assign any but the 10-minute activity as unequivocally due to N 13

Howard (ed.), Electromagnetic Research Division Quarterly, period ending 30 June 1952 — ORNL-1345 (1952) — p. PDF 10 (printed 10) and PDF 11 (printed 11)

Editorial note, tabletop extrapolation: Not a casual check, and not closed to the reference machine by any blanket "threshold": which reactions are open depends on the beam SPECIES and the target ISOTOPES - D-D is exothermic with no threshold, so 150 keV deuterons make neutrons and tritium, and neutrons can then activate surrounding materials by capture, with no charged-particle threshold at all (dg-1041, dg-1047). Before using activation as an energy bound: pick candidate reactions from modern Q-values, thresholds and cross-sections for the actual beam and target; treat a half-life alone as preliminary (ambiguous assignments, tiny near-threshold yields, contaminants that dominate) until backed by an absorber or spectrum check; and accept that deliberately activating a target means prompt radiation, a survey, dosimetry and handling the residual activity. [Corrected 2026-08-23: earlier wording said "below nuclear thresholds the 150-keV reference machine cannot use this" and called the method "only a GM counter and a stopwatch" - the same absolute already corrected at dg-1041, dg-685 and dg-695.]

Unfortunately it is theoretically impossible to filter a transient without introducing time delay. The time delay thus introduced was kept to a minimum.

Foss et al., Cyclotron Component Design Technical Reports — TID-454 (1952) — p. 170-171

Editorial note, tabletop extrapolation: General fast-timing wisdom for beam-pulse and kick timing chains: every smoothing stage costs latency. Measure the chain's end-to-end latency and compensate the FIXED part in the trigger schedule or delay setting; threshold bias (the historical method) only advances the crossing for a given waveform - it walks with amplitude and slew rate, so calibrate it over the expected pulses.

the bias adjustment is made with reference to the actual critical firing voltage.

Foss et al., Cyclotron Component Design Technical Reports — TID-454 (1952) — p. 172

Editorial note, tabletop extrapolation: A self-calibration idiom worth copying into any comparator/discriminator in the DAQ: trim to the observed threshold at session start (their multivibrator = today's comparator with drifting offset). That removes the threshold error present AT calibration - within-session drift, and aging that changes delay or hysteresis rather than threshold, still need periodic re-trim or monitoring.

the automatic pulse-height circuit had to work on a peak-reading principle.

Foss et al., Cyclotron Component Design Technical Reports — TID-454 (1952) — p. 171

Editorial note, tabletop extrapolation: Directly applicable to pulse chains fed by beam pickups or PMTs at low rep rate: stabilize on detected peak height at the discriminator input. This compensates multiplicative gain drift in the stages inside the loop and reduces amplitude-induced time walk - pulse-shape changes, baseline shifts and discriminator drift are outside it, so keep a timing calibration (or constant-fraction discrimination) as well.

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 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

the energy distribution of protons in the cyclotron beam is readily determined by measuring this excitation function and comparing it with the published data.

Cohen, Measurement of Beam Energy and Energy Distribution on an Internal Cyclotron Target — ORNL-1347 (1952) — p. 9

Editorial note, tabletop extrapolation: ENERGY SCOPE: Cu63(p,n)Zn63 needs ~4.2 MeV (verify against evaluated data at use time) - closed at reference-machine energies. What transfers is narrower than the note once claimed: the unfolding needs multiple independent response kernels, so a single B11(p,alpha) yield number constrains but cannot recover a spectrum; measurements at several calibrated degrader settings can build a response matrix, and a PIPS behind degraders is range spectrometry - a different, complementary method.

Cited in: Shielding a Small Cyclotron

There is a slight increase in probe current with increasing radius because of increased thermal emission of electrons from the probe as it was bombarded by protons of higher energy.

Howard (ed.), Electromagnetic Research Division Quarterly, period ending 31 December 1951 — ORNL-1269 (1952) — p. 40

Editorial note, tabletop extrapolation: Same artifact family as the reference machine's Faraday-cup offsets - with the mechanisms kept straight: at nA and sub-MeV, deposited power is ~mW and an ordinary wire will not reach thermionic temperatures (do the conduction arithmetic before invoking it); SECONDARY emission and electronic offsets are the live suspects at that scale, so bias or shield the probe and log the baseline against beam-off checks.

an extension of the energy range much beyond 1.3 E0 requires an unreasonably large vacuum chamber at the exit of the magnet.

Alford, Bilaniuk & Hawrylak, Broad Range Spectrograph for Use with the Rochester 27-inch Cyclotron — NYO-9683 (1961) — p. 7

Editorial note, tabletop extrapolation: SCALE-HONEST only when the scaling is done: the geometry fixes E/E0 ratios, but reaching a given E takes B*R. For ~170 keV protons, B-rho ~ 0.06 T-m, so an R ~ 5-10 cm bench version needs roughly 0.6-1.2 T - iron-pole territory, not a few hundred gauss. Still compelling as a teaching-lab focal-plane instrument; copy the optics and size the field honestly.

Since all exposures were for equal times, the measured intensity of each group provided a measurement of relative solid angle as a function of focal position.

Alford, Bilaniuk & Hawrylak, Broad Range Spectrograph for Use with the Rochester 27-inch Cyclotron — NYO-9683 (1961) — p. 12

Editorial note, tabletop extrapolation: Teaching-lab gold with its conditions stated: one sealed alpha source calibrates the focal-plane acceptance function that theory only estimates - under controlled equal-exposure conditions (stable source output, fixed geometry, detector response and processing held constant, no saturation). What it cannot test: proton-specific detector response and beamline effects, which need their own checks. Validate the peak-position convention against the actual detector's lineshape.

Three emulsions each 80 x 200 mm can be mounted in a special camera ... which allows six different exposures to be made without breaking the spectrograph vacuum.

Alford, Bilaniuk & Hawrylak, Broad Range Spectrograph for Use with the Rochester 27-inch Cyclotron — NYO-9683 (1961) — p. 10

Editorial note, tabletop extrapolation: The principle is vacuum cycles are the tax on focal-plane work - amortize them: a movable frame of film/CR-39 chips (integrating, etched after removal - a survey detector, not prompt readout) or a silicon strip/PIN-diode array (direct charged-particle detection; a bare SiPM is a photon detector and needs a scintillator) behind the next machine's analyzer. Their split - survey in emulsion, precision groups in counters - still maps cleanly.

The output pulses are made about 10 volts high. Their rise time is of the order of 5 ns or less. ... When the cyclotron is operating at about 10 mc the shortest rise time available is about 3 ns, according to sampling oscilloscope observations.

Fulbright et al., A Fast Neutron Time of Flight System for Use with Cyclotrons — NYO-9360 (1962) — p. PDF 8 (printed 4) for the antenna and harmonic-mixture sentences; PDF 9 (printed 5) for the 10 V / 5 ns / 3 ns figures; PDF 10 (printed 6) for the retune time

Editorial note, tabletop extrapolation: Buildable on the reference machine: loose capacitive pickup plus stub-phased harmonic mixing sharpens the oscillator's waveform into a fast edge with zero active electronics at the pickup - noting a passive stub network can only re-phase and weight harmonics ALREADY in the picked-up signal (an oscillator's tank waveform has them; a purified sine does not). Check the pulse shape after every retune, and measure the actual 10-90% rise rather than assuming the vintage figure.

stop trigger pulses emerge only after an event occurs in the neutron detector.

Fulbright et al., A Fast Neutron Time of Flight System for Use with Cyclotrons — NYO-9360 (1962) — p. 8

Editorial note, tabletop extrapolation: The reversed (common-stop) architecture inverts the time axis and slashes unnecessary converter starts and their dead time (pileup in the detector chain is its own problem). With a modern TDC or digitizer you can instead timestamp both the detector and RF streams continuously and form differences offline - the gated arrangement remains the right shape for TAC-style hardware.

The problem was to set the continuously variable slow discriminator dial so that the level of discrimination would correspond to a certain standard light signal from the scintillator. A Cs137 source was used as a standard. The discriminator level was set to correspond to the peak in the observed y-ray pulse height spectrum.

Fulbright et al., A Fast Neutron Time of Flight System for Use with Cyclotrons — NYO-9360 (1962) — p. 13

Editorial note, tabletop extrapolation: Two transfers: keep the background-rejection threshold out of the timing path (the source's chains fought when combined), and standardize the threshold against a reproducible spectral feature - in an organic scintillator a Cs-137 source gives a Compton distribution, so define the set-point on its observed peak or edge, exactly as the source did with its own spectrum. A check source is cheap in effort; acquiring one follows the applicable sealed-source rules.

One channel is equivalent to about one millimicrosecond. ... The full width of the lines at half maximum is about 2 ns in this favorable case. Generally the widths have ranged from approximately this to about 3.5 ns, although it is easily possible to do worse by using incorrect stop signal pulses, or too low photomultiplier voltage, etc. ... the thickness of the [scintillon] neutron detector used in these measurements was 1 in, which made the counting efficiency high, but contributed appreciably to widening the peaks. The flight time of a 5 Mev neutron through the detector is about 0.8 ns, for example.

Fulbright et al., A Fast Neutron Time of Flight System for Use with Cyclotrons — NYO-9360 (1962) — p. 11

Editorial note, tabletop extrapolation: DIRECT budgeting template: list every term (source bunch width, detector transit, electronics jitter, reference-edge slope) and know which one you bought deliberately. A next machine's TOF or coincidence lab should have students build exactly this budget before blaming the electronics.

Most experiments have been made with flight paths less than 1.2 meters long in order to avoid difficulty with neutrons scattered from the solid concrete floor

Fulbright et al., A Fast Neutron Time of Flight System for Use with Cyclotrons — NYO-9360 (1962) — p. 12

Editorial note, tabletop extrapolation: DIRECT pair of lessons: (1) geometry (short path, floor clearance, timing window) is often cheaper background suppression than shielding mass; (2) never bolt on a detector shield whose effect on efficiency you haven't calibrated - it converts a known instrument into an unknown one. Both transfer to any next-machine counting station.

Cited in: Shielding a Small Cyclotron

Calibration curves were obtained by use of the D(d,n) reaction, the cross sections for which are known to 4% accuracy. ... the yield of annihilation radiation from the N13 decay positrons was compared with the known flux of annihilation radiation from a sodium 22 source calibrated at the Bureau of Standards. A coincidence counter setup was used for these measurements. Results obtained in this way agreed to within 10% with expectations from the absolute calibration of the neutron detector

Fulbright et al., A Fast Neutron Time of Flight System for Use with Cyclotrons — NYO-9360 (1962) — p. 12

Editorial note, tabletop extrapolation: Metrology doctrine that transfers whole: one calibration path is an assumption, two are a measurement. For a next machine's yield claims, require a primary calibration plus an activation- or source-based cross-check, use CURRENT evaluated cross sections at the actual energy and angle (the 4% was the authors' 1950s assessment), and treat the disagreement as a diagnostic to explain - folding it into the systematic only once understood.

The first factor in (1) is exact. It does not depend on the exact shape of the response curve (pulse-height vs proton recoil energy) of the scintillator.

Fulbright et al., A Fast Neutron Time of Flight System for Use with Cyclotrons — NYO-9360 (1962) — p. 15

Editorial note, tabletop extrapolation: A lovely teaching derivation - a two-factor closed form students can test against a calibration reaction - and the transferable habit is identifying which factor rests on which assumption. Validate against calibration or Monte Carlo for the actual detector and energy range before leaning on it.

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).

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.

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 monitor and detector employed were aluminum-walled ionization chambers, with DC Amplification, indicating on microammeters placed outside the magnetic field of the cyclotron.

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: Analog meter movements and photomultipliers misread in modest stray fields (PMTs at well under a millitesla); GM tubes themselves are largely field-insensitive, though their electronics may not be. The transferable practice is the source's separation: passive sensing volume at the measurement point, readout where the field is negligible - verified by moving the readout and watching for a change.

Experiments using carbon disc detectors sandwiched between slabs of absorber gave exponential attenuation with half-value determination which were generally made with better precision than those with ionization chambers.

Moyer, Hildebrand, Knable, Parmley & York, Character of the Radiation Field and Shielding at the 184-Inch Cyclotron — AECD-2149, UC Radiation Laboratory (1947) — p. 3

Editorial note, tabletop extrapolation: The C12(n,2n) reaction itself is blind below ~20 MeV and useless at sub-MeV neutron energies; the transferable idea is the energy-thresholded activation foil as a passive, field-immune detector that answers one question cleanly.

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.

blocks of either of two different materials could be placed (without disturbing the vacuum system) immediately in front of the 2-inch brass stopping plate

Harvard University Cyclotron Laboratory, Quarterly Progress Report, 1 June – 31 August 1964 — p. 2

Editorial note, tabletop extrapolation: A cup's reading depends on its stopping surface through secondary emission and backscatter - a two-material comparison tests the SENSITIVITY to that choice, not the absolute error (both materials can be wrong the same way). For an absolute bound: verify full stopping, control geometry and contact, suppress electrons, and bring an independent current reference or a validated emission/backscatter calculation.

most of these data have an accuracy of ~ +-10%.

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. 40

Editorial note, tabletop extrapolation: The one thickness method that needs no balance and works on a mounted film - with a surface-barrier detector and MCA. Quote absolute thickness no tighter than CURRENT stopping tables allow at the actual energies, combine straggling/calibration/fit uncertainties, and remember the alpha source is a regulated sealed source, not generic bench stock.

light intensity change is not a very useful technique for carbon films of thickness greater than 40 or 45 ug/cm2.

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. 43

Editorial note, tabletop extrapolation: A photodiode and lamp sort carbon stripper/backing foils into thickness bins as an incoming-inspection tool - calibrated against weighed foils and RE-checked periodically, since optical response drifts with lamp, alignment and film morphology; expect it to saturate out near the source's 40-45 ug/cm2 carbon ceiling.

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.

This is all the calibration which is necessary since now only energy shifts are of interest. ... the vacuum must be maintained at a pressure of less than 10-4 torr to avoid a glow discharge caused by the detector bias voltage. Such a discharge can damage the detector.

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. 63

Editorial note, tabletop extrapolation: The whole rig is a surface-barrier detector, preamp, biased amp and a stable, linear MCA - Thompson wrote it up precisely so small labs could build it. Estimate fractional channel positions from adjacent-channel counts (peaks are Gaussian) and state the resulting channel uncertainty; whole-channel reading of a small shift is coarse. The pressure threshold for bias-induced glow depends on voltage and geometry - treat 1e-4 torr as his operating requirement and verify your own.

Attempts at single step evaporations to these thicknesses were unsuccessful because of rupturing of the foil due to heat damage.

International Nuclear Target Development Society Workshop — ANL/PHY-84-2, Argonne National Laboratory (1983) — p. 230

Editorial note, tabletop extrapolation: Stretched polypropylene is a workhorse thin window for gas counters and low-energy vacuum isolation, and the step-and-cool discipline is the transferable method - applied to another polymer as a trial with its own thermal and adhesion checks, not as a universal recipe.

a linear translator was developed in order to move the detector, a Faraday-cup in a radial direction behind the dummy dee. In addition to the registered ions the corresponding x-position of the cup is measured, too … The ion source is located at position (-15, 5, 0) (all figures in mm), a Faraday-cup as an ion detector moves along the line y = -31 mm, the so-called sensor-line. This line extends parallel to the lower edge of the dummy dee with a distance of about 1 mm.

Wolf, Rueß & Prechtl, Simulation and Detection of the Helical Ion-Paths in a Small Cyclotron — MOB02, Proceedings of Cyclotrons2016 (2016) — p. 1, 2

Editorial note, tabletop extrapolation: A radially scanned cup with simultaneous position readout turns a single detector into a turn-structure probe, giving I(x) profiles that can be compared point-by-point against a simulated orbit bundle.

Three probes at 120 degrees apart can be used for beam detection ... Particles emerging from the accelerator are detected using a microchannel plate detector

Clark, Halbach, Kunkel, Leung, Li & Young, A Compact Permanent Magnet Cyclotron for Accelerator Mass Spectrometry — Proceedings of Cyclotrons'95, Cape Town (1995) — p. 1

Editorial note, tabletop extrapolation: Editorial note, tabletop extrapolation: multiple azimuthally separated probes let orbit-centering errors be reconstructed rather than inferred from one radial scan — given radial or position data at each azimuth; worth reserving the flange positions even if only one probe is built at first. A microchannel plate is a single-particle-class detector, suited to beam currents far below Faraday-cup sensitivity.

A sensitive electronic microammeter was connected directly between the target and ground, and its reading was taken as an indication of the relative number of protons hitting the target per unit time. The maximum beam current of this machine is about two microamperes. The second and probably more reliable method was to use a Geiger counter to measure the reaction counting rate from the Li7(p,γ)Be8 reaction occurring in the lithium target. The reaction rate is proportional to the beam intensity. The measured beam current has been found to be proportional to the counting rate but only an approximate indication of absolute beam current. The maximum counting rate was about 1500/min against a background of about 20/min ... the data from the beam current indicator served mainly as a check

Burns, Experimental Program with the Iowa State University Undergraduate 1.5 Mev Cyclotron — Proceedings of the Iowa Academy of Science 68(1), 483–491 (1961) — p. 2, 3

Editorial note, tabletop extrapolation: Editorial note, tabletop extrapolation: a nuclear-reaction counting rate is insensitive to the secondary-electron and leakage-current artifacts that plague bare target-current readings — the source itself found current only approximately proportional to count rate. A GM tube on a lithium target makes a cheap second, independent monitor where the rate is statistically significant for the actual current, geometry and detector; the Li7(p,γ)Be8 reaction is exothermic, its yield dominated by the strong 441 keV resonance (the source's 'threshold' wording on p. 488 is loose), and its ~17 MeV capture gammas are the same reason this reaction carries shielding obligations.

The Li7(p,Y)Be8 resonance reaction has a threshold energy of 0.441 Mev and has a large cross section ... A thick (0.5 mm) Li7 target was attached to the target and r2 was set so that the energy of the protons would be about 1 Mev ... The NaI crystal was located about fifty centimeters from the target ... The scintillation spectrometer was calibrated using the unresolved (1.25 Mev) Y-rays from Co60 ... The reaction actually yields two high energy Y-rays, the 17.5 Mev one and also one of energy of 14.5 Mev ... it had an abundance of 30%, as determined by the relative counting rates

Burns, Experimental Program with the Iowa State University Undergraduate 1.5 Mev Cyclotron — Proceedings of the Iowa Academy of Science 68(1), 483–491 (1961) — p. 7-9

Editorial note, tabletop extrapolation: Editorial note, tabletop extrapolation: the strong 441 keV resonance puts high yield within reach of even modest machines, and a ~17 MeV gamma is a distinctive high-energy signature — though NaI response at 15-18 MeV is pair-production-dominated and needs calibrated interpretation (the source's own 15 MeV pulse-height reading needed a +0.5 MeV pair-escape correction and still sat 2 MeV low, within their stated uncertainties). Yield versus target radius maps beam energy against the resonance once target energy-loss and beam-spread corrections are applied; a gamma-onset reading is not a threshold measurement, because capture occurs below the resonance too. Photons this energetic exceed photoneutron thresholds in nearby materials — assess shielding, dose and activation before running the experiment.

The samples to be bombarded were machined (dry) in the form of thin wafers (1 mm thick) from spectroscopic carbon. The target radius was set so the energy of the protons would be only slightly greater than the threshold energy for the reaction. This was done to minimize the absorption of the β+-particles leaving the sample, thus providing the maximum flux at the counter. The sample was then bombarded for about one half-hour. After bombardment, the activated sample was removed from the machine and taped to a two-inch NaI crystal scintillation counter located in a lead house for minimum background. The counting was done for fifteen-second periods every minute for one half-hour ... A plot of the natural logarithm of the counting rate versus elapsed time has a slope equal to 0.693/T1/2, where T1/2 is the half life for the decay ... gave T1/2 = 10.3±0.3 min. The average value of three such determinations also yielded a half life close to 10.3 min. for the N13. This is in reasonable agreement with the published value of 10.1 min.

Burns, Experimental Program with the Iowa State University Undergraduate 1.5 Mev Cyclotron — Proceedings of the Iowa Academy of Science 68(1), 483–491 (1961) — p. 9, 10

Editorial note, tabletop extrapolation: Editorial note, tabletop extrapolation: off-line activation counting decouples the measurement from accelerator-correlated pickup — the machine only has to run for the bombardment, and a known half-life gives a self-grading answer. Barely-above-onset bombardment as a technique for keeping activity near the surface is a subtle, transferable target-design trick.

The difference can be accounted for by the absorption of the aluminum foil covering the NaI crystal, and also by the fact that most of the N13 atoms are located below the surface of the carbon

Burns, Experimental Program with the Iowa State University Undergraduate 1.5 Mev Cyclotron — Proceedings of the Iowa Academy of Science 68(1), 483–491 (1961) — p. 10

Editorial note, tabletop extrapolation: Editorial note, tabletop extrapolation: window and source-layer energy loss can significantly bias an MeV-class endpoint measurement — model each layer's areal density between source atom and scintillator, alongside detector resolution, calibration and backscatter, before doubting the physics. Listing the absorbers explicitly is the difference between a validated measurement and a shrug.

For instance, the placement of the radially adjustable florescent screen at its present azimuthal location was dictated by practical limitations. By happenstance this position was very close to the azimuthal location of the maximum radial betatron amplitude (turn-to-turn spacing is at its greatest), thus providing the ability to discern the axial betatron motion.

Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007) — p. 2

Editorial note, tabletop extrapolation: A design rule worth applying deliberately rather than by luck, as it happened here: put the viewport/screen azimuth where turn-to-turn separation is greatest — that is where individual turns and the vertical oscillation can actually be told apart in a photograph. On a machine with only a handful of usable ports, model or measure the turn-spacing azimuth first and let that decide which port earns the diagnostic.

Presently proton beam currents of order 20µAmps can be focused onto the collector. The increased beam power has been duly noted; it is now sufficiently high to damage the Radeline fluorescent screen. The screen has blistered and no longer fluoresces near the median plane, rather glowing embers can be seen. […] Not directly pertaining to ion production, but worth mentioning is the installation of a reset-able minutes meter to track filament lifetime. Filament lifetime is presently the limitation in operating time.

Koeth, Hanebuth, Hoffman & Schneider, Rutgers 12-Inch Cyclotron Ion Source Studies: Part II (2007) — p. 6

Editorial note, tabletop extrapolation: Two limits this machine hit that yours should be budgeted against, not assumed: its ~20 µA focused beam blistered the Radeline fluorescent screen at the median plane (screen survival is a power-density question — evaluate deposited W/mm² for your own screen, keep screens replaceable, and use a Faraday cup for anything quantitative), and its operating time was bounded by filament hours, tracked with a resettable minutes meter — a trivial addition that turns a nuisance into data and tells you whether filament life is YOUR limiting consumable.

Due to the extremely small geometry and cost of custom manufactured phosphor screens, we elected to produce our own screens. Mastering this technique has proven invaluable, allowing experiments with many different phosphors and target arrangements. […] Initially phosphor type P-22 green, the standard oscilloscope CRT phosphor, was used for maximum visual sensitivity. Using a settling technique, 1-inch square metal plates were coated with a uniform phosphor layer. The phosphor coated plate was attached to a metal carrier plate using electrically insulating screws – the phosphor plate was separated from the carrier plate by 1/8-inch to keep the capacitance reasonably low. … The screen was mounted at a 45° angle with respect to the incident beam and to the axis of a glass view port.

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

Editorial note, tabletop extrapolation: Squarely a tabletop technique — custom screens at this size are disproportionately expensive, and settling powdered phosphor onto a 1-inch plate is small-scale bench work: treat the powder with respect (SDS, containment, no food surfaces). "P-22 green, the standard oscilloscope CRT phosphor" is the authors' description. The Fig. 7 caption enumerates what mastering the process enabled: directly coated carrier plates, solid plates on isolation plates, six identical strips, edge and central fiducial markings, and test strips carrying six different phosphors.

The center conductor of a coaxial cable was connected to the phosphor plate and the coax shield to the grounded carrier plate, the cable was routed to a BNC vacuum feed through connector. The electrical isolation and connectivity permits the phosphor plate to double as a Faraday collector. The low capacitance of the collecting plate should permit time-resolved electrical measurements of the impinging beam.

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

Editorial note, tabletop extrapolation: Excellent value on a port-starved machine: one feedthrough and one insulated plate serve as viewing screen AND current collector. Two honesty limits: the electrical reading is NET collected current (secondary emission, charging and leakage bias it — suppress or calibrate before quoting microamps), and the time-resolved capability is the source's stated expectation from low plate capacitance ("should permit"), with real bandwidth set by the whole readout chain. The fiducial markings on the screen edges (Figs. 7 and 8 captions) are what turn the glowing spot into a position number.

The Hall probe was connected to a Gauss meter whose analog recorder output was the input for a multimeter. The output of the multimeter was fed into a data acquisition unit, and the number of steps taken by the motor was read by the computers serial port. A LabView program wrote the gaussmeter’s value and probe’s position into a text file. The gauss meter was calibrated against a very well known NMR magnet, and a precisely located “magnetic needle” gave the probe’s position calibration.

Koeth, Report on the 12-Inch Cyclotron Magnet Study: Measurements, Modeling, and Future Plans (c. 2005) — p. 3

Editorial note, tabletop extrapolation: Two calibrations, not one: absolute field against an NMR reference, and probe POSITION against a precisely located magnetic needle. Field calibration alone leaves the scan's radial origin unknown — and the interesting structure (taper, edge roll-off, n(r)) is all position-referenced. The magnetic-needle trick is cheap and is the same idea this group later industrialized into the coil-wrapped iron-needle field bumps of the 2011 AVF study.

Our group custom designed and built a computer-controlled stepper-motor driven X-Y stage which utilized zero-backlash acme threads to sweep a magnetic field probe through the median plane. An F. W. Bell 7010 hall probe based gauss meter was used for the AVF measurements; the gauss meter was outfitted with an RS232 data port. The computer program which controlled the X-Y stepper motors also recorded the gauss meter data, fully automating the measurement process.

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: A named, buildable instrument set for a small pole map, with the load-bearing detail being ZERO-BACKLASH acme threads: a serpentine raster reverses direction every row, and lead-screw backlash then puts alternate rows out of registration (scan every row the same direction if your screws are ordinary, or measure the backlash). The meter needs more than a serial port: adequate range, resolution, stability and probe-orientation control, calibrated (this program's NMR-reference practice, dg-1684). The 7010's RS232 port is what let one program drive the stage and log the field together.

This caps thickness was greater than the turn-to-turn spacing of the ion revolutions at a radius greater than 2.1 inches when operating at 14.900MHz with a DEE voltage of 7,500 Vp-p. Such a thick tip would prevent the ions from hitting the sensitive portion of the ion collector, rather the ions would just return to chassis ground. A new, simpler, Faraday cup was installed. It simply consists of an unshielded aluminum block. RF suppression was still a concern, so externally a notch filter, with -100dB of rejection at 14.900MHz, was installed in the Faraday cup line that connects to the electrometer. An RF choke was also installed in this line, just before the electrometer connection.

Koeth, Hanebuth, Schneider & Hoffman, Observation of Betatron Motion in the Rutgers 12-Inch Cyclotron (2006) — p. 4

Editorial note, tabletop extrapolation: A specific, easily repeated mistake: a grounded shield that projects into the incoming beam path intercepts ions before the collector once its effective radial thickness exceeds the local turn spacing — compute Δr(r) (dg-1740) before designing any probe tip. This machine's solution moved RF rejection out of the vacuum entirely (bare aluminum block collector; -100 dB notch filter plus RF choke in the electrometer line); suitably thin or recessed in-vacuum guarding remains an option the memo simply did not need.

We then set the camera to a 15 second exposure and scanned the florescent screen slowly. The resulting image, Fig 10, clearly showed periodic behavior about the median plane with increasing frequency and decreasing amplitude as r increased. This was immediately identified as betatron motion.

Koeth, Hanebuth, Schneider & Hoffman, Observation of Betatron Motion in the Rutgers 12-Inch Cyclotron (2006) — p. 5

Editorial note, tabletop extrapolation: An almost free beam-dynamics diagnostic: a phosphor screen on a manual radial feedthrough plus a long-exposure camera through a viewport records vertical betatron structure across the scanned interval in one frame, no electronics. It is a QUALITATIVE record as taken; a tune number additionally needs calibrated radial coordinates and peak-spacing analysis (dg-1741 is this memo's own worked version).

The instrumentation is based on a phosphor coated screen mounted on a radial probe system. The probe is manually displaced along the chamber's radius by the operator. A view port next to the radial probe allows to take images of the beam induced luminescence of the screen with a DSLR camera. The camera is set for long exposure shots (up to 5 seconds) while the operator maneuvers the radial probe. These beams images then feature a vertical and radial 2-dimensional picture of the beam. ... This measurement technique requires to calibrate the beam images to transform their pixel grid into coordinates in the usual frame of reference centered on the central axis of the magnet. To reach that goal, calibration pictures of the radial probe are taken each time a new set of data is taken.

Hernalsteens, Ponter, Beaudoin, Koeth, Ruisard & Miller, Betatron Tune Characterization of the Rutgers 12-Inch Cyclotron for Different Magnetic Poles Configurations (2016) — p. 2

Editorial note, tabletop extrapolation: A demonstrated low-cost turn-by-turn diagnostic: phosphor screen on a linear feedthrough, a viewport, a consumer DSLR on long exposure. The per-dataset probe calibration image is the detail that makes the images quantitative — the source uses it to transform the pixel grid into magnet-centered coordinates. Turn resolution on another machine still depends on its turn spacing, light yield and optics (the source's own dee-voltage tradeoff, dg-1750, is the knob).

The target, located at the end of a radial probe, is electrically isolated and connected to a BNC vacuum feed through. A short coaxial cable connected the target's signal to the input of oscilloscope's vertical amplifier. With 1MΩ input impedance, a 1µA beam current creates a 1V deflection. The rise time, as well as decay time noted in the beam current (lower) trace of figure 1 is an artifact of the RC response of the measurement circuitry, which utilized a low pass filter to suppress RF pickup from the DEE. The actual ion source current profile is prompt.

Koeth, Neutron Production with a 12-Inch Cyclotron (2017) — p. 2

Editorial note, tabletop extrapolation: A dead-simple current diagnostic for a pulsed machine: isolated target, BNC feedthrough, 1 MΩ scope input — 1 µA reads as 1 V. Three qualifications before trusting the number: it is COLLECTED current (secondary-electron emission makes it differ from incident beam unless suppressed or calibrated), the pulse must be long against the circuit RC for the trace to reach V = IR, and — the source's own warning — the visible rise and decay edges belong to the RF-suppression filter, not the beam.

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.)

At this location the 1.6 cm diameter X 2.5 cm tall BF3 tube was 29.5 cm away from the target. Assuming the most favorable orientation of the cylindrical BF3 tube, the maximum area of the detector is taken to be 4 cm2; the actual effective area may have been as much as one half that, or 2 cm2. Sitting at a radius of 29.5 cm, the tube only intercepted 4 cm2 out of the available 10,930 cm2 4π spherical surface – yielding a geometrical efficiency of 3.7x10-4.

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

Editorial note, tabletop extrapolation: The solid-angle bookkeeping any yield estimate needs, with its assumptions visible: 3.7e-4 is an upper-bound geometric factor under the most favorable assumed orientation (the source's own 2 cm² alternative gives 1.8e-4 — a factor-two spread the source acknowledges rather than bounds). The arithmetic checks (4π × 29.5² = 10,935 cm²; 4/10,935 = 3.7e-4). A real response number still needs intrinsic efficiency, moderation and angular response on top of geometry.

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.

The target was position for a nominal 100keV incident deuteron beam energy (r=0.067m). ... When operating in this fast cyclotron-pulsed mode with a 10us duration of beam-on-target time, an average of 5 D-D fusion neutrons were produced. During most cyclotron pulses, these neutrons would completely miss the detector altogether, with approximately 1 out of 250 cyclotron pulses registering a neutron. The likelihood of more than one striking the detector per cyclotron pulse was vanishing small. This was crucial to the measurement.

Koeth, Gilde & Moroch, Measurement of Neutron Diffusion Time from Fast Pulsed Systems (draft, 2020) — p. 2

Editorial note, tabletop extrapolation: Radial target placement doubles as an energy selector: at fixed field the incident energy follows radius (the 100 keV at r = 0.067 m figure checks against E = q²B²r²/2m at the stated 0.96 T — computed ≈99 keV), and yield follows the energy-dependent D–D cross-section. Detected rate also depends on intercepted current, target loading and geometry, so calibrate yield against position rather than assuming it — and the method requires a movable radial probe, which not every machine has. Draft report. (The quoted passage begins on p.2 and continues on p.3.)

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.

The neutron detector consisted of a ~2-foot-long 3He tube nested within a stack of pure polyethylene blocks. The two sides and back were stacked with neutron absorbing borated poly blocks to set boundary condition.

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

Editorial note, tabletop extrapolation: A simple, buildable moderator/detector assembly: plain polyethylene where you want thermalization, borated polyethylene where you want the diffusion problem bounded. Reported as this source's construction. Draft report.

A preliminary demonstration of the neutron diffusion effect is given by a digital oscilloscope set to infinite persistence which recorded the electronic pulses generated from the detection of neutrons over numerous cyclotron pulse events. … The upper yellow trace in figure 4 is the rectified reference of the actual RF “on time” pulse … The lower blue trace displays the pulses from the 3He detector NIM electronics, which are seen to continue to arrive long after the cyclotron RF is off. After 5 minutes of acquisition at 100 pulses per second a total of 250 neutrons events are observed. One can see the slowest neutron took 550us after production (RF off) to reach the 3He detector. This is not a quantitative measurement, since many of the neutron detector pulses overlap and blur their individual arrival times.

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

Editorial note, tabletop extrapolation: A zero-cost first look before building any timing electronics: infinite persistence on a two-channel scope already shows whether the physics is there — and the source is explicit that this stage is not quantitative. The Fig. 4 caption says "in excess of 500 us" where the text says 550 us. Draft report.

To quantify the thermalization and diffusion time, an Ortec model 567 time-to-amplitude-converter (TAC) was employed as outlined in figure 5. … In the present case, the full-scale time window was set 1ms. The TAC then delivered a proportional output pulse, ranging from 0 to 10V, corresponding to a time period of 0 to 1ms. Thus, if the period between the start and stop pulse was 500us, then the TAC would then output a 5V pulse. The TAC output was then binned by a multi-channel analyzer (MCA) to generate the temporal profile. The MCA used was an Ortec EZMca set to a conversion gain of 512 channels. If the time between start and stop pulses exceeded 1ms, the TAC simply reset without triggering an output pulse, and awaited a new start pulse, thus ignoring cyclotron pulses that did not result in a detected neutron. A ten-point calibration of MCA channel-to-time interval calibration of the TAC-MCA system was performed with 70, 100, 200, …, 900uS time intervals generated from a Tektronix arbitrary waveform generator. … To perform the measurement of neutron thermalization and diffusion time, a TTL pulse synchronized with the beginning of the RF pulse started the TAC clock, and the NIM pulse arising from the 3He detector registering a neutron provided the stop pulse.

Koeth, Gilde & Moroch, Measurement of Neutron Diffusion Time from Fast Pulsed Systems (draft, 2020) — p. 4

Editorial note, tabletop extrapolation: The source's TAC/MCA timing method, built from ordinary NIM modules. Two behaviours matter: an interval exceeding the 1 ms full scale resets the TAC with no output — which conveniently ignores the ~249 of 250 no-detect pulses, but also truncates any genuine event arriving later than 1 ms — and the ten-point AWG-generated calibration is what makes the histogram's time axis trustworthy. Detector conditioning, discriminator settings and grounding are not in the excerpt; treat this as the method's skeleton, not a complete recipe. Draft report.

The neutron propagation from the target, through the chamber wall, through approximately 8 inches of air, and then finally diffusing through the polyethylene before entering the 3He is the measured quantity. That process, presumably dominated by the duration spent in the polyethylene is long compared to the 10us RF pulse (the time window in which a neutron could be produced). The multichannel analyzer's binning created a histogram of cyclotron pulse-neutron detection time intervals over a 1-hour period of acquisition, or 720,000 cyclotron pulses. Figure 6 shows a fit to the data, yielding a measured diffusion time of approximately 94us.

Koeth, Gilde & Moroch, Measurement of Neutron Diffusion Time from Fast Pulsed Systems (draft, 2020) — p. 4

Editorial note, tabletop extrapolation: The headline number — but it is an effective decay constant of the complete target-to-detector timing distribution in this one assembly (chamber wall, ~8 inches of air, then the polyethylene), which the authors presume is polyethylene-dominated. What transfers is the strategy: delayed counting can separate neutron events from the RF transient — with the usable quiet window measured on each machine, not assumed from the 94 µs. 720,000 pulses in one hour is consistent with the 200 pps quoted earlier in the draft. Fit value read from the rendered Fig. 6 image (p.5). 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 photos shown in Fig. 9 demonstrate betatron motion of a proton beam in a ½ Tesla field, with fRF = 7.8 MHz. … All images were gathered using the radial P-22 Phosphor probe and a DSLR camera. … In the spiral pole tips, the motion quickly reaches a focus, due to the comparatively stronger weak-focusing central region. … for DEE powered at 100 Watts.

Ruisard, Hine, Koeth & Rosenberg, The Rutgers Cyclotron: Placing Student's Careers on Target — WE1PB02, Proceedings of Cyclotrons2013 (2013) — p. 4

Editorial note, tabletop extrapolation: PDF p.4 = printed p.294 (the 100 W dee power is the Fig. 9 caption, PDF p.5 / printed p.295; the subscript in "fRF" is printed as f with subscript RF). A phosphor-tipped radial probe, a viewport and an ordinary DSLR turn a pole-tip set's vertical focusing behaviour into a photograph — at half a tesla, within amateur reach. Read it as the qualitative first check that a new taper focuses (this paper's own comparison: adiabatic tightening on the weak-focusing tips, fast focus on the spirals with their stronger central gradient), then quantify with calibrated radial scans or tune measurements before believing details of the image.

Over a decade of experimentation has been focused on transverse beam measurements without any knowledge of the longitudinal behavior. This is because the large residual electric field of the radio frequency (RF) accelerating potential makes standard electronic beam phase and bunch length measurements impossible. RF filtering permits average beam current measurements, but removes any time structure within an RF cycle.

Gonski, Burcher, Lazarov, Krutzler, Koeth & Beaudoin, A Novel Optical Method for Measuring Beam Phase and Width in the Rutgers 12-Inch Cyclotron — WE1PB04, Proceedings of Cyclotrons2013 (2013) — p. 1

Editorial note, tabletop extrapolation: PDF p.1 = printed p.299. Why a small machine cannot simply put a pickup in the chamber and read phase: at these radii a probe sits inside the dee's residual field, and the fix that recovers a current reading (RF filtering) is exactly the one that erases the RF-cycle time structure. Whether a carefully shielded electronic pickup could do better on some machine is untested here — this program's answer was to go optical.

We have developed an optical based measurement that is insensitive to DEE voltage using a fast (3 ns) phosphor screen viewed by a gated camera to create “time sliced” images which longitudinally profile the beam. The phosphor plate is located on the end of a radial positioner that can sweep the entire chamber radius and hence any ion revolution. … This optical method mitigates measurement difficulties due to interfering RF fields near the accelerating gaps, and enables measurements to be made arbitrarily close to the ion source.

Gonski, Burcher, Lazarov, Krutzler, Koeth & Beaudoin, A Novel Optical Method for Measuring Beam Phase and Width in the Rutgers 12-Inch Cyclotron — WE1PB04, Proceedings of Cyclotrons2013 (2013) — p. 1

Editorial note, tabletop extrapolation: PDF p.1 = printed p.299 (conclusion on p.3/printed p.301). The central transferable idea: convert a longitudinal measurement that residual RF spoils into an optical one — the paper's own claims are that it mitigates the RF-field interference near the gaps and reaches anywhere the radial probe does, including the central region. A radial positioner already exists on most small machines as a beam probe; the added cost is the fast phosphor and the gated camera, the camera being the expensive item.

The 0.944-inch diameter ZnO:Ga doped “fast” phosphor deposit was layered between a 0.050 inch thick quartz substrate and a 1000 Å aluminium coating. The plate, mounted at the end of an adjustable radial probe, was electrically isolated for average beam current measurements. The fast phosphor screen has a 1/e relaxation time of 3 ns

Gonski, Burcher, Lazarov, Krutzler, Koeth & Beaudoin, A Novel Optical Method for Measuring Beam Phase and Width in the Rutgers 12-Inch Cyclotron — WE1PB04, Proceedings of Cyclotrons2013 (2013) — p. 2

Editorial note, tabletop extrapolation: PDF p.2 = printed p.300. The reported layer stack for a fast beam-imaging target at tabletop scale — named phosphor (ZnO:Ga), quartz substrate and thickness, 1000 Å Al coating — with deposition, thickness of the phosphor itself, and optics not specified. The dual role (image plus isolated current reading) is worth copying where practical, remembering an isolated target reads net collected charge: secondary-electron emission must be suppressed or calibrated before that number is treated as beam current.

we believe that the aluminium backing attenuated the proton beam and therefore reduced signal from the beam

Gonski, Burcher, Lazarov, Krutzler, Koeth & Beaudoin, A Novel Optical Method for Measuring Beam Phase and Width in the Rutgers 12-Inch Cyclotron — WE1PB04, Proceedings of Cyclotrons2013 (2013) — p. 3

Editorial note, tabletop extrapolation: PDF p.3 = printed p.301. Directly relevant at tabletop energies: 1000 Å (100 nm) of aluminium in front of the phosphor is a real energy-loss layer for protons near 100 keV, and its fractional effect decreases as energy rises toward 1 MeV. The authors present attenuation as a belief, not a measurement; before copying the fix (thinner backing, or beam-side phosphor), evaluate the layer with PSTAR/SRIM at the actual beam energy.

Due to the extreme sensitivity of the camera, and weak light of the phosphor, it was necessary to create a light-tight optical transport between the chamber viewport and the camera … 900 integrations per time step, a complete run of 44 time steps required over half an hour.

Gonski, Burcher, Lazarov, Krutzler, Koeth & Beaudoin, A Novel Optical Method for Measuring Beam Phase and Width in the Rutgers 12-Inch Cyclotron — WE1PB04, Proceedings of Cyclotrons2013 (2013) — p. 2

Editorial note, tabletop extrapolation: PDF p.2 = printed p.300. A realistic cost-of-measurement anchor: at Rutgers' own settings the arithmetic is 44 steps × 900 integrations / 20 Hz = 1,980 s — 33 minutes of stable operation (source, RF and field all required to stay put). Another machine's run length scales with its signal-to-background ratio, camera and beam current; the light-tight enclosure exists because the phosphor light is weak and the camera extremely sensitive — measure your own signal level before deciding it is optional.

At 5 mA, the Mark-III PIG sources operate for greater than 40 hours without requiring servicing. … Beam current from an arc current of 5 mA is sufficient for beam physics demonstrations, operating at greater currents quickly burns the phosphor screens. … Demanding greater arc currents reduces the source’s lifetime.

Koeth, Rosenberg, Krutzler, Ponter, Schneider & Hoffman, Rutgers 12-Inch Cyclotron: Dedicated to Training Through Research and Development — WEPPT024, Proceedings of Cyclotrons2013 (2013) — p. 2

Editorial note, tabletop extrapolation: PDF p.2 = printed p.367. A working-point philosophy worth copying: run the source at a small fraction of its capability and collect the dividends — a 40-plus-hour service interval on this Mark-III, and diagnostic phosphors that survive. On a machine whose main instrument is a phosphor screen (the usual amateur situation), the screen-burn limit binds before the source does; find your own minimum useful arc current the same way.

To estimate a local average tune, Qz, the student notes the radial locations of two adjacent axial peaks and divides by the number of revolutions within that interval. When the radial beam spot is wider than the turn-to-turn spacing, overlap prevents a direct count of individual turns; peak DEE voltage is used to estimate the number of turns within the corresponding energy (radial) increment. By definition, the measured tune directly follows from the ratio of vertical oscillations to revolutions.

Koeth, Beam Physics Demonstrations with the Rutgers 12-Inch Cyclotron — WEPPT025, Proceedings of Cyclotrons2013 (2013) — p. 2

Editorial note, tabletop extrapolation: PDF p.2 = printed p.370 (the printed text reads "can beam measured", a source typo for "can be measured"). A tune measurement needing only a phosphor probe, a viewport and a camera on long exposure — no gated camera, unlike we1pb04's phase method. The dee-voltage fallback is the practical part, and it is an ESTIMATE: turns-per-energy-increment follows from an energy-gain-per-turn model (effective voltage, gap crossings, phase), so calibrate that model before trusting the count on a machine where turns overlap early.

This faraday collector was constructed from a 3/8 inch brass slug and is suspended as well as isolated in a coaxial arrangement by a Teflon spacer inside a 1/2 inch hollow copper cylinder. The copper cylinder forms an RF shielded housing for the brass slug. The copper cylinder has a 0.185 inch slit diametrically traversing one half of the hollow portion near the tip. This slit exposes the brass slug centered inside and is positioned such that it is only exposed to positively accelerated ions, while any negative ions hit the grounded RF housing.

Koeth, The Construction and Operation of a Nine Inch Cyclotron (undated scan; the machine ran 1995–1999) — p. 7

Editorial note, tabletop extrapolation: A buildable Faraday cup that solves the two problems a beginner hits — RF pickup swamping the picoammeter, and wrong-species contamination — with one piece of copper tube: the grounded housing is the RF shield, and the one-sided slit accepts only ions arriving from the correct azimuthal direction. The readout of record ran RG-174 through a coaxial feedthrough to a Keithley 610CR electrometer (per the same section's text beyond this excerpt), and the source notes a small positive bias suppresses secondary electrons while too much deflects the protons — calibrate your own bias by watching the reading turn over. Lengths and the bias arrangement are not fully dimensioned in the document; treat as a demonstrated layout.

It is mounted such that the collector can be inserted radialy with a two inch travel, effectively determining the maximum ion radius. The minimum measurable ion radius, maximum insertion of the collector is 2.50 inches while the maximum ion radius, minimum collector insertion is 4.50 inches. A plot of beam current against radius, Fig.10, shows that the beam current linearly drops off as the radius grows.

Koeth, The Construction and Operation of a Nine Inch Cyclotron (undated scan; the machine ran 1995–1999) — p. 7

Editorial note, tabletop extrapolation: The cheapest radial beam-profile monitor a small cyclotron can have: the movable collector doubles as the radius-defining aperture, so one linear feedthrough yields current-versus-radius — an INVASIVE measurement, with energy then inferred from radius and the calibrated field rather than selected. On this run, collected current fell about eightfold from ~16 nA near 2.6 in to ~2 nA at 4.5 in (read from the rendered Fig. 10) — this machine's outer-turn attrition under its own source and pressure conditions, a shape to expect, not a universal loss factor. ("radialy" as printed.)

However, after a short period of ion bombardment the luminescence ceased. This is due to the charging of the screen, the strong electric field that developed deflected the incident proton beam off target. The screen charging issue was resolved by sputtering approximately 50 Angstroms of gold over all of it's surfaces and ensuring a connection to ground. Such a thin layer of metal is almost completely transparent yet conductive. After metallization the beam indeed re-appeared and remained on the screen without any deflection

Koeth, The Construction and Operation of a Nine Inch Cyclotron (undated scan; the machine ran 1995–1999) — p. 7

Editorial note, tabletop extrapolation: A classic trap with a cheap fix: an insulating phosphor flag charges under beam until its own field steers the beam away — brilliant, then dark. The method transfers: a thin grounded conductive over-coating that preserves light output; ~50 Å of sputtered gold is the value that worked HERE (film continuity at 5 nm depends on substrate and deposition, so verify conductivity, grounding and light yield on your own screen). The photograph (Plate 5) carries a 1.2 cm scale bar across the beam spot — a rare direct beam-size datum at this class.