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

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

the ion gauge is not turned on until the tank pressure is less than 0.5 microns ... 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

Tabletop: Directly applicable gauge practice near a stray-field-rich H-frame magnet.

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

Tabletop: Directly applicable: a cheap Penning head is the right always-on interlock and gas-flow monitor for a next machine, with the ion gauge kept for absolute readings.

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

Tabletop: Proof that p-B11 alphas are observable far below the 675 keV resonance if the builder integrates tens of uA-hours with large solid angle - and that their alphas stop in under 5 cm of air (vacuum path to PIPS required).

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

Tabletop: The master rate table for the reference machine's PIPS count-rate prediction across their entire 150-675 keV window; it quantifies exactly what reaching the resonance is worth.

At -25 kV, 8 mA, and 16 mtorr, neutron levels were 60 cpm. This measurement confirmed that nuclear fusion was achieved.

Kovalchick, Deuterium Fusion Using Inertial Electrostatic Confinement (2012) — p. 45-46

Tabletop: Same lesson as p-B11 cross-section curves: yield is exponential-ish in particle energy, so for the builder every extra 10% beam energy buys far more counts than 10% more current.

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

Tabletop: Reinforces the energy-over-current rule for the builder: sub-Coulomb-barrier reaction rates reward every extra keV exponentially.

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

Tabletop: The close-geometry, calibrate-with-a-known-alpha-source method is exactly how the builder should commission their PIPS geometry before hunting p-B11 alphas.

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

Tabletop: A pulser check separates electronics noise (grounding, RF pickup from the 9 MHz drive) from true detector degradation without risking source contamination.

The six-inch cyclotron has indicated a 7 microampere beam, at a frequency corresponding to about 800 kv protons.

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

Tabletop: Directly comparable scale; microamp-level internal beam is a realistic expectation for a next machine and the choke-protected probe is the right pickup.

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

Tabletop: Partially applicable: the p-Li gamma resonance needs ~440 keV, above the reference machine's 160 keV; a next machine reaching 0.5 MeV could use exactly this LiF-on-probe gamma check with their gamma detector.

At these energies beam intensities varied from 0.5 to 10 nA on target and beam resolution varied from approximately 60 to 70 keV.

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

Tabletop: The single most encouraging number in the batch: professional low-energy p-B11 data were taken at exactly the reference machine's nA beam scale.

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

Tabletop: When the builder converts PIPS counts to a 'cross section' they must divide by ~2 alphas per reaction - or better, publish counts-per-luminosity as this paper does.

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

Tabletop: The builder already owns the pieces: their Faraday cup/Keithley 617 integrates charge, and an Am-241 check source calibrates PIPS solid angle and energy scale.

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

Tabletop: One battery fixes a systematic error in the main diagnostic the builder has; also gives a way to separate true beam from secondaries.

By having only three faces any one face is completely shielded from the material sputtered from that which is in the beam

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

Tabletop: 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

Tabletop: Interlock the PIPS bias supply to chamber vacuum in the beam-diagnostics routine; biasing a humid detector raises leakage and can damage the junction.

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

Tabletop: The ~500-angstrom implanted window scratches easily; in a chamber with pump oil and target debris this is the only sanctioned cleaning 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

Tabletop: A detector near warm cyclotron hardware can legitimately read several times 10 nA; only a rise beyond the temperature-corrected value indicates radiation damage or contamination.

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

Tabletop: 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

Tabletop: The reference machine's PIPS collects alpha charge in nanoseconds; they can choose shaping time purely for noise optimum without worrying about ballistic deficit.

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

Tabletop: For the builder: mount the preamp on the vacuum feedthrough, not at the far end of a coax run - every pF of cable directly worsens alpha energy resolution.

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

Tabletop: Confirms the standard PIPS chain for the p-B11 experiment: a charge-sensitive preamp at the feedthrough, never a plain voltage amp on the diode.

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

Tabletop: Lets the builder compute expected keV-scale resolution of their PIPS chain from datasheet numbers before buying a shaping amplifier, and re-optimize tau if leakage rises.

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

Tabletop: The reference machine's PIPS detectors shrug off the cyclotron's X-ray background but must be shielded or retracted during any neutron-producing (e.g., deuterium) runs.

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

Tabletop: The builder can track their PIPS bias current on the Keithley 617 as a built-in damage log: any secular rise flags beam or neutron exposure of the detector.

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

Tabletop: A Peltier or cold-finger on the PIPS mount is a cheap resolution upgrade if leakage-current shot noise ever dominates the reference machine's alpha spectra.

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

Tabletop: 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.

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

Tabletop: Frees the builder to place their PIPS detectors wherever geometry and shielding are best - solid angle, not angle, is what matters at their energies.

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

Tabletop: Warns the builder that their PIPS spectra will be dominated below ~1 MeV by scattered protons - set the alpha discrimination window above that, or use a thin proton-stopping foil.

the target, which was composed of 56 +/- 2 ug/cm2 of isotopically pure 11B deposited on a 9 ug/cm2 carbon backing

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

Tabletop: Defines 'thin' for the reference machine's boron target (tens of ug/cm2) and gives two independent thickness checks they can perform with their own detectors.

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

Tabletop: Calibrates expectations for any sub-threshold nuclear signal at home: being physically above a reaction threshold is not enough; detection thresholds sit well above it.

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

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

Tabletop: If the builder ever cross-checks their PIPS counting with activation or a moderated tube (e.g., for D-D work), this fixes the moderator thickness to build.

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

Tabletop: The reference machine's aneutronic p-B11 choice sidesteps even this; but if they ever runs deuterium in the cyclotron, D-D is the only license-free fusion fuel.

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

Tabletop: 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.

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

Tabletop: At nA/sub-MeV there is no activation to survey - but the lesson stands: always check holder edges and apertures for beam strike (film, phosphor, or discoloration), since a large fraction of beam can miss the target.

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

Tabletop: A next machine's extraction commissioning should start with on/off comparison images (film, phosphor, or CCD) at the channel exit; integrating detectors see sub-nA deflected beams that electrometers lose in RF noise.

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

Tabletop: The reference machine's best-beam case (5.6x background on the Faraday cup) sits in exactly this evidentiary tradition — and the energy-threshold argument is the template for a source-species test: an observed nuclear signature whose threshold excludes the molecular-ion hypothesis is proof of species without a spectrometer.

A carbon (graphite) target gave rise to 112-minute and 15-hour activities which are assigned to F 18 and Na 24 respectively.

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

Tabletop: Below nuclear thresholds the 150-keV reference machine cannot use this — but it becomes the cheapest absolute energy check the moment any upgrade crosses a low-threshold reaction, needing only a GM counter and a stopwatch; the practice (identify by half-life, bound energy by threshold) is scale-free.

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

Tabletop: General fast-timing wisdom for beam-pulse and kick timing chains - every smoothing stage costs latency; calibrate the chain end-to-end and remove the constant part in the threshold or delay setting rather than chasing zero-delay filters.

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

Tabletop: A self-calibration idiom worth copying into any comparator/discriminator in the DAQ - trim to observed threshold at session start (their multivibrator = today's comparator with drifting offset), and slow drift stops moving the physics timing.

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

Tabletop: Directly applicable to pulse chains fed by beam pickups or PMTs at low rep rate - stabilize on detected peak height at the discriminator input, and amplitude drift stops translating into time walk.

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

Tabletop: The one activation rule that DOES apply 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 null check that sub-MeV operation activates nothing — useful evidence for licensing conversations and for catching surprises if beam or species ever changes.

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

Tabletop: Energy-independent technique. A 2-in lead collimator with a removable plug around a next machine's NaI turns it into a pointing instrument for finding X-ray leaks (RF multipactor, dee-liner discharge bremsstrahlung) on a running machine — the same aim/plug/subtract discipline at keV instead of MeV.

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

Tabletop: ENERGY SCOPE: Cu63(p,n) threshold is ~4.2 MeV — closed on the reference machine and a next machine, so this exact reaction cannot be used below ~4 MeV. The transferable idea is using a steep, well-known excitation function as an energy discriminator: at a next machine's energies the B11(p,alpha) yield curve itself (or Al/Ni step degraders before the PIPS) plays that role, and the same triangular-unfolding trick applies to any stacked measurement.

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

Tabletop: Same artifact family as the reference machine's secondary-emission and background offsets on the Faraday cup; at nA scale a hot-wire thermionic term can dwarf the signal, so bias or shield the probe and log the baseline drift.

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

Tabletop: SCALE-HONEST: geometry is energy-independent (it fixes E/E0 ratios, not E), so a palm-sized R ~ 5-10 cm version at a few hundred gauss would broad-range-analyze a next machine's ~170 keV protons identically - a compelling teaching-lab focal-plane instrument. The 5-ton, 14-kG original is MeV-class; copy the optics, not the iron.

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

Tabletop: DIRECT teaching-lab gold - one sealed alpha source and one afternoon calibrate the whole instrument, no beam required, and the equal-exposure trick measures the acceptance function that theory only estimates. Their peak-position convention (intercept of the straight high-energy edge with the baseline) is also the right lineshape-robust choice.

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

Tabletop: DIRECT principle (vacuum cycles are the tax on focal-plane work; amortize them) with a modern translation: a movable frame of CR-39/film chips, or a silicon-strip array, behind the next machine's analyzer. Their two-detector split - survey in emulsion, precision groups in counters - maps to CR-39-survey vs SiPM/diode-array.

connected to a short (10") antenna of No. 12 wire which extends inside the oscillator house to within a foot or two of the grid circuit of the oscillator.

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

Tabletop: DIRECT recipe, buildable on the reference machine in an afternoon - loose capacitive coupling (never galvanic) plus stub-tuned harmonic mixing is how you sharpen a 9 MHz sine (55 ns rise as a sinusoid) into a few-ns edge with zero active electronics at the pickup. The check-the-pulse-shape-after-retuning discipline (p.9) carries over verbatim.

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

Tabletop: DIRECT - this reversed (common-stop) architecture is still how RF-referenced timing is done; it inverts the time axis but slashes dead time and pileup. With a modern TDC or digitizer the same logic applies: trigger on the detector, timestamp against the next RF zero crossing.

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.

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

Tabletop: DIRECT twice over: (1) never let the background-rejection threshold live inside the timing path (they tried; timing and efficiency fought); (2) a $50 Cs-137 check source turns "what is the threshold today?" into a 5-minute standardization - the calibration habit every counting experiment on a next machine should inherit.

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

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

Tabletop: 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

Tabletop: 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.

Calibration curves were obtained by use of the D(d,n) reaction, the cross sections for which are known to 4% accuracy.

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

Tabletop: DIRECT metrology doctrine - one calibration path is an assumption, two are a measurement. For a next machine's experiment gates (e.g., p-B or (d,n) yield claims), require a primary calibration plus an activation- or source-based cross-check, and quote the disagreement as the systematic.

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

Tabletop: DIRECT for any neutron-counting next-machine experiment and a lovely teaching derivation - a two-factor closed form students can test against a calibration reaction. The identification of which factor is exact vs model-dependent is the transferable habit.

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

Tabletop: 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

Tabletop: 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

Tabletop: THE classic accelerator-survey trap and the reason the program's survey doctrine should prefer current-mode ion chambers over GM counters for any pulsed operation: a counter that reads "60 cps" at a 60 Hz pulse rate is telling you its saturation value, not the dose rate.

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

Tabletop: 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.

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

Tabletop: Justifies planning on one moderated rem meter as the single neutron instrument — its energy band covers everything a D-D contamination source (2.45 MeV) or any near-threshold (p,n) could emit.

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. 130

Tabletop: The measurement-side half of the reference machine's X-ray problem: the machine's entire photon spectrum sits BELOW this misbehavior threshold, so an uncalibrated chamber reading of dee bremsstrahlung can err either direction. Use thin-window instruments with a low-energy calibration point (e.g. Fe-55 or an X-ray tube set) and record orientation.

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

Tabletop: Written for exactly such a bench — a scintillator PMT near a 0.6 T fringe field and a 9-MHz (soon LDMOS) transmitter. 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

Tabletop: Analog meter movements, photomultipliers, and many GM counters misread in a stray field of even tens of gauss; separate the sensing volume from the readout and keep the readout outside the fringe field.

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

Tabletop: 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

Tabletop: Cable ways, viewport lines-of-sight, and door gaps are the paths that matter once any bulk shielding exists; thermal-neutron instruments answer a different question than fast-neutron ones and 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

Tabletop: A Faraday cup's reading depends on its stopping surface through secondary emission and backscatter; measuring the same beam against two stopper materials bounds that systematic without any absolute reference.

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

Tabletop: The one thickness method that needs no balance and works on a mounted film; a surface-barrier detector, a check-source alpha emitter, and an MCA are all standard home-lab equipment. Quote absolute thickness no tighter than the stopping-power tables allow.

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

Tabletop: A photodiode and lamp sort carbon stripper/backing foils into thickness bins in seconds — calibrate once against weighed foils and use it as the incoming-inspection tool.

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

Tabletop: A thoriated source and a -300 V bias produce a fresh, essentially massless (recoil-implanted) alpha source on demand; the 2.7 MeV spread between the 212Pb lines self-calibrates the spectrometer with no external standard. Ventilation for thoron is mandatory.

This is all the calibration which is necessary since now only energy shifts are of interest.

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

Tabletop: The whole rig is a surface-barrier detector, preamp, biased amp and any old 512-channel MCA — Thompson wrote it up precisely so small labs could build it; the differential (shift-only) design makes absolute gain calibration irrelevant.

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

Tabletop: Stretched polypropylene is the standard thin window for gas counters and low-energy vacuum isolation; the step-and-cool metallization discipline applies to coating any plastic film. Same material class as the detector windows the diagnostics literature assumes.