Hand-considered hypotheses, 1601–1700

Radiation and particle measurement: detectors, dosimetry, shielding, counting, imaging, calibration sources

Written one at a time, not composed. Every entry carries its logical form as a label, and the forms are unevenly distributed because the subjects are: identity and misattribution claims are cheap to state and expensive to test, while the no-go and conservation entries would remove a whole family of corrections if they held. None has been tested. Comparative factors in the text, such as “a factor of two (estimate)” or “an order of magnitude (estimate)”, are order-of-magnitude expectations and not measurements; no number here is a datum, and no citation is implied.

Ionisation chambers and gas detectors

Misattribution
H1601. Low-bias collection loss in a vented ionisation chamber is normally booked as initial recombination, but in humid air a large share of it is charge held on water clusters and released over microseconds, so the correction tracks relative humidity rather than dose rate or electrode spacing. Hydrated negative ions drift too slowly to cross the gap inside the collection window even where free-electron theory predicts a flat response. Sweeping humidity at fixed dose rate and fixed geometry separates the two, because true recombination is humidity-blind.
Hidden term
H1602. Proportional-counter gas gain carries a term belonging to the anode's adsorbed skin, which thickens in air and shifts the avalanche onset radius outward, so the slow gain drift seen over weeks is this layer rather than the filling gas. A dielectric film redistributes the field close to the wire. Two counters of identical geometry, one stored under vacuum and one under air, should converge in gain only after the air-exposed wire is baked out.
Identity
H1603. Plateau slope and gain drift in a proportional counter are two readings of one anode-condition parameter, so a counter with a genuinely flat plateau cannot also show a drifting gain. Both are set by the effective wire radius, which adsorption and sputter deposits change together. Logging both quantities on a single counter through a long irradiation should give a one-to-one relation, not merely a correlation.
Bound
H1604. Maximum stable gas gain is bounded by the fraction of avalanche photons that return to the gas rather than by the Raether spark limit, so an opaque cathode stops the counter earlier than geometry alone predicts. Feedback photons seed secondary avalanches whose spread destabilises the discharge before the charge criterion is met. Cathodes differing only in ultraviolet reflectivity should reach measurably different gains.
Threshold
H1605. A self-quenching streamer counter has a minimum quench fraction below which streamers run along the wire and above which they stay localised, set by the photon absorption length in the mixture. The quench species must absorb the streamer's ultraviolet within roughly the wire-to-cathode gap. Stepping the fraction in small increments while imaging the avalanche with a fast camera locates the transition.
Reversal
H1606. A Penning admixture raises gain at low reduced field and lowers the maximum stable gain at high field, so its net value reverses at a crossover that depends on the admixture's ionisation potential. The added ionisation channel helps at low field, while the longer photon range it creates encourages feedback at high field. Gain-versus-voltage curves at three concentrations on one counter show the crossing directly.
Artefact mimics effect
H1607. Count bursts that resemble neutron or alpha events are often microphonic, with the anode acting as a microphone and the pulse-shape filter unable to separate a mechanical ring from a slow ionisation pulse. A vibrating wire changes the capacitance the preamplifier sees. Driving the counter with a piezo below its acoustic resonance, and comparing the spectra with those from a real source, exposes the difference.
Count
H1608. No single proportional-counter pulse constrains more than four shape parameters, so a five-parameter fit is underdetermined however densely that pulse is sampled. Drift, avalanche and ion tail are not independent generators of the shape. Fitting synthetic pulses with known parameters and inspecting the covariance matrix's rank tests the claim.
Scale argument
H1609. Wall effect scales with the ratio of secondary-electron range to cavity diameter rather than with filling pressure, and that ratio decides whether a low-energy photon's full energy can be deposited. Wall electrons enter the sensitive volume only if their range exceeds the layer they must cross. Two chambers of different diameter, pressurised to equal gas density, isolate the ratio.
Inversion of standard practice
H1610. Raising a tritium proportional counter's pressure to improve efficiency is self-defeating past a point, because wall-adsorbed tritium then supplies most of the count rate and the instrument measures its own contamination. The wall monolayer exchanges with the gas, so the gas-phase signal saturates while the wall term keeps growing. Filling at several pressures from one reservoir shows the rate departing from gas density.
Selection effect
H1611. Published gas-counter lifetimes are biased upward because only counters that survived long enough get reported, and failed units are filed as end-of-life rather than as data. Survival is the screening variable, and it is the same one being estimated. Twenty identical counters run to failure would give a median well below the mean of the published values.
Unit trap
H1612. A survey meter's quoted counts per minute per microsievert per hour is not a detector property, because it contains the calibration spectrum; two meters that agree in a caesium field can diverge by a factor of two (estimate) in a plutonium field. Fluence-to-dose conversion is energy dependent while the meter's response is not. Two fields with equal air kerma rate but different fluence-to-dose conversion separate them.
Conservation
H1613. Charge collected at an ion chamber's signal electrode is not the charge liberated in its gas, since the remainder terminates on the guard and the insulator where the electrometer cannot see it. Field lines from ions near the insulator end on the guard. Integrating the guard current and comparing it with expected-minus-measured charge closes the budget.

Scintillators and photodetectors

Misattribution
H1614. The temperature coefficient of a sealed hygroscopic scintillator's light output is usually assigned to the crystal, but much of it can belong to the reflector, whose contact with the crystal changes as the housing expands. A pressed reflector loses optical coupling as it cools. The same crystal measured with a rigid and with a compliant reflector should give different coefficients.
Hidden term
H1615. A plastic scintillator's measured decay time includes the photodetector's transit-time spread, which varies with where the light lands on the photocathode, so the intrinsic decay is shorter than any value obtained with a large cathode. Photons from different cathode positions arrive with different delays. Repeating the measurement through a small scanned cathode aperture tests this.
Identity
H1616. The slow component of a plastic scintillator's pulse and the afterpulsing of its photomultiplier are one feature when both are recorded through the same discriminator, and only a photodetector swap can separate them. Both present as delayed single photoelectrons. Replacing the tube with a silicon photomultiplier should either remove the tail or leave it unchanged, and the answer names the owner.
Bound
H1617. A silicon photomultiplier's linear range is set not by its cell count but by the ratio of recovery time to pulse width, so a device with many cells can still saturate early. Cells that are recharging are invisible, and the effective count falls during a pulse. Two devices with equal cell counts and different recovery times, measured at equal light and equal pulse width, distinguish the two bounds.
Threshold
H1618. There is an overvoltage below which afterpulsing in a silicon photomultiplier is negligible and above which it grows faster than the gain, so the best signal-to-noise sits below maximum bias. Trapped charge release scales with total avalanche charge, which rises faster with overvoltage than the gain does. Afterpulse probability and excess noise factor measured together across bias locate the knee.
Reversal
H1619. Scintillation light yield per unit deposited energy can rise with ionisation density where tracks are dilute and fall where they are dense, so Birks' monotonic quenching reverses somewhere between the two regimes. Triplet-triplet annihilation adds light at low density while quenching dominates at high density. A proton-recoil spectrum from a monoenergetic neutron source spans both regimes in a single exposure.
Artefact mimics effect
H1620. A peak that looks like an unlisted gamma line is frequently the photomultiplier's single-photoelectron pedestal, which sits at a fixed fraction of gain and therefore moves when the bias moves. Its position is set by the tube rather than by the source. Changing the high voltage by ten per cent separates a gain-tracking peak from an energy-fixed one.
Count
H1621. Recoverable light components are bounded in number by the record length divided by the decay time, not by how many terms a fit will accept. Components closer together than the sampling jitter are degenerate. Fitting three-component models to known two-component pulses counts how often the third is declared.
Scale argument
H1622. Light collection uniformity falls with aspect ratio faster than surface area alone implies, because the mean number of reflections before escape grows with length-to-width, so a long thin crystal resolves worse than a short fat one of equal volume. Every reflection loses a fraction of the light. Two equal-volume crystals of different aspect ratio, read by the same tube, test the scaling.
Inversion of standard practice
H1623. Wrapping a bright scintillator in the most reflective available material is not always best, since a partly absorbing wrap can sharpen coincidence timing by cutting the long-path tail at some cost in energy resolution. Reflective wraps create delayed photons that arrive after the first. Black, grey and white wraps on one crystal, compared for timing and for resolution, quantify the trade.
Selection effect
H1624. Reported light yields are biased toward crystals cut from the brightest region of an ingot, because samples are screened for brightness before the definitive measurement. The screen uses the same variable that is later published. Measuring every slab of one ingot without pre-selection gives the honest spread.
Unit trap
H1625. Photons per MeV is ambiguous between photons emitted and photons detected, and the ratio of the two is the collection efficiency, which is rarely stated, so two literature values can differ by exactly that unstated ratio. The conventions coincide only for an ideal collector. Deriving both numbers from one pulse-height spectrum of a known line resolves the comparison.
Conservation
H1626. A wavelength shifter cannot add photons, only relocate them, so any gain in detected signal over the unshifted case is bounded by the ratio of detector quantum efficiency at the two wavelengths; a larger gain means the shifter is scintillating on its own. The bound follows from photon conservation. A shifter-only sample measured under identical excitation exposes the excess.
Hidden variable
H1627. Gain drift that follows counting rate rather than temperature comes from current loading at the last dynode, where the bleeder's voltage sags under signal current. The last stage carries the largest current and holds the smallest reserve. A zener-regulated final stage compared with a purely resistive bleeder at matched mean current isolates it.
Causal ordering
H1628. A scintillator's light output per unit energy in a nanosecond pulse can exceed its steady-state output, because the traps that quench continuous emission have not yet filled; the order of excitation and readout, not the deposited energy, sets the yield. Trap filling is slower than radiative decay. Equal energies delivered in one pulse and over a millisecond give different yields.
Degeneracy
H1629. Two scintillators matched in emission peak, light yield and decay time can still differ in coincidence resolution if their rise times differ, so a catalogue carrying only the first three cannot predict timing. The rise time sets how early the first detectable photons appear. A coincidence sweep on such a pair, with everything else matched, shows the residual.
Bound
H1630. Energy resolution cannot be better than the photoelectron Poisson limit, and the excess above it measures intrinsic non-proportionality, so resolution squared against inverse energy should be linear with an intercept set by that excess. Non-proportionality adds variance that is not counting variance. Fitting that line across several energies separates the two contributions.

Semiconductor detectors

Misattribution
H1631. Polarisation in a cadmium zinc telluride detector, the progressive loss of count rate under bias, is usually blamed on deep-level detrapping in the bulk, but it can be the blocking contact's space charge dominating the field profile. The two produce the same rate sag. One crystal fitted once with a blocking and once with an ohmic contact should polarise differently, or not at all.
Hidden term
H1632. Trapping lengths extracted from a bias sweep with the Hecht relation contain a ballistic-deficit term from the shaping amplifier, so the fitted mobility-lifetime product is a mixture of transport and filtering. Short shaping truncates the slow part of the induced charge. Repeating the sweep at three shaping times and one bias separates them.
Identity
H1633. The parallel white noise attributed to a detector's bulk leakage is often the guard ring's surface current, and the two are indistinguishable in a spectrum because both add variance without peaks. Surface conduction follows humidity while bulk generation follows temperature. Guard-connected and guard-floating noise measurements at controlled humidity tell them apart.
Bound
H1634. Resolution is bounded below by the quadrature sum of Fano variance and trapping variance, so a detector with a perfect Fano factor still cannot beat the trapping term, and the bias dependence of the resolution shows which term dominates. Trapping variance falls with bias while Fano variance does not. Extrapolating resolution against inverse bias to the intercept separates them.
Threshold
H1635. Detectors of cadmium telluride do not polarise below a minimum bias, because detrapping outpaces the space-charge build-up that causes the sag; the threshold is set by the trap's emission rate relative to the field's sweep-out time. Below it, polarisation cannot accumulate. A bias series with a time-resolved count rate records the onset.
Reversal
H1636. Room-temperature semiconductor detectors show a resolution minimum with temperature: leakage current rises with temperature, but detrapping from shallow levels rises too, and the two move resolution in opposite directions. Neither term alone predicts the optimum. A temperature sweep at fixed bias and fixed source shows the turning point.
Artefact mimics effect
H1637. Escape peaks and the fluorescence lines of the detector's own constituent elements can mimic gamma lines from the source, and they shift with geometry while true source lines do not. Characteristic X-rays leave the crystal and carry a fixed energy away with them. Moving the source and changing collimation should move the impostors and leave the real lines fixed.
Count
H1638. Recovering trap levels from a bias series yields at most as many as there are resolvable time constants in the charge-collection transient, so a four-trap fit to a smooth curve is a parameterisation rather than a measurement. Traps whose emission times overlap are degenerate. Fitting synthetic transients with known trap sets tests how many survive.
Scale argument
H1639. When the pixel pitch falls below the carrier drift length, charge sharing between pixels stops being a nuisance and becomes the dominant signal, so small-pixel detectors measure interaction position better than their electrode pattern suggests. Neighbouring pixels collect induced charge from the same cloud. A pitch series at fixed thickness shows where energy resolution stops improving.
Inversion of standard practice
H1640. Cooling a semiconductor detector below a certain temperature can worsen charge collection instead of improving it, because a shallow trap that is ionised and therefore harmless at room temperature becomes an efficient capture centre when cooled. Leakage falls while trapping rises. Collection efficiency against temperature at fixed bias should peak rather than plateau.
Selection effect
H1641. Published mobility-lifetime products for detector-grade material are selected on that same quantity during acceptance testing, so the literature distribution is truncated and its spread understates the material's real variability. Rejected crystals never enter a paper. Measuring an unselected set of ingot slices gives the untruncated distribution.
Unit trap
H1642. Quoting the energy needed to create one electron-hole pair as a material constant is wrong, because it depends on temperature and field through the band structure, so values obtained in different conditions differ by a few per cent, enough to matter when a pair count is converted to dose. The number is a calibration, not a constant. One device measured across field and temperature supplies the coefficient.
Derived quantity
H1643. Active volume derived from photopeak efficiency is not the geometric volume; it is a fitted quantity that absorbs dead layers, contact effects and field non-uniformity, and it changes when the source energy changes. A derived volume has no independent existence. A collimated scan across the detector face shows where the response actually lives.
Irreversibility
H1644. Radiation damage in a semiconductor detector is not a state function of fluence, because annealing between exposures changes the damage constant that later measurements infer, so two devices given equal fluence can differ by history alone. Defect complexes form and dissolve on different timescales. Irradiating in interrupted steps, with and without annealing between them, separates fluence from history.

Dosimetry: passive, calorimetric, reference

Misattribution
H1645. Part of the supralinearity reported for a thermoluminescent material is not trap creation but the reader's integration window, which widens relative to the glow peak as the peak shifts upward in temperature with dose. A fixed window then collects a larger fraction of a hotter peak. Two heating rates on the same aliquots test whether the effect follows the peak or the dose.
Hidden term
H1646. Optically stimulated luminescence fading measured at different stimulation temperatures is not one number, because the readout itself detraps part of the signal in proportion to temperature. The measurement perturbs the quantity it reports. Reading the same irradiated aliquots at two stimulation temperatures separates physical fading from readout depletion.
Identity
H1647. Zero-dose reading and self-dose from naturally occurring trace activity are the same offset in a thermoluminescent dosimeter, and no amount of repeated readout separates them without an annealing step that removes both. Both add a fixed signal. Aliquots annealed and then held for different times before readout show which part grows.
Bound
H1648. Calorimetric dosimetry is bounded in accuracy by its heat defect rather than by thermometry, so improving the thermometer past a point buys nothing. The heat defect is the fraction of deposited energy that does not appear as heat because it drives chemical change. Two calorimeters with different absorbed fractions but the same defect would show the same error.
Threshold
H1649. Track detectors have a registration threshold in restricted energy loss below which no track appears however large the dose, so a null result at low linear energy transfer says nothing about the dose. The etch-rate ratio must exceed a material-specific value. Exposing one detector to a graded series of ions brackets the threshold.
Reversal
H1650. The response of an alanine dosimeter per unit dose can change sign in its dose-rate dependence at high rates, because oxygen that repairs radicals at low rate is consumed faster than it can diffuse in at high rate. Repair and recombination compete. Delivering equal doses at two rates, with and without oxygen, shows the inversion.
Artefact mimics effect
H1651. Cherenkov light generated in the delivery fibre of a scintillating dosimeter mimics dose, and it is worst exactly where the beam enters, so the depth-dose curve is distorted rather than offset. The fibre itself emits when the beam passes through it. Two fibre lengths with the same sensitive tip give different apparent doses if the stem effect is present.
Count
H1652. Independent calibration factors in a reference chain, chamber factor, electrometer, pressure, temperature, humidity and beam quality, bound how small a combined uncertainty can honestly be, and any quoted figure below their quadrature sum is arithmetic rather than measurement. Each factor is separately determined. Propagating each one's own uncertainty to the final dose shows the floor.
Scale argument
H1653. Cavity theory's weighting between wall and gas response depends on cavity size relative to the secondary-electron range, so a chamber that is small at cobalt energies becomes intermediate at low energies and its calibration does not transfer. The weighting is a ratio of two lengths. Chambers of two cavity sizes compared in the same low-energy beam measure the transition.
Inversion of standard practice
H1654. For a parallel-plate chamber used in a low-energy beam, calibration in air can be more transferable than calibration at depth in water, because the phantom's own scatter changes the spectrum more than the air path does. Standard practice inverts this at high energies. Calibrating one chamber both ways, then comparing its response in a third field, tests the claim.
Selection effect
H1655. Intercomparison audits report a discrepancy distribution from laboratories that volunteered, and volunteers are disproportionately those who expect to do well, so the published spread understates the population's. Participation is the selection variable. Comparing audit results with a mandatory, randomly sampled round shows the difference.
Unit trap
H1656. A neutron survey meter reading in microsieverts per hour reports a derived quantity whose conversion coefficient depends on the spectrum, so the same reading corresponds to fluences differing by an order of magnitude (estimate) between a bare source and a moderated one. The instrument applies one coefficient. Two spectra giving one reading, with fluence measured by an independent counter, expose it.
Derived quantity
H1657. Dose in a phantom derived from an air-kerma calibration passes through a conversion coefficient that assumes a spectrum, and when the spectrum at the point of interest differs from the calibration spectrum the derived dose is wrong in a way no repetition of the measurement can reveal. The coefficient is not measured at the point of use. A second chamber of different atomic composition detects the mismatch.
Hidden variable
H1658. Placing a dosimeter in a phantom perturbs the field it is meant to measure, and the perturbation depends on its mass and atomic number relative to the medium, so two dosimeters of different construction disagree in a gradient. The detector's presence is the hidden variable. Measuring one point with detectors of two masses and extrapolating the trend to zero mass gives the unperturbed dose.
Symmetry
H1659. Rotational symmetry of a chamber's response holds only if its stem is symmetric, and the stem's presence breaks that symmetry, so the resulting orientation dependence measures stem scatter rather than averaging out as a nuisance. The asymmetry carries the stem's geometry. Rotating a chamber about its own axis in a fixed field maps the stem's contribution.
No-go
H1660. No passive integrating dosimeter can distinguish dose from dose rate after the fact unless it carries two components with different rate dependence, so a single-element device claiming to reconstruct rate history is fitting its own fading curve. One number cannot carry two variables. A two-element device with deliberately different rate responses tests whether the information exists at all.

Shielding and radiation transport

Misattribution
H1661. Build-up measured behind a shield can include scatter from the source capsule itself, which is present before the shield and does not scale with shield thickness. Capsule scatter enters the detector alongside the primary. An unshielded measurement with two capsule thicknesses separates the capsule's contribution from the shield's.
Hidden term
H1662. Behind a shield the detector also sees photons scattered from walls and floor, which reach it by paths that never cross the shield, so the room's albedo is part of the geometry. That term does not fall when the shield thickens. Repeating the measurement with the room lined in absorber, or with the detector collimated to the shield alone, quantifies it.
Identity
H1663. Collimator and shield are one object described by two names, since the collimator's scatter is the shield's leak and a design that optimises one at a time cannot optimise both. Both are governed by the same mean free path. Measuring the detector's response with and without a collimator of identical mass shows whether the two budgets are one.
Bound
H1664. The attenuation a shield can deliver is bounded by the dose from its own activation, so beyond a certain thickness added material makes the measured dose rate rise rather than fall. Activation grows with the same fluence that attenuation removes. A thickness series with a spectrum-sensitive detector shows the minimum.
Threshold
H1665. In neutron shielding an energy exists below which moderation dominates and above which inelastic scattering does, and the crossover decides whether hydrogenous or high-Z material should come first. The two processes have different energy dependences. A two-layer shield measured in both orders across a range of source energies locates the crossover.
Reversal
H1666. Adding hydrogen to a neutron shield can increase the photon dose past some thickness, because capture gamma rays born in the hydrogenous layer are less attenuated by the material behind it. Moderation and capture are coupled. A hydrogen thickness series read by a gamma-sensitive detector beside a neutron-sensitive one shows the dose turning upward.
Artefact mimics effect
H1667. Leaks confined to one azimuth are usually streaming paths at a joint or a cable penetration rather than a failure of the bulk material, and they will not scale with thickness. Streaming is geometric. Scanning the shield's outer face with a narrow collimator maps the path and shows it is a line, not an area.
Count
H1668. Leakage paths through a shield are independent only if they share no penetration, so a model with more paths than measurements is interpolating. Paths that pass through one opening compound rather than add. A shield with a known number of penetrations, measured at several azimuths, tests whether a fit finds exactly those.
Scale argument
H1669. Attenuation per unit mass depends on the shield's radius relative to the source distance, because a curved shield presents a longer oblique path than a slab of equal areal density, so slab data under-predict a spherical shield. The obliquity factor is purely geometric. The same areal density in slab and spherical form, measured at one detector position, isolates it.
Inversion of standard practice
H1670. Putting the high-Z layer first is the conventional order for a laminated shield, but for a broad spectrum the order that minimises dose can be the reverse, because the low-Z layer scatters photons out of the beam before they generate secondaries in the high-Z layer. The optimum is spectrum-dependent rather than material-dependent. Both orders measured with one detector and one source settle it.
Derived quantity
H1671. The build-up factor is not a physical quantity but a ratio derived under an infinite-medium assumption, so applying a tabulated value to a finite shield of different geometry has no justification beyond coincidence. It absorbs geometry into a single number. Two shields of equal optical thickness but different shape, compared with the tabulated prediction, show the failure.
Unit trap
H1672. Half-value layer is quoted as a material property in millimetres, but it is a property of the spectrum, so two shields of the same material and the same quoted half-value layer can differ in attenuation by a factor of roughly two (estimate) when the source spectra differ. The number carries its spectrum implicitly. Measuring one material with two sources makes the implicit dependence explicit.
Conservation
H1673. Uncollided, scattered and leakage dose at a point sum to a fixed budget for a fixed source, so a total that rises when a shield is added must be recording a new path rather than improved attenuation. The budget cannot exceed the source's emission. Integrating dose over a closed surface around the source checks the accounting.

Counting, dead time and pulse processing

Misattribution
H1674. Dead time measured at the detector is often the electronics' pile-up rejector, which has its own non-extending behaviour and its own rate dependence; a correction that works at low rate therefore fails at high rate although the detector has not changed. The rejector's window is fixed in time. Bypassing the rejector and re-measuring the same source shows which stage owns the loss.
Hidden term
H1675. Live-time corrections built for a single dead-time model fail when the system has both an extending and a non-extending stage, because the mix of the two changes with rate and the effective model is neither. Each stage has its own paralysis. Two sources measured separately and then together, with the correction applied naively, reveal the residual.
Identity
H1676. The two-source method and a decaying source give different dead-time values when the dead time is extending, and their agreement is evidence that it is not. The two methods weight the interval distribution differently. Performing both on one system at the same observed rate shows whether they coincide.
Bound
H1677. The maximum useful count rate is bounded by the discriminator's pulse width rather than by the dead time, because two pulses closer than the width merge regardless of the dead-time setting. The merge happens before the logic sees them. Narrowing the width at fixed dead time raises the usable rate until another limit appears.
Threshold
H1678. Ratio measurements have a rate above which the denominator's fluctuation dominates the variance, and beyond it adding counts to the numerator buys nothing. Variance contributions add in quadrature with weights set by the ratio. A rate series of one ratio, with both channels recorded, shows where the denominator takes over.
Reversal
H1679. Discriminator thresholds raised above the noise floor can increase the net count rate, because rejecting noise pulses shortens the effective dead time more than it removes signal. The two effects have opposite signs. A threshold sweep at fixed source and fixed high voltage should show a maximum rather than a monotonic fall.
Artefact mimics effect
H1680. A periodicity in arrival times at the mains frequency belongs to the detector's gain rather than to the source, because the power supply's ripple modulates gain and the modulation appears in the count rate only where the discriminator sits on a steep part of the spectrum. Ripple moves the gain. Battery supply, or a discriminator on a plateau, removes it.
Count
H1681. Pile-up models with more parameters than there are resolvable pulse separations fit the shaper's own impulse response, so the number of meaningful terms is bounded by the ratio of shaping time to sampling interval. Two pulses inside one shaping time produce a single hump whose height depends on their separation in a way no multiplicity count can invert. Injecting electronically generated pulse pairs of known spacing tests how many separations the fit recovers.
Scale argument
H1682. Histogram bin width interacts with count rate: at fixed acquisition time a coarse bin averages over gain drift while a fine bin resolves it, so one dataset supports different conclusions depending on a choice that looks cosmetic. Binning is a filter. Rebinning one dataset at three widths and repeating the same test shows whether the result is bin-independent.
Inversion of standard practice
H1683. Spending equal time on sample and blank is wasteful when the blank's count rate is the larger one; the variance-minimising allocation gives the blank more time than the sample, inverting the symmetry people assume. The optimum time ratio follows the square root of the two rates. Two allocations at equal total time, compared on a sample of known activity, show which is better.
Selection effect
H1684. Runs retained after a stability check are a selected sample, and the selection acts on the same fluctuations that the reported uncertainty is meant to describe, so the quoted precision is too small. Unstable runs are discarded preferentially when they are low. Keeping every run and comparing the uncertainty with the discarded sample's scatter shows the bias.
Unit trap
H1685. Counts per channel and counts per keV differ by the calibration's slope, and a spectrum analysed in channel units has an effective energy-dependent bin width that changes any fitted width or yield. The two units coincide only for a linear, uniformly binned calibration. Analysing one spectrum both ways with an identical fit exposes the difference.
No-go
H1686. Above a certain rate no correction recovers the true rate from a paralysable system, because the observed rate is non-monotonic in the true rate and two true rates give one observed value. The mapping loses injectivity. Driving a paralysable system with two sources of known but different strengths until their observed rates coincide demonstrates the ambiguity.

Imaging with ionising radiation

Misattribution
H1687. Modulation transfer function degradation blamed on the detector can be the focal spot's, whose size and shape enter the same edge image and cannot be separated from it by one measurement. Both convolve the image, but only one scales with magnification. Two edge images at different magnification separate them.
Hidden term
H1688. Measured noise power spectra contain fixed-pattern noise from the readout, which does not average down with frames the way quantum noise does, so a detective quantum efficiency derived from one frame understates the detector's quantum limit. Fixed pattern is stationary across frames. Subtracting a gain-offset correction map before the transform shows the quantum-only spectrum.
Identity
H1689. Detective quantum efficiency at zero frequency and the detector's absorption efficiency are the same number when the Swank factor is unity, and the difference between them measures the Swank factor directly. Both describe how many quanta survive. A detector of known absorption and a measured zero-frequency efficiency yields the Swank factor without a separate measurement.
Bound
H1690. Sharpness and noise are bounded jointly by the absorber's thickness, because making a scintillator thinner improves the point spread while raising quantum noise per unit exposure, so no design escapes the product. The two move in opposite directions with one parameter. A thickness series measured for both modulation transfer and noise shows the product is nearly constant.
Threshold
H1691. Below a certain number of quanta per pixel an image is noise-limited beyond the reach of post-processing, because the missing information was never recorded; above it, the limit becomes the display. The transition is where noise variance equals signal. An exposure series with a fixed structured phantom locates it.
Reversal
H1692. An anti-scatter grid can lower contrast-to-noise ratio when the scatter fraction is already small, because the grid removes primary photons and adds its own attenuation faster than it removes scatter. Grid performance depends on the scatter it is asked to reject. Two grids of different ratio measured across several scatter fractions show the crossing.
Artefact mimics effect
H1693. Rings in reconstructed slices are usually one bad detector channel rather than a physical annulus, and they are identifiable because they are centred on the rotation axis and their radius does not change with the object. A channel error propagates to a circle. Masking that channel in the sinogram removes the ring without changing the object.
Count
H1694. Dual-energy imaging with two measurements separates at most two basis materials, so a three-material decomposition needs an additional assumption, and any method claiming three without one is using prior knowledge as if it were data. Two numbers cannot determine three unknowns. A phantom with three inserts of known composition tests whether the decomposition is unique.
Scale argument
H1695. A voxel smaller than the system's point spread function adds no information but does change the noise texture, so an image reconstructed at half the voxel size can look sharper while carrying the same resolution. The sampling is finer than the blur. Comparing the modulation transfer function of the two reconstructions shows resolution is unchanged.

Calibration sources and metrology

Misattribution
H1696. An activity discrepancy between a source certificate and a re-measurement is often assigned to decay-correction error when it is ingrowth of a daughter the calibration geometry did not see. The daughter's contribution grows with time since separation. Measuring the source at two times and in two geometries separates ingrowth from decay.
Hidden term
H1697. An efficiency calibrated with a source close to the detector includes true-coincidence summing, which removes counts from the full-energy peak in a way set by the source's decay scheme rather than by the detector. Two photons emitted in cascade can be summed into one event. Calibrating at two distances and extrapolating to zero solid angle gives the summing-free efficiency.
Identity
H1698. Traceability and accuracy are not the same property, and a calibration chain cannot make a value more accurate than the standard at its root, since each transfer adds uncertainty and none removes it. A chain propagates whatever number its root supplies. Two chains tracing to different roots show that the root's uncertainty is common-mode within one and not the other.
Threshold
H1699. Self-absorption in a pressed source pellet becomes the dominant term below a certain photon energy, where the attenuation correction stops being a correction and becomes the measurement. The pellet's own mass sets the path length. Pellets of two thicknesses carrying the same activity, measured at one position, bracket the threshold.
Selection effect
H1700. Recommended half-lives are averages over measurements that were themselves screened for consistency, so the quoted uncertainty reflects the survivors' agreement rather than the population's spread, and the screen removes exactly the discrepant values that carry systematic information. The selection is on agreement. Comparing the recommended value with the full set, rejected measurements included, shows the truncation.

Status

One hundred entries, 1601 to 1700, contiguous. The distribution of forms is deliberately uneven and was not fixed in advance; a list with equal counts in each category would have been a grid wearing labels.

Three that could be settled with apparatus most laboratories already own: H1632, that a fitted trapping length is partly the shaping amplifier; H1676, that the two-source and decay methods measure different dead times whenever the dead time is extending; and H1683, that the variance-optimal split of counting time gives the blank more time than the sample whenever the blank is the stronger source.

If one of these is worth an afternoon, it is H1632 — repeat a single bias sweep at three shaping times on one detector and see whether the mobility-lifetime product moves. It is checkable with a pulser, a source and the shaping amplifier already on the bench.

Incoprea Research · hand-considered hypotheses 1601–1700 · radiation and particle measurement · 3 November 2026 · ~/Desktop/Nov3/