Assessment of the uncertainty budget associated with 4πγcounting

Abstract

The 4πγ-counting technique is recognized as a powerful primary method for the standardization of radionuclides decaying with abundant gamma emissions. Based on the use of a gamma detector in quasi 4π-geometry, a detection efficiency close to 100% and a low uncertainty can be achieved thanks to the summing effect of subsequent gamma transitions. Uncertainties have to be assigned to the realistic modelling of the source-detector geometry with respect to dimensions, density and material composition, the calculation of the total counting efficiency of the detector for the various emitted radiation, and the effect of possible flaws in the decay scheme of a radionuclide on the calculated total efficiency. Other uncertainty factors pertain to typical metrological sources of uncertainty, such as weighing, nuclear counting with pulse pile-up and system dead-time effects, impurity corrections, decay corrections, timing and frequency, etc. In order to ensure good metrological practices at NMIs, the uncertainties particular to the method are discussed.

Evidence against solar influence on nuclear decay constants

“…The measurement techniques employed are as follows: ionisation current measurements in a re-entrant ionisation chamber (IC) or a hospital calibrator (HIC) [31,32], net area analysis of full-energy γ-ray peaks (and integral spectrum counting) by γ-ray spectrometry with a HPGe detector (HPGe) [33], particle counting in a planar silicon detector in quasi-2πconfiguration (PIPS) [34], X-ray counting at a small defined solid angle with a gas-filled proportional counter (PC) [35,36], live-timed β–γ anti-coincidence counting (LTAC) [37], triple-to-double coincidence counting with a liquid scintillation vial and three photodetectors (TDCR) [38], liquid scintillation counting (LSC) [38], particle and photon counting in a sandwich CsI (Tl) spectrometer (CsI) [39], internal gas counting (IGC) [40], and α-particle counting at a small defined solid angle with a large planar silicon detector (αDSA) [35,36]. An overview of standardisation techniques and their sources of error can be found in the special issues 44(4) and 52(3) of Metrologia [41,42] and references in [25,28].…”

When the model doesn’t cover reality: examples from radionuclide metrology

“…Monte Carlo (MC) simulations are frequently used to model various aspects of the measurement process [46]. General purpose particle transfer codes [14][15][16][17][18] can reproduce physical processes in customer designed geometries, which has important applications such as the calculation of detection efficiency of a radioactive source in gamma spectrometers [47], ionisation chambers [48] and various other set-ups [49][50][51][52]. Additionally, detailed analytical models have been developed for specific applications, such as efficiency calculations in liquid scintillation counting [51], high-geometry 4πγ counters [52] and defined solid angle counters [53].…”

On the recent claim of correlation between radioactive decay rates and space weather

“…Most of the counterevidence, on the other hand, was performed by experienced metrologists using superior detection techniques and showing awareness of the vulnerability of detector stability to external factors. This is witnessed by dedicated literature discussing factors contributing to the uncertainty budget for primary and secondary standardisation techniques [55][56][57][58][59][60][61][62].…”