Digital coincidence counting for radionuclide standardization

Abstract

The 4πβ-γ coincidence method for the absolute determination of nuclear disintegration rates has for decades been successfully applied to a variety of radionuclides, via the use of suites of dedicated analogue electronic modules. The high cost of procurement and maintenance of such systems, as well as the requirement for highly experienced technicians to perform the data collection have prompted the design of more flexible data collection techniques. Recent advances in digital signal acquisition technology have facilitated the possibility of storing pulse information from multiple detector systems along with a time stamp for each recorded event, allowing various radionuclide standardization techniques (based on the concept of 4πβ-γ coincidence counting) to be implemented 'offline' via the use of dedicated software routines. This brief paper reviews the progress in the development of such 'digital coincidence counting' systems used in the field of radionuclide metrology and may be viewed as a companion article to other papers (in this issue) on primary methods for radionuclide standardization.

Absolute intensities of the γ-ray emissions originating from the electron capture decay of 153Gd

“…The amplified pulses resulting from both detector systems were digitised and processed by the NPL Digital Coincidence Counting system, which has been described elsewhere [16,21,22]. This digital system handles the offline imposition of dead-times in both channels, selection of photon windows, imposition of appropriate delay/s and coincidence resolving times and provides data in a format suitable for the "Computer Discrimination" efficiency extrapolation method described by Smith [23,24].…”

“…In this work the absolute activity of a solution of 153 Gd has been determined by 4π (Liquid scintillation (LS))-γ Digital Coincidence Counting (DCC) [16], which has subsequently been used to determine the 153 Gd absolute γ -ray emission intensities by high purity γ -ray spectrometry. Throughout this article, uncertainties are stated as standard uncertainties or combined standard uncertainties as defined in the Guide to the Expression of Uncertainty in Measurement (GUM) [17].…”

Standardisation of 223Ra by liquid scintillation counting techniques and comparison with secondary measurements

“…The LS channel employed was an NPL-built liquid scintillation counter (with two photomultiplier tubes (PMTs) operating in coincidence for background reduction purposes). Processing of the pulse trains from each channel and formation of coincidences for efficiency estimation was performed using the NPL digital coincidence counting (DCC) system described elsewhere (Keightley and Watt, 2002), (Keightley and Park, 2007). The digitisation of the pulse trains along with appropriate timestamping of recorded events enabled off-line processing of the data, and imposition of multiple γ-gates for LS channel efficiency monitoring.…”

“…The first decay product, 219 Rn, is a noble gas with a half-life of approximately 4s, and standardisation techniques in which the sample remained in liquid form were preferred to avoid problems with the loss of 219 Rn and subsequent short-lived contamination of counting equipment. The techniques selected were efficiency-traced liquid scintillation counting with a commercial scintillation counter (the CIEMAT/NIST technique; Broda et al, 2007) and 4π liquid scintillation-γ digital coincidence counting (Keightley and Watt, 2002), (Keightley and Park, 2007) utilising the computer discrimination technique for efficiency variation detailed in Smith (1975) and Smith (1987).…”

Instrumentation et gestion numérique des temps morts pour la métrologie de la radioactivité

“…Les premiers développements d'instrumentation numérique pour la métrologie de la radioactivité ont concerné la méthode des coïncidences 4πβ − γ [4]. Dans cette méthode, on doit détecter les évènements en coïn-cidence entre deux voies de mesure, l'une sensible au rayonnement bêta (électrons) et l'autre au rayonnement gamma (photons).…”