Abstract A gamma-gamma ({ }-{ } γ - γ) coincidence spectrometer was modelled using the Geant4 toolkit and validated against experimental measurements. Incorporation of a decay-time estimation method enabled the generation of time-stamped list mode (T-List) data, facilitating a quantitative assessment of the performance advantages of high-resolution { }-{ } γ - γ coincidence spectrometry relative to conventional high-resolution { } γ -spectrometry. The detection limit sensitivity for specific radionuclides of interest in the presence of a specified contaminant were investigated and the relative benefits of coincidence analysis discussed. The detection limit for ^ {134} 134 Cs, using the 605-795 keV signature, is shown to be independent of ^ {137} 137 Cs activity but sensitive to ^ {132} 132 I due to the presence of abundant high-energy coincident photons. Similarly, the potential acceleration of analytical timelines through the combination of partial radiochemical separation and { }-{ } γ - γ coincidence spectrometry is explored. For example, ^ {156} 156 Eu is predicted to be detectable in fission product matrices containing other lanthanide radionuclides using { } γ – { } γ coincidence spectrometry, despite remaining below conventional { } γ -spectrometric detection limits, with quantifiable results obtainable several hours earlier than via full radiochemical separation followed by standard { } γ -spectrometry. In the analysis of compositionally complex samples, this approach also enables the identification of radionuclides that adversely affect detection limits, thereby highlighting candidates for removal by radiochemical separation.
Stokes et al. (Wed,) studied this question.