Publication Date:
2013-12-27
Description:
Publication date: Available online 26 December 2013 Source: Radiation Measurements Author(s): Fabien Courtine , Serge Sanzelle , Thierry Pilleyre , Didier Miallier Radiation sources of 60Co are commonly measured by means of HPGe gamma spectrometers, either as unknown sources or as calibration sources. However, the two gamma rays that are emitted by this nuclide, at 1.17 MeV and 1.33 MeV respectively, follow each other so rapidly that in the cases where both photons interact with the crystal, the electronics will record a single additive pulse. This is a cascade or coincidence summing effect. Such effect induces in the gamma spectra a "sum-peak", appearing at 2.5 MeV on the energy axis, generated by the pair of photons which have both been entirely absorbed by the detector. Also, the second photon is correlated for direction to the first one, i.e., it will not be emitted at random, with an isotropic probability. Then the question arises of to what extent the two effects, cascade and correlation, might affect the count rates for the three peaks. Various answers have already been published, but without practical solutions. In this context, the present work was devoted to further explore the question by means of Monte Carlo simulation, in the case of a welltype detector. As a result, inside the well the sum peak only is not affected and it allows accurate evaluation of the detector efficiency at 1.25 MeV. Outside the well, near the detector, none of the three peaks can be directly used for efficiency evaluation, unless the relevant corrections can be evaluated. At a distance from the detector, the two single peaks can be used, but with the drawback of a low efficiency.
Print ISSN:
1350-4487
Electronic ISSN:
1879-0925
Topics:
Electrical Engineering, Measurement and Control Technology
,
Physics
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