MONTE-CARLO SIMULATION OF SEVERAL GAMMA-EMITTING SOURCE AND DETECTOR ARRANGEMENTS FOR DETERMINING CORRECTIONS OF SELF-ATTENUATION AND COINCIDENCE SUMMATION IN GAMMA-SPECTROMETRY

A Monte Carlo simulation technique has been developed for gamma-spectrometric measurement systems which allows calculation of photon path lengths in source and detector as well as total efficiency. From these parameters correction factors for self-attenuation and coincidence summation can be estimated. The calculations require only readily available data e.g., dimensions and relative positions of the gamma-emitting source and the detector as well as the appropriate emission probabilities of the gamma lines under study. The simulation involves relating the point of emission and the path of the photon to an axis of symmetry and therefore applies to any axially symmetric arrangement of source and detector. The calculated total efficiency curves for well-defined arrangements of point source and detector are practically identical to those reported in the literature. Similarly, correction factors for coincidence summation of Na-22, Co-58, Co-60, and Y-88 as point cylindrical volume and Marinelli beaker sources agree very well with values established by experiment or by a different model approach. In addition, total efficiency curves and average path lengths of photons in the source are given for several other measurement systems with Ge(Li) or p-type (Hp)Ge detectors.