Unfolding of pulse height distributions due to low energy gamma-ray

A 30×30 response matrix was derived to evaluate low energy (10-200keV) γ-ray spectra for a measuring system which consisted of a scintillation counter coupled with a 25mmφ×2mmt Nal (T1) crystal, a collimator and a log-amplifier. The collimator was used to measure a comparatively parallel beam incident on the scintillator, and the log-amplifier for magnifying the pulse height distribution of low energy γ-rays. The observed pulse height distributions were unfolded by iterative method with an automatic computer using the response matrix. An incident γ-ray spectrum for ²⁰³Hg unfolded by the method coincided within 10% with the values estimated by the ^Table of lsotopes^. This method was applied to evaluate low energy γ-ray spectra around a nuclear reactor. The pulse height distributions were observed at a place close to the thermal column of the KUR (Kyoto University Reactor) at 5MW thermal output. The results showed that low energy γ-rays leaking through the reactor shielding were comparatively weak, and that high energy γ-rays, when leaking, became low energy by scattering in the air. (author)