Measurement of gamma-ray exposure rate by means of scintillation spectrometry

Exposure rate due to a gamma-ray beam of 137Cs source embeded in a collimating lead castle was measured using a scintillation spectrometer of a Nal(Tl) well-type crystal. The exposure rate was calculated from the observed spectrum in accordance with ''spectrum-exposure rate conversion'' method instead of response matrix correction which necessitates computer operation. Calculation of the numerical values of the conversion operator, G(E), was carried out using photofraction and interaction ratio determined as a function of incident photon energy for the scintillator used. The result is in good agreement with the exposure rate estimated on the basis of specific gamma-ray constant of the source when the contribution of scattered photons from the lead castle to the collimated primary beam is taken into account. The ratio of exposure due to those scattered photons to the total exposure was estimated to be 2.25%. (author)