A Spectrometric Method for Measurement of Low-level Gamma Exposure Dose

Abstract

A spectrometric method for the exposure dose estimation of low level gamma-radiation with the use of a NaI(Tl) crystal gamma-ray spectrometer was presented. A function G(E) which is applied to a given gamma-spectrum and can eliminate the energy dependence of the crystal for the estimation of the gamma-exposure dose, was introduced. The paper describes the principle of the method and the determination of the G(E) function, and presents the results obtained for gamma-radiations from 137Cs and Ra sources, and for environmental gamma-radiations in different locations in the Tokai Area. The exposure doses obtained were compared with those measured by an ionization chamber and the agreement was good. Discussions are given on the angular response of the 5 × 4-in. crystal for incoming photons, particularly in connection with the measurement of environmental radiation. This method provides a simple procedure to estimate the exposure dose of gamma-radiations, independent of their energy and energy distribution without a tedious procedure of spectral analysis. If it is desired, a fractional dose contribution, including that of scattered radiation, can be estimated with the aid of the spectral analysis technique.