Environmental gamma-ray exposure rates measured by in-situ Ge(Li) spectrometer

A conversion function (G(E) function) was determined to obtain an exposure rate directly from a γ-ray spectrum measured by an in-situ Ge(Li) spectrometer. In order to verify the utility of the G(E) function method, three kinds of detector, namely, a portable Ge(Li) detector, a NaI(Tl) detector and an ionization chamber, were used to measure exposure rate due to environmental γ-rays at the same place, and the measured values of exposure rate were compared with each other. Two exposure rate values were obtained from a γ-ray spectrum measured by the Ge(Li) detector, using two different methods, namely, the G(E) function method and the HASL method. The average of exposure rates obtained by four different methods was 4.15 μR/h, and the deviation was 15% of the average. By applying both the G(E) function method and the HASL method to an environmental γ-ray spectrum, a total exposure rate can be determined directly without information on the distribution of the radionuclides in soil, and individual exposure rates due to 40K, 238U and 232Th series and 137Cs of the known distribution in soil can be also determined. (author)