휴대용 HPGe 검출기를 이용한 in-situ 감마선 분광분석법에 관한 연구

Abstract

When an accident of nuclear facilities is occurred, an in-situ spectrometry method with the portable HPGe detector has a merit that can be determined the concentrations of the natural and the artificial nuclide as well as the exposure rate quickly. In fifteen sites, in-suit gamma-ray spectra were measured and the specific activities of U-series, Th-series, 40K, and 137Cs were obtained by the in-suit gamma spectra. The factor to convert the count-per-minute to the specific activity was also obtained. The specific activity of in-situ spectrometry was compared with the value measured in the laboratory after the pre-treatment for soil.

The mean specific activity for 238U series and 232Th series was estimated to be 1.02 and 1.12 to the measured value in laboratory, respectively. For the case of 40K, the mean specific activity was obtained to be 0.77, which is determined less than that of laboratory. In spite of their differences, the technique of the in-situ spectrometry can be applied to measure the environmental radiation in soil because the ratio is almost like 1.0 but, for 137Cs, the mean specific activity was estimated to have large difference than that of laboratory, because the depth distribution of the cesium to happen in nuclear weapon tests in the atmosphere during the 1950 and 1960th had had a large disturbance.

The energy band theory has been generally used to calculate the dose rate for the natural nuclide from the in-suit gamma ray spectrum. But, the method is inadequate for analyzing the component to be largely affected in the spectrum. The G(E) method can be compensative for that method.

For a few gamma ray, G(E) factor was calculated by the MCNPX code that could simulate the interaction of gamma in the portable HPGe detector. The gamma spectrum by the in-situ spectrometry was conversed to the exposure rate by the G(E) factor. When the exposure rate by the G(E) factor are compared with that by energy band theory, two data have agreement with the ratios of 0.87~ 1.04 in the measured sites.

The in-situ spectrometry with the portable HPGe using G(E) factor will be an available method for analyzing the accident of nuclear facilities