In-Situ Gamma-Ray Measurement Using Ge(Li) Detectors

A portable 73cm3 closed-end coaxial Ge(Li) gamma-ray spectrometer was made and in-situ measurement of environmental gamma-rays has been carried out. The detector has 17.5% peak detection efficiency and 2.5keV FWHM energy resolution for 1333keV gamma-rays at a source-to-detector distance of 25cm. The peak counting rate per unit flux of 662keV gamma-rays was 3.62cps/photon/cm2sec and FWHM was 2.1keV. Peak counting rate dependence on incident direction of parallel beam of gamma-rays was measured to find correction factors for in-situ data analysis. From the in-situ measurements, the concentrations of U-238, Th-232, K-40, and Cs-137 in the soil and their contributions to the total exposure rate at the detector were induced. These results are compared with those of low level Ge(Li) spectrometer measurement of soil samples and with those of in-situ measurement using a 3"×3" NaI(Tl) detector spectrum-to-dose conversion operator method. Another Ge(Li) detector having a special lead shield was made to detect only gamma-rays from plumes.