High sensitive measurements of Cs-137 and other radionuclides in environmental samples using germanium detectors

Three types of high-purity germanium (HPGe) detector systems for low-level radioactivity measurement were constructed in the laboratory near sea level . An anti-Compton system was set up by combining a large volume HPGe (rei. eff. 115%) with a well type NaI(TI). The detection limit (D.L.) of Cs-137 o f an ashed oyster sample for the anti-Compton mode of 115% Ge was 0.023 Bq/ sample for 8.10(4) s counting, whereas 0.035 Bq/sample for the normal mode. Under similar measuring conditions, D.L. of Cs-137 for a medium volume HPG e (rel. eff. 51%) was 0.042 Bq/sample, A low-background Ge-LEPS (Low Energy Photon Spectrometer) was sufficiently sensitive for low level measurements of Pb-210, Th-234 and other low energy gamma-emitters. The detection limit for Pb-210 in the sample shape of 60 mm diameter by 2 mm thick was about 0 .05 Bq/sample for 5.0.10(5) s background counting. Using this LEPS, it was found that Pb-210 behaves similarly to Be-7 in both air and precipitation ( snowfall).