Study of the minimum detectable activity in gamma-ray spectrometry with various shielding configurations

Abstract

In the environmental radioactivity analyzing methods using gamma-ray spectrometry, the natural activities of radionuclides were required to be higher than the minimum detectable activity (MDA). To reduce MDA, one of the popular methods is to improve the ability of reducing the background radiation of the gamma-ray spectrometry. In this work, we designed the shielding configuration with 5 cm lead and 2 mm copper (thickness of walls and top). The MDAs of gamma-ray spectrometer were 2.6–4.24 times times for ⁴⁰K (1460.8 keV), ²³²Th (²⁰⁸Tl- 2614.5 keV) and ²³⁸U (²¹⁴Pb- 352 keV; ²¹⁴Bi- 609.3 keV, ²¹⁴Bi- 1764.5 keV). In the other hand, MDA for ²³⁸U with this shielding configuration is smaller than the activity of ²³⁸U inside surface soils in Vietnam. These results showed that the gamma spectrometer with NaI(Tl) detector and this shielding configuration was suitable for measurements activity of ²³⁸U in the environmental samples.