Speaker
Description
Gamma-ray spectrometer with a single HPGe or NaI:Tl detector shielded with lead is often used to measure the activity concentration of radionuclides in soil samples. A passive water shield to reduce background radiation reaching the detectors was designed using GEANT4 Monte Carlo simulations and then constructed. IAEA-375 soil and beach sand each placed in Marinelli beaker were measured for 48 hours using two LaBr$_3$:Ce detectors placed inside the constructed water shield. The samples were also measured for 24 hours using a NaI:Tl detector inside the constructed water shield and HPGe shielded with lead and copper to compare and validate the results from measurements with the LaBr$_3$:Ce detectors. Both the simulated and measured results show that the water shield attenuates the 2614.5 keV gamma rays by over 90 % and energies lower than the 2614.5 keV by far above 90 %. The activity concentration of $^{40}$K radionuclide in IAEA-375 soil and beach sand measured using the LaBr$_3$:Ce detectors was below the minimum detectable activity (MDA) due to the internal activity of the detector. The measured activity concentrations of $^{238}$U and $^{232}$Th series and $^{40}$K radionuclides in IAEA-375 soil were comparable with certified values to within measurement uncertainties. The activity concentrations of $^{238}$U and $^{232}$Th series radionuclides in beach sand were determined using all the measurement geometries and consistent to within 1$\sigma$ to 2$\sigma$ level.
