Optimization of measurement counting time in Gamma-ray spectrometry of soil samples

The method of optimal measurement counting time in Gamma spectrometry for soil samples was studied. Gamma spectrometry was done based on minimum detectable activity using the HPGe- p type with efficiency of 30% and FWHM 1.7keV (for 1.33 MeV 60Co). The samples were IAEA-RG Th-1, IAEA-RGU-1 and IAEA-RGK-1 prepared in bottles. The measurements were done for 12 different counting times from 5 min to 36 hour. The minimum detectable activity (MDA) was determined for daughters’ of 232Th, 238U, 235U and radionuclide 40K. The counting time in which the changes of the MDA is less than 0.05 Bq/kg·h was considered as the optimal counting time.