Minimum detectable activity in in situ γ-ray spectrometry

The algorithm used to calculate a minimum detectable activity (A_D) of an environmental volume sample measured by γ-ray spectrometry was modified and adapted for in situ measurements performed at the standard 1m height above ground. A_D values of target radionuclides were determined from the in situ spectra collected at two disparate sites. A linear relationship between the two sets of A_Ds was found and the ratio between these two sets is equal to the square root of the ratio of the two respective absorbed dose rates measured at the sites at 1m height. Absorbed dose rates were calculated using the concentration of potassium, thorium and uranium in the soils at the sites and found to agree well with the measured values. A_D values can be predicted easily in in situ γ spectrometry applying a simple experimental procedure that is based on the linear relationship.