Minimum detectable activity in in situ gamma-ray spectrometry.

The algorithm used to calculate a minimum detectable activity (A(D)) of an environmental volume sample measured by gamma-ray spectrometry was modified and adapted for in situ measurements performed at the standard 1 m height above ground. AD 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(D)s 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 1 m 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 gamma spectrometry applying a simple experimental procedure that is based on the linear relationship.