In-situ determination of deposited radionuclide activities: improved method using derived depth distributions from the measured photon spectra.

When applying the standard method of in-situ gamma spectrometry to determine deposited radionuclide activities, an assumption is needed regarding the depth distribution of radionuclides in the ground. The method can be improved by assessing, from information contained in the spectrum, the attenuation of the radiation by the soil and vegetation. By comparing the count rates of the x ray and the gamma-ray lines of its daughter nuclide 137mBa, the 137Cs activity per area can be determined. The range of applicability of the method is discussed by means of an uncertainty analysis, and the method is applied to post-Chernobyl measurements. A comparison with the results of the standard method of in-situ spectrometry demonstrates the progress achieved by the proposed method. Nevertheless, the method still has some shortcomings for the peak analysis that could be improved by better detector resolution or better computer software.