“…The issue of depth distributions of gamma emitting radionuclides has been the subject of several studies in the field of in-situ gamma spectrometry. Mainly three approaches have been proposed: a) the differential attenuation of gamma emission lines as a function of energy, sometimes referred to as the two lines method (Miller et Thummerer and Jacob, 1998); b) the forward scattering or photopeak to valley method, based on the ratio of count-rates in the full energy peak of a specific emission line and the count-rate in the valley between the corresponding Compton edge and the photopeak (Zombori et al, 1992;Tyler et al, 1996;Tyler, 1999Tyler, , 2004Kastlander and Bargholtz, 2005;Tyler and Copplestone, 2007); c) the use of lead plates and/or collimators (Korun et al, 1994;Benke and Kearfott, 2001). While the application of the two first approaches is limited to simple depth distributions of radioelements -e. g. exponential decrease for 137 Cs -the third suffers from the need for repeated measurements and long counting times.…”