neutrons and gamma-ray interactions with different media

although the experimental determination of the absolute efficiency is by far the most accurate method, it can sometimes be difficult or impossible. indeed, accurately calibrated gamma -ray sources are different to be prepared for all the geometrical arrangements used in gamma-ray spectroscopy. several methods have been proposed and applied to overcome the above problem . the basic concept of these methods is essentially the same and is composed of two steps: the precise determination of the absolute full peak efficiency for a point source and a numerical (mainly monte Carlo) correction for the source extended dimensions (including self-absorption).this work introduces two new concepts to determine the full-peak efficiency of the gamma spectrometers for analyzing volumetric samples with : 1- unknown elemental compositions (concept 1) and 2- unknown elemental compositions (concept II)