[en] In order to calculate the efficiency of a cylindrical sample, it can be divided into disks parallel to the face of the detector and the activities of all disks can be integrated according to their distance Tom the detector face. Two factors lead to the decreasing contribution of the disk as it's distance from the detector face increases, i.e. the absorption of the gamma photons in the sample and the decrease of the angle of the detector with increase of the distance. As a first step the dependence of the efficiency for a radioactive disk was studies in order to eliminate the absorption factor and single out the geometric one. It was found experimentally that high volume Ge detectors can be taken as an average effective plate detector with an efficiency function