Determination of the efficiency of a detector in gamma spectrometry of large-volume samples

The experimental - calculated method is proposed to determine the full energy peak efficiency (FEPE) of detectors {\epsilon}(E) in case a measurement of the large-volume samples. Water is used as standard absorber in which the linear attenuation coefficients for photons {\mu}0 (E) is well known. The value {\mu} (E) in sample material (matrix of the sample) is determined experimentally by means of spectrometer. The formulas are given for calculation of the ratio {\epsilon}(E)/ {\epsilon}0(E), where {\epsilon}0(E) is FEPE of the detector for photons those are arising in the container filled with water (it is found by adding in the container of the Reference radioactive solutions). To prove the validity of the method ethanol (density 0,8 g/cm3) and water solutions of salts (density 1,2 and 1,5 g/cm3) were used for simulation of the samples with different attenuation coefficients. Standard deviation between experimental and calculated efficiencies has been about 5 %.