A method of calculating the corrections to the true summation of the γ radiation for arbitrary radionuclides for measuring point and volume sources using scintillation and ultrapure germanium detectors is described. The calculations are based on the Monte Carlo method using ENSDF evaluated data on the structure of atomic nuclei. An experimental check made using IAEA test spectra confirms that the calculations of the correction factors are reliable. The method is integrated into the γ spectrometric packages LSRM-2000 and AkWin, where the corrections for the ture summation are used for developing a library.The increase or decrease in the number of counts recorded in the total-absorption peaks as a result of summing the impulses at the exit of a detector can strongly influence the accuracy of the results of γ spectrometry. Taking account of this effect is now one of the mandatory requirements for modern γ-spectrometric software.The effect appears in measurements of radiation from cascade sources and is due to the summation of impulses while simultaneously detecting two or more γ rays in the sensitive volume of a detector. This distorts the measured γ-ray spectrum, specifically, it changes the areas of the total-absorption peaks, deforms the continuous Compton distribution, and results in the appearance of spurious peaks in the energy, which are absent in the true emission spectrum of the source.In contrast to the random summation, where the probability of detecting impulses simultaneously is proportional to the squared counting rate at the entrance into the spectrometric channel, the intensity of true summation is determined by the measurement geometry, the characteristics of the detector, and the special features of the radionuclide cascade scheme. The difficulty of introducing corrections for the true summation is due, first and foremost, to the fact that it is necessary to know the γ-ray detection efficiency along the total-absorption peak and the total efficiency which depends on the relative arrangement and configuration of the source and detector, as well as of the environment in which scattering and backward reflection of γ rays occur. The problem is exacerbated during measurement of radiation from a volume source, which effectively absorbs and scatters its own radiation.An accurate calculation requires taking into account the possible anisotropy of the angular distribution of the emitted cascade photons. In addition, the coincidence of γ radiation with annihilation (511 keV) photons must be taken into account when measuring a source of β + radiation. A coincidence of the γ radiation from the source and the characteristic and

A γ-ray detector based on pressurized xenon is described, and the characteristics of the processing of the spectrum of the detector are examined. It is shown that the SpectraLine computer program, where these characteristics are taken into account, makes it possible to process successfully the spectra measured with a pressurized-xenon detector, which greatly expands the possibilities of instruments of this class for performing spectrometric measurements. The possibilities of using pressurized-xenon detectors to solve complex problems of gamma-spectrometric analysis using the GammaLab program system are analyzed. The results obtained show that it is indeed possible, in principle, to use a pressurized-xenon detector together with the SpectraLine computer program for quantitative analysis of samples with a complex radionuclide composition, specifically, to determine the isotopic composition of plutonium.For a long time now, the Monte Carlo method has been used successfully to simulate spectra. One application developed on the basis of this method is the virtual gamma-spectrometric laboratory GammaLab [1, 2], which makes it possible to simulate the spectra obtained for point and volume sources with an arbitrary radionuclide composition using semiconductor and scintillation detectors. The resolution of the new detectors, based on LaBr, LaCl, or pressurized xenon and developed at the Moscow Engineering Physics Institute [3,4], is lower than that of detectors based on ultrapure germanium, but they are free of drawbacks such as the need for low-temperature cooling and high cost, and their resolution is approximately 5 times higher than that of NaI scintillation detectors.The present article analyzes the possibilities of using gamma spectrometers based on pressurized xenon for quantitative analysis of samples with a complex radionuclide composition using the GammaLab program system and presents the principles and results of the simulation of experiments using a pressurized-xenon gamma-ray detector.The simulation consists in calculating the radiation spectrum of a source at the position of the detector, converting the spectrum taking account of instrumental effects, and transferring it into an external program for display and further processing. A possible variant of a solution of this problem is to use the Monte Carlo method to play out the decay chain of the radionuclide and radiation transfer in the container and detector materials. This method leads to long calculations of the spec-