DEVELOPMENT OF A GERMANIUM DETECTOR COMPUTER MODEL AND OBTAINING MODEL SPECTRA OF STANDARD URANIUM U₃O₈ SRM-969 SAMPLES

Computer modeling was carried out for gamma-ray spectra of nuclear materials, which were measured by using a semiconductor high-purity germanium detector ORTEC GEM25P4-70. The standard SRM-969 samples were used as sources of gamma radiation, which are cylindrical tanks of fixed volume, made of aluminum alloy 6061, filled with a dispersed uranium oxide powder (U₃O₈) with different concentrations of ²³⁵U. The products from radioactive decay chains are determined for uranium isotopes ²³⁵U and ²³⁸U, which give the main contribution to the gamma spectrum of uranium oxide (U₃O₈). A technique that makes it possible to compare the results of measurements with model spectra is developed. The correlation of the measured spectra to the model spectra was made by comparing the areas of the total absorption peaks for energies of 185 keV and 1001 keV, which are often used in gamma spectrometry to determine uranium enrichment. The selected parameters of the model and the source of the detector allowed to describe the measured gamma-ray spectra with an accuracy of better than 6 % at the total areas of the absorption peaks in the energy range 150–1100 keV. The developed model makes it possible to obtain the model of gamma spectra of various fissile materials, provided that there are the data available about the isotopic composition, the quantum yield of gamma lines for each isotope, and the activity of fissile material. These model spectra can be used for the development of measurement techniques and software testing in the field of nuclear spectroscopy.

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