Abstract

Purpose. One of the most important tasks of the nuclear industry is to control the non-proliferation of fissile nuclear materials (for example²³²Th, ²³⁵U, ²³⁸U, ²³⁹Pu) at all stages of their use (movement, storage, etc.). To successfully solve this problem, reliable information about their isotopic composition is required. The present study aims to simulate the yields of pairs of photofission products of ²³²Th, ²³⁵U, ²³⁸U, ²³⁹Pu nuclei, the delayed gamma radiation of which can be used for nondestructive isotopic analysis of nuclear materials at electron accelerators. 

Methods. Calculations of the mass distributions of the photofission products of ²³²Th, ²³⁵U, ²³⁸U, ²³⁹Pu nuclei were carried out using the GEF code. The bremsstrahlung spectrum was simulated during the interaction of electrons (E=12.5 MeV) with a tantalum converter (1 mm) using a GEANT4 10.7.

Results. Simulations of mass distributions of photofission products of ²³²Th, ²³⁵U, ²³⁸U, ²³⁹Pu nuclei have been carried out. The yields ratios for product pairs (Y₈₈/Y₁₃₅, Y₉₂/Y₁₃₅, Y₉₂/Y₁₃₈, Y₈₇/Y₁₃₈, Y₈₈/Y₁₃₈, Y₈₉/Y₁₃₈, Y₈₇/Y₁₄₂,Y₈₈/Y_142,Y₈₉/Y₁₄₂) are calculated for the indicated cores. Estimates of the difference between the numerical values of the ratio of yields of pairs of fragments for pairs of nuclei ²³²Th and ²³⁵U, ²³⁵U and ²³⁸U, ²³⁸U and ²³⁹Pu are made on a percentage basis. The values of the difference in the ratios of the yields of these pairs of products are – 5.0÷43.2%, 14.1÷39.3%, and 14.1÷39.3% for nuclear pairs²³²Th and ²³⁵U, ²³⁵U and ²³⁸U, ²³⁸U and ²³⁹Pu, respectively.

Conclusions. The results of the simulation indicate the possibility of using the above pairs of fission products as sources of delayed gamma radiation when performing nondestructive isotopic analysis of nuclear materials. The results obtained can be used to optimize experiments on electron accelerators, which will improve the accuracy and reliability of the results

Keywords: nuclear materials, isotope analysis, photofission, product yields, delayed gamma radiation

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