Research Progress and Prospect of Fission Yield in China Institute of Atomic Energy

Fission yield is one of the crucial data for nuclear power application and nuclear devices development, and plays an important role in the fundamental research such as nuclear fission physics research, element synthesis in nuclear astrophysics, and the mechanisms of superheavy nucleus synthesis. In this paper, the progress of nuclear fission yield research made by China Institute of Atomic Energy was mainly introduced. First, a series of fission yields measurements were introduced, including: the cumulative yields measurements of important fission systems using direct γ-ray spectrometry, especially the high-precision measurement of fission yields related to burnup; the cumulative yields measurements of low-yield nuclides from ²³⁵U fission induced by neutrons, and those of short-lived products from ²⁵²Cf spontaneous fission, as well as the mass chain yields and yield-energy relationships of important fission systems using the radiochemical method; measurements of mass distribution of primary fission products from ²⁵²Cf spontaneous fission and thermal neutron-induced fission of ²³⁵U and ²³⁹⁵Pu based on the kinetic energy-velocity (E-v) method and the established fission fragment identification spectrometer (FFIS). In addition, the innovative work carried out using the microscopic theory of fission was introduced. Within the framework of covariant density functional theory, the two-center harmonic oscillator basis and Fourier parameterization improve the theoretical calculation of the large deformation region close to the scission point, laying a solid foundation for the research on microscopic methods of nuclear fission. Within the framework of the macroscopic-microscopic model, the Langevin method coupled with neutron evaporation model has been developed, in order to consistently describe the fission dynamics and de-excitation process of fission fragments, and the prompt fission quantities including the independent fission yields, and the multiplicities and energy spectra of prompt neutron in ²³⁵U fission induced by neutrons are well reproduced using this method. Moreover, the progress of fission yield evaluation and database establishment was introduced, including fission yield evaluation methods based on machine learning, the 5-Gaussian model and the Z_p model, as well as the evaluation of experimental data. Finally, the future development and prospects of fission yield research were presented. In terms of experimental measurement, efforts will be made to continuously improve measurement technologies, achieving high-precision measurements of yield-energy relationship data and independent yields. In the research on fission theories, models will be further improved to gradually realize the accurate description of various types of fission data. In addition, experimental data evaluation technologies and fission phenomenological models will be improved, and the evaluation of yields and yield-energy relationships for a series of important fission product nuclei will be completed.