Pre-neutron-emission Mass Distributions For Intermediate Neutron-induced Reaction²³²Th Fission

Neutron-induced actinide fission is concerned by nuclear physicists not only for the study of nuclear reaction mechanisms, but also for the effective utilization of nuclear energy. Pre-neutron-emission mass distributions is associated with pre-fission and fission products. And important information for the description of products and fission mechanism can be extracted from it. Due to the rapidly increase demand of energy, nuclear fuel are demanded more. So, utilization of thorium-based nuclear fuel get more attention. There are some advantages of thorium-based nuclear fuel. Thorium is more abundant than uranium.232Th is a better fertile material than238U in thermal reactors. ThO2is higher chemical and radiation stability than UO2. Thorium-based nuclear fuel with a higher conversion of232Th/233U, have intrinsic proliferation-resistance, and lesser quantity of long-lived minor actinides are formed. So, it is meaningful to study the pre-neutron-emission mass distributions of neutron-induced232Th fission.From the investigation of the pre-neutron-emission mass distributions for intermediate neutron induced232Th fission, one can be found that,(1) at low energy, the pre-neutron-emission mass distributions have double-humped characteristics,(2) at intermediate en-ergy, pre-neutron-emission mass distributions transform to triple-humped shape gradually,(3)both in the case of low-energy or intermediate-energy, the positions, heights and the width of the peak-valley of the distributions which depend on the incident neutron energies,(4) the evaporation neutrons before scission depend on the incident neutron energies. For these various characteristics of the neutron-induced232Th fission, consistent description is far from being achieved at present. Therefore, based on the experimental data and the advantages of previous work, The phenomenological fission potential theory are improved to calculate the pre-neutron-emission mass distributions of the intermediate-energies neutron induced232Th fission. The fission potential describe by three harmonic oscillators is expanded to five harmonic oscillators. The correlation of parameters of the model can be obtained by strict inference. The correlation that positions, heights and the width of the peak-valley of the distributions which depend on the incident neutron energies are obtained by ana-lyzing experimental data. The correlation that evaporation neutrons before scission which depend on the incident neutron energies are obtained from cross section and other relevant information. Based on the above conclusion, there is no any adjustable parameter. The pre-neutron-emission mass distributions of different energies neutron induced232Th fission are calculated. The results of the calculations shown that, fission potential theory not only can well reproduce the measured data, but also can reasonably predict the unmeasured incident energies. Comparing the results of various theoretical models show that, this work is better accord with the experimental data. In addition, pre-neutron-emission mass distributions vary with incident neutron energies. The critical energies while the pre-neutron-emission fragment mass distributions turned to triple-humped from double-humped and while turned to single-humped from triple-humped are predicted firstly in this work. So, this work is helpful for further study of fission products and fission mechanisms.