Induced By Neutrons <sup> 6,7 </ Sup> Li Reaction Secondary Neutron Double Differential Cross Section Measurement And Evaluation

In this thesis the double-differential measurements of neutrons emission cross section have been described for ~6,7Li at the incident energies 10.27 Mev. Meanwhile, the measurement results have been analysed and interpreted with a new light nuclear reaction model.Double differential neutron emission cross section (DDX) is one of the most important nuclear data used in nuclear engineering design, particularly in nuclear device and neutron shielding design. However the evaluations and measurements of DDX is sparse. Up to now, most of DDX measurement data performed are at around 14 MeV and below 8 MeV, since the mono-energetic neutron sources are available. While the DDX measurements are scarce at 8 ~ 13 MeV region due to the lack of mono-energetic neutron source. Hence, only a few evaluation nuclear data files including DDX data are available. On the other hand, the theoretical calculation results are different from each other with different light nuclear reaction models, therefore DDX measurement is necessary for checking and improving nuclear reaction models and evaluation nuclear data file at different energy region. As a result of the present available nuclear reaction models are mainly employed to calculation for medium-heavy mass, as well as fissile nuclei, and in the relevant nuclear reaction model codes the reaction process is only the sequential particle emissions processes which could not be applied to description of the neutron induced light nucleus reactions. For this reason, it is necessary to establish and develop a new nuclear reaction model for light nucleus and to measure double-differential cross sections precisely for some key nuclei within 8 ~ 13 MeV region.The cross section data for neutron induced reactions on ~6Li and ~7Li are the prime requirements of the design of breeding blankets for D-T fueled thermonuclear reactors. Tritium is produced by the ~6Li(n,α)T and ~7Li(n, n'α)T reactions, which also dominate nuclear heating in addition to (n, n), (n, n') and (n, 2n) reactions, which are employed as neutron multiplication and coolant for D-T fueled thermonuclear reactors. It is well known that ~6,7Li are the nuclei with predominant cluster structure. Their characters occur at their reaction processes obviously.In this thesis, the procedure to deal with the DDX measurement data reduction and the results of the DDX of neutron emission from ~6,7Li at 10.27 MeV was described;on the other hand, with the new theoretical model, the characters of reaction mechanism and analysis in the calculations was depicted.The DDX of neutron emission from 6'7Li at 8 and 10.27 MeV were measured by using normal and normal+abnormal fast neutron Time-of-Flight (TOF) spectrometers in China Institute of Atomic Energy (CIAE), respectively. The problem on the influence from breakup neutrons of the d-D neutron source and the Aluminum shell on secondary neutron spectra were successfully solved. For the purpose of the experimental data reduction, Monte-Carlo method was employed to simulate TOF spectra, which were compared with the experimental TOF spectra. Then, the corrections for finite sample size effects, flux attenuation and multiple scattering were performed. Moreover, for 6Li and 7Li sample contain approximative 10% 7Li and 5%6Li, respectively, so by using simultaneity Monte-Carlo simulated and iterated to solve the problem on the influence from each other. Through this reduction process, the final measured DDX data were obtained.To describe the reaction behave of light nuclei, especially the particle pre-equilibrium emissions from compound nuclei to the discrete levels of the residual nuclei, the angular momentum dependent exciton model must be used in the reaction model. Therefore, in the light nuclear reaction model the angular momentum coupling effects must be taken into account, as well as the accurate kinematics should also be considered for all kinds of reaction processes. If the secondary particle emissions exist, which are all from discrete levels to discrete levels, or through two body breakup such as 5He —> n + a and 5Li —> p + a, as well as the three-body breakup processes of 6He* —> n + n + a. The pre-equilibrium mechanism dominate the whole reaction processes, even over 80%. Moreover, in light nucleus reactions the recoil effect also has been taken into account exactly to give the correct energy spectra. For n+6Li reaction, the direct three-body breakup of n+d+a has been taken into account, and the systematic formula of direct three-body breakup was established and introduced in this model calculations. The calculated DDX of n+6'7Li were obtained by the new reaction models. All of the fittings agree well with measurements. The analysis and interpretation of the double-differential measurements have been performed. Since the relevant level schemes have been updated, so the modified theoretical calculations will be performedin future.