To Establish Pre-equilibrium Fission Dynamics And N + (12) C-response Theory Analysis And Neutron Nuclear Data

This thesis is consists of two parts: first, the research of the pre-equilibrium fission processes for n＋²³⁸U and p＋²⁰⁸Pb reactions based on the diffusion model; second, the theoretical analysis and the establishment of nuclear databases for n＋¹²C reaction based on light nuclear reaction model.In pre-equilibrium fission fields, n＋²³⁸U and p＋²⁰⁸Pb reactions are studied by numerical solution of Smoluchowski equation, and their results can be extended to the fission reactions of those nuclei in actinium and sub-actinium family. It is suggested that the contributions of the pre-equilibrium fission can be ignored for the projectile with low or medium incoming energy to the target in actinium family, and even with high energy(GeV) to the target in sub-actinium family. The evidences are provided theoretically in this paper for overlooking the contributions of pre-equilibrium fission to calculating the fission cross sections used equilibrium statistics and to stimulating the nuclear material on target physics of the accelerator driven sub-critical system (ADS). In fission processes at higher nuclear temperature for fissile nuclei, the fission rates appear Overshooting phenomena, which are induced by the fission current at saddle. However, there is no Overshooting phenomenon for sub-actinium family nuclei. Simultaneously, the physical figures are obtained and analyzed by views saddle or scissor as the fission point in this paper. It is reasonable that the saddle is regarded as the fission point in the diffusion model. If the light particle emissions are considered in fission processes, Overshooting will weaken gradually, even vanish. The exited energy of compound nuclear decreases because of the light particles emission, so the contribution of pre-equilibrium fission decreases. It is proved more qualitatively that the contribution of the pre-equilibrium fission can be ignored in some fields at the suitable projectile energy mentioned above.In this paper, the analytical solution of Smoluchowski equation, of which diffusive term is constant and drift term harmonic oscillator potential (including the well and the barrier potentials), is derived from a simple Gaussian distribution in a easy and wizard method. This analytical solution covers all analytical expressions published nowadays. The properties of probability density distributions and probability currents are analyzed with time evolution at the different nuclear temperatures or the different initial distributions. The stationary and the steady solution are derived from the analytical solution, and their bound conditions are given too. The stationary and the steady solutions offer some advices for the applied studies in some strong friction coefficient fields.The angular momentum factors of all kinds of transition matrix elements, which are kernel of the light nuclear reaction model, are derived through the transformation from coupled and un-coupled representations each other. Based on the new light reaction model, four aspects of n＋¹²C reaction are extended or modified. Firstly, the incident neutron energy extends up to 30 MeV. Secondly, more open reaction channels are considered, including (n, 2n), (n, t), (n, ³He), (n, pα), (n, ⁶Li) and (n, dα) channels, which are closed below 20 MeV. Thirdly, some updated level schemes are used, in stead of old and pseudo ones. Finally, we obtained a new set of neutron and charged particles optical potential parameters. On the basis of four improved aspects, LUNF code is modified to calculate the total outgoing neutron double-differential cross sections from the threshold energy to 30 MeV. The calculated results agree fairly well with the experimental measurements. The analysis of the total energy angular spectra shows that the elastic channel and the inelastic channels of the 1st and 2nd excited levels largely con tribute to the first three peaks, the third excited level of inelastic channel and (n, nα) channel commonly to the 4th peak of the total spectra at high outgoing energy region. Because theγde-excitation mechanism of the 3rd excited state belongs to E3 module, which is not described successfully in Systematics up to now and not calculated accurately in LUNF code in other way, the calculated total spectra are generally lower than the experimental data at the 4th peak region. Thus, the neutron angular flux spectra are low too at the same location. In order to improve this deficiency, the evaluation method is used to set up the neutron nuclear databases below 30 MeV and below 20 MeV (CENDL-3.1), whose 3rd excite level inelastic cross sections (MF=3, MT=53) are modified in virtue of the results of JENDL-3.3 calculated in coupled channel and statistic model. The validation of ¹²C evaluation for the updated database CENDL-3.1 was performed with neutron angular flux experiment (FNS) in this paper. The results agree very well with the benchmark measurements, and have obvious improvement contrast to ENDF/B-â…¦. It is one of the great characteristics that the file-6, which is not included in ENDF/B-â…¦, JENDL-3.3 and so on, comprises the information of all charged particles in accompany with outgoing neutron. Simultaneously, using the method of least squares, a code is developed to stimulate the Legendre coefficients of the 1st and 2nd excited level inelastic angular distributions, which are absent in ENDF/B-â…¦and JENDL-3.3 above 20 MeV for lacking suitable theory. Furthermore, the new light nuclear reaction model extended in this paper provides a good method, which can study the Kerma (Kinetic Energy Released from Material) coefficients of the charged particles.