权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

Theoretical study of multistep direct reaction mechanism in preequilibrium nuclear reaction processes

预平衡核反应过程多步直接反应机理的理论研究

基本信息

批准号：
07640416
负责人：
WATANABE Yukinobu
金额：
$ 1.28万
依托单位：
KYUSHU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1997
项目状态：
已结题

项目摘要

We have proposed a new semi-quantal model to describe the multistep direct (MSD) reaction processes in preequilibrium nuclear reactions, which is called the semi-classical distorted wave model : it is referred to as the SCDW model. The purpose of this work is to investigate the MSD mechanism in the preequilibrium particle emission of nucleon-induced reactions in the intermediate energy region.First of all, we have developed a way of calculating the MSD cross sections with the Quasi-Random Number Monte Carlo method, and succeeded in the SCDW calculations for the leading three MSD steps. The code was applied to proton-induced reactions on medium-heavy nuclei (i.e., ^<58>Ni and ^<90>Zr) for incident energies of several tens of MeV to 200 MeV.The result showed good agreement with the experimental data without any adjustable parameters, except at very forward and backward angles. We found that the underestimation seen at large angles is due to the momentum distribution of target nucleons given by the local Femi-gas model. To improve this situation, we have developed a new approach in which the Wigner transform of one-body density matrix is incorporated in the SCDW model. The discrepancy was indicated to be removed by using more realistic single-particle wave functions in the harmonic oscillator or Woods-Saxson ponetial, instead of the local Fermi-gas model.In addition, we have found that the SCDW model is applicable to analyzes of (p, nx) reactions by taking into account the Q value correctly. Moreover, the result of SCDW calculations with in-medium NN cross sections showed that the in-medium effect is not much apreciable in the MSD process for incident energies up to 200 MeV.Finally, we have attempted to extend the SCDW model so that the matrix elements of sffective interaction is directly calculated, and investigated the off-shell effect on the MSD cross sections. As a result, we have not found a strong off-shell effect in the MSD reaction process continuum.

本文提出了一种新的半量子模型，即半经典扭曲波模型，用于描述预平衡核反应中的多步直接反应过程，简称SCDW模型。为了研究中能区核子反应预平衡粒子发射中的MSD机制，我们首先发展了一种用准随机数蒙特卡罗方法计算MSD截面的方法，并成功地计算了MSD前三步的SCDW。该代码被应用于质子诱导的中重核反应（即，在<58><90>入射能量为几十MeV到200 MeV的情况下，计算结果与实验数据符合得很好，不需要任何可调参数，除了在非常向前和向后的角度。我们发现，在大角度下观察到的低估是由于局部费米气体模型给出的目标核子动量分布造成的。为了改善这种情况，我们已经开发了一种新的方法，其中的Wigner变换的单体密度矩阵被纳入SCDW模型。用谐振子或Woods-Saxson势函数中更真实的单粒子波函数代替局域费米气体模型，可以消除这种差异，另外，我们还发现，正确考虑Q值后，SCDW模型也适用于（p，nx）反应的分析。此外，用介质内NN截面计算的SCDW结果表明，入射能量在200 MeV以下时，介质内效应在MSD过程中的影响不大。最后，我们尝试扩展SCDW模型，直接计算有效相互作用的矩阵元，并研究了离壳效应对MSD截面的影响。因此，我们没有发现一个强烈的离壳层效应的MSD反应过程连续。