EXPERIMENTAL STUDY ON THE HEAVY ELEMENT SYNTHESIS AT THE SUPERNOVA EXPLOSION

在这个项目中，我们研究了在II型超新星爆炸瞬间可能的快速中子俘获之前的种子核的产生过程，他的过程被认为是从质子和中子发生的，质子和中子通过(α，n)和(n，γ)等核反应在种子区产生由铁和镍同位素组成的重元素。到目前为止，基于统计模型的预测反应速率的大型核反应网络程序已经估算了该过程中相关元素丰度的时间依赖性。然而，由于能级密度较小，DAIS轻核区的统计预测对其可预测性的可预测性缺乏信心。因此，直接测量天体物理反应速率成为进一步定量研究上述合成传感器的问题。我们利用轻中子束和高效的探测器系统系统地测量了(α，n)反应截面，这使得只在精细的宽能区测量激发函数成为可能。在这个项目中，我们观察到了8^Li，^&lt；12&gt；B和^&lt；16&gt；N(α，n)反应截面。^8Li实验得到的激发函数的统计量比前人提高了10倍，推导出的反应速率约为前人的一半。作为项目的一部分，我们还开展了激光离子源和自旋极化放射性核的新核谱学技术方面的研究，这些都是在JAERI建造的新的放射性核束设施的进一步天体物理研究的重要进展。

In this project, we studied seed-nuclei creation process prior to the possible rapid neutron capture at the moment of the type II supernova explosion his process has been believed to occur from proton and neutron, which create heavy elements in the seed region consisting of iron and nickel isotopes thorough nuclear reactions like (alpha, n) and (n, gamma). So far, time dependence of relevant element abundance in this process has been estimated by a large nuclear reaction network code based on the predicted reaction rates of the statistical model. However, the statistical prediction in dais light nuclear region keeps little confidence for its predictability due to the small level densities. Therefore a direct measurement of astrophysical reaction rate becomes issue to further quantitative investigation of the above synthesis senarios.We have measured systematically the (alpha, n) reaction cross sections by using light neutron rich radioactive nuclear beams and efficient detector system, which makes it possible to measure excitation functions exclusively in fine broad energy region. In this project, we observed 8^Li,^<12>B, and ^<16>N (alpha, n) reaction cross sections. The obtained excitation function of the ^8Li experiment has 10 times higher statistics and deduced reaction rates are about a half values compared to the previous ones. This indicates that the ^8Li(alpha, n) reaction rate as well as resultant neutron number density should be suppressed in the element synthesis senarios so that mass abundance pattern of the r-process will be changed.As a part of this project, we have also proceeded to study technical aspects of a laser ion-source and a new nuclear-spectroscopy with spun-polarized radioactive nuclei, which are important developments for further astrophysical studies at a new radioactive nuclear beam facility constructing at JAERI.