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Nucleosynthesis of heavy elements in metal-deficient stars and the neutron capture reaction study

缺金属恒星重元素核合成及中子俘获反应研究

基本信息

批准号：
17340078
负责人：
NAGAI Yasuki
金额：
$ 9.79万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2005
资助国家：
日本
起止时间：
2005 至 2006
项目状态：
已结题

项目摘要

Recently, the nucleosynthetic yields of massive stars of solar metallicity have been calculated from the onset of central hydrogen burning through explosions as Type II supernovae by Rauscher et al.. According to the calculation, the yields from Ni isotopes and Sr isotopes are overproduced by about 30. This overproduction factor is compared to the general overproduction of 10. Hence, the yields of former isotopes are overproduced by a factor three. This problem of overproduction has been one of the problems remaining in such calculations of the slow process nucleosynthetic yields. The origin of the overproduction is considered to be due to the uncertainty of the neutron capture cross section of nuclei relevant to the nucleosynthesis. In the present study we aimed at measuring the neutron capture cross section of ^<62>Ni in the resonance energy region of 4.5 keV by developing an experimental method. We succeeded to accurately determine the cross section, and thus the overproduction mentioned above turned out to be the uncertainty of the cross section used in the nucleosynthetic calculations.The neutron capture cross section of ^<18>O has been also measured at thermal and keV energies to study a possible influence of ^<18>O as a neutron poison. In this study, we found for the first time that the thermal capture reaction proceeded via a neutron capture by the two-hole four-particle configuration of ^<18>O. This finding would affect considerably in the neutron capture process both at thermal and keV energies.

最近，Rauscher等人计算了太阳金属丰度的大质量恒星的核合成产额，这些产额来自于中心氢通过II型超新星爆炸燃烧的开始。根据计算，Ni同位素和Sr同位素的产额超额约30。这个生产过剩系数与一般生产过剩系数10相比。因此，以前的同位素的产率被超额生产了三倍。这种过量生产的问题一直是在计算慢过程核合成产率时存在的问题之一。过剩产生的起源被认为是由于与核合成有关的核的中子俘获截面的不确定性。在本研究中，我们旨在<62>通过发展一种实验方法来测量4.5 keV共振能区的^ Ni的中子俘获截面。我们成功地精确测定了反应截面，从而证明了上述的过量产生是核合成计算中反应截面的不确定性。<18>为了研究^O作为中子毒物的可能影响，我们还在热能和keV能量下测量了^ O的中子俘获截面<18>。在这项研究中，我们首次发现热俘获反应是通过^ O的两孔四粒子组态俘获中子来进行<18>的。这一发现将影响相当大的中子俘获过程在热和keV的能量。