Nuclear astrophysics studied by neutrons

最近有很多的努力是为了在超金属隐形恒星中观察到大量的重元素，以获得银河系早期历史中恒星核合成的信息。根据命令，要揭示银河系的历史，它是关键的，以构建恒星进化和恒星核合成的固体模型，这些超金属缺陷恒星。这些星星具有非常少的铁种子光，如C、O和Ne等。Hence，这些核将是中子中毒的行为，并将有力地减少重元素的生产年份，如果中子捕获的交叉部分的核核将是更大的。因此，有必要衡量中子捕获（n， γ）的交叉部分，这些光核在天体物理上相关的能量来构建模型之上。在目前的工作中，我们实际测量了（n，γ）的交叉部分^&lt;6，7&gt;Li， ^<13>C，^&lt;16，18&gt;O和^&lt;20，22&gt;Ne，其中一些还没有很好地研究过。这是一项衡量标准。 ... More 成功地通过显著地提高了现有抗康普顿NaI（Tl）光谱仪的噪声信号和γ·射线检测的有效性，并通过新的构造气体Ne样品的液体器。实际上，我们可以通过一个因素4和一个因素2来提高噪声的信号。measured cross sections of ^7 Li，^<13>C， ^&lt;16，18&gt;O and ^&lt;20，22&gt;Ne clearly indicate that these nuclei act as a neutron poison in ultra metal deficient stars.Concerning the primordial D problem we measured the D（n， γ） T reaction cross section。这种反应是非常重要的，因为它是D（n， γ）的镜像反应，是他的反应摧毁了原始D。我们的结果将是有用的，以产生D（p， γ）的S因子^3他的反应自由地从一个冠军效应中产生。由于^6Li（n， γ）^7 Li反应，我们的结果清楚地表明，兴奋功能不会跟随L/V定律预期的曲线，也可以通过一个s-wave中子捕获来确定反应过程。这些可以建议s_&lt;1/2&gt;粒子状态在棉花状态中，但尚未被识别，这对交叉部分的能量依赖负有责任。关于^7 Li（n， γ）^8 Li反应，我们第一次测量了γ-射线分支比率，从中子捕获的状态到地面和第一个激动人心的状态，使用反康普顿HpGe光谱仪。The result gives a vital information to determine to S_<17>factor for the ^7 Be（p，\）^8 B reaction。最后，我们也成功地测量了KENS的绝对keV中子通量，并得出结论表明，在核天体物理学中使用spallation neutron的结果。Less（低）

Recently a lot of efforts are being made to observe an abundance of heavy elements in ultra metal deficient stars to obtain information of stellar nucleosynthesis in the early history of Galaxy. In order to reveal the history of Galaxy it is crucial to construct solid models of stellar evolution and stellar nucleosynthesis these ultra metal deficient stars. These stars are characterized to have very few iron seed light nuclei such as C, O and Ne etc. Hence, these nuclei would act as a neutron poison and would strongly reduce the production yields of heavy elements, if the neutron capture cross section of the nuclei would be large. Therefore, it is necessary to measure the neutron capture (n, γ) cross section of these light nuclei at astrophysically relevant energy to construct the models mentioned above.In the present work we aimed at accurately measuring the (n, γ) cross section of ^<6,7>Li, ^<13>C,^<16,18>O and ^<20,22>Ne, which have not been well studied. The measurement has been ca … More rried out successfully by significantly improving the signal to noise ration and the γ・ray detection efficiency of the existing anti-Compton NaI(Tl) spectrometer, and by newly constructing the liquefier for gaseous Ne sample. Actually we could improve the signal to noise ration by a factor 4 and the γ-ray efficiency by a factor 2. The measured cross sections of ^7Li,^<13>C, ^<16,18>O and ^<20,22>Ne clearly indicate that these nuclei act as a neutron poison in ultra metal deficient stars.Concerning the primordial D problem we measured the D(n, γ) T reaction cross section. The reaction is quite important, since it is a mirror reaction of the D(n, γ)^3He reaction, which destroys the primordial D. Our result would be quite useful to derive the S-factor of the D(p, γ)^3He reaction free from a Coulomb effect. As for the ^6Li(n, γ)^7Li reaction, our result clearly indicates that the excitation function does not follow the curve expected from a l/v law, although the reaction proceeds via an s-wave neutron capture. These could suggest that the s_<1/2> particle state in the cotinuum state, which has not yet been identified, is responsible for the energy dependence of the cross section. Concerning the ^7Li(n, γ)^8Li reaction we have for the first time measured the γ-ray branching ratio from the neutron capturing state to the ground and first excited states using an anti Compton HpGe spectrometer. The result gives a vital information to determine to S_<17> factor for the ^7Be(p, γ)^8B reaction. Finally we have also measured successfully the absolute keV neutron flux at KENS and the result indicates that the use of spallation neutrons for nuclear astrophysics is promising. Less