STUDAY OF NUCLEOSYNTHESIS USING keV NEUTRONS

使用 keV 中子进行核合成研究

基本信息

批准号：
04452024
负责人：
NAGAI Yasuki
金额：
$ 5.38万
依托单位：
TOKYO INSTITUTE OF TECHNOLOGY
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1992
资助国家：
日本
起止时间：
1992 至 1993
项目状态：
已结题

项目摘要

It is quite important to measure the cross section of the ^<14>N(n, p) ^<14>C reaction at the stellar neutron energy, 10 - 250 keV, to investigate the nucleosynthesis in stara. In order to measure the cross section we have developed the new type of a gas scintillation drift chamber, operating in the N_2 gas. After constructing the chamber we did the off-line test using the alpha source. Good resolutions of energy and time were obtained as expected. In the on-line test, the average cross section of 1.3 mbarn was obtained at the average of 40 keV.Although another ezperiment to get higher statistics is certainly important, the above preliminary result indicates that the N is likely to absord neutrons for the s-process especially in metal deficient stars.The experimental data of the ^<12>C(n, gamma) ^<13>C reaction have been analyzed and for the first time we obtained the accurate cross section in the neutron energies between 10 - 250 keV.From the present resunt it turned out that the carbon acts as a neutron poison in massive metal-deficient stars. The result may affect strongly the scinario of the nucleosynthesis in stars. Furthermore, it was shown for the first time that the cross section increases as the neutron energy increases. This is due to the contribution of the non-direct p-wave capture, which was deduced from the energy dependence of the cross section and the gamma -ray branching ratio from a capturing state.In the neutron capture reaction large amounts of samples are used, as the cross section is usually very small. Therefore it is important to correct properly the multiple scattering events in the thick sample. For the correction wedeveloped a Monte Garlo code and the validity of the code was tested by using paraffine samples with various thickness.

测量恒星中子能量10-250 keV的 ^<14> n（n，p） ^<14> C反应的横截面以研究stara中的核合成。为了测量横截面，我们开发了在N_2气体中运行的新型气体闪烁漂移室。构造腔室后，我们使用Alpha源进行了离线测试。按预期获得了良好的能量和时间分辨率。在在线测试中，平均在40 kev中获得1.3 mbarn的平均横截面。尽管获得更高统计的另一个ezperiment肯定很重要，但上述初步结果表明N可能会吸收S中子的中子S中子S - 尤其是在金属不足的恒星中的过程。已经分析了 ^<12> c（n，gamma） ^<13> C反应的实验数据，这是我们首次获得了10 - 中子能量中的准确横截面的准确横截面。 250凯夫。从目前的储议中，碳在巨大的金属缺陷恒星中充当中子毒物。结果可能会严重影响恒星中核合成的Scinario。此外，首次表明，横截面随着中子能量的增加而增加。这是由于非直接p波捕获的贡献，这是从横截面的能量依赖性和从捕获状态的伽马射线分支比率推导的。在中子捕获反应中，使用了大量样品，因为横截面通常很小。因此，重要的是要正确纠正厚样品中的多个散射事件。为了进行校正，通过使用具有各种厚度的石蜡样品测试了代码的蒙特Garlo代码，并测试了该代码的有效性。