arXivDaily arXiv每日学术速递 周一至周五更新
arXiv nucl-th/0209037nucl-th
收藏

235-U的77个eV异构体的Fission截面的理论计算

Theoretical Evaluations of the Fission Cross Section of the 77 eV Isomer of 235-U

J. Eric Lynn, A. C. Hayes

备注：
17 pages including 8 figures
发表信息：
Phys.Rev. C67 (2003) 014607
阅读 PDF
arXiv 页面 ↗HTML 原文 ↗

摘要：

我们已经开发了模型的裂变势垒（势垒高度和过渡态光谱），再现合理以及测量的裂变截面的$^{235}$ U从中子能量为1千电子伏至2兆电子伏。从这些模型，我们已经计算了裂变截面的77 eV异构体的$^{235}$ U在相同的能量范围。我们发现，在低中子能量下，同质异能态截面与基态截面的比值在0.45和0.55之间。在1 MeV以上，横截面变得近似相等。的中子俘获截面裂变截面的异构体的比例被预测为约3倍的大比$^{235}$ U在keV中子能量的基态的异构体。计算了$^{235}$ U基态中子非弹性散射的布居截面。我们发现，异构体是强烈的人口，和$E_n = 1 MeV$的$(n,n'γ)$截面导致人口的异构体是0.5谷仓的顺序。因此，在高中子注量下，涉及铀同位素的中子反应网络计算可能会受到$^{235}$ U的77 eV异构体的影响。用这些相同的模型，只需对势垒高度作微小的调整，就可以近似地再现$^{233}$ U和$^{237}$ U的裂变截面。随着外势垒的显著降低，也可以再现$^{239}$ Pu裂变截面的一般行为。

英文摘要：

We have developed models of the fission barrier (barrier heights and transition state spectra) that reproduce reasonably well the measured fission cross section of $^{235}$U from neutron energy of 1 keV to 2 MeV. From these models we have calculated the fission cross section of the 77 eV isomer of $^{235}$U over the same energy range. We find that the ratio of the isomer cross section to that of the ground state lies between about 0.45 and 0.55 at low neutron energies. The cross sections become approximately equal above 1 MeV. The ratio of the neutron capture cross section to the fission cross section for the isomer is predicted to be about a factor of 3 larger for the isomer than for the ground state of $^{235}$U at keV neutron energies. We have also calculated the cross section for the population of the isomer by inelastic neutron scattering form the $^{235}$U ground state. We find that the isomer is strongly populated, and for $E_n = 1 MeV$ the $(n,n'γ)$ cross section leading to the population of the isomer is of the order of 0.5 barn. Thus, neutron reaction network calculations involving the uranium isotopes in a high neutron fluence are likely to be affected by the 77 eV isomer of $^{235}$U. With these same models the fission cross sections of $^{233}$U and $^{237}$U can be reproduced approximately using only minor adjustments to the barrier heights. With the significant lowering of the outer barrier that is expected for the outer barrier the general behavior of the fission cross section of $^{239}$Pu can also be reproduced.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

↑