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arXiv 2203.11073nucl-thnucl-exphysics.app-ph
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239 Pu(n,2n)238 Pu截面形状高于发射阈值的质疑

Questioning the 239Pu(n,2n)238Pu cross section shape above emission threshold

O. Bouland, V. Meot, O. Roig

摘要:

根据JEF(F)欧洲项目长期以来的故事,根据Meot等人对239 Pu(n,2n)238 Pu反应截面最精确形状的确定和最近的测量,本文旨在通过提出新的理论反馈,对这一主题进行另一种阐释。为了实现这一目标,AVXSF-LNG计算机程序已升级为使用其衰变概率模块模拟二次机会反应,然后链接到TMS-ECIS 06核反应系统代码。目前对从阈值到约12 MeV的第三次裂变开始的能量范围内的(n,2n)截面的勤奋计算表明,目前的评估低估了10 MeV以下的239 Pu(n,2n)截面;相对于JEFF-3.1评估,低估了7%。在此基础上,我们提出了一个向上修正的测量标准化Meot等人。修正因子约为1.24,目前拟合模型的最大不确定性估计为11.6%。后一个值是从计算路线的灵敏度分析中提取的,该计算路线选择用于非平衡剩余核的能级密度模型,以及我们可以在238 Pu和239 Pu靶核的中子裂变截面测量参考方面做出的替代选择。

英文摘要:

In the light of the JEF(F) European project longstanding story according to the determination of the most exact shape of the 239Pu(n, 2n)238Pu reaction cross section and a recent measurement by Meot et al., this paper aims to shed another light on this topic by bringing new theoretical feedback. To achieve this goal, the AVXSF-LNG computer program has been upgraded to model second-chance reactions using its decay-probability module and, then chained to the TALYS-ECIS06 nuclear reaction system of codes. Present diligent calculation of the (n,2n) cross section over the energy range from the threshold to the onset of third-chance fission at about 12 MeV, suggests that current evaluations under-estimate the 239Pu(n,2n) cross section below 10 MeV; under-estimation of the order of 7% relatively to the JEFF-3.1 evaluation. On this ground, we propose an upward correction to the normalization of the measurement by Meot et al. Correction factor of about 1.24 with a maximum uncertainty on present fitted model estimated to 11.6%. Latter value is extracted from a sensitivity analysis of the calculation route to the level density model that is selected for the non-equilibrated residual nucleus and to alternative choices we can make in terms of neutron fission cross section measurement references for the 238Pu and 239Pu target nuclei.

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