{"title":"首次同时评估钚裂变同位素的裂变概率和中子诱发截面","authors":"Olivier Bouland , Paola Marini","doi":"10.1016/j.nds.2024.01.005","DOIUrl":null,"url":null,"abstract":"<div><p>Surrogate reactions are a powerful tool to access neutron-induced reaction cross sections of short-lived nuclei. However, to infer neutron-induced reaction cross sections from measured deexcitation probabilities requires a consistent and rigorous theoretical framework describing both charged-particle and neutron-induced reactions. This work presents the first practical application of the new approach developed in O. Bouland, Phys. Rev. C 100, 064611 (2019) to Pu fissile isotopes, <sup>237,238,240,242,244</sup>Pu*. Average neutron-induced reaction cross sections and deexcitation probabilities measured in surrogate reactions are simultaneously analyzed with an efficient Monte Carlo <span><math><mi>R</mi></math></span>-matrix-extended theory algorithm using a unique set of nuclear-structure parameters to describe both observables. Fission probabilities allow one to estimate fission-barrier heights, not otherwise accessible in fissile isotopes. The theoretical framework is here extended to model 'giant' resonance structures observed in the fission probabilities of some nuclides. A careful study of the impact of the uncertainties on nuclear parameters and on the populated compound system angular distribution has been carried out. This study raises questions on the normalization of some fission probabilities measured in the 70's in (<span><math><mi>t</mi><mo>,</mo><mi>p</mi></math></span>) reactions, that could not have been pointed out without the use of the here-presented complex technique. This finding is especially important for the peculiar <sup>240</sup>Pu* system. 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A careful study of the impact of the uncertainties on nuclear parameters and on the populated compound system angular distribution has been carried out. This study raises questions on the normalization of some fission probabilities measured in the 70's in (<span><math><mi>t</mi><mo>,</mo><mi>p</mi></math></span>) reactions, that could not have been pointed out without the use of the here-presented complex technique. This finding is especially important for the peculiar <sup>240</sup>Pu* system. 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引用次数: 0
摘要
替代反应是获取短寿命原子核中子诱导反应截面的有力工具。然而,从测量到的脱激发概率推断中子诱导反应截面需要一个一致而严谨的理论框架来描述带电粒子反应和中子诱导反应。这项工作首次将 O. Bouland,Phys. Rev. C 100, 064611 (2019)中开发的新方法实际应用于钚裂变同位素 237、238、240、242、244Pu*。利用一套独特的核结构参数来描述这两个观测值,并采用高效的蒙特卡洛 R 矩阵扩展理论算法,同时分析了在代用反应中测得的平均中子诱发反应截面和脱激发概率。通过裂变概率可以估算裂变势垒高度,而这在裂变同位素中是无法获得的。理论框架在此得到扩展,以模拟在某些核素裂变概率中观察到的 "巨型 "共振结构。我们仔细研究了不确定性对核参数和填充化合物系统角分布的影响。这项研究提出了 70 年代在(t,p)反应中测量到的一些裂变概率的归一化问题,如果没有使用这里介绍的复合技术,这些问题是不可能被指出来的。这一发现对于奇特的 240Pu* 系统尤为重要。此外,我们的研究还揭示了 237Pu* 复合物系统中唯一进行过的低能中子诱导裂变截面测量值(Gerasimov 等人,JINR-E-3-97-213 (1997))偏高 10%至 30%,以及随后对 236Pu 低于 50 keV 的裂变截面的评估值偏高 10%至 30%。
First simultaneous evaluation of fission probabilities and neutron-induced cross sections for the Pu fissile isotopes
Surrogate reactions are a powerful tool to access neutron-induced reaction cross sections of short-lived nuclei. However, to infer neutron-induced reaction cross sections from measured deexcitation probabilities requires a consistent and rigorous theoretical framework describing both charged-particle and neutron-induced reactions. This work presents the first practical application of the new approach developed in O. Bouland, Phys. Rev. C 100, 064611 (2019) to Pu fissile isotopes, 237,238,240,242,244Pu*. Average neutron-induced reaction cross sections and deexcitation probabilities measured in surrogate reactions are simultaneously analyzed with an efficient Monte Carlo -matrix-extended theory algorithm using a unique set of nuclear-structure parameters to describe both observables. Fission probabilities allow one to estimate fission-barrier heights, not otherwise accessible in fissile isotopes. The theoretical framework is here extended to model 'giant' resonance structures observed in the fission probabilities of some nuclides. A careful study of the impact of the uncertainties on nuclear parameters and on the populated compound system angular distribution has been carried out. This study raises questions on the normalization of some fission probabilities measured in the 70's in () reactions, that could not have been pointed out without the use of the here-presented complex technique. This finding is especially important for the peculiar 240Pu* system. In addition, our study reveals for the 237Pu* compound system a 10 to 30 % too high value of the only-performed low-energy neutron-induced fission cross section measurement (Gerasimov et al., JINR-E–3-97-213 (1997)) and, subsequently of the evaluated fission cross section below 50 keV for the 236Pu.
期刊介绍:
The Nuclear Data Sheets are current and are published monthly. They are devoted to compilation and evaluations of experimental and theoretical results in Nuclear Physics. The journal is mostly produced from Evaluated Nuclear Structure Data File (ENSDF), a computer file maintained by the US National Nuclear Data Center