Systematic Study on Fast-Neutron Capture Cross Sections of Stable Isotopes related Long-Lived Fission Products

本研究的主要目的是：（1）提高γ射线探测系统的灵敏度;（2）系统测量长寿命裂变产物Zr-93和Sn-126的杂质同位素Zr-90、91、92、94和Sn-117、118、119、120、122、124的快中子俘获截面和俘获γ射线谱;（3）通过对实验数据的系统分析，阐明了Zr和Sn同位素的快中子俘获反应机理，提高了理论预测的准确性;（4）精确估算了长寿命裂变产物Zr-93和Sn-126的快中子俘获截面。研究成果总结如下：（1）将现有的主NaI（Tl）探测器更换为直径15 cm、长30 cm的更大的NaI（Tl）探测器，提高了γ射线探测器的灵敏度。(2)对Zr-90，91，92，94和Sn-116，117，118，119，120，122，124进行了系统测量。完成了Zr-90、91、92、94和Sn-117、118、119的数据处理，并求出了这些同位素的俘获截面和俘获γ能谱。(3)利用核反应理论中的统计模型，对Zr-90、91、92、94和Sn-117、118、119的俘获截面和俘获γ能谱进行了理论分析，获得了Zr和Sn同位素快中子俘获反应的信息。(4)基于所获得的信息，对长寿命裂变产物Zr-93和Sn-126的快中子俘获截面进行了评估，并初步获得了评估值。

The main objectives of this study are (1)improvemant in the sensitivity of gamma-ray detection system, (2)systematic measurement of fast-neutron capture cross sections and capture gamma-ray spectra for Zr-90,91,92,94 and Sn-117,118,119,120,122,124, which are impurity isotopes of the long-lived fission products Zr-93 and Sn-126, respectively, (3)improvemant in accuracy of theoretical prediction by the elucidation of fast-neutron capture reaction mechanism for Zr and Sn isotopes through the systematic analysis of experimental data, and (4)accurate evaluation of fast-neutron capture cross sections of the long-lived fission products Zr-93 and Sn-126. The summary of research results are as follows :(1) The existing main NaI(Tl) detector was replaced with a larger NaI(Tl) detector with a diameter of 15 cm and a length of 30 cm, and the sensitivity of gamma-ray detector was improved.(2) The systematic measurement was performed for Zr-90,91,92,94 and Sn-116,117,118,119,120,122,124. The data processing was completed for Zr-90,91,92,94 and Sn-117,118,119, and the capture cross sections and capture gamma-ray spectra were derived for those isotopes.(3) The derived capture cross sections and capture gamma-ray spectra of Zr-90,91,92,94 and Sn-117,118,119 were theoretically analyzed by using the statistical model in nuclear reaction theory, and information on the fast-neutron capture reaction by Zr and Sn isotopes was obtained.(4) The evaluation of fast-neutron capture cross sections of the long-lived fission products Zr-93 and Sn-126 was performed based on the obtained information, and evaluated values were obtained tentatively.