中子俘获反应截面先进实验技术研究

Cross-sections of radiative neutron capture reactions are foundation of the nucleosynthesis in nuclear astrophysics and are basic data in the research of the atomic energy application. There are strong request for improvement of accuracy for the neutron capture cross-sections..China Spallation Neutron Source (CSNS) will provide the first neutron beam in 2017. With wide energy range and high beam flux, the white neutron source at back angle with respect to the proton beam direction will play an important role in the field of neutron induced reaction study especially for the neutron capture reaction cross-section measurements. A BaF2 scintillation calorimeter with the ability of absorbing γ rays totally (GTAF) was constructed at China Institute of Atomic Energy. Advantage of GTAF for the neutron capture reaction cross-section measurements owe to characteristics of fast response, high efficiency and low neutron sensitivity. Present task is to perfect the GTAF and to optimize the experimental technique for the neutron capture reaction cross-section measurement. .In this project, experimental technologies for the (n,γ) reaction cross-section measurement by prompt γ-ray method will be studied. Neutrons within energy range from 10 to 200 keV will be produced by Li-7(p,n)Be-7 reactions and the pulsed incident proton beam should be provided by HI-13 tandem accelerator. Techniques for the backgrounds discrimination and suppression will be focused in the study. Objective is to support accurate measurement of the neutron capture cross-sections by using GTAF, as soon as CSNS come into use. If the application is implemented, domestic nuclear data blank will be filled and the experimental ability about neutron reaction research will be improved significantly.

(n,γ)反应截面是核天体物理研究和核能应用研究重要的基础数据。.2017年CSNS将出束，其白光中子源具有能区宽、强度高的特点，可为(n,γ)反应实验研究提供极好的中子源条件；CIAE建造了一套γ全吸收型BaF2装置（GTAF），具有时间响应快、探测效率高、中子灵敏度低的特点，用于(n,γ)反应截面的在线测量独具优势。在CSNS进行物理实验之前，需要进一步完善现有的GTAF装置、研究建立(n,γ)反应的高精度实验测量技术。.项目拟利用CIAE的基础、HI-13串列加速器的脉冲化质子束、通过Li-7(p, n)Be-7反应产生中子、研究建立一个能量主要分布在10-200keV的准白光中子源实验条件，以开展基于GTAF的(n,γ)反应实验测量技术研究，特别是识别、剔除各种本底的方法和技术。旨在CSNS出束后尽早开展项目研究工作，填补数据空白，使我国的中子核反应实验研究能力跻身国际前列。

在自然科学基金的资助下，基于瞬发γ射线的(n,γ)反应截面测量技术得到了研究。GTAF设备的性能得到了显著提升，在线实验中的本底得到了有效的抑制。.在HI-13串列加速器上构建了一个keV能区中子源实验条件，通过对Au, C, Nb 和空白等样品的测量，并且将197Au(n, γ)198Au反应截面的实验测量结果和文献进行了比对分析，对GTAF设备和(n,γ)反应实验技术进行了检验。