基于HI-13串列加速器的中子俘获反应截面测量方法

Cross section measurement of neutron capture reaction based on HI-13 tandem accelerator

利用BaF2晶体对γ射线探测效率高、时间分辨率好的特点,研制了国内首套由40个BaF2探测器单元组成的γ全吸收型探测装置,用于在线测量中子俘获反应截面。在HI-13串列加速器上建立250~850 keV的中子源,其0°角的源强约为5.09×10^(6) n/(Sr·s),使用γ全吸收型探测装置,通过瞬发γ射线法测量了^(93)Nb、^(197)Au、^(nat)C和空样品的实验数据。根据BaF2探测器信号的特征,采用了基线补偿、软件阈值设置、时间窗限定、脉冲幅度积分增长率设置和快慢成分比设置等多种数字化波形分析方法,剔除噪声信号以提高效应本底比。以^(197)Au样品数据为标准,^(nat)C样品数据为样品相关性本底,空样品数据为样品无关性本底,采用相对测量法得到了^(93)Nb的中子俘获反应截面实验数据。通过与ENDF评价库数据的比较,验证了测量装置和技术方法的可行性。

The first gamma-ray total absorption facility composed of 40 BaF2 detector units has been constructed in China.Utilizing the property of high detection efficiency and good time resolution for gamma rays of BaF2 crystal,the facility will be used to measure on-line the cross section of neutron capture reaction.Neutron source of 250 keV~850 keV was set up on the HI-13 tandem accelerator,its source intensity at 0°was about 5.09×10^(6) n/(Sr·s).The experimental data of ^(93)Nb,^(197)Au,^(nat)C and empty samples were measured by the prompt gamma ray method with gamma-ray total absorption facility.According to the characteristics of BaF_(2 )detector signal,a variety of digital waveform analysis methods were adopted to eliminate noise signal as much as possible to improve the effect background ratio,such as baseline compensation,software threshold setting,time window limitation,pulse amplitude integral growth rate setting and fast slow component ratio setting.The experimental data of ^(93)Nb neutron capture reaction cross section was obtained by relative measurement method.The data of ^(197)Au sample was the standard,the data of natC sample was the sample correlation background,and the data of empty sample was the sample independence background.The feasibility of the measurement facility and technical method was verified by comparing with the data of ENDF evaluation library.