基于3 MV串列加速器的中子源特性研究

A Study of Neutron Source Characteristics Based on a 3 MV Tandem Accelerator

针对四川大学3 MV串列加速器中子源,本工作开展了中子靶材料伴生中子及大厅散射中子本底的细致研究,采用核反应运动学公式及TALYS程序对常用中子靶吸氘(氚)材料(Ti、Zr)、底衬材料(Mo、Ta、Cu)的(p,n)、(d,n)反应出射中子能量、反应截面随质子(氘)能量变化规律进行了理论计算分析;并实验测量了不同能量的质子(氘)轰击不同靶片(氚靶或氘靶、空靶、Ti、Zr、Mo等金属靶)时出射中子强度变化情况,结果表明,质子(氘)在吸附材料(Ti、Zr)及底衬材料(Mo、Ta、Cu)上打出的伴生中子强度会随能量增加而持续上升,严重制约该加速器中子源的单色能区;采用影锥法测量了距中子源1.4、2.4和3.6 m处散射中子本底分布情况,并与蒙特卡罗模拟计算结果进行了比对,结果显示,该加速器大厅内的散射中子本底近似于均匀分布,离中子源距离越近,散射中子本底干扰越小。相关研究结果对利用该加速器开展精确的中子反应截面及高水平的中子物理研究工作具有重要意义。

The background neutron from target materials and the scattered neutron background within the accelerator hall of the 3 MV tandem accelerator neutron source at Sichuan University were systematically investigated.The energy and cross-section variations of neutrons emitted from(p,n) and(d,n) reactions on commonly used neutron target deuterium(tritium) absorbing materials(Ti,Zr) and substrate materials(Mo,Ta,Cu) were theoretically analyzed using nuclear reaction kinematics and the TALYS program as a function of proton(deuteron) energy.Experimental measurements were also carried out to determine the variation in neutron intensity as protons(deuterons) of varying energies bombarded different targets(tritium or deuterium targets,empty targets,and metal targets such as Ti,Zr,Mo,etc.).The results indicated that the background neutron intensity from protons(or deuterons) interacting with absorbing materials(Ti,Zr) and substrate materials(Mo,Ta,Cu) increases with energy,which severely limits the monochromatic neutron energy region of this accelerator source.The shadow cone method was employed to measure the scattered neutron background distribution at 1.4,2.4 and 3.6 m from the neutron source,and the results were compared with Monte Carlo simulations.It was found that the scattered neutron background in the accelerator hall was approximately uniformly distributed,with interference from scattered neutrons diminishing as the distance to the neutron source decreased.These results are of significant importance for conducting precise neutron reaction crosssection measurements and high-level neutron physics research using this accelerator.