硼中子俘获治疗的加速器中子源7Li(p,n)7Be的中子特性研究

目的 通过研究质子加速器 ⁷Li(p,n)⁷Be 反应的中子特性,为研究和制作适用于硼中子俘获治疗(BNCT)的加速器中子源提供基础数据。方法 加速质子使其轰击Li靶后产生中子;通过金属箔活化法,测量中子与In箔发生阈值反应后放出的γ射线;然后计算出In箔的放射性活度、加速器反应后放出中子的注量和反应的微分截面。结果 质子加速轰击Li靶后,在不同方向产生不同能量和注量的中子。加速器电压分别为3.0、2.8和2.6 MV,出射中子与入射质子束的方向一致时, ⁷Li(p,n)⁷Be 反应的微分截面约为50 mb/mr;夹角为60°时,反应的微分截面减小到30 mb/mr左右。由于部分中子与其他金属原子等发生弹性散射而射向后方,提高了这一范围内In箔的比放射性活度,影响了其微分截面的准确性。结论 用金属箔活化法测定中子简便易行,可同时测得多个方向的中子分布,但需对中子与其他金属弹性散射产生的影响进行进一步的研究; ⁷Li(p,n)⁷Be 反应后发射出的中子经慢化后,能得到适于BNCT治疗的热中子和超热中子;若作为BNCT的中子源,加速器的质子束流需达到10 mA。

Characterization of 7Li(p,n)7Be neutron yields from an accelerator for boron neutron capture therapy

Objective To provide the scientific basis for investigating and developing neutron source of boron neutron capture therapy(BNCT) by means of studying the characterization of~7Li(P,n)~7Be neutron yields iuduced by an accelerator. Methods When acceleration voltage were 3.0, 2.8 and 2.6 MeV.proton fluxes were accelerated to strike Li target to produce~7Li(P,n)~7Be reaction,and the produced neutron fluxes activated~(115)In metal foils at different directions. γ-rays emitted from~(115)In foil neutron threshold reaction were measured. Radioactivity of~(115)In foil were calculated and differential cross sections of~7Li(P,n)~7Be were analyzed.Results Neutron fluxes with numerous energy sources were produced at different directions after the nuclear reaction~7Li(P,n)~7Be.When the neutron fluxes had the same directions with the proton beam, the differential cross sections of ~7Li(P,n)~7Be were about 50 mb/mr,but the differential cross sections declined to 30 mb/mr when the angles between the neutron fluxes and the proton beams were 60 degree.Some neutrons with higher energy reached the behind area because of the elastic scattering of neutrons and affected the differential cross sections of the field.Conclusions The neutron distributions can be easily determined simultaneously at several directions via foil activation method.The influence of elastic scattering of neutrons and other metals should be taken into account. After the production of~7Li(P,n)~7Be was slowed down,thermal neutron and epithermal neutrons which were suitable for BNCT should be acquired.As BNCT neutron source,the flux of proton beam should be over 10 mA.