基于D-D/D-T中子源的中子受激辐射计算机断层扫描成像的比较研究

A comparative study of neutron stimulated emission computed tomography based on D-D/D-T neutron source

对比研究了D-D和D-T中子源在中子受激辐射计算机断层扫描成像(NSECT)中的应用,建立了TiT/TiD靶、水体模内放置/未放置铁球4种计算模型,并利用MCNP程序分别模拟了D-D,D-T中子源产生2.5和14 MeV左右中子束在该系统中的中子输运过程,记录并获得了出射中子和特征γ射线通量分布及能谱图,该研究对中子成像方面中子源的选择及平台的搭建有指导作用.从出射中子和特征γ射线通量分布发现,激发的特征γ射线会保持与入射中子束同样的前倾方向,为了得到尽可能多的特征γ射线,确定了在D-D和D-T两种中子源成像中,实验上应该在Z=0的平面上与中子束传播方向呈43.6°–50.9°范围内布置γ射线探测器.D-D和D-T两种中子源的NSECT高能γ探测器最佳的放置位置稍有不同,但都需要保持在43.6°–50.9°的范围内.从特征γ射线能谱发现,^(56)Fe和^(16)O对应的特征峰能量与模拟数据的激发能完全吻合,证明了NSECT技术识别元素的能力,很有可能在追踪治疗过程以及研究活体(包括人体)分子过程中崭露头角.

In this paper, we investigated the applications of D-D and D-T neutron sources in Neutron Stimulated Emission Computed Tomography （NSECT）. Four NSECT models were established, including the TiT/TiD targets to generate neutron sources and the presence/absence of iron balls in water phantom to mimic tumors. NSECT system was simulated by using MCNP software, in which the D-D and D-T neutron sources were generated, collimated, transported, and recorded. We studied flux distributions and typical spectrum of both outgoing neutrons and the characteristic gamma-rays for D-D and D-T NSECT. Results show that the optimized NSECT gamma-ray detector locations will be in the direction from 43.6~ to 50.9~ along the neutron beam propagation direction. The best NSECT gamma-ray detector locations for D- D and D-T NSECT are slightly different, but in both cases the detectors should be aligned in the direction from 43.6° to 50.9°. We found the characteristic peaks of 56Fe and 160 from the energy spectrum of characteristic gamma-ray. This demonstrates that NSECT has the ability to identify elements, which would be very useful in tracking the treatment process and in studying the molecular process of living body （including human-beings）. This study gives a comprehensive understanding on the selection of neutron sources and the placement of gamma-ray detectors in NSECT applications.