Study on Hyper Thermal Neutron Irradiation Field for Neutron Capture Therapy

本研究的目的是通过实验和模拟计算，阐明超热中子对活体的辐照特性，以及超热中子辐照场的可行性。1996年（Heisei 8），以模拟计算为主的基础研究成果为基础，设计了“试验型”超热中子发生器，并组装了“高温散射体”部分。该发电机的设计目标是可达到的最高温度接近1200摄氏度（1500K）。从高温试验安全第一的角度出发，选用具有良好耐热、耐腐蚀特性的不锈钢作为结构框架的主要材料。采用钼高温加热器电加热、钼热反射器排热、r型热电偶测热。选用石墨分散剂是因为它在高温下具有较强的稳定性。该散射体可以用另一个散射体代替。1997年（平成9），“控制器”部分制作完成，并与高温散射体部分结合，最终完成了发电机。在该发生器用于中子辐照场前，进行了加热试验。试验结果证实，散射体最高温度可达1200℃，在高温下使用时热稳定性、热可控性和安全性均无问题。作为特性估计的实验之一，利用日本京都大学反应堆研究所（KURRI）的LINAC（电子直线加速器）中子发生器，采用TOF （time of flight）方法估计了散射体温度对中子能谱的影响。通过仿真计算进行了估计。实验和计算结果证实，中子温度随散射体温度的升高而升高。目前，京都大学反应堆重水设施正在进行模拟实验，目的是在假设将超热中子辐照应用于实际核反应堆的情况下，估计活体中的中子剂量分布。少

The purpose of this research is to clarify the irradiation characteristics of hyper-thermal neutrons for a living body, and the feasibility of hyper thermal neutron irradiation field, by experiments and simulation calculations.In 1996 (Heisei 8), a "test-type" hyper-thermal neutron generator was designed from the results of the basic researches mainly with simulation calculations, and the "high-temperature scatterer" part was assembled. The design goal of this generator was that the attainable maximum temperature was almost 1200 degrees centigrade (1500K). From the standing-point of safety first at high-temperature experiments, stainless steal, which has good characteristics of heat-proof and corrosion-proof, was selected as main material of the structural frame. The electric heating using molybdenum high-temperature heaters, the heat remove by molybdenum heat reflectors, and the heat measurement by R-type thermo-couples were applied. Graphite scatterer was selected because of its stab … More ility at high temperature. The scatterer is possible to be replaced with the other scatterer.In 1997 (Heisei 9), the "controller" part was made and combined with the high-temperature scatterer part, and finally, the generator was completed. Before the employment of the generator at neutron irradiation field, the heating tests were performed. From the test results, it was confirmed that the scatterer maximum temperature was attainable to be 1200 degrees centigrade, and that there was no problem for thermal stability, thermal controllability and safety at the high temperature employment. As one of the experiments for the characteristics estimation, the neutron energy spectrum dependent on the scatterer temperature was estimated by TOF (time of flight) method using the LINAC (Electron Linear Accelerator) neutron generator at KURRI (Kyoto University Research Reactor Insitute). The estimation by simulation calculations were also performed. From the experiment and calculation results, it was confirmed that the neutron temperature shifted to be higher according to the scatterer temperature.At present, phantom experiment at the KUR (Kyoto University Reactor) Heavy Water Facility are planning in order to estimate the neutron dose distribution in a living body, on the assumption of the application of hyper-thermal neutrons irradiation to actual NCT. Less