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来阐明超热中子对活体的辐照特性，以及超热中子辐射场的可行性。1996年(平成8号)，根据基础研究的结果，主要通过模拟计算，设计了一台“试验型”超热中子发生器，并组装了“高温散射体”部件。该发电机的设计目标是可达到的最高温度几乎为1200摄氏度(1500K)。从高温试验安全第一的角度出发，选用耐热、耐腐蚀性能好的不锈钢作为结构框架的主要材料。采用了钼高温加热器电加热、钼热反射器散热、R型热电偶测热等方法。石墨散射体因其刺激性…而被选中在高温下具有更高的灵活性。这种散射体是有可能被其他散射体替代的。1997年(平成9号)，制造了“控制器”部分，并与高温散射体部分结合，最终完成了发生器。在中子照射场使用该发生器之前，进行了加热试验。测试结果表明，散射体的最高温度可达到1200℃，在高温使用中不存在热稳定性、热可控性和安全性问题。作为特性估计的实验之一，利用京都大学研究堆研究所的LINAC(电子直线加速器)中子发生器，用飞行时间(TOF)方法估计了与散射体温度有关的中子能谱。并通过模拟计算进行了估算。根据实验和计算结果，证实了散射体温度越高，中子温度越高。目前，在KUR(京都大学反应堆)重水装置上，基于超热中子辐照应用于实际NCT的假设，正在计划进行体模实验，以估计活体中的中子剂量分布。较少

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