Characteristics of Formation of Nanometer-Size Tracks and Application to Dosimetry of High-LET Radiation

固体核径迹探测器在空间活动、飞机飞行、高强度质子加速器（如J-PARC）周围操作以及发生临界事故等紧急情况下的辐射防护中具有重要作用，是个人中子剂量测量中最有前途的元件之一。本研究的目的是阐明纳米蚀刻轨迹的特性，建立一种有效测量高能中子的技术。研究结果总结如下：1。纳米径迹的特征O、Ne、Si、Ar、Fe、I、Xe、Au等离子辐照CR-39径迹探测器后，进行短时间的化学蚀刻，在原子力显微镜下观察到非常小的蚀刻径迹。测量了每个离子的早期生长曲线，直至几十nm，由此可以得到轨道核半径。同时发现，在局部剂量超过100kgy左右的区域，会形成磁道核。高能中子测量的应用从第一个实验中发现，聚乙烯，一种最流行的辐射材料，对能量为几十兆电子伏或更高的中子没有足够的效率。从理论上考虑，提出了一种由聚乙烯和氘化烃组成的双层结构的新技术。后一种材料既可以作为氘核的辐射体，又可以作为聚乙烯外层产生的高能质子的降解剂。在日本原子能机构高崎核研究中心进行的45 MeV和70 MeV中子辐照实验证实了其性能。

The solid state nuclear track detector is one of most promising elements for personal neutron dosimetry, which is very important for radiation protection in space activities, aircraft travel, operations around high-intensity proton accelerators such as J-PARC, and emergent situations such as an accident of criticality. It is the purpose of this study to clarify the characteristics of nanometer-size etched track and to establish a technique for effective measurement of high-energy neutrons. The results are summarized as follows :1.Characteristics of nanometer-size tracksAfter irradiation of O,Ne,Si,Ar,Fe,I,Xe,Au ions to CR-39 track detectors and succeeding chemical etching of short duration, very small etched tracks were observed with an atomic force microscope. The growth curve for each ion was measured for early stage up to several tens of nm, from which the radii of track core could be obtained. It is also found that the track core were formed in the region where the local dose exceeded about 100 kGy.2.Application of high-energy neutron measurementIt was found from the first experiment that a polyethylene, a most popular radiator material, has insufficient efficiency for neutrons with an energy of a few tens of MeV or higher. As a result of theoretical consideration was proposed a new technique of two-layer structure consisting of polyethylene and a deuterized hydrocarbon. The latter material should play both roles of a radiator of deuterons and a degrader for energetic protons produced in outer polyethylene layer. Its performance was confirmed from the experiments of 45 and 70 MeV neutron irradiation at TIARA, Takasaki site, JAEA.