Measurement of Neutron Radiation Doses by Accelerator Mass Spectrometry

由于长寿命放射性核素^<36>Cl（半衰期：30 x 10^4 y）的宇宙射线产生的β射线只发射低能β射线，其在环境样品中的辐射测量比较困难。近年来，加速器质谱（AMS）在低能级计数方面取得了很大的进展。筑波大学加速器中心<36>从1999年开始建造AMS的^ Cl测量系统。在这项研究中，我们试图确定中子辐射剂量的^<36>Cl/Cl测量使用AMS 1。通过测量<36>JCO事故中受辐照土壤样品中的^ Cl/Cl估算了中子辐射剂量。这一结果与事故2的中子辐射剂量估算相一致。通过测定<36>投在广岛的原子弹辐照样品中的^ Cl/Cl，重新估算了中子辐射剂量。在原子弹爆炸的已知地点采集了从墓石中开采的花岗岩样品并进行了分析。测量的^<36>Cl/Cl 1比值与新计算的辐射剂量估算系统DS 023一致。通过测量<36>各种加速器设施屏蔽混凝土中的^ Cl/Cl来估算中子辐射剂量。本文对东京大学核研究中心的SF回旋加速器、东北大学核科学研究室的300 MeV电子直线加速器和高能加速器研究机构的12 GeV质子同步加速器三种加速器装置<36><35>的束线附近混凝土样品中的^ Cl/^ Cl比深度分布进行了分析。估算AMS<36>测量的^ Cl/Cl比值是评价中子剂量的良好工具

Since long-lived radionuclide ^<36>Cl (half life : 30 x 10^4 y) produced by cosmic-ray in upper atmosphere emits only low energy β-ray, its radiation measurement in the environmental samples makes difficult. Recently, Accelerator Mass Spectrometry (AMS) has been developed in low level counting. In Accelerator Center, University of Tsukuba, ^<36>Cl measurement system by AMS has been constructed since 1999. In this study we tried to determine the neutron radiation dose by ^<36>Cl/Cl measurement using the AMS1. Neutron radiation dose has been estimated by measuring ^<36>Cl/Cl in the irradiated soil samples by JCO accident. This result is agreed with estimation of neutron dose emitted from the Accident2. Neutron radiation dose has been re-evaluated by measuring ^<36>Cl/Cl in the irradiated samples by atomic bomb dropped to Hiroshima. Granite samples quarried from tomb stones were collected in the known places of atomic bombed area and analyzed. The measured ^<36>Cl/Cl1 ratios were agreed with newly calculated radiation dose estimate system DS023. Neutron radiation dose has been estimated by measuring ^<36>Cl/Cl in the shielding concrete of various accelerator facilities. For three kinds of accelerator facilities, SF cyclotron (Center for Nuclear Study, The University of Tokyo), 300 MeV electron LINAC (Laboratory of Nuclear Science, Tohoku University) and 12GeV proton synchrotron (High Energy Accelerator Research, Organization), the depth profiles of ^<36>Cl/^<35>Cl ratios in concrete samples near the beam lines were analyzedIn the three cases mentioned above the neutron radiation dose were successfully estimated. The ratios of ^<36>Cl/Cl measured by AMS is a good tool to evaluate the neutron dose