Measurement of Neutron Radiation Doses by Accelerator Mass Spectrometry

由于高层大气中宇宙射线产生的长寿命放射性核素^&lt；36&gt；Cl(半衰期：30×10~(-4)y)只发射低能β射线，给环境样品中的辐射测量带来了困难。近年来，加速器质谱学(AMS)在低能级计数中得到了发展。自1999年以来，筑波大学加速器中心已经建成了AMS的36&gt；氯测量系统。在这项研究中，我们试图通过使用AMS1的^&lt；36&gt；氯/氯测量来确定中子辐射剂量。通过测量JCO事故辐照土壤样品中的~(36&t；t；36&gt；Cl/Cl)，估算了中子辐射剂量。这一结果与Acsident2发射的中子剂量估算是一致的。通过测量原子弹投放到广岛的辐照样品中的^&lt；36&gt；氯/氯，重新估算了中子辐射剂量。在已知的原子弹轰击区采集了墓碑上的花岗岩样品并进行了分析。测得的^&lt；36&gt；Cl/Cl1比值与最新计算的辐射剂量估算系统DS023一致。通过测量各种加速器设施屏蔽混凝土中的~(36)C l/C l，估算了中子辐射剂量。对三种加速器装置--SF回旋加速器(东京大学核研究中心)、300 MeV电子直线加速器(东北大学核科学实验室)和12GeV质子同步加速器(高能加速器研究组织)，分析了束线附近混凝土样品中~(36)Cl/~(35)Cl的深度分布，成功地估算了上述三种情况下的中子辐射剂量。AMS测量的~(36)C l/C l比值是评价中子剂量的一个很好的工具

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