Environment Safety and Health Directorate, Radiological Control Division, Brookhaven National Laboratory, Upton, NY 11973-5000.
Health Phys. 2019 Jul;117(1):99-105. doi: 10.1097/HP.0000000000001061.
Personal property exposed to particle beams and stray radiation at high-energy particle accelerators may contain induced volumetric radioactivity. At both the Brookhaven National Laboratory's (BNL) Collider-Accelerator and National Synchrotron Light Source II Facilities this radioactivity contains both gamma-emitting and beta-emitting radionuclides. The US Department of Energy (US DOE) recently published Technical Standard 6004-2016. This standard provides radionuclide-specific volumetric screening levels (Bq g) below which accelerator materials are eligible for clearance and release from radiological control. The standard also establishes several approaches for decision-making relative to the clearance process implemented, one of which is the "Indistinguishable from Background" (IFB) approach. BNL implements the IFB approach for survey of potentially activated accelerator materials. Radiological control technicians perform on-contact measurements using portable scintillators that are sensitive to gamma and x-ray radiation. Instrument decision thresholds are usually estimated by measuring total background counts over a pre-determined counting interval using an integrating count-rate instrument and then applying an appropriate confidence level factor. Measurement results obtained in a low background area are then directly compared to these detection thresholds. This paper presents an alternative statistical approach using logistic regression for estimating instrument decision thresholds for small-mass items using the IFB method and compares them to established release criteria. On-contact Micro-R meter measurements are correlated with analytical data obtained for activated materials weighing 0.3 kg to 3 kg. Analytical sample results show that Co and Na accounted for more than 90% of total sample radioactivity. Co and Na emit high-energy gamma rays and are both group one radionuclides as defined in DOE-6004-2016. For this size material the results show that the probability of detecting residual volumetric radioactivity at the Group One screening level concentration of 0.11 Bq g under normal field conditions is about 68%. This increases to 95% at 0.16 Bq g. The 95% confidence interval is 0.09 Bq g to 0.23 Bq g. Grouping low-mass items during the survey process could mitigate this concern if all items are expected to have similar activity concentrations.
个人财产在高能粒子加速器的粒子束和散射辐射下可能会含有诱导的体积放射性。在布鲁克海文国家实验室（BNL）的对撞机加速器和国家同步辐射光源 II 设施中，这种放射性既包含发射伽马射线的放射性核素，也包含发射β射线的放射性核素。美国能源部（US DOE）最近发布了技术标准 6004-2016。该标准规定了加速器材料的放射性核素特定体积筛选水平（Bq/g），低于该水平的材料有资格免除辐射控制，并放行。该标准还为实施清除过程的决策制定了几种方法，其中一种是“与背景无法区分”（IFB）方法。BNL 对潜在激活的加速器材料采用 IFB 方法进行调查。辐射控制技术人员使用便携式闪烁体进行接触式测量，这些闪烁体对伽马和 X 射线辐射敏感。仪器决策阈值通常通过使用积分计数率仪器在预定的计数间隔内测量总背景计数来估计，然后应用适当的置信水平因子。然后将在低背景区域获得的测量结果直接与这些检测阈值进行比较。本文提出了一种替代的统计方法，使用逻辑回归来估计使用 IFB 方法的小质量物品的仪器决策阈值，并将其与既定的释放标准进行比较。微-R 米计的接触式测量与对 0.3 公斤至 3 公斤重的激活材料进行的分析数据相关联。分析样本结果表明，Co 和 Na 占总样本放射性的 90%以上。Co 和 Na 发射高能伽马射线，并且均为 DOE-6004-2016 中定义的第一类放射性核素。对于这种尺寸的材料，结果表明，在正常现场条件下，在第一类筛选水平浓度为 0.11 Bq/g 时，检测到残留体积放射性的概率约为 68%。当浓度为 0.16 Bq/g 时，概率增加到 95%。95%置信区间为 0.09 Bq/g 至 0.23 Bq/g。如果所有物品的活性浓度都预计相似，则在调查过程中对低质量物品进行分组可以减轻这种担忧。
