北京大学辐射防护科研组环境放射性核素研究进展

Research progress on environmental radionuclides by the Radiation Protection Research Group.Peking University

本文展示了北京大学技术物理系辐射防护科研组自成立以来在环境放射性核素研究领域的发展历程,介绍了部分代表性工作.其中,针对天然辐射照射中剂量最大的贡献者——氡及其子体相关领域,开展了以剂量评价和探究其环境行为为目的一系列测量方法和技术研究,特别是对大气氡、水体氡和土壤氡活度浓度的在线连续测量成果进行了重点阐述,建立的便携式测量技术使氡子体连续测量和放射性气溶胶粒径分布现场测量成为可能.在与核军工和核电反应堆密切相关的人工放射性核素方面,着重介绍了围绕环境中以痕量水平存在的钚核素开展的同位素精准测量和迁移行为研究工作.作为现场测量与评价研究,本文还介绍了针对我国唯一的重水堆核电基地外围环境开展的14C测量、水平分布和剂量贡献的研究成果.

This paper presents a simple review of the progress and primary achievements of the radiation protection laboratory over its two decades of research.The main research subjects of the laboratory are naturally occurring radionuclides,their environmental behaviors,and the dose evaluation of radon exposure to the public.We developed several precise measurement methods for real environmental surveys and investigations on radon and its progeny.Furthermore,to support related research fields that use radon as a radioactive tracer,in situ continuous measurement techniques for radon in the atmosphere,soil,and water bodies were established.A one-year continuous measurement provided the typical year average(4.9±2.7Bq/m^(3))of radon progeny concentration in Beijing,which is consistent with the world average(5Bq/m^(3))recommended by UNSCEAR.Furthermore,for artificial radionuclides,we conducted wide research on Pu isotopes in Chinese environments.Our study focused on the development of analytical methods for the analysis of Pu in various environmental samples based on ICP-MS.Moreover,we investigated Pu distribution in the downwind area of the Lop Nor nuclear test site and assessed the vertical distributions and migration of Pu in the soil in Southwest China.In the Jiuquan region,we collected surface and core soil samples and determined the^(239+240)Pu activities and^(240)Pu/^(239)Pu atom ratios in these to assess the level of Pu contamination and the sources of Pu in this region.Using Pu isotopes from the Chinese muclear tests,we found that in most Jiuquan soil samples,the 240 Pu/239Pu atom ratios were below the global fallout value,suggesting thisarea was contaminated by Puisotopes from the Chinese nuclear test sites.The average^(240)Pu/^(239)Pu atom ratio in the soil samples was-0.16.Besides plutonium,^(14)C is another artificial radionuclide we investigated.^(14)C is a radioisotope produced as a byproduct in various nuclear facilities and released in the environment under normal operation;it is considered the main dose contributor to the public,making it one of the most important radioisotopes in environmental radiation evaluation.The^(14)C analysis of the tree ring samples collected 2 km away from Qinshan NPP revealed that the enhanced values were primarily owing to^(14)C discharged from two heavy reactors of Plant Ⅲ.Moreover,a good correlation existed between the^(14)C discharged from Plant Ⅲ in the growing season and the increased concentration of^(14)C.We found that almost all^(14)C released from Qinshan NPP was deposited within a radius of 6.5 km in 2010,and the maximal^(14)C specific activity of most samples is 265.6 Bq/kg C,which is 41.8 Bq/kg C higher than that of the background.For dose contribution to the public,the effective dose resulting from the^(14)C discharged from Qinshan NPP was estimated to be 0.5μSv in 2010,which is negligible compared with the annual dose limit for the public(0.25 mSv).