氡子体未结合态份额的变化规律研究

氡及其子体对公众的辐射照射占天然辐射照射的一半以上,而室内氡子体未结合态份额是影响氡子体剂量转换系数的重要参数。为探究氡子体未结合态份额的变化及受室内外环境因素的影响规律,本研究采用自行开发的累积式氡子体未结合态份额采样装置,在北京大学技物楼室内外环境中开展了氡子体未结合态份额的年变化测量,并利用商用连续式氡子体测量仪测量了室内氡子体未结合态份额的日变化。实测结果表明：在室内和室外不同环境中,氡子体未结合态份额的年平均值分别为8.8%(6.4%～12.5%）和9.7%(4.9%～12.8%);室内环境中氡子体未结合态份额相对稳定;室外环境中氡子体未结合态份额受环境因素影响大,波动较大;关于日变化,虽然室内平衡当量氡子体浓度呈现出明显的上午高下午低的日变化规律,但没有观察到未结合态份额有规律性的日变化。     

小体积氡室中氡子体状态参数调控的模拟研究

基于空气中氡子体和气溶胶粒子的行为规律,研究了一种小体积氡室中氡子体状态参数稳定调控方法,即通过调节小体积氡室总换气率和气溶胶粒子数浓度实现氡及氡子体浓度、平衡因子和未结合态份额等状态参数稳定调控方法。建立了调控物理模型,根据模拟条件甄选氡子体和气溶胶粒子行为参数,采用Matlab模拟计算了小体积氡室氡子体状态参数的调控范围,并将模拟计算值与实验值进行比对,部分验证本文建立的调控方法。模拟计算结果表明,本研究所建立的调控方法可在小体积氡室内实现氡子体浓度、平衡因子和未结合态份额的稳定调控。本研究建立的调控方法为实验研究提供了初步的理论基础。     

某些场所氡及其子体平衡因子的测量

环境氡子体所致剂量大多采用环境氡暴露量和推荐的氡及氡子体平衡因子来近似估算。但不同场所的环境条件差异很大,氡及氡子体的平衡因子也相差较大,从而导致此种估算方法存在较大的误差。为了提高基于氡暴露量估算氡子体所致剂量的质量,典型场所氡及其子体平衡因子的测量是必要的。采用南华大学研制的NRL-Ⅱ氡连续测量仪和NR-200A氡子体连续监测仪,在秦山核电基地、湖南省湘雅附一医院、湖南省肿瘤医院、锦原铀业等几个特殊工作场所进行空气中氡及其子体的平衡因子测量。测量结果表明,在沿海地区室内及放疗场所的平衡因子都比推荐值要小约40%;有些通风好且采取空气净化措施的区域平衡因子更小;内陆大部分室内的平衡因子与推荐值相近。     

室内氡子体行为模型研究

室内氡气体衰变产生短寿命氡子体,其子体的行为受室内换气状况、墙壁附着、子体同气溶胶粒子结合等物理过程的影响,宏观表征是未结合态份额和平衡因子受换气率、气溶胶浓度及气溶胶粒径分布状况等参数的影响。本文通过建立模型对室内氡子体行为进行了理论研究,重点考虑了换气率、气溶胶状况对未结合态份额和平衡因子的影响。计算结果表明平衡因子随换气率的增加而迅速减小,未结合态份额随气溶胶粒径分布的减小而迅速增加,气溶胶浓度只有在非常低的情况下才对未结合态份额和平衡因子产生明显影响。     

室内氡子体有效剂量转换系数的影响因素分析

室内氡子体有效剂量转换系数受室内环境参数的影响。为了理解和评价室内氡子体有效剂量转换系数随换气率、气溶胶浓度和气溶胶粒径分布的变化关系,从室内氡子体模型出发,结合前人实测的室内环境参数,计算了典型室内环境氡子体剂量转换系数值,并重点分析了室内环境参数中换气率、气溶胶浓度、气溶胶粒径分布对室内氡子体剂量转换系数的影响。在换气率为0.55 h-1,气溶胶浓度1.0×104 cm-3,AMTD为1.0 nm,AMAD为200 nm的典型室内环境,氡子体有效剂量转换系数为28.4 nSv.(Bq.h.m-3)-1,考虑到室内环境参数的变化范围,该值可以在19.9~33.9 nSv.(Bq.h.m-3)-1范围内变化。     

氡子体比的现场测量及其对剂量转换系数的影响

氡子体比是指其短寿命子体218 Po、214 Pb、214 Bi的活度浓度的比值,是氡子体剂量评价中的重要参数,但环境中氡子体比的数据非常有限。为了解和把握城市典型环境中氡子体比的现状,并分析其对剂量转换系数的影响,本文利用便携式α谱仪,现场测量了城市典型室内外环境的氡子体比,并通过分析室内外环境氡子体比数据的特点,讨论了环境氡子体比对剂量转换系数的影响。测量结果显示,城市典型室内环境中氡子体比的平均值为1∶0.59∶0.58,典型室外环境中氡子体比的平均值为1∶0.50∶0.67。因各子体的剂量系数与它们的α潜能呈正比,所以氡子体比对剂量转换系数的影响很小。     

Potential of High Thoron Exposure in China

Compared with radon (²²²Rn) and its progeny, thoron (²²⁰Rn) and its progeny have not been well studied in the natural radiation fields. In this paper, some important factors (²³²Th content in soil and building material as well as building structure) relating to the level of indoor thoron and its progeny in China are reviewed. Limited results of small-scale surveys are also cited. The facts indicate that the public exposure from the inhalation of thoron progeny may be higher than the representative value in the UNSCEAR 1993 report, and thoron and its progeny may be a significant indoor pollutant in some regions or specific dwellings in China.     

ICRP Publication 115. Lung cancer risk from radon and progeny and statement on radon

Recent epidemiological studies of the association between lung cancer and exposure to radon and its decay products are reviewed. Particular emphasis is given to pooled case-control studies of residential exposures, and to cohorts of underground miners exposed to relatively low levels of radon. The residential and miner epidemiological studies provide consistent estimates of the risk of lung cancer, with significant associations observed at average annual concentrations of approximately 200 Bq/m3 and cumulative occupational levels of approximately 50 working level months (WLM), respectively. Based on recent results from combined analyses of epidemiological studies of miners, a lifetime excess absolute risk of 5 × 10?? per WLM [14 × 10?? per (mJh/m3)] should now be used as the nominal probability coefficient for radon- and radon-progeny-induced lung cancer, replacing the previous Publication 65 (ICRP, 1993) value of 2.8 × 10?? per WLM [8 × 10?? per (mJh/m3)]. Current knowledge of radon-associated risks for organs other than the lungs does not justify the selection of a detriment coefficient different from the fatality coefficient for radon-induced lung cancer. Publication 65 (ICRP, 2003) recommended that doses from radon and its progeny should be calculated using a dose conversion convention based on epidemiological data. It is now concluded that radon and its progeny should be treated in the same way as other radionuclides within the ICRP system of protection; that is, doses from radon and its progeny should be calculated using ICRP biokinetic and dosimetric models. ICRP will provide dose coefficients per unit exposure to radon and its progeny for different reference conditions of domestic and occupational exposure, with specified equilibrium factors and aerosol characteristics.     

Airborne Radon-222 Measurement by Active Sampling with Charcoal Adsorption and Gamma-Ray Spectrometry

A simple method for measuring radon concentration in air is presented. Airborne radon is adsorbed in a charcoal bed by an active air sampling. In time, the adsorbed radon comes to attain radioactive equilibrium with its short-lived progeny ²¹⁴Pb. Utilizing this fact, radon concentration is derived from γ-ray measurement of ²¹⁴Pb. This method is estimated to be capable of detecting radon concentration in air down to 0.79Bq·m^?3 The adsorption coefficient obtained with the method is compared with what is obtainable with passive sampling. Applications of this method to indoor and outdoor radon measurements are described.     

新风换气对室内氡浓度的影响

使用RAD7测氡仪对氡模拟实验房进行氡浓度连续测量,研究不同新风换气率对室内氡浓度的影[JP2]响。结果表明：氡模拟实验房内氡浓度最高可累积至2 000 Bq/m³,墙面平均氡析出率为14.5 Bq·m^-2·h^-1;氡模拟实验房在连续均匀地通入新风情况下,室内氡浓度随时间呈指数递减趋势;当新风换气率变化时,氡模拟实验房内的平衡氡浓度和平衡时间随新风换气率的增加呈指数递减趋势;当新风换气率由大变小时,室内氡浓度会再次累积增加。     

单层丝网法氡子体未结合态份额测量中结合态氡子体的影响评估

为系统研究单层丝网法测量氡子体未结合态份额中结合态氡子体的影响,本研究基于理论分析和实验测量,评估了同一种环境下不同目数的丝网对结合态氡子体的收集效率,分析了同一种丝网应用于不同的环境测量时结合态氡子体对未结合态份额测量的影响。研究表明,不同目数的金属丝网对结合态氡子体的收集效率并不高（0.7%～1.0%）,但由于典型室内环境中结合态氡子体占比较高（～92%）,结合态氡子体的存在会导致氡子体未结合态份额的测量值出现一定的系统性正偏差（3.1%～9.5%）,且该系统性正偏差随丝网目数的增加而增加。同一目数丝网,从室内环境直接应用于室外、矿山环境时,由于结合态氡子体中粗粒子模态占比较高,导致氡子体未结合态份额测量值出现较大偏差。从理论计算结果看,典型室外、矿山环境的偏差分别达40.3%和113%,这说明在使用单层丝网法测量氡子体未结合态份额时,有必要针对不同环境对金属丝网进行优选,尽量减少氡子体未结合态份额测量偏差。     

室内氡的来源、水平和控制

本文介绍室内氡的来源、水平和控制方法。根据文献资料汇集得出了截至1994年中国室内、室外和地下室氡浓度平均值（分别为23．7、12．6和373Bq/m^3）、氡子体平衡因子（分别为0．47、0．59和0．43）以及室内氡浓度水平的地区分布,室内氡的季节变化和昼夜变化。讨论了室内氡浓度控制的必要性、控制依据和控制措施,指出了建筑材料按放射性比活度分类对控制室内氡的意义。     

Radon Levels in China

This paper reviewed and summarized the results and problems of a nation-wide environmental radon survey which was carried out from 1984 to 1990 in China. Indoor radon concentrations were measured in 10,811 dwellings, and which covered 26 provinces and cities all over China. The range of indoor radon concentrations was <LLD-386.8Bq·m^?3, the average was 22.5 Bq·m^?3 and 19.6 Bq·m^?3 for arithmetic mean and geometric mean, respectively. Both outdoor radon concentrations and indoor radon progeny concentrations were also reported. Even though the grab sampling was taken as the main method of the survey, it was still a valuable reference.     

我国部分地区室内外氡水平及其剂量评价

本文汇总了我国部分地区室内外氡浓度调查结果,特别指出了铀矿区附近、煤渣砖和石煤渣砖建筑物、窑洞、地下室及高本底地区室内的氡水平。确定了剂量评价中所采用的氡子体暴露量-有效剂量转换因子、平衡因子及室内停留因子,给出有效剂量估计值,最后,简单讨论了有关室内氡的防护问题。     

吸入氡子体肺部有效剂量转换系数的影响因素研究

基于ICRP 66号报告中的呼吸道生物动力学模型,采用MATLAB软件中的Simulink仿真工具,建立了人体呼吸道的廓清模型,利用建立的廓清模型计算了不同参数条件下肺部有效剂量转换系数(mSv/WLM)的变化规律。结果显示吸入氡子体粒径对肺部有效剂量转换系数的影响最大,当粒径在0.7～10 000 nm之间变化时,肺部有效剂量转换系数的变化能达到10倍以上;其次是呼吸率,呼吸率直接决定了吸入氡子体粒子的数量,当成年男性重度工作状态时肺部有效剂量转换系数是睡眠状态下的4.2倍;未结合态份额对剂量转换系数的影响会随着吸入氡子体粒径值不同而发生改变,当未结合态份额从0变化到0.08时,肺部有效剂量转换系数最多能增大79%;相比而言吸收入血速率对肺部有效剂量转换系数的影响只有不到4%。     

A new sampler for simulating aerosol deposition in the respiratory tract

Abstract For estimation of the deposition fractions of radon progeny in different regions of the respiratory tract, a new sampler consisting of three different configurations of sampling heads was developed. The deposition fractions of aerosols on the wire screens inside the sampling heads were calculated with the fan model of filtration theory. The deposition fractions of aerosols in different regions of the respiratory tract were calculated with the lung dose evaluation program (LUDEP (C)) developed by National Radiological Protection Board (NRPB) as References. In general indoor and mine environments, the deviation between the deposition fractions of attached aerosol on the wire screens designed in this study and its reference values in the respiratory tract is less than 5%. It is possible to accurately estimate the deposition fractions of radon progeny in different regions of the respiratory tract through mimic measurements of radon progeny collected with the new sampler.     

一种调控氡子体平衡因子的高浓度单分散性气溶胶发生器的研制

为了满足氡室内氡子体辐射场的调控要求,结合蒸发冷凝法的原理,利用电子烟发生器产生的癸二酸二辛酯(DEHS)与雾化器产生的NaCl颗粒结合再冷凝的方法,研制了高浓度单分散的气溶胶发生器。将该发生器应用于中国计量科学研究院20 m³氡室,充胶1分钟后气溶胶浓度最高可达到2.26×10⁵ cm^-3,平均粒径156.8 nm,单分散性1.38,氡室内氡子体平衡因子可调控达到0.65。     

Radon and thoron progeny integrated measurement based on high-voltage sampling

For the purpose of directly measuring radon and thoron progeny concentrations simultaneously, an unattended battery-operated progeny measurement (UBPM) device, which samples aerosol particles in an electric field, was improved by adopting two different thickness aluminum foils for alpha particles discriminating. The equations for the calculation of the results were derived, and a series of calibration experiments and comparison tests were carried out in the potential alpha energy concentration calibration chamber in BfS Berlin and the HMGU experimental thoron house, respectively. Results show that the calibration coefficients are stable in different levels of radon and thoron progeny. The lower level detection limits of the device for radon and thoron progeny concentration are 1.22 and 0.14 Bq m^?3, respectively, for three months exposure. The instrument proved to be independent from environmental conditions in ordinary living room conditions (humidity <65% RH, aerosol particle concentration >1500 cm^?1). Comparison results show that the measurement results of the UBPM device are comparable with the reference instrument and suitable for long-term radon and thoron survey in dwellings.     

ICRP新剂量限值对氡子体职业性照射年照射量限值影响的探讨

本文简介ICRP第60号出版物附件B中有关氡子体照射诱发肺癌的概率的内容,并探讨新剂量限值对氡子体职业性照射年照射量限值的影响。