连续测氡仪内存留气体的探讨

在民用建筑工程室内环境中氡浓度的测定方法中,用连续测氡仪测定氡浓度是一种方便、快捷的方法。本文以RAD7连续测氡仪为例,探讨了如何解决前一次取样存留气体对后一次取样检测影响的办法,得出用“干净空气”冲洗探测器的整个气路是较快和较好的解决办法。     

氡室建标中几个技术问题的解决办法

标准氡室在氡浓度量值溯源和传递中起着重要作用。为了保证测氡仪量值统一、准确可靠,建立了测氡仪检定装置。针对在建立标准过程中出现的流气式氡源泄漏、氡室实验累积氡浓度值与理论值不一致和液体镭源结晶等问题,重点研究多重密封、改造洗气管路、优化洗气模式及多重过滤等技术方法,并建立氡室累积氡浓度经验曲线和质量管理措施等。按照新建立的实验方法和实验流程,氡室实验调节氡浓度和理论累积氡浓度相对偏差在±3.8%以内,液体镭源长期稳定性在0.7%以内,符合氡室建标的计量性能要求。     

标准氡室内氡气体积活度的计算方法与测量验证

标准氡室内氡气的体积活度值是刻度与校准测氡仪的约定真值,通常由仪器准确测量获得.通过对标准氡室氡体积活度理论计算方法及相关参数实验测定方法的探讨,并对标准氡室氡体积活度进行实验测量,验证了理论计算方法及实验测定参数的可行性.     

彭州市丽春镇地区土壤氡浓度测量

在彭州市丽春镇地区大约4km的区域内，利用IED3000R土壤测氡仪开展多剖面土壤氡浓度测量。根据测量结果绘制土壤氡测量剖面图及目标区土壤氡浓度分布的平面等值图，得出丽春镇地区隐伏断裂的位置、走向以及宽度等信息。将断裂信息与前人成果相比较，讨论汞污染与隐伏断裂的关系。     

室内空气中氡浓度测量的不确定度评定

本实验室采用Model-1027连续测氡仪作为检测工具.在正确使用仪器的情况下,室内空气中氡浓度测定的不确定度主要由仪器读数的不确定度和仪器检定的不确定度两部分组成.建立适当的测量不确定度数学模型,将两个不确定度分量合成得到合成标准不确定度,再选扦包含因子k=2,从而求得其扩展不确定度.     

氡测量方法与标准氡室综述

本文介绍了常用的氡测量方法和测氡仪器,对氡测量技术进行了较详细分析,为选择适宜的方法进行氡浓度监测提供了参考。标准氡室的研制为各种测氡仪器的刻度和量值溯源性提供了技术支撑,保证了测量结果的准确可靠,文章简要介绍了国内外标准氡室的发展状况。     

标准测氡仪的量值溯源方法研究

研究了利用氡活度绝对测量装置制备高准确度标准氡源的方法,得到了活度扩展不确定度为0.8%(k=2)的量传用氡源。依据计算标准氡体积活度的基本原理,对用于氡源活度量传所配套的小氡室的有效体积进行了校准,其有效体积的扩展不确定度为0.46%(k=2),对一般氡标准装置(标准氡室)所用的参考仪器(AlphaGUARD型标准测氡仪)进行校准,得到其平均体积活度响应为1.01,体积活度响应的扩展不确定度为3.2%(k=2)。     

三种进口测氡仪在环境中比对试验

RAD7,1027,PQ2000三种测氡仪均为进口仪器,通过在氡室和地下室的比对试验,1027具有不需要干燥、受环境湿度影响小的优点,但在氡浓度较低时测量结果偏差相对较大,最大偏差为14.6%;当环境氡浓度骤然变化时,三种仪器均有良好的响应;在地下室连续7昼夜的监测过程中,三种仪器测量的潮汐变化幅度略有差别,但变化趋势十分吻合。     

氡测量仪检定/校准装置的研制

为建立氡测量的计量标准,研制以多功能的标准氡室为核心的氡测量仪检定/校准装置。采用氡浓度动态稳定技术以实现氡浓度的自动调控;设计用夹胶钢化玻璃制作氡室以减少箱体对氡的吸附,并具有良好的保温效果;设计制作温湿度调控系统和气溶胶发生与采集装置,实现氡子体放射性气溶胶的检测功能。装置氡室体积为4m3,氡浓度测量范围为370～20000Bq/m3,氡浓度值测量结果的相对扩展不确定度不超过5.8%,可用于测氡仪器的检定校准和氡子体放射性气溶胶的实验研究。     

流气式氡源的制备方法研究

研究建立有效的氡浓度检测计量标准,满足测氡装置的计量溯源需求关键在于流气式氡源的制备及其浓度的控制.文章利用化学性质稳定的氯化镭(226 RaCl2)溶液,通过高效的阳离子交换树脂,将镭(226Ra)阳离子交换到树脂上固定下来,构成产生氡(222 Rn)的母体,通过α衰变产生氡气,氡气随空气或氮气载带,用于调控氡浓度.     

A self-calibrating radon monitor with statistical discrimination

A radon monitor, able to perform the measurement of the radon and its progeny volumic activity, in a gamma-ray or natural radiation background field, was developed. The instrument consists of a 10 l ionization chamber, a high voltage source, an integrating preamplifier, a data acquisition system and a personal computer. A new method for self-calibration of Radon volumic activity measurements, based on the alpha counting with an ionization chamber is also presented.     

Czech primary radon measurement equipment

The Authorized Metrological Centre (AMS) working by SUJCHBO (National Institute for Nuclear, Chemical and Biological Protection) ensures for the Czech Republic the metrological traceability for devices that measure the radon concentration and the energy equivalent radon concentration connected with the radon decay products (RnDP). The evaluation and the calibration of measuring devices for radon and RnDP require the stable conditions (first of all radon and the RnDP concentrations). The new AMS radon-aerosol chamber in Kamenná consists of the walk-in testing chamber with a volume of 10 m(3) and of the handling box with a volume of 0.3 m(3). The design of the chamber allows measurement and a control of environmental parameters such as the temperature, the pressure of air inside and outside of the chamber, the relative humidity of air, the concentration and the size distribution of aerosol particles and the air velocity.     

Measurement of radon concentration in water using the portable radon survey meter

A measurement method for measuring radon in water using the portable radon survey meter (RnSM) was developed. The container with propeller was used to stir the water samples and release radon from the water into the air in a sample box of the RnSM. In this method, the measurement of error would be <20 %, when the radon concentration in the mineral water was >20 Bq l(-1).     

Significance of independent radon entry rate and air exchange rate assessment for the purpose of radon mitigation effectiveness proper evaluation: case studies

Two new single-family houses identified as insufficient with regard to existing radon barrier efficiency, have been selected for further examination. A complex set of radon diagnosis procedures has been applied in order to localise and quantify radon entry pathways into the indoor environment. Independent assessment of radon entry rate and air exchange rate has been carried out using the continuous indoor radon measurement and a specific tracer gas application. Simultaneous assessment of these key determining factors has turned out to be absolutely crucial in the context of major cause identification of elevated indoor radon concentration.     

Characterisation of an electronic radon gas personal dosemeter

The monitoring of radon exposure at workplaces is of great importance. Up to now passive measurement systems have been used for the registration of radon gas. Recently an electronic radon gas personal dosemeter came onto the market as an active measurement system for the registration of radon exposure (DOSEman; Sarad GmbH, Dresden, Germany). In this personal monitor, the radon gas diffuses through a membrane into a measurement chamber. A silicon detector system records spectroscopically the alpha decays of the radon gas and of the short-lived progeny 218Po and 214Po gathered onto the detector by an electrical field. In this work the calibration was tested and a proficiency test of this equipment was made. The diffusion behaviour of the radon gas into the measurement chamber, susceptibility to thoron, efficiency, influence of humidity, accuracy and the detection limit were checked.     

Indoor and soil gas radon simultaneous measurements for the purpose of detail analysis of radon entry pathways into houses

Detailed knowledge of radon transport mechanisms from the subsoil into the indoor environment is essential for the correct interpretation of results of short-term indoor radon measurements and for proper and effective design of radon mitigation systems. Radon transfer factor time variations have been studied based on simultaneous continuous indoor and soil gas radon measurements within the framework of complex radon diagnosis of individual buildings. In this context, the key influencing factors have been identified and analysed in order to provide satisfactory explanation on radon entry variations under different measurement conditions. Moreover, a new significant manner of radon entry into the indoor environment has been identified and will be discussed in detail.     

Results of the 2010 National Radiation Protection Institute intercomparison of radon and its short-lived decay product continuous monitors

During the Sixth European Conference on Protection Against Radon at Home and at Work held in autumn 2010 in Prague, the first intercomparison of continuous radon and its short-lived decay product monitors was organised and held by the Natural Radiation Division of the National Radiation Protection Institute (NRPI) in Prague. Eight laboratories submitted eight continuous radon monitors, two electronic monitors, three passive integral systems based on charcoal and three continuous radon short-lived decay product monitors. The intercomparison included exposures to both the radon gas concentration and equivalent equilibrium radon concentration (EEC) under different ambient conditions similar to the ones in dwellings. In particular, the influence of the equilibrium factor F, unattached fraction of EEC f(p) and absolute air humidity were investigated. The results of the radon gas measurements were performed on a calibration level of about 8 kBq m(-3). The results of all monitors were compared with the reference NRPI monitor.     

Measurement of radon diffusion in polyethylene based on alpha detection

Radon diffusion in different materials has been measured in the past. Usually the diffusion measurements are based on a direct determination of the amount of radon that diffuses through a thin layer of material. Here we present a method based on the measurement of the radon daughter products which are deposited inside the material. Looking at the decay of ²¹⁰Po allows us to directly measure the exponential diffusion profile characterized by the diffusion length. In addition we can determine the solubility of radon in PE. We also describe a second method to determine the diffusion constant based on the short-lived radon daughter products ²¹⁸Po and ²¹⁴Po, using the identical experimental setup.Measurements for regular polyethylene (PE) and High Molecular Weight Polyethylene (HMWPE) yielded diffusion lengths of (1.3±0.3) mm and (0.8±0.2) mm and solubilities of 0.5±0.1 and 0.7±0.2, respectively, for the first method; the diffusion lengths extracted from the second method are noticeably larger which may be caused by different experimental conditions during diffusion.     

Measurements of radon exhalation rate for monitoring cement hydration

The paper deals with one of the physical methods, which can be used for monitoring hydration of cementitious materials: the radon exhalation method. Experiments with two types of hydrating cement paste (made with water to cement ratios of 0.25 and 0.33) are described. The kinetics of shrinkage and hydration heat development are discussed. Different mechanisms influencing the radon exhalation rate E from cement and hydration products are considered. The initial E-values determined in the beginning of the tests were 0.01–0.02 mBq  kg⁻¹ s⁻¹ for the cement pastes made at water/cement ratios of 0.25 and 0.33, respectively. In 3 days both pastes showed E = 0.04 mBq  kg⁻¹ s⁻¹. However, the most important finding seems to be the dramatic increase of the radon exhalation rate up to the maximum observed a few hours after mixing with water (0.66 and 0.58 mBq  kg⁻¹ s⁻¹ for 0.25 and 0.33 pastes, respectively). This was registered in the radon chamber within the time period usually classified as set. The test results showed a strong correlation between radon exhalation rate and liberation of hydration heat. Peaks of the radon exhalation rate coincide with those of temperature measured on the surface of the cement paste. Analysis of the literature data shows that heating of the materials weakens physical adsorption of radon gas atoms on newly formed solid surfaces and can enhance the radon exhalation rate by several times. However, the performed experiment shows that the radon exhalation rate drastically increases (by dozens of times), and then decreases again. Such a dramatic growth can be explained by a synergy between temperature effect and two more phenomena: (a) intensive formation of microstructure with an extremely high specific surface area, when cement sets and while porosity is still high and (b) intensive flow of water, which traps radon from the newly formed solid surfaces of C-S-H and brings it to the sample surface, enhancing the radon flux.