氡析出率测量中的218Po非平衡修正

通过对传统的累积法测量氡析出率模型实验验证,发现得到的氡析出率明显偏低。对测氡仪器的工作原理与集氡罩中氡的浓度变化规律进行分析,发现是由于被测介质表面析出的氡不断进入集氡罩,218Po与氡没有平衡,造成测量的氡浓度明显偏低。通过非平衡修正得到了修正后的氡析出率测量理论模型。利用修正后的该模型得到的介质表面氡析出率与参考值符合得较好,误差小于7%。此外比较优值函数的取值也可发现:修正后的理论模型优值函数的取值小于传统模型,这表明修正后的理论模型更符合实际,该理论模型可应用于氡析出率仪的研制与改进。     

连续测氡仪测定空气中氡浓度方法探讨

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,但在实际检测过程中,由于操作等原因,仪器的测量准确度较低。在标准氡室(HD-1型)里模拟实验用标准氡浓度,以RAD7连续测氡仪为例,探讨了取样测量时间、空气湿度对空气中氡浓度测量的准确性的影响。结果表明,在取样测量时间不低于30min、较低空气湿度(10%)条件下,用连续测氡仪测量空气中氡浓度可以获得满意的数据。     

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。     

氡子体体积活度的液体闪烁计数方法研究

基于液体闪烁计数原理和滤膜采样技术,建立了一种氡（²²²Rn）子体体积活度和α潜能浓度的测量方法。应用该方法对氡室中处于放射性平衡状态的氡子体体积活度进行了取样测量,氡子体α潜能浓度测量结果的扩展不确定度小于1.5%（k=2）;用α能谱法对氡子体液体闪烁计数测量方法进行了旁证,两种方法的测量结果在不确定度范围内一致。     

浅谈活性炭盒法对室内空气中氡浓度的测量

研究了活性炭盒法测定室内空气中氡浓度的影响因素,考察了采样时间、平衡时间、样品测量时间等对空气中氡浓度的影响。     

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。     

地底深处氡浓度的测量方法探究

天然或人工辐射源对人体有影响的辐射剂量的50%以上来源于氡及其子体,在开挖隧道时会穿过地底深处,监测和防护氡及其子体对隧道工人来说变得尤为重要。根据《氡及其子体在大气环境中的测量方法》(NFM60—763)和《氡及其子体测量规范》(EJ/T 605—91)的相关规定,并利用集气法就可以较准确地对浅层地表土壤氡浓度进行测定;而目前没有相应的监测手段对地底深处氡浓度测量进行监测,该文拟采用利用连续测氡仪与地勘使用的钻杆相结合的方式组成的监测系统测定地底深100 m～500 m处的氡浓度,在开挖隧道之前测量该地底的氡浓度,可以避开氡浓度较高的区域或者可以提前为氡防护提供数据支撑。     

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。     

几种常用土壤氡浓度测量技术分析

土壤测氡广泛应用于环境评价、地质构造勘查和资源勘查等领域。首先,该文结合实际工程的应用分析土壤氡浓度特征及土壤中氡浓度测量技术需求特点,对现有土壤氡气测量技术进行简要分析。然后,重点介绍α杯法土壤测氡技术、泵吸式α能谱土壤测氡技术、RaA土壤测氡技术工作原理,并详细分析其各自优缺点。最后,通过测试对比实验数据,验证α杯法土壤测氡技术具有反应弱异常能力,对土壤氡异常信息具有重现性和多台仪器测量数据一致性的优点,也验证土壤中氡气累积测量方法准确性优于瞬时测量方法。该文工作对从事土壤中氡气测量工作人员合理选用测量方法和正确使用相应的测量仪器具有参考意义。     

连续式水氡测量装置测量结果的不确定度评定与优化

依据连续式水氡测量装置的测量数据及相关参数,分析和评定了水氡放射性测量中水氡浓度测量结果的不确定度。研究结果表明,在水氡浓度约为7 227 Bq/m^3时,水氡测量结果的不确定度为6.8%(k=2)。根据测量不确定度评定结果提出相应的优化方案,可使得测量不确定度降为5.0%。     

MCP-N (LiF:Mg,Cu,P) TLDs for radon measurements with charcoal canisters

A method of measurement of radon concentration in air was developed, based on high-sensitivity LiF:Mg,Cu,P (MCP-N, TLD Poland) thermoluminescent detectors installed in charcoal canisters. The canisters were exposed typically for 72 h in a calibration chamber with a radon concentration ranging from 100 Bq x m(-3) to 87 kBq x m(-3). It was found that in these conditions the signal registered by the TL detectors was proportional to the 222Rn concentration and the lowest limit of detection (LLD) was at a level of 100 Bq x m(-3). The proposed method can be used in large-scale, multi-site surveys aimed at screening for high levels of indoor radon concentration or for measuring ground radon exhalation rates.     

Effect of Grain Size on Radon Exhalation Rate in the Soils of Hassan District of Southern India

The radon concentration and radon exhalation rates were studied in 39 soil samples collected from Hassan district of southern India. LR-115 Type II solid-state nuclear track detector was used to measure the radon exhalation rate using the sealed can technique. The radon exhalation rate increases with a decrease in the soil grain size. A strong positive correlation was observed between the radon exhalation rate and effective radium content. The α index and annual effective dose were also determined.     

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.     

Validation of a geographic information system for the evaluation of the soil radon exhalation potential in South-Tyrol and Veneto, Italy

The PERS (soil radon exhalation potential) project was promoted by ANPA (Italian Environmental Protection Agency) together with the Università Cattolica del Sacro Cuore of Rome: the aim was to produce a geographic information system allowing the discovery of regions with different radon exhalation potential starting from some territorial knowledge. Some environmental measurements were carried out within this project in selected areas in South-Tyrol and Veneto. The measurement of radon in springwater and groundwater as well as in soil gas plays a decisive role for the validation of the algorithm for computing the PERS. Along with technical aspects, a possible use of the PERS method by the Regional Environmental Protection Agencies and by other agencies is discussed with the scope of identifying radon prone areas, as stated in the Italian 'Decreto Legislativo' 26 May 2000, n. 241. Moreover the forecasting power of PERS regarding indoor radon concentration is analysed.     

Radon Exhalation Rate Study of Sand Samples Collected from Sea Coast of Tirur,Kerala, India Using Track Etch Technique

The sand samples have been collecting from the sea coast (Unniyal beach) of Tirur of Malappuram district of Kerala state (India) by the grab sampling method. Radon exhalation rates have measured by “Sealed Can Technique” using LR-115 type II plastic track detector to estimate the health risk level in the environment. The value of radon activity varies from 444.44 to 2204.44 becquerel meter^?3 (Bq m^?3) with a geometric mean (G.M.)/standard deviation (S.D.) value of 1017.21 Bq m^?3/433.27. The value of mass exhalation rate for radon varies from 0.01 to 0.05 Bq kg^?1 h^?1 with a G.M./S.D. value of 0.024 Bq kg^?1 h^?1/0.010. The value of area exhalation rate for radon varies from 0.27 to 1.33 Bq m^?2 h^?1 with a G.M./S.D. value of 0.62 Bq m^?2 h^?1/0.26. The values of radon emanation ranged from 2.90?×?10^?3 to 2.98?×?10^?3 (%) with a G.M./S.D. value of 2.98?×?10^?3(%)/0.05. The alpha dose equivalent of the studied area is found and it varies from 0.68 to 1.66 milli sievert year^?1 (mSv yr^?1) with a G.M./S.D. value of 1.03 mSv yr^?1/0.24. Good positive correlation is observed between the effective radium content and area exhalation rate for sand samples. Therefore, the obtained result shows that this region is safe as for as the health risk effects of radium and radon exhalation rate are concerned.     

Anomalous indoor radon concentration in a dwelling in Qatif City, Saudi Arabia

An indoor radon survey was carried out recently in nine cities of Saudi Arabia using nuclear track detectors (NTD)-based passive radon detectors. The survey included Qatif City in the Eastern Province of Saudi Arabia, where 225 detectors were collected back successfully. It was found that the average indoor radon concentration in the dwellings was 22 +/- 15 Bq m(-3). However, one of the dwellings showed an anomalous radon concentration of 535 +/- 23 Bq m(-3). This finding led to a detailed investigation of this dwelling using active and passive techniques. In the active technique, an AlphaGUARD 2000 PRQ radon gas analyser was used. In the passive technique, CR-39 based passive radon detectors were used in all the rooms of the dwelling. Radon exhalation from the wall and the floor was also measured using the can technique. The active measurement confirms the passive one. Before placing the passive radon detectors in all the rooms of the two-storey building, the inhabitant was advised to ventilate his house regularly. The radon concentration in the different rooms was found to vary from 124 to 302 Bq m(-3). Radon exhalation from the floor and the wall of the room with the anomalous radon concentration was found to vary from 0.5 to 0.8 Bq m(-2) h(-1). These low radon exhalation rates suggest that the anomalous radon concentration is most probably due to underground radon diffusion into the dwelling through cracks and joints in the concrete floor.     

A theoretical and experimental investigation of spatial distribution of radon in a typical ventilated room

The aim of this work is to studying indoor radon distribution using the Finite Volume Method (FVM). This paper focuses on effects of exhalation from different sources (wall, floor and ceiling) and the ventilation profile on distribution the concentrations of radon indoor. The rate of radon exhalation and ventilation were measured and are used as input in FVM simulation. It has been found that the radon concentration is distributed in non homogeneous way in the room. The radon concentration is much larger near floor, and decreases in the middle of the room. The experimental validation was performed by measuring radon concentration at different locations in room using active and passive techniques. We notice that the results of simulation and experimental are in agreement. The annual effective dose of radon in the model room has been also investigated.     

The Closed-Can Exhalation Method for Measuring Radon

Results from closed-can radon exhalation experiments must be interpreted bearing the time-dependent radon diffusion theory in mind. A rapid change from the free to final steady-state exhalation rate will take place for all samples that are thin compared with the radon diffusion length. The radon gas accumulating in a closed can corresponds to a free exhalation rate only if the outer volume of air is much larger than the pore volume of the enclosed sample, or the thickness of the sample is much larger than the radon diffusion length.     

Simultaneous measurements of indoor radon, radon-thoron progeny and high-resolution gamma spectrometry in Greek dwellings

Simultaneous indoor radon, radon-thoron progeny and high-resolution in situ gamma spectrometry measurements, with portable high-purity Ge detector were performed in 26 dwellings of Thessaloniki, the second largest town of Greece, during March 2003-January 2005. The radon gas was measured with an AlphaGUARD ionisation chamber (in each of the 26 dwellings) every 10 min, for a time period between 7 and 10 d. Most of the values of radon gas concentration are between 20 and 30 Bq m(-3), with an arithmetic mean of 34 Bq m(-3). The maximum measured value of radon gas concentration is 516 Bq m(-3). The comparison between the radon gas measurements, performed with AlphaGUARD and short-term electret ionisation chamber, shows very good agreement, taking into account the relative short time period of the measurement and the relative low radon gas concentration. Radon and thoron progeny were measured with a SILENA (model 4s) instrument. From the radon and radon progeny measurements, the equilibrium factor F could be deduced. Most of the measurements of the equilibrium factor are within the range 0.4-0.5. The mean value of the equilibrium factor F is 0.49 +/- 0.10, i.e. close to the typical value of 0.4 adopted by UNSCEAR. The mean equilibrium equivalent thoron concentration measured in the 26 dwellings is EEC(thoron) = 1.38 +/- 0.79 Bq m(-3). The mean equilibrium equivalent thoron to radon ratio concentration, measured in the 26 dwellings, is 0.1 +/- 0.06. The mean total absorbed dose rate in air, owing to gamma radiation, is 58 +/- 12 nGy h(-1). The contribution of the different radionuclides to the total indoor gamma dose rate in air is 38% due to 40K, 36% due to thorium series and 26% due to uranium series. The annual effective dose, due to the different source terms (radon, thoron and external gamma radiation), is 1.05, 0.39 and 0.28 mSv, respectively.