大气降雨俘获空气中短寿命氡子体实验研究

为了研究降雨对空气中短寿命氡子体的清洗机制,设计了分别模拟大气降雨的水汽凝结过程和雨粒下降过程的两个实验装置,并进行了多次实验,实验水样采用低本底 能谱仪进行测量。实验结果表明:凝结水的短寿命放射性计数与本底相近,说明水汽凝结不能俘获短寿命氡子体。某一次自来水冲刷空气后获得了高出本底30.9% 的初始 计数,其半衰期为35.7 min,纯净水冲刷空气后获得了高出本底19.6%的初始计数,这些计数主要是由氡子体214Pb 和214Bi 引起的。可见,无论是自来水还是纯净水,它们冲刷空气后都能俘获短寿命氡子体,且半衰期和放射性核素种类均与雨水相似。这一实验结果充分说明:大气降雨的短寿命放射性不是在水汽凝结阶段而是在降落阶段对空气的冲刷获得的,是在降落过程中俘获了空气中的短寿命氡子体214Pb 和214Bi 而引起的。本次实验结果为降雨对空气中短寿命氡子体的冲刷清洗机制提供了最有力的证据。To investigate the underpinning mechanism of rainfall-scavenging of the atmospheric short-lived radon daughters, two experiments simulating water vapor condensing procedure and raindrop falling procedure were conducted. The radioactivity of the tested water was measured by low-background   γ spectrometry. The obtained results showed that the γ-ray counts of condensed water was on the same level as the background,which proved that water vapor condensation cannot trap short-lived radon daughters. In contrast, the initial γ-ray count of washout water (35.7 min half-life) was increased by 30.9% after washing the atmosphere with tap water. Similarly, the initial  -ray count of washout water was increased by 19.6% after washing the atmosphere with puri ed water. These counts originated mainly from radon daughters 214Pb and 214Bi. Obviously, both tap water and puri ed water can trap short-lived radon daughters when washing the atmosphere. Furthermore, the half-life and the kinds of radioactive nuclides in the washout water are similar to that in the rainfall water.These experimental results are able to ascertain that short-lived radon daughters in precipitation come mainly from scavenging (washout) and not from water vapor condensation within the cloud. It is in the process of falling that raindrops trapped short-lived radon daughters 214Pb and 214Bi. The obtained results as demonstrated here provide a powerful evidence for understanding the washout mechanism of short-lived radon daughters from theatmosphere by rainfall.     

理想条件下氡及其子体垂直运移实验数据分析

对氡及其子体的长距离运移实验数据进行了分析,发现利用氦氡团簇解释氡的快速向上运移,α粒子的数量远远不够.如果假定氡有很强的从空气中吸附氦气的能力,从而获取足够的氦组成氦氡团簇垂直运移,则又与相关实验中加有氦气后氡及其子体向上、向下运移概率与自然状态相同的结论矛盾.提出氦氡团簇可能不是氡具有快速向上运移能力的主要原因,氡的快速向上运移能力可能另有更深层次的原因,有待进一步深入研究. 关键词： 氡 垂直运移 氦氡团簇     

理想条件下氡及其子体运移新理论及其运移方程

论述了氡及其子体运移的新理论,认为氡及其子体在垂直方向的运移机理是氡及其子体经α 衰变所放出的α粒子减速后，将成为He核，He核可与氡及其子体形成团簇，当团簇在介质中 所受的浮力大于其重量时，团簇便能自行向上运移，否则团簇就向下运移.在此理论基础上 建立了氡运移理论分布方程，并对运移方程进行了验证. 关键词： 团簇 氡运移 运移方程     

西藏羊八井ARGO实验大厅内氡浓度的变化规律研究

利用Lomb-Scargle傅里叶变换法和统计折叠周期分析法,对2009年8月到2011年10月期间西藏羊八井国际宇宙线站的ARGO实验大厅内的氡浓度监测数据进行研究。结果表明,实验大厅内的氡浓度具有1日和半日周期变化规律,其中以1日周期变化为主。在1 d中氡浓度的平均值为(567.2±1.1)Bq/m3,变化幅度为(79.0±1.4)Bq/m3,北京时间约11:20时达到最大,北京时间约23:20达到最小。分析还表明,在一年中月平均浓度的最小值出现在6月份,而较大值出现在下半年的某些月份,每月的日变化幅度和浓度最大时的时间多变。这些结果对环境氡的浓度变化规律及其相关理论模型研究具有重要的意义,同时对西藏地区居住环境监测评价提供了重要的参考。     

温度及围护通风对独头巷道氡浓度分布的影响

根据计算流体力学以及氡的物理性质,建立具有硐室的独头巷道内氡的三维稳态传输模型,采用Fluent软件求解控制方程,使用UDF实现巷道内壁氡的析出和氡的衰变,得到独头巷道内的风场结构及氡的浓度分布.研究发现:通风量一定时,温度对氡的浓度影响显著,巷道内温度越高,巷道各处氡浓度越高.整个巷道硐室氡浓度最大,相比于修建防氡围...     

地下坑道周围山体内氡运移力学解析

基于连续介质力学原理,建立氡在地下坑道周围山体内运移的-维径向对称模型,分析在浓度扩散和气体渗流条件下,坑道周围山体内氡浓度分布,并给出氡浓度的解析表达式.用有效运移距离的概念,定量描述对坑道内氡浓度有影响的山体范围,给出有效运移距离和有效孔隙率、比渗流速度之间的关系式,同时给出坑道壁面上氡析出率的表达式.     

地球,空气,氡和住宅

本世纪核技术在医疗、能源和武器等方面的应用加深了人们对有害辐射效应的了解.很多人已认识到,核武器试验和核电站正常运行所产生的辐射远低于来自宇宙射线和地球的自然辐射.在放射医学上,为了诊断和治疗所采用的辐射剂量才可能与自然辐射相接近. 自然辐射产生的年平均辐射剂量约为lmSv(millsievert,用传统单位表示为0.1rem2)),并随地点的不同而有所变化.人体除受到自然辐射外,更重要的是受到由 Rn222衰变到Pb210的过程中放射出的a射线对肺部区域的辐射. 在我们呼吸的空气中含有放射性元素氡Rn222,由它衰变产生了短寿命的放射性核素钋.人…     

CAEP FEL-THz低温系统氦气纯化方法研究

鉴于氦的稀缺性,中国工程物理研究院高平均功率太赫兹大型科研装置(CAEP FEL-THz)低温系统中,必须除去回收粗氦中的杂质,以实现循环再利用。文中通过对常规氦气分离方法的比较和对低温系统低纯度氦气中所含杂质成分的分析,提出了一种基于高压低温冷凝分离和吸附的氦气纯化方法,旨在将低纯度氦气的纯度提升至满足低温系统使用的要求。据此,初步设计了一套氦气纯化系统,介绍了其工艺流程和主要部件。     

基于白光中子源的197Au中子辐射俘获截面测量及共振参数分析

中子辐射俘获反应在反应堆运行、核装置设计及核天体物理研究中起重要的作用. 4πBaF₂探测装置有着高时间分辨能力、低中子灵敏度、高探测效率等优点,适合开展中子辐射俘获反应截面数据的测量.中国原子能科学研究院核数据重点实验室建立了伽马全吸收装置(Gamma total absorption facility, GTAF),该装置用28块六棱BaF₂晶体和12块五棱BaF₂晶体构成了外径25 cm,内径10 cm的球壳,覆盖了95.2%的立体角.利用GTAF在中国散裂中子源Back-n束线上,测量了197Au(n, γ)的反应截面数据.测量数据通过能量筛选、PSD方法、晶体多重性筛选进行了初步本底扣除,随后结合对^natC及空样品的测量数据对本底进行了分析及扣除,获得了197Au俘获反应的产额,利用SAMMY程序拟合得到了¹⁹⁷Au在1—100 e V的共振能量、中子共振宽度和伽马共振宽度参数.实验测量结果与ENDF/B-VIII.0数据库符合良好,其共振参数存在一定差异,分析原因可...     

真空条件下低温红外辐射测量技术研究

针对红外载荷在轨服役期间低温目标的红外辐射探测需求,提出一种真空条件下的低温红外辐射测量方案,并研制了测量装置。测量装置主要由低温红外光学系统、低温机械结构、低温红外探测系统及微弱信号处理系统构成。低温红外辐射经过光学系统会聚到探测器像面,锁相放大器利用相干检测技术将目标信号提取,完成低温红外辐射的测量。测量装置研制完成后,在真空仓内使用标准黑体辐射源,在198 K～423 K温度范围内进行了低温红外辐射定标试验,取得了有效的试验数据,测量不确定度在5%以内。该文提出的真空条件下低温红外辐射测量技术可为在轨空间红外载荷低温红外目标探测设计提供重要数据支撑。     

Radon exhalation studies in building materials using solid-state nuclear track detectors

Indoor radon has been recognized as one of the health hazards for mankind. Building materials constitute the second most important source of radon in dwellings. The common building materials used in the construction of dwellings are studied for radon exhalation rate. The ‘Can’ technique using LR-115 type-II solid-state nuclear track detector has been used for these measurements. The radon exhalation rate in these samples varies from 4.75 m Bq m⁻² h⁻¹ (0.14 m Bq kg⁻¹ h⁻¹) for limestone to 506.76 m Bq m⁻² h⁻¹ (15.24 m Bq kg⁻¹ h⁻¹) for soil.     

Radon activity measurements around Bakreswar thermal springs

²²²Rn concentrations were measured in the bubble gases, spring waters, soil gases and in ambient air around the thermal springs at Bakreswar in West Bengal, India. This group of springs lies within a geothermal zone having exceptionally high heat flow about 230 mW/m², resembling young oceanic ridges. The spring gas has a high radon activity (～885 kBq/m³) and is rich in helium (～1.4 vol. %) with appreciably large flow rate. The measured radon exhalation rates in the soils of the spring area show extensive variations from 831 to 4550/mBqm² h while ²²²Rn concentrations in the different spring waters vary from 3.18 to 46.9 kBq/m³. Surface air at a radius of 40 m around the springs, within which is situated the Bakreswar temple complex and a group of dwellings, has radon concentration between 450 and 500 Bq/m³. In the present paper we assess the radon activity background in and around the spring area due to the different contributing sources and its possible effect on visiting pilgrims and the people who reside close to the springs.     

Radon exhalation rate in Chhatrapur beach sand samples of high background radiation area and estimation of its radiological implications

Chhatrapur beach placer deposit, situated in a part of the eastern coast of Orissa, is a newly discovered high natural background radiation area (HBRA) in India. The sand samples containing heavy minerals, were collected from Chhatrapur region by the grab sampling method at an interval of ∼1 Km. Radon exhalation rates were measured by “Sealed Can Technique” using LR-115 type type II in the sand samples containing heavy minerals collected from the beach. Radon activity is found to vary from 1177.1 to 4551.4 Bq m-3 whereas the radon exhalation rate varies from 423.2 to 1636.3 mBq m⁻²h⁻¹ with an average value of 763.9 mBq m⁻²h⁻¹. Effective dose equivalent in sand samples estimated from exhalation rate varies from 49.9 to 193.0 μSv y⁻¹ with an average value of 90.1 μSv y⁻¹. From the activity concentration of ²³⁸U, ²³²Th and ⁴⁰K computed radium equivalent is found to vary from 864.0 to 11471.5 Bq kg⁻¹ with an average value of 3729.0 Bq kg⁻¹. External hazard index, H_ex range from 2.3 to 31.0 with a mean value of 10.1, which is quite high. This value supports the conclusion based on high mean absorbed gamma dose rate in air due to the naturally occurring radionuclides as 1627.5 nGy h⁻¹. A positive correlation has been found between U concentration and radon exhalation rate in the sand samples. The use of sand as construction material may pose a radiation risk to ambient environment.      

Radon decay products attached to clothes in a nuclear laboratory

A whole body counter determined the presence of radioactivities up to 21.8 kBq for ²¹⁴Bi and up to 18.7 kBq for ²¹⁴Pb attached to clothes of workers in a Nuclear Research Laboratory. A radon survey reveals that 80% of the monitoring areas have radon concentration values lower than 500 Bq m⁻³, while 10% of the sampling points with values bigger than 1 kBq m⁻³ correspond to the workers mentioned above. By exposing samples of 0.04 m² clothes in a radon chamber, it was observed that radon decay products ²¹⁴Bi and ²¹⁴Pb were attached to them with an activity of 315–618 Bq per each kBq m⁻³ of Rn concentration additionally, fibres characterised with a lower electrostatics build up showed the lower attachment.     

In situ measurements of radon levels in water and soil and exhalation rate in areas of Malwa belt of Punjab (India)

Radon concentration levels in water and soil gas from 36 locations pertaining to some areas of Malwa region of Punjab have been measured on an in situ basis using a continuous active radon detector (AlphaGuard, Model - PQ 2000 PRO, Genitron instruments, Germany). Exhalation rate measurements have also been carried out at these places, using a closed-circuit technique. The radon concentrations in soil and water varied from 1.9 to 16.4?kBq?m(-3) and 5.01 to 11.6?kBq?m(-3), respectively. The exhalation rate (E (Rn)) ranged between 7.48 and 35.88?mBq?m(-2)?s(-1) with an average value of 18.17?mBq?m(-2)?s(-1). Annual dose rates have been calculated for water radon concentrations. The minimum to maximum values of dose rates were found to be 13.42-31.08?μSv?y(-1). The recorded values of radon concentration in water are within the safe limit of 11?Bq?l(-1) recommended by the US Environment Protection Agency [National Research Council, Risk Assessment of Radon in Drinking Water (Academy Press, Washington, DC, USA, 1999)]. All measurements were made in similar climatic and environmental conditions to ensure minimal variations in meteorological parameters. An intermediate correlation coefficient (0.5) was observed between radon exhalation rates and soil gas values.     

Radon in soil and its concentration in the atmosphere around Mysore city, India

Radon concentration in soil-gas and in the atmospheric air has been studied around Mysore city (12°N and 76°E) using Solid State Nuclear Track Detectors. The radon in soil-gas is found to be higher at a depth of 1 m than at a depth of 0.5 m from the ground surface. The higher radon concentration in soil was observed near Chamundi Hills and Karigatta village with average values of 5.94 kBq.m⁻³ and 5.32 kBq.m⁻³ at 1 m depth from the ground surface. Seasonal variations in radon in soil gas shows that, the concentration is lower in summer with an average value of 0.60 kBq.m⁻³ and higher in monsoon season with an average value of 4.70 kBq.m⁻³. Estimation of ²²⁶Ra in soil at these locations is also made using HPGe detector. The activity of ²²⁶Ra, varies from 4.82 to 74.23 Bq.kg⁻¹ with an average value of 32.11 Bq.kg⁻¹. Radon concentrations in soil-gas shows good correlation with the activity of ²²⁶Ra in soil with a correlation coefficient of 0.76     

Ion-pulse ionization chamber for direct measurement of radon concentration in the air

A large-volume (24.8l in total volume, 16.8l in fiducial volume) multiwire pulse ion collection ionization chamber was examined as a detector of α particles from radon decays in the air inside the chamber. The possibility of obtaining spectrometric information from slow ion pulses was tested. An energy resolution of 3.9% for 5.49-MeV α particles was obtained in preliminary measurements. It was shown that a detector of this kind could be used for direct measurements of radon activities in flowing air at a level less than 1 Bq/m³. A radon concentration at a level of 10 Bq/m³ can be measured with an accuracy better than 10 % for a counting time of 10³ s. The detector will be used for continuous accurate monitoring of the ²²²Rn concentration in the air of low-background laboratories.     

The BiPo low-background detector project

A low-background detector designed to search for weak radioactive pollution by ²⁰⁸Tl and ²¹⁴Bi in thin samples of a large area is described. The samples are 12-m² source foils made of ⁸²Se or ¹⁵⁰Nd enriched isotopes. Such samples are planned for use in investigating neutrinoless double β decay in the SuperNEMO experiment. The principle of the detector operation is based on registering the delayed β-α coincidence from the uranium and thorium radioactive chains. The sensitivity of the detector is planned to be at the level of ²⁰⁸Tl < 2 μBq/kg and ²¹⁴Bi < 10 μBq/kg. Alternate versions of the detector are described. The first results obtained by the prototype detector, operated in the Frejus Underground Laboratory in France, are presented.     

Radon in groundwater of eastern Doon valley, Outer Himalaya

The radon content in water may serve as a useful tracer for several geohydrological processes. The hydrodynamic factor, presence of radium in host rocks, as well as the soil porosity and permeability control its concentration in groundwater. In order to understand the factors that control the occurrence of radon in groundwater of Doon valley in Outer Himalaya, a total of 34 groundwater samples were collected from handpumps and tubewells covering three hydrogeological units/areas in the eastern part of Doon valley. Radon variation in tubewells and handpumps varies from 25.4±1.8 to 92.5±3.4 Bq/l with an average of 53.5±2.6 Bq/l. A significant positive correlation between radon concentration and depth of the wells was observed in the Doiwala–Dudhli and Jolleygrant areas suggesting that radon concentration increases with drilling depth in areas consisting of sediments of younger Doon gravels, whereas samples of the Ganga catchment show negative correlation. The high radon levels at shallower depths in the Ganga catchment (consisting of fluvial terraces of Ganga basin) indicate uranium-rich sediments at shallower depth.     

Uranium, radium and radon exhalation studies in some soil samples using plastic track detectors

Radium concentration and radon exhalation rate have been measured in soil samples collected from some areas belonging to upper Siwaliks of Kala Amb, Nahan and Morni Hills of Haryana and Himachal Pradesh states, India using LR-115 type II plastic track detectors. Uranium concentration has also been determined in these soil samples using fission track registration technique. Radium concentration has been found to vary from 5.30 to 31.71 Bq.kg⁻¹, whereas uranium concentration varies from 33.21 to 76.26 Bq.kg⁻¹. The radon exhalation rate in these samples varies from 216.87 to 1298.00 mBq.m⁻²hr⁻¹ (6.15 to 36.80 mBq.kg⁻¹.hr⁻¹). Most of the samples have uranium concentration above the worldwide average concentration of 35 Bq.kg⁻¹. A good correlation (R ² = 0.76) has been observed between uranium concentration and radon exhalation rate in soil. The values of uranium, radium and radon exhalation rate in soil are compared with that from the adjoining areas of Punjab.