Sensitivity of LR115 detector in diffusion chamber to Rn in the presence of Rn

Determination has been made of the sensitivity of LR115 type 2-track detectors (in units of m) to ²²²Rn, measured in the presence of ²²⁰Rn. Measurements have been made by means of a widely used diffusion chamber while Monte Carlo simulations have also been conducted. The experimentally derived sensitivities for ²²²Rn and ²²⁰Rn were found to be 0.470±0.022 and 0.486±0.042 m, respectively. For Monte Carlo simulations, the sensitivities to ²²²Rn gas were found to range from 0.618×10^–2 m (assuming that all ²¹⁸Po progeny decay before deposition onto the internal walls of the diffusion chamber) to 0.405×10^–2 m (assuming that all ²¹⁸Po progeny are deposited on the internal walls of the same containment vessel before decaying). The sensitivity to ²²⁰Rn gas of 0.465×10^–2 m found from Monte Carlo simulations agrees to within uncertainty with experimental findings. The experimentally derived sensitivity value for ²²²Rn indicates that 30% of the ²¹⁸Po progeny decay before deposition onto the internal walls of the diffusion chamber.     

Theoretical basis for long-term measurements of equilibrium factors using LR 115 detectors

In this paper, we propose a method to determine the equilibrium factor using a bare LR 115 detector. The partial sensitivities ρ_i of the LR 115 detector to ²²²Rn and its alpha-emitting short-lived progeny, ²¹⁸Po and ²¹⁴Po, were investigated. We first determined the distributions of lengths of major and minor axes of the perforated alpha tracks in the LR 115 detector produced by ²²²Rn, ²¹⁸Po and ²¹⁴Po through Monte Carlo simulations. The track parameters were calculated using a track development model with a published V function, by assuming a removed active layer of 6.54 μm. The distributions determined for different alpha emitters were found to completely overlap with one another. This implied equality of partial sensitivities for radon and its progeny, which was also confirmed through analytical considerations. Equality of partial sensitivities makes possible convenient measurements of the proxy equilibrium factor F_p, which is defined in the present work as (F₁+F₃) and is equal to the ratio between the sum of concentrations of the two alpha emitting radon progeny (²¹⁸Po+²¹⁴Po) to the concentration of radon gas (²²²Rn). In particular, we have found F_p=(ρ/ρ_itC₀)−1, where ρ (track/m²) is the total track density on the detector, ρ_i=0.288×10⁻² m, t is the exposure time and C₀ (Bq/m³) is the concentration of ²²²Rn. If C₀ is known (e.g. from a separate measurement), we can obtain F_p. The proxy equilibrium factor F_p is also found to be well correlated with the equilibrium factor between radon gas and its progeny through the Jacobi room model. This leads to a novel method for long-term determination of the equilibrium factor.     

Effects of heating on the emanation rates of radon-222 from a suite of natural minerals

The emanating power of radon provides information on the internal structure of a mineral and the radiation damage caused by the decay of ²³⁸U, ²³⁵U and ²³²Th (and their daughters) that are present in the mineral. The concentration of ²²²Rn in groundwater is primarily controlled by the concentration of U and Th in the underlying rocks, as well as the emanation coefficient for that particular rock. The variations in the emanation coefficient for ²²²Rn caused when subsurface rocks are subjected to tectonic forces results in changes in ²²²Rn in groundwater. Increased emanation rates of radon from a mineral grain can potentially alter the ²³⁸U–²⁰⁶Pb, ²³⁵U–²⁰⁷Pb and ²³²Th–²⁰⁸Pb chronological clocks.

We have measured radon emanation coefficients on a suite of minerals comprised of one oxide (uraninite), three silicates (thorite, zircon, and cerite) and one phosphate (monazite) at room temperature and after heating at 200°C and 600°C. Annealing of some of the nuclear tracks within a mineral significantly reduces the emanation rates of radon in these minerals, suggesting that the tracks created by decay events serve as conduit pathways for the release of ²²²Rn. Higher emanation rates of ²²²Rn from mineral grains that are surrounded by liquid as compared to air indicate that a major portion of the escaping ²²²Rn in air gets embedded into adjacent mineral grains and/or opposite walls of a pore.     

Radon in groundwaters from Guarany aquifer, South America: environmental and exploration implications

Groundwater and sandstone samples were analyzed for radon in Guarany aquifer, Paraná sedimentary basin, South America. The dissolved radon ranged between 3 and 3303 pCi/l, being lognormally distributed, with a modal value of 1315 pCi/l, and a median value of 330 pCi/l. ²²²Rn leakage experiments for sandstones yielded a theoretical value of 1390 pCi/l for ²²²Rn in water, showing that theoretical modeling can reliably be used to interpret laboratory and field data.     

A primary standard for activity concentration of 220Rn (thoron) in air

Due to the short half-life of Rn-220, a primary standard for activity concentration of Rn-220 (thoron) in air (i.e. a homogeneous reference atmosphere consisting of a certified activity in a certified volume) has been considered unachievable in the past.Traceability of Rn-222 reference atmospheres is achievable using radon gas activity standards (Picolo, 1996; Dersch, 1998) and standard volumes, and is an established method (Paul et al., 2002). For the short-lived radionuclide Rn-220 this procedure is not feasible, since no Rn-220 gas activity standard with a reasonable activity can be produced. This leads to a lack of traceability for measurements of Rn-220 activity concentration: only atmospheres monitored by reference instruments (i.e. secondary standards) are available. The new primary standard for the activity concentration of ²²⁰Rn developed by PTB now closes this gap in radon metrology.     

Unattached fraction and size distribution of aerosol-attached radon progeny in the open air

Unattached fractions of the radon progeny ²¹⁸Po and ²¹⁴Pb, size distributions for both unattached ²¹⁸Po and ²¹⁴Pb, and attached ²¹⁴Pb and ²¹⁴Bi, along with condensation nuclei (aerosol-particle concentrations), were measured in the open air of the city of El-Minia, Egypt. The measurements were performed with a wire-screen diffusion battery and a low-pressure Berner cascade impactor using standard methodologies. The results for parameters of derived distributions demonstrate that the distributions for the former (unattached ²¹⁸Po and ²¹⁴Pb) are nearly similar. The diffusion equivalent diameters (d_f) of ²¹⁸Po and ²¹⁴Pb were determined to be 1.4 and 1.55 nm with relative geometric standard deviations (σ_g) of 1.65 and 2.1, respectively. The latter distributions (attached ²¹⁴Pb and ²¹⁴Bi) are nearly identical. Most of the activities were associated with the aerosol particles of the accumulation mode. The mean activity median aerodynamic diameters (AMAD) of ²¹⁴Pb and ²¹⁴Bi have the same value of 380 nm but the relative geometric standard deviation of the log-normal distribution of ²¹⁴Pb shows a broader activity distribution than ²¹⁴Bi (σ_g = 2.2 for ²¹⁴Pb and σ_g = 2.05 for ²¹⁴Bi).     

Simultaneous determination of 222Rn and 220Rn exhalation rates from building materials used in Central Italy with accumulation chambers and a continuous solid state alpha detector: influence of particle size, humidity and precursors concentration.

A method to determine simultaneously the rates of 222Rn and 220Rn released from building materials quarried in Central Italy is presented. The method makes use of a continuous monitor equipped with a solid state alpha detector, in-line connected to a small accumulation chamber. The effects of chamber leakage and back diffusion on 222Rn free exhalation rate is evaluated. The influence of available exhalation surface, humidity content and precursors concentration on radon and thoron exhalation rates is investigated.     

The radon emanation power of building materials, soils and rocks

The ²²²Rn emanation power of building materials, soil and rock samples is determined by collecting exhalated radon on activated charcoal. Median values are 0.2 for dry soils and stones, 0.06 for sand, 0.025 for bricks, 0.006 for ceramic tiles, 0.008 for mineral slag and 0.3 for gypsum. The emanation power of soil rises with water content, in accordance with literature. For water content above 10% the emanation power of soil is about twice as high as for dry soil.     

Internal exposure from building materials exhaling 222Rn and 220Rn as compared to external exposure due to their natural radioactivity content

The main scope of this paper is to point out the importance of introducing radon and thoron exhalation measurements from building materials in the regulating frame. Currently (2009), such a regulation of this kind of exposure is not explicitly included in the Serbian regulating network. To this end, this work reports concentration measurements of ²²⁶Ra, ²³²Th and ⁴⁰K and radon and thoron exhalation rates from building materials used in Serbia. Following detailed analysis, it was noticed that both internal exposures to radon and/or thoron exhaling from building materials may exceed external exposures to their precursors contained therein.     

Age-dependent changes in oxygen tension,radiation dose and sensitivity within normal and diseased coronary arteries–Part A: Dose from radon and thoron

Purpose: There is mounting evidence that a significant fraction of radiation-induced mortality and years-life lost are non-cancerous in nature. This study quantifies the radon dose to the coronary artery walls, especially the intimal layer, vunerable to the development of atherosclerosis, and associated cardiovascular disease (CVD). Two accompanying papers determine the oxygen levels (Part B) in coronary arteries and the oxygen effect for radon and other exposures (Part C).

Materials and methods: The alpha-radiation dose to coronary artery walls was calculated from the proportion of inhaled radon (²²²Rn), thoron (²²⁰Rn) and their short-lived progeny, which was not deposited in the lung and passed into blood. Age- and gender-dependent morphology and composition for the wall layers of coronary arteries were developed from published data for a normal population and also for individuals with cardiovascular disease. The alpha particle dose to the coronary artery walls was evaluated taking account the diffusion of radon from blood and the solubility of radon-gas in tissues.

Results: Diseased arteries exhibited a moderate increase in the solubility of lipophylic radon (190%) in arteries with 88% luminal narrowing, as the high Rn solubility in fat was partially offset by the lower solubility in calcium deposits. The average worldwide dose rate to the diseased intimal layer from ²²²Rn and its short-lived progeny was estimated to be as high as 68 μSv y^?1 per 40 Bq m^?3 in air, whereas the corresponding dose rate from ²²⁰Rn per 0.3 Bq m^?3 in air was ≤0.1% in comparison. Gender had little influence on the dose.

Conclusion: The Rn dose to the coronary arteries is significant, but has a large uncertainty due to poor knowledge of Rn and its progeny concentrations in the body.     

Mitigation of the effective dose of radon decay products through the use of an air cleaner in a dwelling in Okinawa,Japan

Field measurements were conducted to assess the effects of an air cleaner on radon mitigation in a dwelling with a high radon concentration in Okinawa, Japan. The measurements included indoor radon concentration, individual radon progeny concentration, equilibrium equivalent concentration of radon (EECRn), unattached fraction, and size distribution of aerosol-attached radon progeny. These measurements were conducted in a 74 m³ room with/without the use of an air cleaner. The results showed that the mean radon concentration during the measurement was quite high (301 Bq m⁻³). The operation of air cleaner decreased the radon progeny activity concentration, EECRn and equilibrium factor by 33%, 57% and 71%, respectively, whereas the unattached fraction increased by 174%. In addition, the activity concentration of attached radon progeny in the accumulation mode (50–2000 nm) was obviously deceased by 42%, when the air cleaner was operated. According to dosimetric calculations, the operation of air cleaner reduced the effective dose due to radon progeny by about 50%.     

Seasonal levels of radon and thoron in the dwellings along southern coastal Orissa,Eastern India

Inhalation of radon (²²²Rn) and thoron (²²⁰Rn) are a major source of natural radiation exposure. Indoor radon–thoron study has been carried out in some dwellings of Ganjam district, southern coastal Orissa, India using LR-115 type II plastic track detectors. Seasonal variation of indoor radon and thoron shows high values in winter and low values in both summer and rainy. The inhalation dose lies in the range of 0–0.06 μSv h^?1 and is not high from those found elsewhere in India.     

The German thoron progeny chamber—Concept and application

Following completion of the project “Generation and characterisation of reference atmospheres of thoron decay products for the calibration of measuring devices for thoron decay products”, the Physikalisch-Technische Bundesanstalt (PTB) now operates a thoron progeny chamber in which ²²⁰Rn (thoron), ²²²Rn and its progenies can be made available under almost all ambient conditions. This allows all measuring systems to be calibrated under realistic climatic conditions with an accuracy unique worldwide.     

Accounting for 222Rn loss during oven drying for the immediate laboratory gamma-ray spectroscopy of collected soil samples.

Drying soil samples in an oven to remove water alters the 222Rn emanation rate. Measurements of the oven drying 222Rn emanation rate from soil were made with a continuous radon monitor and the degree of 222Rn disequilibrium was quantified by laboratory gamma-ray spectroscopy. This paper presents a disequilibrium correction where the 226Ra activity in oven-dried soil samples is inferred from immediate laboratory gamma-ray spectroscopy of 214Bi before 222Rn and its decay progeny reach secular equilibrium.     

Theoretical foundation for a simple method for simultaneous measurements of the unattached fraction and activity median diameter of attached radon progeny

Calculation of lung dose from established lung dosimetry models requires use of the unattached fraction of potential alpha energy concentration (PAEC) of radon progeny and the activity median diameter (AMD) of attached radon progeny, in addition to the total PAEC. In the present work, for indoor environments without the nucleation mode of aerosols, a method based on the wire screen penetration theory using two wire screens and a filter is proposed for simultaneous measurements of these two parameters. It is shown that the traditional wire screen method can overestimate or sometimes underestimate the unattached fraction, depending on the properties of the wire screen and the true unattached fraction. The present method eliminates such uncertainties.     

Primary and secondary measurements of 222Rn.

In the past few years, a primary measurement system has been established at the PTB allowing absolute measurements of 222Rn. The activity can be determined by counting the emitted alpha particles in a defined solid angle after condensing the radon at a cold point under vacuum conditions. This primary measurement system is connected to a solid 226Ra source, where 222Rn can be produced up to an activity of about 2MBq. After the measurement, radon can be completely transferred into a glass bulb or a stainless steel cylinder for use as a transfer standard. The results of the measurements, the uncertainties and the realization of the primary measurement system are described. For quality assurance and fast determination of radon activity, a secondary measurement system with an NaI(Tl) detector is also used. Together, both systems provide a reliable tool for the production of gaseous 222Rn activity standards with relative uncertainties of less than 1%.     

Indoor radon measurement with The Lucas cell technique

Rn-222 is the most important source of natural radiation and is responsible for approximately half of the received dose from all sources. Most of this dose is from inhalation of the Rn-222 progeny, especially in closed atmospheres. A Lucas cell technique, using a portable device, “PRASSI” (SILENA mod. 5S), for Rn-222 measurements inside the Centre for Radiation Protection and Radioecology (ZSR), Hannover University was used. The portable radon monitor PRASSI is suitable for radon gas continuous or grab sampling measurements with the scintillation cell technique. In recognition of the wide periodic variations in concentration, measurements were made daily for extended periods. At the same time, meteorological variables, such as temperature and humidity were observed so that their influence on radon levels could be evaluated. The radon average concentration during the year was about 55.9 Bq/m³ which gives rise to an annual effective dose 2.2 mSv y⁻¹. The radon concentration is within the limits prescribed by the International Commission for Radiation Protection. A detailed analysis of radon distribution with seasonal variation is presented.     

浙江部分地区室内222Rn和220Rn水平及剂量估算

目的 调查浙江省余杭区和三门县居室内²²²Rn、²²⁰Rn及其子体水平,明确其所致公众有效剂量。方法 采用固体径迹探测器测量余杭区和三门县两地居室中²²²Rn和²²⁰Rn浓度,探测器均放置于卧室或客厅,在不改变居民日常通风习惯情况下连续暴露6个月。结果 不同房屋类型室内²²²Rn和²²⁰Rn测定,均显示平房室内氡浓度最高。室内²²²Rn浓度与不同建筑年代无关(F =0.53, P >0.05),而室内²²⁰Rn浓度与不同建筑年代有相关性(F =3.56, P <0.05)。室内²²⁰Rn浓度未装修居室高于装修居室(t =2.33, P <0.05)。余杭区调查的居室内平均²²²Rn浓度为32.5 Bq/m³,²²⁰Rn为314.3 Bq/m³,所致有效剂量分别为0.88 和0.42 mSv;三门县调查的居室内平均²²²Rn浓度为26.8 Bq/m³,²²⁰Rn为399.5 Bq/m³,有效剂量分别为0.72 和0.53 mSv。结论 浙江余杭和三门室内²²²Rn浓度属正常天然本底水平,两地农村居室内²²⁰Rn浓度较高,²²⁰Rn及其子体的剂量贡献超过了²²²Rn及其子体引起的年有效剂量的50%。     

Radon, thoron and their progenies measured in different dwelling rooms and reference atmospheres by using CR-39 and LR-115 SSNTD.

Detection efficiencies of the CR-39 and LR-115 type II solid state nuclear track detectors (SSNTD) for alpha-particles emitted by radon, thoron and their decay products inside the air of different dwelling rooms and in various reference atmospheres were determined by using a Monte Carlo computer code. Alpha- and beta-activities per unit volume of air due to radon, thoron and their progenies were measured in the studied atmospheres by exploiting data obtained for the detection efficiencies of the SSNTD and measuring the resulting track density rates. Equilibrium factors between radon and its progeny and thoron and its daughters were evaluated in the studied atmospheres.     

Determination of 222Rn in natural water samples from health resorts in the Sudety mountains by the liquid scintillation technique.

A method involving a Wallac 1414 WinSpectral alpha/beta liquid scintillation counter for determining 222Rn in aqueous samples is described. Samples were collected from 23 springs and 4 taps in health resorts of the Klodzka valley in the Sudety mountains in Poland. Half of the investigated spring water samples were radon enriched with an activity concentration higher than 74 Bq/l. In the tap waters the radon concentration level is very low or below the lower limit of detection. Owing to the statistical nature of radioactive decay the uncertainty of the measurement was determined as the standard deviation of 222Rn activity. The method introduced is fast and simple and does not require a chemical sample preparation procedure.