Characterization of Radon Decay Products in a Domestic Environment

Field measurements of the concentration and activity size distribution of radon decay products were conducted in a one-story house located in the Princeton, NJ area. Radon concentration and particle number concentration were also measured. The concentration and activity-weighted size distribution of radon decay products were determined using a microcomputer-controlled, semi-continuous screen diffusion battery system with 6 parallel sampler/detector units. A condensation nuclei counter was used for the measurements of indoor panicle number concentration. Several measurements were made in the living room as well as more than one hundred measurements in the master bedroom of the Princeton house. Aerosols were generated from taking a shower, burning a candle, smoldering a cigarette, vacuuming, and cooking. Therefore, the influence of various indoor panicle sources on the behavior of radon decay products was investigated. With panicles generated from typical household activities, Potential Alpha Energy Concentration (PAEC) increases and the unattached fraction decreases. Larger panicles generated from cigarette smoke and cooking dramatically shifted most of the radon decay products into the attached mode (15-500 nm). With regard to the higher attachment rate, the size distributions of radon decay products remained stable for long periods of time after particle generation. On the other hand, aerosols produced from candle burning and vacuuming were much smaller, with an average attachment diameter of 15 nm. These panicles did decrease the unattached fraction, especially during the aerosol generation period. However, the size distributions of radon decay products returned to the background condition within ISO minutes after the end of particle generation. In these cases, the panicles had a higher deposition rate and a lower attachment rate. The dose of alpha radiation per unit radon concentration resulting from each of these aerosol conditions was calculated using the measured activity size distributions and the most recent James dosimetric model. These doses to basal cells at a breathing rate of 0.45 m³ hr¹ ranged from 3 to 14 μGy Bq^?1 hr while the dose to secretory cells at a breathing rate of 1.5 m³ hr¹ ranged from 13 to 77 μGy Bq^?1 hr for the various aerosol conditions.     

The control of radon progeny by air treatment devices

The effect of air treatment devices on the behaviour of radon decay products has been studied in laboratory conditions. An HEPA filter and an electrostatic precipitator were used. Both of the filters were found to decrease the equilibrium factor of daughters and increase the unattached fraction of decay products. In a clean air they also decreased the activity of unattached daughters. The effect of the devices on the health risk caused by radon progeny was estimated by dosimetric calculations. The results corresponding to different models show considerable discrepancy, mainly due to different assumptions about the influence of unattached decay products on the dose.     

Measurements of the equilibrium factor for 222Rn daughters in dwellings in India

As part of an ongoing project to assess the population dose from indoor radon and its daughters in India, a set of parallel measurements was made in more than 150 houses of different types to estimate indoor radon and progeny levels. Time-integrated solid state nuclear track detectors were employed for the measurement of radon concentration and potential alpha energy exposure level. From these values the equilibrium factor (F) between radon and its progeny was estimated for each house. An average F value of 0.39 was obtained.     

The use of reference levels in the dose limitation procedure

In this paper the use of reference levels for occupational exposures and for exposures to enhanced natural radiation are compared and related with the annual dose limits. It is concluded that the ICRP recommendations on action levels of indoor exposures to radon and thoron and daughter nuclides suggest a stricter dose limitation for occupational exposures than for exposure of the population to enhanced natural radiation.     

Indoor Radon Concentrations In Homes Of Sichuan Residents And The Dose To The Population Exposed To Radon And Its Daughters

This paper presents the results of indoor radon surveys in the Sichuan province of China. The indoor radon concentrations found using scintillation or the two-filter method, ranged from 1.0 Bqm^?3 to 170.2 Bqm^?3. The arithmetic mean concentrations of indoor radon and its progeny were 17.8 Bqm^?3 and 10.8 Bqm^?3 EER (2.9 m WL), respectively. A seasonal pattern of the maximum in winter and the minimum in summer was observed for radon and its progeny concentrations. The annual effective dose equivalent resulting from indoor and outdoor inhalation of radon progeny totalled 0.93 mSv. Of the 109 million people living in Sichuan, 3000-6800 may die annually from lung cancer induced by the inhalation of radon progeny.     

Using rainfall radar data to improve interpolated maps of dose rate in the Netherlands

The radiation monitoring network in the Netherlands is designed to detect and track increased radiation levels, dose rate more specifically, in 10-minute intervals. The network consists of 153 monitoring stations. Washout of radon progeny by rainfall is the most important cause of natural variations in dose rate. The increase in dose rate at a given time is a function of the amount of progeny decaying, which in turn is a balance between deposition of progeny by rainfall and radioactive decay. The increase in progeny is closely related to average rainfall intensity over the last 2.5 h. We included decay of progeny by using weighted averaged rainfall intensity, where the weight decreases back in time. The decrease in weight is related to the half-life of radon progeny. In this paper we show for a rainstorm on the 20th of July 2007 that weighted averaged rainfall intensity estimated from rainfall radar images, collected every 5 min, performs much better as a predictor of increases in dose rate than using the non-averaged rainfall intensity. In addition, we show through cross-validation that including weighted averaged rainfall intensity in an interpolated map using universal kriging (UK) does not necessarily lead to a more accurate map. This might be attributed to the high density of monitoring stations in comparison to the spatial extent of a typical rain event. Reducing the network density improved the accuracy of the map when universal kriging was used instead of ordinary kriging (no trend). Consequently, in a less dense network the positive influence of including a trend is likely to increase. Furthermore, we suspect that UK better reproduces the sharp boundaries present in rainfall maps, but that the lack of short-distance monitoring station pairs prevents cross-validation from revealing this effect.     

Coping with radon problem in a private house

In one of the 50 houses in which, during a national radon survey of 1000 homes in Slovenia, indoor radon concentrations exceeded 1000 Bq m⁻³, radon was further investigated. Except in the attic, elevated radon concentrations were found everywhere in the home, ranging from 0.5 to 12 kBq m⁻³. Applying ICRP 65 methodology, an annual effective dose in the range from 9 to 35 mSv was estimated for an inhabitant for different exposure scenarios. The radon problem was successfully mitigated and radon concentration reduced below 200 Bq m⁻³.     

Nanosize radon short-lived decay products in the air of the Postojna Cave

At two points in the Postojna Cave, short-term monitoring in summer and in winter of air concentrations of radon and radon decay products, equilibrium factor, unattached fraction of radon decay products (f_un), barometric pressure, relative air humidity in the cave and air temperature in the cave and outdoor has been carried out, with the emphasis on f_un. Dose conversion factors, calculated on the basis of f_un values obtained (ranging from 0.09 to 0.65) exceed 5 mSv WLM^− 1, by a factor of 11.5-14.0 in summer and of 3.0-4.0 in winter for mouth breathing, and 3.1-3.5 in summer and 1.5-1.7 in winter for nasal breathing.     

Approaches to the assessment of long term exposure to radon and its progeny

In recent years, a number of case-control epidemiological studies have taken place and others are in progress to evaluate the lung cancer risk to the general population from exposure to radon and its short-lived progeny in the indoor residential environment. While it is actually long term exposure over past decades to radon progeny by inhalation that dominates lung doses, for a number of practical reasons it is radon gas that is measured in these studies. Because the risk from radon and its progeny results from cumulative exposure over past decades rather than from contemporary exposure, it is necessary to reconstruct the historical exposures of subjects. A number of factors limit the accuracy of this approach of which the following are perhaps the most important: the mobility and residential history of the subjects; radon exposures elsewhere; and changes that may have occurred in the radon levels in current and previous residences. Measurement techniques to assist in making more direct retrospective assessments of radon exposure have appeared in the recent past and are the subject of this paper. These are based on the measurement of the long-lived radon progeny 210Po trapped in household artefacts such as glass or porous and spongy materials. In vivo measurements of skeletal 210Pb in exposed persons is also a method that is currently being investigated as a means to assess historical exposures to radon. The advantages and disadvantages of these methods are described here as well as their potential in future radon epidemiological studies.     

Air Filtration and Radon Decay Product Mitigation

Air cleaning as a means of mitigating the risks arising from exposure to indoor radon progeny has been evaluated in a single-family house in the north eastem US. using an automated, semi-continuous activity-weighted size distribution measurement system. The measurements included radon concentration, condensation nuclei count, and activity-weighted size distribution of radon decay products. Measurements were made in the house with and without an operating air filtration system and with various particle sources common to normal indoor activities operating. Aerosols were generated by running water in a shower, candle burning, cigarette smoking, vacuuming, opening doors, and cooking. Using a room model, the changes in attachment rates, average attachment diameters, and deposition rates of the unattached fraction with and without the air cleaning system were calculated. In the presence of active aerosol sources, the air filtration unit typically reduced the concentration of particles within the hour following the end of particle generation. After candle burning, cigarette smoking, and vacuuming in the bedroom, the reductions of PAEC by air filtration are about 60% with the air filtration system operating in the bedroom. During cooking in the kitchen, the reductions of PAEC in the bedroom with the air filtration system were about 40%. However, for all cases the dose reductions were smaller than the particle and PAEC reductions. For those particles that were generated within the bedroom, there was a 20% to 50% reduction in dose. In the case of cooking where the door was open and particles infiltrated from the rest of the house, the dose reduction was only 5% on average and appears to be insignificant. Thus, the dose reductions were h e r than the reductions in activity concentration, but there were no cases where the estimated dose actually increased.     

Modelling radon progeny concentration variations in thermal spas

Radon and its short-lived progenies (218Po, 214Pb, 214Bi and 214Po) are well known radioactive indoor pollutants identified as the major radiation burden component of the thermal spa users. Monitoring of short-lived progeny concentration is of great importance for short-term dose estimations both for bathers and working personnel. A prediction model of the short-lived progeny concentration variations was developed and applied on published data of the thermal spas of Lesvos Island. The physical procedures involved were modeled in a set of differential equations describing radon progeny concentration variations on the basis of radon measurements. Published daughter data were fitted on model predictions adjusting non-measured parameters, e.g. attachment and deposition rate constants for attached and unattached progenies. Attachment rate constants were estimated between 50 and 200 h-1 while the deposition rate constants between 0.25 and 5 h-1 for attached progenies and 0.5 and 170 h-1 for the unattached ones. In addition, unattached 218Po, 214Pb and 214Bi progenies were found to be shifted forward in respect to radon approximately 0.001 h, 0.05 h and 0.40 h respectively, while attached 218Po, 214Pb and 214Bi progenies 0.05 h, 0.45 h and 0.65 h respectively.     

A model to predict radon exhalation from walls to indoor air based on the exhalation from building material samples

In recognition of the fact that building materials are an important source of indoor radon, second only to soil, surface radon exhalation fluxes have been extensively measured from the samples of these materials. Based on this flux data, several researchers have attempted to predict the inhalation dose attributable to radon emitted from walls and ceilings made up of these materials. However, an important aspect not considered in this methodology is the enhancement of the radon flux from the wall or the ceiling constructed using the same building material. This enhancement occurs mainly because of the change in the radon diffusion process from the former to the latter configuration. To predict the true radon flux from the wall based on the flux data of building material samples, we now propose a semi-empirical model involving radon diffusion length and the physical dimensions of the samples as well as wall thickness as other input parameters. This model has been established by statistically fitting the ratio of the solution to radon diffusion equations for the cases of three-dimensional cuboidal shaped building materials (such as brick, concrete block) and one dimensional wall system to a simple mathematical function. The model predictions have been validated against the measurements made at a new construction site. This model provides an alternative tool (substitute to conventional 1-D model) to estimate radon flux from a wall without relying on ²²⁶Ra content, radon emanation factor and bulk density of the samples. Moreover, it may be very useful in the context of developing building codes for radon regulation in new buildings.     

State of the art of practical countermeasures and techniques and cost-benefit considerations

The doses and risks from exposure to high concentration of radon in indoor air are discussed in the perspective of other risks in modern life as an average for the population and as individual risk to the inhabitants of houses with very high concentration of radon. Interpretation and application of ICRP publication 39 are discussed. It is suggested that in existing structures with infiltration of radon from the soil remedial action be based on the principle of first trying to caulk obvious and accessible openings and, if this is not possible, installing a sub-floor depressurising system. Ventilation of the building is used only if these methods are not effective. Radon exhaling from building materials is controlled by ventilation. In new construction, materials with high activity of radium should not be used and the design should be modified to prevent infiltration of soil gas.     

Theoretical aspects of the design of a passive radon dosemeter

Some mathematical aspects of the development and design of a passive radon dosemeter are considered. In particular, a mathematical model is presented that is concerned with the gaseous diffusion of radon into a confined region bounded by a plastic material of known diffusion coefficient. The relationship between the time-integrated radon concentrations, inside and outside a sealed plastic container are derived. Estimates of the exposure of people to radon can be made using the time integrated radon concentration inside a calibrated container containing a CR-39 etched-track device. As a consequence of the analysis, it is possible to design a passive radon dosemeter that will be accurate, resistant to moisture and whose response will be independent of rapid variations in radon concentration. The possibility of using a container of this type for the measurement of diffusion coefficients is discussed.     

Simultaneous absorption of SO2 and NO from flue gas with KMnO4/NaOH solutions

This paper presents the experimental results of utilizing a flexible thin-film membrane as a passive barrier to radon gas diffusion. Nine commercially available membranes of various compositions and thicknesses were evaluated as retardant to radon gas diffusion. The radon gas concentration ratios across the thin-film membranes alone and in combination with an adjacent concrete sample (effective diffusion coefficient) were measured in a laboratory system with state-of-the-art instrumentation. An 8.89-cm diameter, 10.2-cm thick concrete sample of standard composition (w/c = 0.5 and cement:sand:gravel = 1:2:4) was used to simulate a basement and slab-on-grade foundation typical of Wisconsin. The radon gas transport characteristics of this concrete sample (porosity, permeability and diffusion) are documented. The experimentation has identified two superior flexible thin-film membranes that may be employed as effective barriers to radon gas diffusion. These include: Polyethylene Naphthalate (7.62 x 10(-5) m) and Polyethylene Terephthalate Glycol, PETG (7.62 x 10(-5) and 1.27 x 10(-4) m) which had average diffusion coefficients, D, of 4.10 x 10(-14) and 1.66 x 10(-14) m2 s(-1), respectively. Measurements of the effective membrane/concrete diffusion coefficient yielded a further average reduction in D of 98% for the Polyethylene Naphthalate and 96% for the PETG. Details of the experimental set-ups and procedures are described. The results of this investigation have shown that the application of an effective thin-film membrane adjacent to an intact concrete slab can significantly reduce the diffusion of radon gas entry. Therefore, the employment of a flexible thin-film membrane should be considered as a viable radon reduction technology method for residential new construction.     

Methods for measuring diffusion coefficients of radon in building materials

Two methods for determining the Rn-222 diffusion coefficient in concrete are presented. Experimentally, the flush and adsorption technique to measure radon release rates underlines both methods. Theoretically, the first method was developed for samples of cubical geometry. The radon diffusion equation was solved for boundary conditions imposing zero flux conditions successively on each side. In practice, a 100% effective covering would ensure this condition to be satisfied. The diffusion coefficient is then determined by comparing the computed and respectively measured normalized ratios of the radon release rates with respect to the rate corresponding to the open-boundaries (uncovered) specimen. As in practice, none of the investigated coverings showed to be effective in reducing radon exhalation, indicating that radon-tight sealing of surfaces is far from trivial, no clear conclusions could be drawn with respect to the diffusion coefficient. The second method can be applied to specimens that are first reshaped into hollow cylinders. A one-dimensional situation can be inforced by requiring that the flux vanishes at the two ends of the hollow cylinder. The theoretical and experimental ratios are again compared. In practice, the radon flux originates from a radon source enclosed inside the hollow cylinder, the effectiveness of the sealing being previously tested on an aluminum dummy of similar dimensions. The radon bulk diffusion coefficient for the used concrete sample resulted in a value of D = (4.6 +/- 0.4) x 10(-6) cm2 s(-1).     

天津地区地基土中氡含量的初步调查

在天津市域内选择适宜地点实地测量,从目前仅有的30余点实测资料统计,天津市土壤氡的平均浓度为8 572 Bq/m3。根据氡及其短寿命子体的形成、衰变、运移、富集规律以及实测结果得出,天津市域内的断裂经过地带以及凹陷地区,如蓟县、宁河、宝坻、武清、汉沽、市区及塘沽的海河沿线地区,氡浓度较高。     

Correlations between radon concentration and indoor gamma dose rate, soil permeability and dwelling substructure and ventilation

Correlations between radon concentration and indoor gamma dose rate, soil permeability and dwelling substructure and ventilation were studied using data from 84 low rise residential houses collected in an area of enhanced indoor radon concentration. The radon concentrations varied from 30 to > 5000 Bq m(-3). Cross-tabulation, comparisons of means and multiplicative models were used to test the significance of the effects. In this study a quite high percentage of explained variation R2 (68%) was found. It was found that the most important factors were the substructure and the permeability of the soil. Due to the rather small sample size and moderate variation in the uranium content of the bedrock of the area, the effect of the indoor gamma dose rate was not so prominent. The effects of ventilation habits and sleeping with open windows were not detected in this study.