Radon-222 concentrations and decay-product equilibrium in dwellings and in the open air

Results are presented of measurements of the activity concentrations of 222Rn and its short-lived decay products and the 212Pb/212Bi concentrations in more than 200 dwellings in West Germany and in the open air. For more than 130 measurements of the equilibrium factor F in dwellings the median value was found to be 0.3. Measurements of F in the open air under various conditions resulted in a mean value of about 0.4. The results of the investigations showed that indoors F depends only slightly on ventilation, indoor 222Rn concentration and other parameters. The equilibrium factor F in the open air, however, was found to depend on meteorological conditions. Empirical correlations from the data obtained for the daughter/222Rn concentration ratios were derived to provide relations for the prediction of the individual daughter product concentrations at a measured 222Rn level. It was established that the daughter/222Rn concentration ratios for indoor air do not change within the range of 222Rn concentrations investigated (1-370 Bq X m-3). These relations, however, are not valid for the daughter/222Rn concentration ratios in outdoor air. The correlations derived further suggest that the individual daughter product concentrations may be assessed with sufficient accuracy by only measuring the 222Rn concentrations. Thus the daughter ratios obtained in this way should enable good estimates of the lung dose for members of the public due to inhalation of the short-lived 222Rn daughters and the dose contribution of the individual 222Rn-daughter products.     

Indoor 222Rn measurements in the region of Beijing, People's Republic of China

Passive integrating activated C detectors were used to study the regional distribution and temporal variation of 222Rn in indoor air in dwellings in the Beijing region. Measurements were made in 537 dwellings, which were either detached houses or multi-family apartments. The city-wide study was completed in 1985. The distributions are approximately log-normal with 90% of the dwellings having 222Rn levels less than 60 Bq m-3. The weighted average 222Rn concentration has been found to be 22.4 Bq m-3. Averages for detached houses and multi-family dwellings are 25.9 and 15.2 Bq m-3, respectively. Assuming an equilibrium factor of 0.5 and an occupancy factor of 0.8, the average equilibrium equivalent concentration of 222Rn progeny is 11.2 Bq m-3 and the annual average effective dose equivalent is 1.1 mSv.     

Preliminary experiences with 222Rn gas in Arizona homes

Results of a survey of 222Rn gas using four-day charcoal canister tests in 759 Arizona homes are reported. Although the study was not random with respect to population or land area, it was useful in identifying areas at risk and locating several homes having elevated indoor 222Rn air concentrations. Approximately 18% of the homes tested exceeded 150 Bq m-3 (4 pCi L-1), with 7% exceeding 300 Bq m-3 (8 pCi L-1). Several Arizona cities had larger fractions of homes exceeding 150 Bq m-3 (4 pCi L-1), such as Carefree and Cave Creek (23%), Paradise Valley (30%), Payson (33%), and Prescott (31%). The Granite Dells and Groom Creek areas of Prescott had in excess of 40-60% of the houses tested exceeding 150 Bq m-3 (4 pCi L-1). Elevated 222Rn concentrations were measured for a variety of home types having different construction materials. Private well water was identified as a potentially significant source of 222Rn gas in Prescott homes, with water from one well testing over 3.5 MBq m-3 (94,000 pCi L-1). A 222Rn concentration in air exceeding 410,000 Bq m-3 (11,000 pCi L-1) was measured using a four-day charcoal canister test in a house in Prescott which had a well opening into a living space. Additional measurements in this 150-m3 dwelling revealed a strikingly heterogeneous 222Rn concentration. The excessive 222Rn level in the dwelling was reduced to less than 190 Bq m-3 (5.2 pCi L-1) by sealing the well head with caulking and providing passive ventilation through a pipe.     

Radon-222 levels in New York State homes

Results are presented from a statewide survey that measured annual 222Rn concentrations in over 2000 single-family, owner-occupied homes in New York state. The participants were selected by a random-digit-dialing telephone interview approach developed by Mitofsky-Waksberg which allows inferences to be made from the sample to the statewide population. After completing a telephone questionnaire and agreeing to have their homes monitored, eligible households were mailed alpha-track detectors with instructions to place one detector in the main living area for 2 mo (during the winter heating season), a second in the main living area for 1 y, and a third in the basement (if applicable) for 1 y. The statewide median concentration for the heating-season, living-area readings was 31.6 Bq m-3, with a median of 24.0 Bq m-3 for the annual living-area readings and 51.8 for the annual basement readings. For the state, approximately 95% of the living-area concentrations and 86% of the basement concentrations were below 148 Bq m-3 (4 pCi L-1). In addition, only 1.4% of the readings in the basement were above 740 Bq m-3 (20 pCi L-1).     

Indoor Rn levels in different geological areas in Switzerland

The distribution of indoor Rn concentrations in different geological areas in Switzerland was studied using passive alpha-track detectors. Measurements involving a sample of 400 single-family homes were made in the cellar, on the ground floor and the first floor, respectively. On the basis of a pilot survey, the country was divided into four zones in which the Rn distribution in houses was analyzed separately. The indoor exposure to Rn and Rn decay products is quite variable from region to region. The geology of the different areas was found to be an important factor in determining the mean value Rn levels. In the basin north of the Alps, where the population centers are located, a median Rn gas level of 47 Bq m-3 for the living area was found. The arithmetic mean value of 60 Bq m-3 in this region leads to an annual effective dose equivalent of about 1.8 mSv. For the population living in alpine areas, an arithmetic mean value exceeding 200 Bq m-3 will lead to an annual effective dose equivalent in the range of 6 mSv. The estimated exposure to Rn and Rn decay products for the upper one-percentile of the homes in the most affected alpine region even exceeds the annual limit of 50 mSv effective dose equivalent for occupational exposure.     

An electrostatic integrating 222Rn monitor with cellulose nitrate film for environmental monitoring

This paper describes a new type of electrostatic integrating 222Rn monitor designed for the environmental 222Rn monitoring. The window area of the monitor was selected to make the exchange rate optimal. The collecting electrode was positioned on the basis of calculating the internal electric field. A drying agent, P2O5, was placed in the bottom of the monitor, since the collection efficiency of 218Po+ atoms depends on the humidity of the air. The monitors have been calibrated against known 222Rn exposures. The detection limit is 1.2 Bq m-3 for an exposure time of 2 mo. In a small survey, annual mean 222Rn concentrations between 3.7 and 9.5 Bq m-3 in outdoor air and between 6.4 and 11.9 Bq m-3 in indoor air were measured.     

Indoor 222Rn measurements in Sweden with the solid-state nuclear track detector technique

Measurements of the indoor radon and radon daughter concentrations were performed in several thousand Swedish houses during the years 1979-1984 with the solid state nuclear track detector technique (SSNTD technique). The investigation focused on structures containing building materials of light-weight concrete with enhanced amounts of U. The detectors used nuclear track films exposed for 1 mo. The film basically measures total airborne alpha activity but may be calibrated in units of EER in an environment with known 222Rn and daughter concentrations. (EER is here the equilibrium equivalent concentration of Rn with the equilibrium factor F = 0.5.) The investigation was performed in various municipalities in collaboration with the local public health and environmental authorities. The investigation included 6700 individual measurements in detached (single-family) houses as well as in apartment houses. A small percentage of the dwellings exhibited Rn daughter concentrations (EER) exceeding 400 Bq m-3. It was found in detached houses that the concentrations were higher in the basement floor than in the entrance floor of a house. The Rn daughter values in the bedrooms were similar to values in any other room (mainly on the same floor) of the structure. The Rn daughter levels in apartment houses were lower than in single-family houses. The seasonal variations of the Rn daughter levels are presented and show that the levels in summertime are approximately equal to the levels in the winter.     

Determining the charged fractions of 218Po and 214Pb using an environmental gamma-ray and Rn detector

The rate of 218Po and 214Pb atoms collected electrostatically inside an environmental gamma-ray and 222Rn detector (EGARD) was measured. These measurements were used to directly infer the charged fraction of 218Po and to calculate the charged fraction of 214Pb. Thirty-two percent of the 218Po was collected electrostatically using approximately -1500 V on a 2.54 cm diameter Mylar covered disc inside a vented A1 EGARD of 1 L volume. About 91% of the 214Pb is collected electrostatically under the same conditions. The measurements were performed in a calibrated 222Rn test chamber at the Environmental Measurements Laboratory (EML) using the Thomas alpha-counting method with 222Rn concentrations averaging about 4300 Bq m-3. The atomic collection rates were used with other measured quantities to calculate the thermoluminescent dosimeter (TLD) signal acquired from EGARD for exposure to 1 Bq m-3 of 222Rn. The calculations account for 222Rn progeny collection using a Teflon electret and alpha and beta detection using TLDs inside EGARD. The measured quantities include the energies of 218Po and 214Po alpha-particles degraded by passage through the 25 microns thick electret. The TLD responses to these alpha- and beta-particles with an average energy approaching that obtained from the combined spectra of 214Pb and 214Bi were also measured. The calculated calibration factor is within 30% of the value obtained by exposing EGARD to a known concentration of 222Rn. This result supports our charged fraction estimates for 218Po and 214Pb.     

Radon-222 on the island of Hawaii

The island of Hawaii, like other locations in a marine environment, has low levels of atmospheric 222Rn. The low concentrations of 222Rn and its decay products result from a low average flux density of 9.8 mBq m-2 s-1, the mixing of marine air from the Pacific having a 222Rn concentration of only 0.04 Bq m-3 with air from over the island, and the decay of 222Rn as it is transported in air masses across the Pacific primarily from the Asian continent. The overall mean concentration over the Island The overall mean concentration over the Island was found to be 0.44 Bq m-3 compared with a figure of about 8 Bq m-3 for air over continents. A consideration of the island as a source of 222Rn must take into account the relatively low average flux density associated with the lava fields and accompanying thin soils. The 222Rn formed from the U and 226Ra present in the lava cannot escape to the atmosphere. The deep agricultural soils, on the other hand, provide relatively high flux densities. When the areas of the soil types are taken into account, the exhalation for the lava fields, thin organic soils, and deep agricultural soils were 0.25, 1.7, and 32 MBq s-1, respectively. Measurements of indoor 222Rn on the island indicate levels of approximately 25 Bq m-3 which is appreciably lower than 40 Bq m-3 taken as an average for indoor levels on the mainland. Based on an assumed indoor occupancy level of 0.8, the effective dose equivalent for inhaled 222Rn and its decay products on Hawaii is 1.2 mSv y-1. This is only a little more than one-half of that for a resident of the continental United States who is estimated to receive an effective dose equivalent of 2 mSv y-1. The relatively low effective dose equivalent for the population on the island may have interesting effects in comparison with people living in areas where the inhaled dose from 222Rn is much higher.     

Seasonal variation of indoor Rn at a location in the southwestern United States

Radon-222 concentrations have been measured in 12 homes typical of a small town in the southwestern United States. Nine of the houses, in which both summer and winter data are available, have an annual mean of 63 +/- 18 Bq m-3 (1.7 +/- 0.5 pCi L-1) and a range of 41 to 96 Bq m-3 (1.1 to 2.6 pCi L-1). These results were obtained with passive Rn dosimeters using polycarbonate nuclear track detector foils. The overall results fall slightly above the middle of the range of values obtained in other studies in the United States. Winter levels clearly exceed summer by a factor of from two to three. This result is attributed primarily to wide use of evaporative air conditioners for daytime cooling in the summer together with the fact that doors and windows are left open frequently during evening and nighttime hours. Both practices enhance the exchange of outdoor air with indoor air contributing to a decrease in the indoor Rn levels during the summer season. Room-to-room differences were evident during the winter season only. Bedrooms and bathrooms were generally higher in Rn than kitchens and living rooms but by only about 25%. The two adobe houses in the group showed higher Rn concentrations during the winter season than did those of frame-stucco, concrete, or cinder block construction. Dose equivalent calculations yielded a mean figure of 0.29 WLM y-1 for typical occupancy patterns in these New Mexico houses.     

Indoor 222Rn levels in New York State, North Carolina, and South Carolina

Results are presented from approximately 9000 Rn measurements made in New York state, North Carolina, and South Carolina. The estimated statewide geometric mean concentrations were 28.1 Bq m-3 and 55.8 Bq m-3 for basements in New York state, 27.5 Bq m-3 for living rooms and 108.9 Bq m-3 for basements in North Carolina, and 25.0 Bq m-3 for living rooms in South Carolina.     

Correlation among the terrestrial gamma radiation, the indoor air 222Rn, and the tap water 222Rn in Switzerland

The external gamma radiation and the indoor air Rn (222Rn) concentration were measured in 55 houses of the South East Grisons, the Urseren valley, and the Upper Rhine valley (crystalline subsoils) and in 39 houses of the Molasse basin and the Helvetic nappes (sedimentary subsoils). In homes located on a crystalline subsoil, a mean cellar gamma level of 1.40 mGy y-1 was measured, which is twice the mean gamma level of 0.70 mGy y-1 found in homes built on a sedimentary subsoil. The cellar 222Rn gas concentration is about six times higher in houses with a crystalline subsoil (1232 Bq m-3) than in houses with a sedimentary subsoil (201 Bq m-3). Although a weak correlation is observed between the mean gamma radiation levels and mean cellar 222Rn gas concentrations for the five subregions investigated, the gamma levels and the 222Rn gas concentrations do not correlate for single homes. For the population living on the ground floor of a house with a crystalline subsoil, the gamma radiation and the indoor air 222Rn lead to estimated mean exposures of 1.16 mSv and 9.44 mSv effective dose equivalent per year, respectively. In houses with a sedimentary subsoil, these mean exposures lead to 0.68 mSv y-1 and 3.22 mSv y-1, respectively. A mean tap water 222Rn content of 38.3 Bq L-1 and 10.4 Bq L-1 was measured in 31 villages with a crystalline subsoil and 73 villages with a sedimentary subsoil, respectively. Radon-222 degasing from the tap water into the indoor air leads to an additional exposure of about 0.11 mSv y-1 and 0.03 mSv y-1 in homes with a crystalline subsoil and homes with a sedimentary subsoil, respectively.     

Study of neutralization of 218 Po ions by small ion recombination in O2, Ar, and N2.

Three mechanisms of neutralization of Po(+)--electron transfer, electron scavenging, and small ion recombination--have previously been suggested. Considerable work has been conducted on the first two mechanisms. However, little information about small ion recombination is available. In the present study, this mechanism was studied by examining the neutralization rates of different Rn concentrations in N2, Ar, and O2 with the aid of a continuous Rn progeny monitoring system. The results showed that the neutralization rates in the three gases are of the order 1-4 s-1 at high Rn concentrations (higher than 40,000 Bq m-3). A linear relationship between the neutralization rate and the square root of Rn concentration (from 40,000 Bq m-3 to 810,000 Bq m-3) was obtained. Neutralization rates were higher in the gas with lower ionization potential. Further, the existence of a neutralization rate plateau at high Rn concentrations was strongly suggested.     

An evaluation of radiation and dust hazards at a mineral sand processing plant

This three-part article discusses the results of a 2-y study on radiation and dust hazards in a mineral sand processing plant involving: (1) evaluation of external gamma radiation levels and determination of isotopic composition of the different sand products; (2) evaluation of radiation carried in long-lived radioactive dust (LLRD) particles; (3) evaluation of Rn gas concentrations within the working environs of the plant. Gamma radiation levels had a mean value of approximately 40 nSv h-1, and monazite sand returned the highest activity concentrations of 0.16% and 3.4% for 238U and 232Th, respectively. Low volume gross respirable dust sampling revealed an average long-lived airborne alpha activity concentration of 0.07 +/- 0.02 Bq m-3 and an average dust mass concentration of 3.3 +/- 2 mg m-3. Gamma spectroscopy applied to high-volume air samples showed average airborne 232Th and 238U activities of 0.012 +/- 0.004 Bq m-3 and 0.005 +/- 0.002 Bq m-3, respectively, giving an airborne 232Th: 238U ratio of 2.4:1. Air sampling using a high volume, five-stage cascade impactor indicated an average activity median aerodynamic diameter (AMAD) of 3.2 microns with an associated average geometric standard deviation (GSD) of 2.8. Average radiation dose arising from the inhalation of LLRD was estimated to be 7 mSv per annum. CR-39 (polycarbonate plastic) nuclear track detectors indicated that Rn gas concentrations in the environs of the processing plant dry mill and main product warehouse ranged from 30 Bq m-3 to 220 Bq m-3, with an average value of 100 Bq m-3, which presents a possible inhaled dose from Rn daughters of 1.5 mSv y-1 (assuming an equilibrium ratio of 0.5).     

Study of radon concentrations in oil refinery premises and city dwellings.

Radon and its progeny concentrations were measured in several dwellings at an oil refinery premises and these concentrations were compared with those found in dwellings in Mathura and Agra cities. Radon progeny concentrations were measured using LR-115 type II nuclear track etch detectors. The radon concentrations were estimated by using a value of 0.42 for the equilibrium factor. The geometric means (GM) of radon concentrations in the refinery dwellings, Mathura city and Agra city dwellings were 97, 91 and 75 Bq m(-3) with geometric standard deviations of 1.7, 1.8 and 1.8 respectively. The average lifetime risk of lung cancer for an adjusted annual average chronic radon exposure of 69 Bq m(-3) (7.8 mWL; WL = working level) with an occupancy factor of 0.7 comes out to be 5.4 x 10(-3).     

Estimating Rn-induced lung cancer in the United States

The proportion of lung cancer deaths attributable to Rn among residents of single-family homes in the U.S. (approximately 70% of the housing stock) is estimated using the log-normal distribution of Rn concentrations proposed by Nero et al. (1986) and the risk model developed by the National Academy of Sciences' BEIR IV Committee. The risk model, together with the exposure distribution, predicts that approximately 14% of lung cancer deaths among such residents (about 13,300 deaths per year, or 10% of all U.S. lung cancer deaths) may be due to indoor Rn exposure. The 95% confidence interval is 7%-25%, or approximately 6600 to 24,000 lung cancer deaths. These estimated attributable risks due to Rn are similar for males and females and for smokers and nonsmokers, but higher baseline risks of lung cancer result in much larger absolute numbers of Rn-attributable cancers among males (approximately 9000) and among smokers (approximately 11,000). Because of the apparent skewness of the exposure distribution, most of the contribution to the attributable risks arises from exposure rates below 148 Bq m-3 (4 pCi L-1), i.e., below the EPA "action level." As a result, if all exposure rates that exceed 148 Bq m-3 (approximately 8% of homes) were eliminated, the models predict that the total annual lung cancer burden in the U.S. would drop by 4-5%, or by about 3800 lung cancer deaths, in contrast to a maximum reduction of 14% if all indoor Rn exposure above the 1st percentile were eliminated.     

Regulatory control of indoor Rn

Regulation of indoor Rn is explored in the context of cost-effectiveness of regulatory action. Evaluation of cost (i.e., mitigation expenses) and benefits (i.e., savings associated with medical expenses and lost productivity related to lung cancer) at various action levels indicate that regulatory programs would be economically inefficient and unreasonable if standards were established at or below the current EPA action guide (150 Bq m-3 or less). For the approximately 95% of U.S. homes with Rn levels near or below 150 Bq m-3, government programs should continue to focus on public information and consumer protection. For the small number of homes with high Rn levels, government programs should focus on identifying high risk homes and encouraging homeowners to reduce Rn levels. Because of the potential for substantial risk reduction, such efforts would be cost-effective in these homes.     

Airborne radon and its progeny levels in the coal mines of Godavarikhani, Andhra Pradesh, India.

In India, out of about 0.7 million miners, nearly 0.5 million persons are directly engaged in coal operations. Radon and its progeny levels have been quantified in the coal-mining environment of Godavarikhani, Andhra Pradesh, India using solid-state nuclear track detectors. Seasonal and mine depth variations in radon levels have been recorded resulting in the identification of locations with a high radon level as areas with no mining activity, active mining operational zones and return air ventilation paths. All these radon levels were below the permissible levels. The average concentrations of radon and its progeny levels were found to be 144 +/- 61 Bq m(-3) and 20 +/- 11 mWL (working level) respectively in the two-incline mine, and these values for the five-incline mine are recorded as 315 +/- 71 Bq m(-3) and 30 +/- 9 mWL respectively.     

Influence of subsoil geology and construction technique on indoor air 222Rn levels in 80 houses of the central Swiss Alps

The indoor 222Rn level depends mainly on the subsoil geology, the cellar floor permeability, the cellar aeration, the air-tightness of the homes, and the aeration habits of the occupants. These five parameters and the 222Rn levels in the cellar and in the living room on the ground floor were compiled in 80 one- or two-family houses of the central Swiss Alps. The 222Rn levels were measured with passive alpha track detectors. Houses located on a granite, ortho-gneiss or verrucano subsoil have a cellar 222Rn level that is on the average 4.4 times higher than houses which are built on grey-schist or sediments. The cellar level is on the average 5.4 times higher if the cellar has partially a gravel or earth floor than if the whole cellar surface is covered with a concrete floor. Energy-efficient, highly air-tightened homes have a living room level that is on the average 1.8 times higher than normally insulated conventional homes. In the cellars and the living rooms of the 80 houses considered, arithmetic mean 222Rn levels of 724 Bq m-3 (20 pCi L-1) and 178 Bq m-3 (4.8 pCi L-1), respectively, were found. In the central Swiss Alps 222Rn and 222Rn decay products lead to an estimated mean exposure of 5.3 mSv effective dose equivalent per year.     

Radiation data input for the design of dry or semi-dry U tailings disposal

Before discussion of design criteria for the handling of dry or semi-dry tailings, it is necessary to obtain an insight into the radiation levels associated with the tailings particles and to study the basic physical properties of dry tailings. This article presents the experimental results of assessing Ra and specific alpha-activity distribution with respect to particle size of the Ranger (RUM) and Nabarlek (QML) uranium mines dry tailings samples. The variation of Rn emanation coefficient versus particle size of dry tailings has also been measured. The nuclear-track detection technique, gamma spectrometry and alpha counting were used for the above measurements. Surface Rn flux from the hypothetical Nabarlek semi-infinite dry tailings pile is 32 Bq m-2 s-1 and the Rn flux for Ranger is 10 Bq m-2 s-1. The theoretical exposure rates for 1 m above these hypothetical tailings piles are 0.95 microC kg-1 h-1 and 0.28 microC kg-1 h-1, respectively. The derived air alpha-contamination limits (DAAC) for the tailings dust were calculated to be 1.2 Bq m-3 for workers and 0.034 Bq m-3 for a member of the public. The limit for workers corresponds to the air tailings dust concentration of 0.79 mg m-3 for QML tailings and 2.2 mg m-3 for RUM tailings. The DAAC limit for the public corresponds to the air tailings dust concentration of 0.022 mg m-3 for QML tailings and 0.064 mg m-3 for RUM tailings.