Ground-truthing predicted indoor radon concentrations by using soil-gas radon measurements

Predicting indoor radon potential has gained in importance even asthe national radon programs began to wane. A cooperative study to produceradon potential maps was conducted by the Environmental Protection Agency(EPA), U.S. Geological Survey (USGS), Department of Energy (DOE), and LawrenceBerkeley Laboratory (LBL) with the latter taking the lead role. They developeda county-wide predictive model based dominantly on the National Uranium ResourceEvaluation (NURE) aerorad data and secondly on geology, both small-scale databases. However, that model breaks down in counties of complex geology anddoes not provide a means to evaluate the potential of an individual home orbuilding site. In this current study, soil-gas radon measurements on a largescale are shown to provide information for estimating radon potential at individualsites sort out the complex geology so that the small-scale prediction indexcan be validated. An example from Frederick County, Maryland indicates a positivecorrelation between indoor measurements and soil-gas data. The method doesnot rely on a single measurement, but a series that incorporate seasonal andmeteorological considerations.     

Continuous measurements of radon and radon progeny as a basis for management of radon as a hazard in a tourist cave

A six month survey of radon, radon progeny and condensation nuclei (CN) has been conducted in an Australian tourist cave. The measurements have been made continuously at two sites within the cave: one a small chamber with a high air exchange rate close to one entrance and connected to several other entrances by complex passages; the other a large chamber with a low air exchange rate 1 km from the nearest entrance. The measurements form a basis for evaluation of the accuracy with which dose due to radon can be determined for different monitoring strategies. It is shown that the estimate of dose based on the measurement of radon concentration and recommendations in ICPR-65, is low by a factor of 1.3 at the well ventilated site and 1.5 at the site with a low air exchange rate and low CN. At each site the weekly average equilibrium factor and unattached fraction were steady, leading to the possibility of establishing a cave system average of these factors. However, given the technical diffuculties involved, it may not be practicable to make enough unattached fraction measurements to fully represent the cave system. Therefore it may be necessary to use a conservative approach to the dosimetry and add 50% to values determined by the ICRP-65 conversion convention.     

Determination of air-loop volume and radon partition coefficient for measuring radon in water sample

A simple method for the direct determination of the air-loop volume in a RAD7 system as well as the radon partition coefficient was developed allowing for an accurate measurement of the radon activity in any type of water. The air-loop volume may be measured directly using an external radon source and an empty bottle with a precisely measured volume. The partition coefficient and activity of radon in the water sample may then be determined via the RAD7 using the determined air-loop volume. Activity ratios instead of absolute activities were used to measure the air-loop volume and the radon partition coefficient. In order to verify this approach, we measured the radon partition coefficient in deionized water in the temperature range of 10–30 °C and compared the values to those calculated from the well-known Weigel equation. The results were within 5 % variance throughout the temperature range. We also applied the approach for measurement of the radon partition coefficient in synthetic saline water (0–75 ppt salinity) as well as tap water. The radon activity of the tap water sample was determined by this method as well as the standard RAD-H₂O and BigBottle RAD-H₂O. The results have shown good agreement between this method and the standard methods.     

Measurement of the radon exhalation rate from the medium surface by tracing the radon concentration

The paper will present a method based on the accumulation chamber technique for measuring of radon exhalation from the medium surface. A radon monitor traces the change of radon concentration in the accumulation chamber, and then the radon exhalation can be obtained accurately through linear fit. Based on our recent experiments, the radon exhalation rate from the medium surface obtained from this method is in good agreement with the actual exhalation rate of our simulation facility. This method is superior to the competition method which obtains the radon exhalation through the exponential fit by an external PC-system. The calculation for the exponential fit is very easy by computer and related software. However, for portable instruments, the single chip microcomputer can’t calculate the exponential fit rapidly. Thus, this method is usable for developing the new portable instrument to classify building materials, etc.     

Consideration of measurement error when using commercial indoor radon determinations for selecting radon action levels

An examination of year-long, in-home radon measurement in Colorado from commercial companies applying typical methods indicates that considerable variation in precision exsts. This variation can have a substantial impact on any mitigation decisions, either voluntary or mandated by law, especially regarding property sale or exchange. Both long-term exposure (nuclear track greater than 90 days), and short-term (charcoal adsorption 4–7 days) exposure methods were used. In addition, periods of continuous monitoring with a highly calibrated alpha-scintillometer took place for accuracy calibration. The results of duplicate commercial analysis show that typical results are no better than ±25 percent with occasional outliers (up to 5 percent of all analyses) well beyond that limit. Differential seasonal measurements (winter/summer) by short-term methods provide equivalent information to single long-term measurements. Action levels in the U.S. for possible mitigation decisions should be selected so that they consider the measurement variability; specifically, they should reflect a concentration range similar to that adopted by the European Community.     

On the vapour pressure of radon

The few, rather scarce, and old data on the vapour pressure and sublimation pressure of radon are re-examined in light of the Wagner equation, which is applied for the first time (as far as we are aware) to the sublimation curve. Numerical coefficients have been established for the representation of both equilibrium curves, and estimates are advanced for the coordinates of the critical point, the triple-point, and the normal boiling temperature of radon. Some important thermodynamic properties, e.g., the enthalpies of vaporisation, sublimation, and fusion are derived, and a (p, T) phase diagram is sketched.     

State of radon in crystalline polymers

The state of radon in crystalline polymers, polyethylene and polypropylene, has been studied by methods of macro- and microauto-radiography. Radon-222 was introduced into the samples by diffusion from the gas phase at various temperatures and time intervals. Effects on the state of radon of such factors as density and polymer crystallinity, extent of macromolecular chain branching, spherulite radius, content of different admixtures, -ray photon irradiation dose or irradiation with accelerated electrons, etc., were investigated. In pure polymers, radon was found to be in an atomically dispersed state. Radon forms thermally stable accumulations at the surface as well as in the bulk of the material due to admixtures, gas bubbles and crazes. The probable effect of radon's tendency to form accumulations on the kinetics of its diffusion in crystalline polymers is discussed.     

Indoor radon risk potential of Hawaii

Summary A comprehensive evaluation of radon risk potential in the State of Hawaii indicates that the potential for Hawaii is low. Using a combination of factors including geology, soils, source-rock type, soil-gas radon concentrations, and indoor measurements throughout the state, a general model was developed that permits prediction for various regions in Hawaii. For the nearly 3,100 counties in the coterminous U.S., National Uranium Resource Evaluation (NURE) aerorad data was the primary input factor. However, NURE aerorad data was not collected in Hawaii, therefore, this study used geology and soil type as the primary and secondary components of potential prediction. Although the radon potential of some Hawaiian soils suggests moderate risk, most houses are built above ground level and the radon soil potential is effectively decoupled from the house. Only underground facilities or those with closed or recirculating ventilation systems might have elevated radon potential.     

Peculiar radon spot in Hungary

For the public, indoor radon is the main source of exposure from ionizing radiation. Radon gas originates from the radioactive decay chain of uranium deposited in rocks or in building materials. In the reviews mostly a rather steady radon exhalation has been assumed. In a village of North-East Hungary, however, high radon concentrations have been measured, differing strongly in neighbouring houses and varying in time, due to the interplay of several geochemical phenomena.     

Determination of radon in groundwater of Quebec

The groundwater around Montreal in the province of Quebec, Canada, was analyzed for radon by argon purging and proportional counting. Based on 50 samples measured, we obtained the following concentrations/in Bq 1^–1/: a mean of 16.9, standard deviation 61, median 2.3 and mode /or, most probable concentration/ 2.1. The values ranged from 0.2 to 439 Bq 1^–1. These concentrations are similar to those found in other countries and with one exception do not represent a danger to the water users.     

Effects of residential radon on cancer incidence

Radon activity concentrations of 1077 homes were surveyed in two villages of Northern Hungary to obtain the yearly averages. The distribution of indoor radon activity concentrations covered a wide range. Cancer incidences of all the 2680 inhabitants for the last 30 years were also studied in these villages in order to establish a possible correlation with radon exposure. The methods applied in the analysis allow to draw up statistically supported statements concerning the relative cancer risks of different radon level groups. The results show that among non-smoking middle-aged women the frequency of cancer, regardless to tumor types, is lower for those who live in residential radon activity concentrations of a level between 110 and 185 Bq^.m^-3 compared to those living in radon levels outside this range. A minimum value in the cancer frequency exists at a level of significance p<0.008 (determined with the help of Fisher's test). In general, the present study corroborates the outcome of other studies demonstrating the existence of a biopositive effect, and suggests a wider concept of radon health effects.     

Influence of clay properties on radon emanation

The emanation factor of clay strata was measured in a series of experiments. The clay emanation factor grows with increased dispersion and can reach values of up to 67%. This can be explained, in our view, by the increased number of nanodimensional particles with good emanation characteristics.     

Two EPA approaches to radon surveys

In an attempt to characterize radon distribution in residential settings, the USEPA initiated two distinct survey programs, the National Residential Radon Survey (NRRS) and the State/EPA Residential Radon Survey (SRRS). Each survey is different in their level of analysis, with the NRRS concentrating on a national sample, and the SRRS concentrating on individual statewide samples. Both surveys are random and statistically-valid, enabling the survey samples to be extrapolated to represent a much larger population. This paper details each survey's design and provides an examination of the unique approach each program uses to generate sound characterizations of radon distribution in the United States.     

Evidence for cathodic electrodeposition of radon species

Phase change effects on the total organic yield have been studied in crystalline chlorobenzene derivatives activated by radiative neutron capture. Irradiation of the compounds in benzene solution decreased the organic yield considerably while these values remained unchanged when 11 benzene + DMSO or 11 benzene + acetonitrile solvent mixtures were used, the 11 benzene + THF solvent gave the lowest yield in all the cases. Heat treatment to the neutron activated solids enhanced the organic yield only in the case of 2-amino 5-chlorobenzophenone by 7%.     

Indoor radon concentration survey in Mexico

Indoor radon evaluations in specific regions of the country have been performed in an effort to assess the magnitude of the radon problem and its public health consequences. The survey of this paper covers four large non-tropical regions of north and central Mexico, and reports the results of measurements of indoor radon concentrations in houses of towns with between 100,001 and 500,000 inhabitants. The measurements were done by using passive detectors, namely, the closed-end-cup system with CR-39 polycarbonate chips as detector material. The measurements were performed throughout the two coldest seasons (between 5 and 20°C), winter and spring, in integration periods of 28 days covering the six month cycle. The results show a moderate average radon concentration below 200 Bq·m⁻³ with occasional higher values. This is very probably due to the climate conditions and the traditional habits of open door and window ventilation. The IFUNAM (Instituto de Física, Universidad Nacional Autónoma de México) Laboratory, where the closed-end cup system for radon was developed, has gained experience though this survey and is willing to share it for future surveys at regional or national levels.     

Study of radon exhalation from the soil

The influence of meteorological parameters on radon exhalation rate was analyzed. The analyses show a significant influence of precipitation on radon exhalation rate. The highest exhalation rate was found during dry periods and the lowest during the periods of strong precipitation. We also tested two different types of detectors for the measurement of radon exhalation rate—the ionization chamber (AlphaGUARD) and the scintillation chamber of Lucas type. The exhalation rates measured by these detectors were in a good agreement. Likewise, there was an agreement in radon exhalation rates determined from short term and long term increases in radon activity concentration.     

A simple laboratory-based radon calibration system

Measurements of ²²²Rn (“radon”) in the environment are important in the geosciences and radiation-protection fields. We demonstrate here a simple laboratory-based calibration system to evaluate the efficiency of radon detectors with a reproducibility of about ±2%. The system uses a closed-loop air circulation design with ²²⁶Ra adsorbed onto MnO₂-impregnated fiber as a radon source. Two RAD7 radon detectors (Durridge Co., Inc.) that were precisely calibrated at Durridge’s in-house calibration facility are used as secondary standards. By parallel analysis of the radon-enriched air within the closed loop, the test RAD7s are assigned a calibration coefficient to be applied to future measurements. We also performed a side-by-side intercomparison with two RAD7s in a high-radon natural environmental setting (limestone cave in Florida) that produced comparable results.     

Determination of the radon diffusion coefficient and radon exhalation rate in Moroccan quaternary samples using the SSNTD technique

Measurements have been made of radon (²²²Rn), release from diverse quaternary samples collected from different sediment deposits in the Errachidia and Beni-Mellal areas (Morocco). The radon diffusion coefficient as one of some important parameters of radon transport in the soil has been measured using solid state nuclear track detectors (SSNTD). Radon -activity, uranium content and radon exhalation rate have been determined in the studied samples. Uranium concentrations were found to vary from 0.14 to 9.52 ppm whereas the radon exhalation rate varied from 0.003 to 0.145 Bq^.m^-2.h^-1. A positive correlation has been found between radon exhalation rate and uranium content in the studied samples. The average radon diffusion coefficients were found to vary from (1.26±0.09)^.10^-6 m^2.s^-1 to (4.3±0.36)^.10^-6 m^2.s^-1. Furthermore, the correlation between ²²²Rn diffusion coefficient and porosity are also discussed.