Radon activity measurements

In Table I results of Rn-226 activity measurements cn geological samples are shewn together with measurements cn Rn exhalation rates from the sanples. The exhalation rates varies considerably with the moisture content of material. The exhalation rate is lew for dry samples and when the moisture content increases, the exhalation rate increases until it reaches a plateau. When the moisture content increases further, a rapid increase in radon exhalation occur. When the saturation level of moisture is reached, the exhalation rate drops dramatically. The exhalation rates given in Table I are obtained by assuming that the most probable moisture content is whithin the plateau of exhalation rate/moisture curve. (Stranden et al, 1984, Stranden et al, 1984a). 

A radiochemical method for the determination of Rn-220 in fumarolic gas is studied. Both condensed water and non-condensing gas are collected together and Pb-212 is precipitated as PbS. After dissolving the precipitate in conc.HCI, it is mixed with an emulsion scintillator solution for activity measurements. As Pb-214 is simultaneously measured, the observed ratio of Pb-212 /Pb-214 gives Rn-220/Rn-222. This method is superior to the method of directly measuring Rn-220 for the samples in which Rn-220/Rn-222 ratios are less than unity. This method and the previously proposed direct method were applied in the field, and new data obtained. An attempt was also made to understand the formation and transport of radon underground. 

This paper deals with the plate-out characteristics of a variety of materials such as metals, plastics, fabrics and powders to the decay products of radon and thoron under laboratory-controlled conditions. In a previous paper, the author reported on measurements on the attachment rate and deposition velocity of radon and thoron decay products (Bigu, 1985). In these experiments, stainless steel discs and filter paper were used. At the time, the assumption was made that the surface a-activity measured was independent of the chemical and physical nature, and conditions, of the surface on which the products were deposited. The present work was partly aimed at verifying this assumption. 

Large Radon/Thoron Test Facility (RTTF). Figures 1 to 5 show the surface a-activity measured on several materials exposed to a radon progeny atmosphere (Figures 1 and 2), and to a thoron progeny atmosphere (Figures 3 to 5). 

The underlying physical and/or chemical mechanisms responsible for the differences observed between the radon progeny and the thoron progeny as related to different materials are not clearly understood. Finally, it should be pointed out that the main thrust in this paper was to determine differences in surface a-activity measured on different materials with the same geometrical characteristics exposed to identical radioactive atmospheres. The calculation of deposition velocities and attachment rates, although it follows from surface a-activity measurements, was not the intent of this paper. This topic is dealt with elsewhere (Bigu, 1985). 

The radon in the air i/as measured continuously by electroprecipitation of the positively charged Po-218 ions in an electric field (10 kV) on a surface barrier detector (Porstendorfer, et al., 1980). For this purpose the air i/as dried, filtered and sucked into an aluminium sphere ( 2 1) with a flowrate of 0.5 lmin-1. The counts due to Po-218 and Po-214 were proportional to the radon activity concentration. Their disintegrations were directly detected by alpha spectroscopy with an energy resolution of about 80 keV. The monitor could detect down to 5 Bq m 3 with a two hour counting time and 30 % statistical accuracy. 

In a certain period of time there is a steady state condition in a room and a constant radon activity concentration cj(°°) could be measured. By means of this value and equations (2) (with t = 00) and (3) the actual ventilation rate of a room can be calculated ... 

Table IJa. The aerosol concentration (Z), the activity concentrations of radon (cj) and the free (cjf, C2 ) and attached (c a, c 3, C3 ) radon daugthers, measured in rooms i/ith moderate ventilation (partly opened windows).

Although several analytical methods for measuring and determining radon and radon progeny from environmental media or biological tissues exist, several on-going studies have been identified in the Federal Radon Activities Inventory. There are a number of animal studies underway. Occupationally exposed individuals are continually monitored in order to obtain more accurate models and better measurement techniques. 

During an DSA measurement, the carrier gas (air, nitrogen or other gas) carries the inert gas released by the sample situated in a reaction vessels into a detector for the inert gas. For example, to measure the a-activity of radon, a scintillation counter, ionization chamber or semiconductor detectors can be used. On the other hand, / -activity measurements of Kr, are made by Geiger-Miiller tubes. Gamma-active radionuclides of xenon can be measured by a gamma-spectrometer. The stable nuclides of inert gases are measured by a mass spectrometer. 

The seventh item in the decay chain is Rn, with a half-hfe of 3.825 d. After loss of Rn, there is ample time for the decay of the daughter nuclides preceding before re-growth of the Rn. If, as is often the case, post-radon nuclides were measured to estimate activity, loss of radon would affect the whole activity measurement process. The solution is simple - encapsulate the sample and wait for about 10 half-lives of the Rn to allow equilibrium to be re-established - say one month. Having said that, experience shows that it is, in fact, possible to grind some geological materials without apparent loss of radon. However, that cannot be relied upon. Different materials have different radon-emanating powers, which will depend upon the moisture content and other factors. 

Static sampling systems are defined as those that do not have an active air-moving component, such as the pump, to pull a sample to the collection medium. This type of sampling system has been used for over 100 years. Examples include the lead peroxide candle used to detect the presence of SO2 in the atmosphere and the dust-fall bucket and trays or slides coated with a viscous material used to detect particulate matter. This type of system suffers from inability to quantify the amount of pollutant present over a short period of time, i.e., less than 1 week. The potentially desirable characteristics of a static sampling system have led to further developments in this type of technology to provide quantitative information on pollutant concentrations over a fked period of time. Static sampling systems have been developed for use in the occupational environment and are also used to measure the exposure levels in the general community, e.g., radon gas in residences. 

Since radon is a colorless, odorless, and tasteless gas, the only way to detect its presence is to sample and analyze an area s air using a conventional radon measurement test. If the test reveals elevated radon levels, the homeowner will have to decide what steps to take to reduce the levels.7 The higher the level of radon present in a home, the more likely an active radon reduction system such as subslab depressurization (SSD)8 may be required. Lower radon levels may require only a passive reduction system, such as simple sealing. 

As part of the radon program at EML to develop or improve and field test radon monitors, a modified activated carbon device (Warner, 1986) was developed to obtain higher measurement sensitivity. As a result, we have surveyed 380 buildings in six states in the eastern United States. The purpose of the measurements reported in this paper was to test the feasibility of the new version of the passive activated carbon device and to obtain data on indoor radon levels in different geographical locations. 

The detector used to measure indoor radon was the latest version of the passive activated carbon device developed at EML (George, 1984 Warner, 1986), which consists of a thin-walled aluminum canister with a screen cover to expose 80 g of carbon to the test atmosphere. Although not as physically rugged as earlier models, properly packed this monitoring device was as successful in conducting the surveys through the mail. 

George, A. C., Passive Integrated Measurement of Indoor Radon Using Activated Carbon, Health Phvs. 46 867 (1984). 

The variations in the background, the sensitivity to moisture, the alpha activity of the chamber itself and the influence of recombination were discussed by Hultqvist. The standard deviation due to counting statistics was estimated to be about 3 % (in a few measurements 6 %). The calibration was made by counting each alpha particle by a proportional counter specially designed at the Department for this purpose. The statistical uncertainty of the calibration of the equivalent radon concentration was estimated to be 12 %. 

Commission of the European Communities., Results of the Second CEC Intercomparison of Active and Passive Dosemeters for the Measurement of Radon and Radon Decay Products, EUR Report 10403 EN (1986). ... 

Khan, A., F. Bandi, C.R. Phillips and P. Duport, Underground Measurements of Aerosol and Radon and Thoron Progeny Activity Distributions, to be published in Proc. 191st American Chemical Society National Meeting, New York, April 13-18 (1986). 

In order to assess the accuracy of the present method, we compared it with two other methods. One was the Track Etch detector manufactured by the Terradex Corp. (type SF). Simultaneous measurements with our detectors and the Terradex detectors in 207 locations were made over 10 months. The correlation coefficient between radon concentrations derived from these methods was 0.875, but the mean value by the Terradex method was about twice that by our detectors. The other method used was the passive integrated detector using activated charcoal which is in a canister (Iwata, 1986). After 24 hour exposure, the amount of radon absorbed in the charcoal was measured with Nal (Tl) scintillation counter. The method was calibrated with the grab sampling method using activated charcoal in the coolant and cross-calibrated with other methods. Measurements for comparison with the bare track detector were made in 57 indoor locations. The correlation coefficient between the results by the two methods was 0.323. In the case of comparisons in five locations where frequent measurements with the charcoal method were made or where the radon concentration was approximately constant, the correlation coefficient was 0.996 and mean value by the charcoal method was higher by only 12% than that by the present method. 

Formation and transport of radon ) In the present work, lead isotopes were chemically separated from the sample gas as lead sulfide since the formation of lead sulfide was inevitable under the presence of H2S in the fumarolic gas. The lead sulfide was then dissolved in a small amount of concentrated HCI and mixed with the Insta Gel(emulsion scintillator solution, Insta Gel, Packard Inc.) for the liquid scintillation counting. The chemical yield and the volume of the collected non-condensing gas were obtained from the measurement of the activities of Pb-214 and its progeny which were in radioequilibrium with their precursor Rn-222 whose concentration was determined separately by the direct method. 

Underground Measurements of Aerosol and Activity Distributions of Radon and Thoron Progeny... 

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