Radon decay, measurement

Numerous radon and radon decay measurements in houses are now being made by a large number of private and governmental organizations. In order to assure valid and consistent measurements, it is important that proven methods be used following standardized procedures. To address this need, EPA issued "Interim Indoor Radon and Radon Decay Product Measurement Protocols" and established a Radon/Radon Progeny Measurement Proficiency program. 

Establishment of data quality programs which will result in consistent and reliable radon and radon decay products measurements for both individuals and governmental agencies. 

In February 1986, EPA issued a document (Ronca-Battista et al., 1986) titled "Interim Radon and Radon Decay Product Measurement Protocols," describing seven methods for measuring radon and its decay products in houses. The methods addressed are those that have been evaluated by EPA and found to be satisfactory other methods may be added as they are reviewed by EPA. In addition, portions of the document may be revised as new information and data becomes available. 

E., Interim Indoor Radon and Radon Decay Product Measurement Protocols, EPA 520/1-8604, U.S. Environmental Protection Agency, Washington, D.C. (April 1986). 

The selection of the 1980-82 measurements (Swedjemark and MjOnes, 1984) was made on dwellings built before 1976 and with the aim of determining dose distributions and the collective dose to the Swedish population from the exposure of the short-lived radon decay products. This was done by using the statistical selection made by the National Institute for Building Research intended for an energy study of the Swedish stock of houses. From a selection of 3 100 houses in 103 municipalities, 2 900 were inspected. The data was found to be in substantial conformity with data from the land register and the population census of 1975. For the study of the radon concentration 752 dwellings were selected at random. 

An equilibrium factor of 0.35, derived from measurements made during the local surveys, has been assumed to typify conditions in UK dwellings. This value has been used to convert the average radon concentrations measured in the national survey to potential alpha-energy concentration of radon decay-products. On average, persons in the UK spend 75% of their time in their homes and 15% of their time elsewhere indoors (Brown, 1983). The occupancy factor of 0.75, together with an equilibrium factor of 0.35, results in an annual exposure of 1.3 10"5 J h m"3 (0.0037 Working Level Months,... 

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). ... 

Together with the radon daughter measurements, nearly continuous measurements of the ventilation rate are performed by means of the release of N2O tracer gas and observation of its decay with an infrared spectrometer (Miran 101). Furthermore the aerosol concentration and size distribution are monitored every 20 to 30 min with an automated aerosol spectrometer (Raes et al.,1984). 

Miles, J.C.H. and Sinnaeve, J., Results of the second CEC intercomparison of active and passive dosemeters for the measurement of radon and radon decay products (1984)... 

It has been reported for many years that condensation nuclei can be produced by ionizing radiation. Recent studies have improved the measurement of the activity size distribution of these ultrafine particles produced by radon and its daughters (Reineking, et al., 1985 Knutson, et al., 1985). It seems that the Po-218 ion is formed by the radon decay, is neutralized within a few tens of milliseconds, and then attached to an ultrafine particle formed by the radiolysis generated by the polonium ion recoil. Although there will be radiolysis along the alpha track, those reactions will be very far away (several centimeters) from the polonium nucleus when it reaches thermal velocity. The recoil path radiolysis therefore seems to be the more likely source of the ultrafine particles near enough to the polonium atom to rapidly incorporate it. 

Few data are available on the deposition of ultrafine particles (dradon decay products in a rubber latex cast of a human windpipe which extended from the epiglottis to a few cm below the Carina. Martin and Jacobi (1972)... 

Measures to reduce radon concentrations have been studied in an old house in which the radon decay-product concentration initially exceeded 0.3 Working Level (WL). Some of the measures were only partially successful. Installation of a concrete floor, designed to prevent ingress of radon in soil gas, reduced the radon decay-product concentration below 0.1 WL, but radon continued to enter the house through pores in an internal wall of primitive construction that descended to the foundations. Radon flow was driven by the small pressure difference between indoor air and soil gas. An under-floor suction system effected a satisfactory remedy and maintained the concentration of radon decay products below 0.03 WL. 

Before standards for indoor exposure to radon can be formally established, work is necessary to determine whether remedies are feasible and what is likely to be involved. Meanwhile, the Royal Commission on Environmental Pollution (RCEP) in the UK has considered standards for indoor exposure to radon decay products (RCEP, 1984). For existing dwellings, the RCEP has recommended an action level of 25 mSv in a year and that priority should be given to devising effective remedial measures. An effective dose equivalent of 25 mSv per year is taken to correspond to an average radon concentration of about 900 Bq m 3 or an average radon decay-product concentration of about 120 mWL, with the assumption of an equilibrium factor of 0.5 and an occupancy factor of 0.83. 

Continuous measurements of the potential alpha energy concentration of the radon decay products were made with a Continuous Working Level Monitor (WLM-300) (EDA Instruments Inc., Toronto). 

After the concrete floor had been installed, measurements indicated radon decay-product concentrations of 160 mWL and 140 mWL on the ground floor and upstairs, respectively. There were noticeable gaps between the concrete floor and the wall surfaces in a number of places, some of which extended to the foundations. The radon production rate was estimated to be 1300 Bq m"3 h"1, more than four times the value found in the initial study with all internal doors open. Radon was obviously entering the dwelling with ease, even though the area of underlying material exposed in gaps between the floor and the walls was much smaller than that exposed beneath... 

The fans were switched on at time E, causing a further decrease in concentration. Low concentrations were maintained for 4 days, at the end of which only one of the fans was kept in operation (office system F to G, sitting room system G to H). The increase in the concentration of radon decay-products after switching off one or both fans is evident. After time I, the radon decay-product concentration decreased, but less rapidly than in the first trial and the final value was not as low. However, a trend to still lower values was apparent when the exercise was concluded on day 19. Measurements of the concentration of radon in the exhausts of the two suction systems were made on three days and the results are given in Table II. 

Whilst the under-floor suction systems were operated, further measurements were made of the radon concentration in the pores of the wall dividing the office area from the scullery. On day 7 (Figure 11), when the concentration of the radon decay-products was low (approximately 7 mWL), the concentration of radon near the base of the wall was about 8800 Bq m 3. This had risen to more than 13000 Bq m 3 when measurements were made over-night between days 10 and 11. 

The subsoil is the principal source of radon in this house. Both the activity concentration of radium-226 in subsoil and of radon in soil gas are above levels for building ground that might result in significant indoor radon concentrations. The radon decay-product concentration in the dwelling before remedial measures were taken was substantially higher than the reference value of 120 mWL. 

Radon is present in the air and soil. It can leak into the indoor environment through dirt floors, cracks in walls and floors, drains, joints, and water seeping through walls. Radon can be measured by using charcoal containers, alpha-track detectors, and electronic monitors. Results of the measurement of radon decay products and the concentration of radon gas are reported as working levels (WL) and picocuries per liter (pCi/L), respectively. The continuous exposure level of 4 pCi/L or 0.02 WL has been used by USEPA and CDC as a guidance level for further testing and remedial action [33]. 

The calculated size distribution of newly attached decay products is shown as curve C in Fig. 1.9. The activity median diameter is 0.16 /zm. With passage of time, the distribution would be shifted to larger particle sizes, as coagulation proceeds. George (1972) used diffusion batteries to measure the size distribution of nuclei carrying radon decay products and found activity median diameters (AMD) averaging 0.18,0.11, and 0.30 /um in a city basement, fifth floor room, and rural outside air, respectively. 

George, A.C. (1972) Indoor and outdoor measurements of natural radon and radon decay products in New York City air. In The Natural Radiation Environment 11, ed. J.A.S. Adams, W.M. Lowder T.F. Gesell, CONF-720805, pp. 741-50, Springfield, Va. NTIS. 

Radon ( Rn) measurements made by the ARCAS provide a simple, reliable, real-time indicator of the relative maritime or continental nature of the air over coastal or oceanic areas (8). With a half-life of 3.8 days, Rn originates from the decay of Ra, a member of the decay chain. At least 98% of Rn originates from land masses (9). The radon flux at the surface depends on the radium content of the soils and rocks, the permeability of the source materials, atmospheric pressure, soil moisture, and vegetative cover (10). Relatively abrupt changes in the radon concentration over the ocean usually indicate changes in air masses and the passage of frontal systems. 

There have been hundreds of radon profiles measured in the surface ocean. Examples are presented in Fig. 10.5. These data are used to determine the gas exchange mass transfer coefficient by calculating a mass balance for Rn. The change in concentration (mol m ) of Rn in surface waters with time integrated to the depth, z, at which secular equilibrium is achieved, usually 200 m or less, is equal to the sum of three terms production by the integrated Ra concentration, and losses due to radioactive decay (mol m d ) and flux to the atmosphere ... 

What can be done to combat radon pollution indoors The first step is to measure the radon level in the basement with a rehable test kit. Short-term and long-term kits are available (Figure 17.28). The short-term tests use activated charcoal to collect the decay products of radon over a period of several days. The container is sent to a laboratory where a technician measures the radioactivity (y rays) from radon-decay products lead-214 and bismuth-214. Knowing the length of exposure, the lab technician back-calculates to determine radon concentration. The long-term test kits use a piece of special polymer film on which an a particle will leave a track. After several months exposure, the film is etched with a sodium hydroxide solution and the num-... 

Radon is a radioactive gas produced when radium in soil and rock decays. It is a known carcinogen. The data above show radon levels measured in a community in Australia. Select a method for graphing these data. Explain the reasons for your choice, and graph the data. 

To aid in the effort in standardizing procedures for making accurate and reproducible measurements and to ensure consistency, the EPA has issued two reports recommending measurement techniques and strategies. The 1986 report, "Interim Radon and Radon Decay Product Measurement Protocols," provides procedures for measuring radon-222 concentrations with continuous monitors, charcoal canisters, alpha-track detectors and grab techniques (EPA 1986). 

The second report, "Interim Protocols for Screening and Follow-up Radon and Radon Decay Product Measurements" (EPA 1987a), outlines the recommendations for making reliable, cost effective radon measurements in homes (Ronca-Battista et al. 1988). 

EPA. 1986. Interim indoor radon and radon decay product measurement protocols. Washington,... 

EPA. 1987a. Interim protocols for screening and follow-up radon and radon decay product measurements. EPA 520/1-86-014-1. Springfield, VA National Technical Information Service. 

The personal aerosol particle size sandier developed for EMSP is ciqiable of measuring most integrated airborne particulate substance of interest depending uran the measurement technique applied to die filtration stages. In this study b was measured as a tracer for radon decay product aerosol size and was acconqilished at normal outdoor concentrations at the DOE Femald site and a home in northern New Jersey. 

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