Decay products of radon

High concentrations of 220Rn, in the range 1 to 100 Bq m-3, have been found in factories handling large amounts of thorium (Duggan, 1973 Kotrappa et al., 1976). 

The dose to the human lung depends less on 222Rn than on the decay products, and the dose to the bronchial epithelium depends particularly on the decay products present as free atoms, molecules, ions or ion clusters as distinct from those attached to condensation nuclei, which are less readily deposited in the respiratory tract. A great deal of work has been done recently on the activities of decay product relative to 

unit for the PAEC is J m-3, and the unit for the time integrated PAEC, or dosage, is Jh m-3. The equivalent radon concentration is that concentration of radon, with decay products in equilibrium, which has the same PAEC as have the decay products actually present. In indoor air, the equivalent concentration is often about half the actual radon concentration. High in the atmosphere, the equivalent and actual radon concentrations are the same. 

In the uranium mining industry, the Working Level (WL) is defined as a concentration of decay products having PAEC equal to that of decay products in equilibrium with 100 pCi l-1 (3.7 x 103 Bq m-3) of radon. The Working Level Month (WLM) is defined as exposure to decay products equivalent to 1 WL for 170 h, this being the nominal number of hours worked per month in a mine. The WLM is still used in discussions of the epidemiology of lung cancer in relation to exposure to radon and its decay products. 

The following notation will be used Xo Activity of 222Rn in air (Bq m-3) 

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The average annual effective dose equivalent received by a member of the UK population is currently estimated to be 2150 ySv. Of this total, 87% arises from exposure to radiation of natural origin, the largest single contributor being inhalation of the short-lived decay products of radon. This exposure occurs predominantly in the home. 

Table III. Annual exposures to the decay-products of radon in UK dwellings, WLM...

Raghunath, B. and P. Kotrappa, Diffusion Coefficients of Decay Products of Radon and Thoron, J. Aerosol Sei. 10 133 (1979). 

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. 

The effect of surface electrostatic charge on a material on the attachment of the decay products of radon has been known since pioneering work on atomic structure by Rutherford. Extensive research into this area for the radon and thoron progeny has been conducted in this laboratory for environmental monitoring purposes. Several authors have reported on the effect of electrostatic charge on the collecting characteristics of copper for the radon progeny for exploration purposes (Card and Bell, 1979). 

The data on the electrostatic effect discussed above is relevant in the context of this paper because certain materials can esily acquire electrostatic charge which could, therefore, alter or mask their plate-out characteristics to the decay products of radon and thoron. 

A model has been developed to calculate the size distributions of the short lived decay products of radon in the indoor environment. In addition to the classical processes like attachment, plate out and ventilation, clustering of condensable species around the radioactive ions, and the neutralization of these ions by recombination and charge transfer are also taken into account. Some examples are presented showing that the latter processes may affect considerably the appearance and amount of the so called unattached fraction, as well as the equilibrium factor. 

Chamberlain, A.C. and E.D. Dyson, The Dose to the Trachea and Bronchi from the Decay Products of Radon and Thoron, Brit. J. 

The decay sequence for Rn-222 is given in Figure 2. Because of the 4 day half-life of Rn-222, it has the time to penetrate through the soil and building materials into the indoor environment. There is some recent evidence that in spite of its short half-life, 55 seconds, Rn-220 can also penetrate into structures in significant amounts (Schery, 1985). However, the data are limited and the extent of the thoron problem is quite uncertain. It is, therefore, the short-lived decay products of radon that are considered to be particularly important in the exposure of the general public and it is these isotopes on which this report will concentrate. 

D. R. Corson, K. R. Mackenzie, and E. G. Segre prepare element 85 (astatine) by bombarding bismuth with helions. W. Minder and Hulubei and Cauchois independently give evidence for the existence of element 85 in the decay products of radon. 

Tihe atmosphere contains many radionuclides which result from nuclear weapons testing and from natural processes. The nuclear weapons-produced radionuclides include both fission products and activation products from the construction materials of the device. The natural radionuclides include the decay products of radon and thoron, the natural radionuclides in the airborne dust, and the cosmic-ray-produced radionuclides which result from spallation reactions in the atmosphere. Through the determination of the absolute and relative concentrations of this wide spectrum of radionuclides, it should be possible to define the rates of both the long term stratospheric processes and the shorter term tropospheric processes. At the beginning of 1962 a ground-level... 

Chamberlain, A.C. Dyson, E.D. (1956) The dose to the trachea and bronchi from the decay products of radon and thoron. British Journal of Radiology, 29, 319-25. 

Kruger, J. and Nothling, J.F. (1979) A comparison of the attachment of the decay products of radon-220 and radon-222 to monodispersed aerosols. Journal of Aerosol Science, 10, 571-9. 

Radon progeny - the decay products of radon gas - are a well-recognized cause of lung cancer in miners. When radon was found to be a ubiquitous indoor air pollutant, however, it raised a more widespread alarm for public health. Since 1994, a systematic radon survey has been done in 1,524 buildings and dwellings of 14 cities in China. The results showed that the highest indoor radon concen-... 

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-... 

In addition, consideration must be given to the fact that the decay products of radon are solids which are themselves again subject to radioactive decay. The vessels with radioactive water samples are therefore contaminated to a greater or lesser extent, so that before they are used again the radioactivity should have subsided and the vessels must be thoroughly cleaned. If the water contains dissolved radium 226, with the... 

Radon is a colorless, odorless, and radioactive gas that comes from the complex decay of uranium. It occurs naturally in many locations in soil, rock, and water. It often appears in mines and ore tailings. The decay products of radon, called radon daughters, emit alpha, beta, and gamma radiation. Most of these products have very short half-fives. In the late 1980s, radon gained much national attention and... 

Reactor pre-operational and operational surveys can be performed including collecting and analysing air, water and swipe (smear) samples. The experiments can include the use of counting equipment such as gas flow proportional counting systems, Nal and Ge or detector systems to identify radioisotopes. If no real activity or contamination exists, the decay products of radon will show up in high volume air samples. 

The largest proportion of the natural radiation dose to humans results from the inhalation of the short-lived radon decay products Po, Pb, and " Po. During respiration these radioactive decay products of radon are deposited within different regions of the lung and can lead to substantial local doses there. For this reason, the natural radiation dose receives strong consideration in radiation protection. Thus, the surveillance of radon exposure in homes and in workplaces has emerged as an important operation. 

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