Radon decay products system

Method. Figure 3 shows the equipment used by us for loading a culture medium with radon and decay products. Air was circulated in a closed system, driven by a membran pump (MP). The system consisted of a Ra-226 solution (Ra), a security bubble flask with water (H20), a membran bacteria filter (MF) and a second bubble flask containing 100 ml RPMI 1640 culture medium (CM). This medium contains 100 IE/ml penicilin and streptomycin and 0.75% L-glutamin. Foetal calf serum, an essential part of blood cultures, must not be added, else the airstream would develop foam. Furthermore we added a small amount of Pb(N03)2 and Bi(N03)2, about 10 ng of each, as "carriers" for the radon decay products to avoid a "wall effect". 

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. 

Mechanical ventilation Room or area system Ventilation rate, h-1 Radon decay-product cone., mWL... 

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. 

Figure 11. Variation in radon decay-product concentrations before and during the operation of the underfloor under-pressure system.

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. 

Suction on cavities created under the concrete floor with low-power fans was highly successful in reducing the radon decay-product concentrltions below the reference level. Such under-floor suction systems are relatively easy to instal and cheap to operate. They appear to hold considerable promise. 

Another concept relating to the decay products is that of the "unattached" fraction. Although it is now known that the decay product atoms are really attached rapidly to ultrafine particles (0.5 to 3 nm in diameter), there is a long history of an operationally defined quantity called the "unattached" fraction. These decay products have much higher mobilities in the air and can more effectively deposit in the respiratory system. Thus, for a long time the "unattached" fraction has been given extra importance in estimating the health effects of radon decay products. Typically most of the "unattached" activity is Po-218 and the value of unattached frac-... 

The four-stage low-pressure cascade impactor incorporates both the impactor and wire screen methods (Tokonami et al., 1997). This system can measure the activity size distribution of radon decay products in a low level environment within 90 min. Figure 6.9 shows a block diagram of the activity-weighted size distribution instrument. In the first air inlet, unattached radon decay products are collected on a metal wire screen (300 mesh openings 118.2 cm wire diameter 3.75 x 10 cm). A silicon semiconductor detector, SSD, is set opposite the metal wire screens where both collection and detection are concurrent. Output signals from the silicon semiconductor detector are sent through a preamplifier, PA, and the internal amplifier of a multichannel analyser, MCA, and then to the multichannel analyser. 

The dotted line in Figure 7 shows the time evolution of the ratios of radon daughters in closed system in which initially Rn is present but its decay products are absent. We refer to this model age as the batch process time. 

Our sampling device, the automatic radon counter and aerosol sampler (AR-CAS), was used to collect the continuous set of aerosol samples. This instrument also counted the radon daughter-product decay and printed a nearly real-time record for each sample (see Reference 6 for photographs and details of operation). The ARCAS I system consists of a deck-mounted sampling unit and an indoor electronic unit containing sampler controls, calendar clock with display, thumbwheels for manual data entry, and a thermal printer. 

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. 

Measurements of the radiation dose exposure to radon and its decay products is carried out by an electronic radon gas personal dosimeter. Such a dosimeter is that named DOSEman (Sarad, Dresden, Germany) (Grundel and Porstendorfer, 2003). Using the dosimeter, the radon concentration is measured in the environment, e.g. in dwellings, mines, caves, etc., and can be converted to a personal dose. The entire measuring system is accommodated in a handy housing, so that it can be carried comfortably on the body. 

The most significant source of radioactivity in the indoor microatmosphere is radon, a noble gas product of radium decay that is produced below ground and that may leak into the basements above. Radon may enter the atmosphere as either of two isotopes, Rn (half-life 3.8 days) and °Rn (half-life 54.5 seconds). Both are alpha emitters in decay chains that terminate with stable isotopes of lead. The initial decay products, Po and Po, are nongaseous and adhere readily to atmospheric particulate matter. In some areas where radon is produced, homes have had to be fitted with ventilation systems to prevent radon infiltration. 

Because there are few data on the results of human exposure to actinides, the health effects of these radioelements are more uncertain than those discussed above for ionizing radiation, radon, and fission products. Americium accumulates in bones and will likely cause bone cancer due to its radioactive decay. Animal studies suggest that plutonium will cause effects in the blood, liver, bone, lung, and immune systems. Other potential mechanisms of chemical toxicity and carcinogenicity of the actinides are similar to those of heavy metals and include (i) disruption of transport pathways for nutrients and ions (ii) displacement of essential metals such as Cu, Zn, and Ni ... 

Such systems are called radioisotope generators. Rn is sometimes used for the radiotherapeutic treatment of cancer. This product is isolated by separating it as a gas from the parent substance Ra which is normally in the form of solid or a solution of RaBr2. Rn grows into the radium sample with a half-life of 3.8 d. After a 2-week period, following a separation of radon from radiiun, approximately 90% of the maximum amount of radon has grown back in the radium sample. Consequently, it is useful to separate Rn each 2 weeks from the radium samples since further time provides very little additional radioactivity. The Rn is an a emitter the ther utic value comes from the irradiation of the tissue by the y-rays of the decay daughters Pb and Bi which reach radioactive uilibrium extremely rapidly with the Rn. 

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