The reduction of indoor air concentrations of radon daughters without the use of ventilation.

The possibility of using filtration and electric fields both separately and in combination to reduce the indoor air concentrations of radon daughters is described in theoretical terms and with reference to investigations in experimental rooms. For energy conservation considerations these investigations were carried out without reducing the radon concentration by ventilation or other means. The importance of aerosols to the effectiveness of these methods is also described. It is demonstrated that it is possible by use of filtration rates of 3 - 4 times per hour to reduce the potential alpha energy concentration by a factor of 4 - 5. In case of low aerosol concentration the corresponding reduction in lung dose may be much smaller, depending upon the dose-exposure model used, due to the filtration-caused change in the partitioning of the radon daughters between the attached and un-attached states.

The determination of radon exhalation rates.

The exhalation of radon from porous materials like mining wastes and building materials can be determined by studying the growth of radon activity in vessels containing samples of the materials. It is demonstrated that the initial part of the activity growth curve determines the total free exhalation rate of the sample used, independently of container leakage and back diffusion. It is furthermore shown that a specific area exhalation rate adequately describes the exhalation process, when the exhalation is restricted to take place in one direction only, and when the dimension in the exhaling direction is greater than approx. 2 times the diffusion length. A determination of the free surface exhalation rate as a function of the sample thickness also yields information on the diffusion length, as well as the radon production rate per unit volume of material. In case of sample dimensions smaller than about half the diffusion length, the total exhalation rate is shown to be proportional to the mass or volume of the sample.

The effect of electric fields on 222Rn daughter products in indoor air.

A fraction of the short-lived airborne daughter products of 222Rn are charged (positively) and can thus be removed from the air by means of an electric field. A theory is presented which gives the relation between the charged fraction and the total individual daughter activity at equilibrium as a function of the field applied. The theory also allows a deduction of the mobilities of the charged daughter products. Preliminary measurements were performed in a basement room with very low ventilation rate and fairly high radon concentration (5-10 pCi/l.). The electric field was established by applying a voltage to a wire mounted at a height of 1.7 m above the floor and 1 m from the walls. The radon concentration of the air as well as the concentration of the individual 222Rn daughter products were measured at various wire voltages. As an approximation the field was assumed to have a cylindrical configuration. The preliminary results indicate that, at moderate radon activities (lower than approx. 10 pCi/l.) and low condensation nucleus concentrations, the relative activities of the positively charged daughter products are about 1:4:0.8 at equilibrium in the absence of an electric field. The measurements also show that the Working Level may be lowered by a factor of 2-3 applying a voltage of a few thousands volts to the wire.