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.