Properties of 220Rn progeny ( 212Pb) in the presence of trace gases

Abstract

The charge neutralization of 220Rn progeny ( 212Pb) was studied in nitrogen and argon environments containing trace concentrations of ethylene, propylene and propane. The diffusion coefficient of 212Pb atoms in the presence and in the absence of oxygen and hydrocarbons was determined using a diffusion tube method which measured the penetration fraction of the 220Rn decay products. The results are explained in terms of the formation of lead dioxide with an ionization potential in the range of 10.5–11.1 eV. The ionization potential of 212PbO 2 was found to be higher than that of 218PoO 2. Charge neutralization was found to occur in a gas mixture of argon and oxygen containing 600 ppm ethylene (C 2H 4) and also in a mixture of nitrogen and oxygen containing 600 ppm propylene (C 3H 6). Charge neutralization was not found to occur in a mixture of argon and oxygen containing up to 5000 ppm propane (C 3H 8) and in a mixture of argon and nitrogen containing 600 ppm ethylene. In pure oxygen, nitrogen, argon, dry air and a mixture of nitrogen and oxygen, no neutralization was observed to occur through charge transfer from neutral molecules. The 220Rn concentration was found to influence the neutralization mechanism. Diffusion coefficients for partially neutralized and neutralized 212Pb ranged from 0.050 to 0.067 cm 2 s −1 at a 220Rn concentration of 3.7 × 10 4 atoms cm −3 and a relative humidity of < 5%.