Neutralization of thoron progeny in gases

This paper reports charge neutralization phenom­ena of²¹²Pb particles in nitrogen or oxygen atmospheres with trace amounts of other gases. Newly produced thoron or radon progeny are positively charged, stable molecular clusters that are subsequently neutralized by several mechanisms. The charged clusters have a smaller diffusion coefficient than neutral clusters of the same size due to the interaction of the charge with the surrounding gas molecules. In this study, we have found that the diffusion coefficients of²¹²Pb in 0₂, N₂, NHj/Oj, NH3/N₂, and C₆H₁₂/N₂ (IPs between 15.58 and 9.8 eV) ranged between 0.015 and 0.030 cm² s^-1. In the case of C«Hi2/0₂, N0₂/0₂, N0/0₂, and dimethylamine/0₂ (ionization potential between 9.8 and 8.23 eV), the diffusion coefficients have increased to between 0.046 and 0.69 cm² s^-1. These results are consistent with previous results of²¹⁸Po, indicating that charged progeny are neutralized by electron transfer from a gas molecule with a lower ionization potential than lead oxide. We estimate the ionization potential of lead oxide to range between 9.8 and 10.2 eV.²¹²Pb was also neutralized by an electron scavenging mechanism in NOnitrogen.