Polonium-216 mobility measurements using a differential mobility analyzer

Abstract

A differential mobility analyzer was developed to determine the mobility distribution of Po-216 ions formed following the decay of Rn-220 and charge neutralization rates for Po-216 ions in air containing trace levels of nitrogen dioxide or aniline. The mobility range for the ions of average age 0.035 s was found to be between 2.2 and 0.5 cm2V−1 s−1 with an average value of 1.04 cm2V−1 s−1. The mobility histogram fitted approximately a log normal distribution with a log mean value of 0.04 and a log standard deviation of 0.29 (a geometric standard deviation of 1.34 cm2V−1 s−1). The charge neutralization rate of the Po-216 ion in air at 20°C and 0.2 kPa water vapor pressure was found to be 43.3 s−1 (S.D. 24.7 s−1). The enhancements in charge neutralization rate for nitrogen dioxide and aniline were 15.5 and 12.5 s−1, respectively (S.D. 6.8 s−1). The nominal nitrogen dioxide and aniline concentrations were 1.9 × 10−6 and 3.1 × 10−3 kg m−3, respectively. For nitrogen dioxide-air mixtures, the specific rate constant for electron transfer was between 1 × 10−10 and 5 × 10−9 s−1.