POLONIUM-216 MOBILITY MEASUREMENTS USING A DIFFERENTIAL MOBILITY ANALYZER

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 cm2 V-1 s-1 with an average value of 1.04 cm2 V-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 cm2 V-1 s-1). The charge neutralization rate of the Po-216 ion in air at 20-degrees-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 X 10(-6) and 3.1 x 10(-3) kg m-3, respectively. For nitrogen dioxide-air mixtures, the specific rate constant for electron transfer was between 1 x 10(-10) and 5 x 10(-9) s-1.