Volume 9, No. 4, December 2009, Pages 453-457 PDF(316 KB)
First Differential Mobility Analysis (DMA) Measurements of Air Ions Produced by Radioactive Source and Corona
Manuel Alonso1, José P. Santos2, Esther Hontañón2, Emilio Ramiro2
1 National Centre for Metallurgical Research (CSIC), Avenida Gregorio del Amo 8, 28040 Madrid, Spain
2 RAMEM S.A., Sambara 33, 28027 Madrid, Spain
A recently developed Differential Mobility Analyzer (DMA) of high resolving power (50 for ions of mobility equivalent diameter ~1 nm) has been used to measure the mobility distribution of laboratory air ions generated by 241Am and corona discharge. In the case of 241Am, it has been possible to follow the changes in mobility during the early stages of ion aging: within the time interval between 10 and 30 ms after ion formation, the mean reduced mobility of positive ions decreased from 1.30 to 1.15 cm2/Vs, and that of negative ions from 2.0 to 1.75 cm2/Vs. The mobility distribution of air ions at the outlet of a corona ionizer strongly depends on the corona voltage, mainly due to the mobility-dependent extent of electrostatic losses within the ionizer. The mean reduced mobility of corona ions ranged between 1.01 and 1.20 cm2/Vs (positive) and 1.76 and 1.96 cm2/Vs (negative).
Differential mobility analyzer; Resolution; Ion aging; Radioactive source; Corona discharge.