The use of soft X-rays in a neutrahzer represents an alternative technique that could replace conventional radioactive sources.In this study,we evaluated the charging characteristics of a soft X-ray aerosol neutralize!“.In addition,the results from the evaluation of the soft X-ray charger were compared with results obtained using a neutralizer incorporating an ~(241)Am radioactive source.The tandem differential mobility analyzer technique was used previously to determine the size-dependent positive,negative,and neutral charge fractions of a soft X-ray neutralizer.This technique was used to show that the neutral fractions obtained using the soft X-ray charger agreed well with the predictions of bipolar diffusion charging theory,and that the soft X-ray charger could be used as a neutralizer for a scanning mobility particle sizer system. The use of soft X-rays in a neutrahzer represents an alternative technique that could replace conventional radioactive sources. In this study, we evaluated the charging characteristics of a soft X-ray aerosol neutralize! ”. In addition, the results from the evaluation of the soft X-ray charger were compared with the results obtained using a neutralizer incorporating an ~ (241) Am radioactive source. The tandem differential mobility analyzer technique was used previously to determine the size-dependent positive, negative, and neutral charge fractions of a soft X-ray neutralizer. This technique was used to show that the neutral fractions obtained using the soft X-ray charger agreed well with the predictions of bipolar diffusion charging theory, and that the soft X-ray charger could be used as a neutralizer for a scanning mobility particle sizer system.