| Autor: |
María M. Vivas, Andreas Schmidt-Ott, E. Hontañón |
| Rok vydání: |
2008 |
| Předmět: |
|
| Zdroj: |
Journal of Aerosol Science. 39:191-210 |
| ISSN: |
0021-8502 |
| DOI: |
10.1016/j.jaerosci.2007.11.001 |
| Popis: |
A low-level radioactive charger based on 241Am was developed and tested. Its activity ( 0.24 μ Ci ) is below the exemption limit of IAEA. The design leads to values of the N i t product ( ∼ 10 13 m - 3 s ) comparable to current radioactive ionizers with activities up to three orders of magnitude higher. The performance of the weak radioactive 241Am ionizer was assessed experimentally and by means of a numerical model based on Fuchs theory. The results show that the 241Am ionizer charges to steady state particles less than 250 nm at number concentrations up to 10 6 cm - 3 at a maximum flow rate of 2.5 l min - 1 . These conditions correspond to values of the particle to ion concentration ratio N p / N o less than unity and a residence time of 5 s. For particle to ion concentrations above unity, the model predicts that the time to steady state increases strongly with both particle size and aerosol particle concentration. For N p / N o ≅ 10 , the minimum time to achieve stationary charging conditions in the 241Am ionizer is 10 s, for particles of 50 nm. In accordance with the numerical results, a simple analytical criterion is derived, which predicts whether an aerosol of given concentration and mean particle size is charged to steady state in an arbitrary radioactive bipolar ionizer. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
|
Full Text from ScienceDirect