Optical Emission from Alpha-Particle Excited Environmental GAses in the Deep Ultraviolet Regime

Alpha emitting radiation sources are hard to detect due to the short range of alpha particles in air. A remote detection of alpha radiation in air is possible by measuring ionization-induced fluorescence of air molecules [1]. Alpha-induced ultraviolet (UV) light is mainly emitted by molecular nitrogen (N2) and its fluorescence properties are well studied. The benefit of this method comes with the long range of UV-photons in air. However ultraviolet fluorescent light of N2 is weak compared to the solar background lighting, which makes special discrimination methods necessary [2]. To further develop this concept and reduce the influence of daylight the deep ultraviolet optical emissions from different atmospheric gases excited by alpha-particles have been studied. N2, O2 and Ar have been mixed in varying proportions to compound gases in order to study interdependent quenching effects on the emission properties in the solar-blind region (<300 nm). Static and dynamic quenching effects on these gases and their alpha-radiation induced chemical products have been identified. The results support the notion that the presence of alpha-particles disturbs the electronic-vibrational population density of N2 in such a way that it can be utilized for active solar-blind spectroscopy. [1] Lamadie F. et al. “Remote alpha imaging in nuclear installations: New results and prospects” IEEE Transactions on Nuclear Science 52: 3035-3039 (2005) [2] Ville H., Toivonen J., Toivonen H., Sand J. ”Optical remote detection of alpha radiation” Oral Presentation S11-04 at the Third European IRPA Congress 2010, Helsinki, Finland