Radioluminescence of Alpha-Particle Excited Gases in 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 investigate the suitability of N2 as a medium to remote detect alpha radiation, the weak but detectable alpha induced fluorescence signal in the solarblind region (lambda<300nm) have been studied. Nitrogen has been mixed with varying amounts of O2 and Ar in order to find an optimal mixing ratio to achieve maximal signal intensity.Studies of the fluorescence signal have shown that the observed spectrum can be described by assigning the alpha particle excited N2 an effective temperature. Quenching processes within a single electronic excitation of the nitrogen redistribute the vibrational population density in such a way that it resembles the population density described by the Boltzmann distribution.[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