Multispectral UV-Visual Imaging as a Tool for Locating and Assessing Ionizing Radiation in Air

Ionizing radiation passing through air leads to the ionization of nitrogen in the air; as this nitrogen de-excites it is accompanied with the emission of near-ultraviolet (NUV) light. NUV-sensitive optical imaging may be used to analyze this light to infer the spatial location and distribution of ionizing radiation fields in air. Due to their high linear energy transfer alpha particles are the most readily located and detected using this technique. Overlaying visible light images onto ultraviolet light images of air fluorescence provides a novel, selective method for assessing spatially-inhomogeneous ionizing radiation fields around alpha-emitting sources. The air ionization dose fields near alpha sources are quite high. Near a 0.185 MBq Am-241 source the air dose rate can be as high as 1.57 Gy/hour (157 Rad/hr). Experiments have been performed to evaluate the detection of UV air fluorescence. The range of the high-energy alpha particles from Am-241 is clearly seen with the technique. When evaluating this technique for other radiation fields it may be useful to compare expected dose rates with published alpha ionization field imagery, including a simple measurement described here, for estimating signal strength.