Remote optical detection of alpha particle sources.

Spectral investigations of the phenomenon of alpha-radioluminescence in the atmosphere have been carried out in the UV-V region. It was found that: (1) more than 95% of the intensity of the alpha radiation induced luminescence (alpha-radioluminescence) falls in the narrow range between 310 and 400 nm, (2) the alpha-radioluminescence spectrum consists of a small number of bands typically 2-3 nm wide and belonging to the 2+ system of nitrogen molecule transitions, (3) each alpha particle emitted from the surface causes creation of approximately 30 UV photons in ambient air, (4) alpha particles emitted from the source surface have an angular distribution proportional approximately to cos8 (theta). By determining the main features of the alpha-radioluminescence spectrum, it should be possible to design optical methods and techniques for the indirect remote detection of alpha particle sources even in the presence of a high background of beta or gamma radiation. With the aim of proving this possibility, a laboratory model of an optical receiving system was designed and tested. From a distance of 30 m, the optical image of a clean alpha source (239Pu, 3.7 x 10(7) Bq) placed close to a high activity gamma ray source (60Co, 18.5 x 10(7) Bq) was captured photographically by the model system. The possibility of the practical indoor implementation of such a passive optical method for the remote (hundreds of metres) detection of alpha particle sources even in intense beta/gamma radiation fields is discussed. The potential for an active version of the method is also considered.