Remote optical detection of alpha particle sources

Abstract

Spectral investigations of the phenomenon of alpha-radioluminescence in the atmospherehave been carried out in the UV–V region. It was found that: (1) more than 95% of theintensity of the alpha radiation induced luminescence (alpha-radioluminescence) falls in thenarrow range between 310 and 400 nm, (2) the alpha-radioluminescence spectrumconsists of a small number of bands typically 2–3 nm wide and belonging to the2+ system of nitrogen molecule transitions, (3) each alpha particle emitted from the surfacecauses creation of approximately 30 UV photons in ambient air, (4) alpha particles emittedfrom the source surface have an angular distribution proportional approximately tocos8(θ).By determining the main features of the alpha-radioluminescence spectrum, it should bepossible to design optical methods and techniques for the indirect remote detection of alphaparticle 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 systemwas designed and tested. From a distance of 30 m, the optical image of a clean alpha source(239Pu, 3.7 × 107 Bq) placed close to a high activity gamma ray source(60Co, 18.5 × 107 Bq) was captured photographically by the model system.The possibility of the practical indoor implementation of such a passive optical method forthe remote (hundreds of metres) detection of alpha particle sources even in intensebeta/gamma radiation fields is discussed. The potential for an active version of the methodis also considered.