Observing Short-wave Infrared Atmospheric Fluorescence Near Radioactive Sources: A Feasibility Study.

摘要

We attempted to image atmospheric fluorescence in the short-wave infrared (SWIR) from several radioactive sources. Our detection system was an InGaAs camera, fitted with a 25 mm lens to image the scene. No definitive fluorescence was detected. We also used our system to observe the SWIR emission from a proton beam source and established certain criteria for use as fluorescence diagnostics. For example, we clearly observed an enhancement at 1050 nm relative to 1600 nm, consistent with known emission features of molecular nitrogen and with previously published results. However, even for a high activity cobalt-60 source, our recorded signal was not consistent with these diagnostics. Rather, we hypothesize that the small signal which was recorded may have been due to direct incidence of gamma rays on our detector. Compared with the ultraviolet (UV), the infrared emission is expected to be only 20% as bright. We suggest that to increase the signal to noise in the SWIR may require either a telescope to collect a greater fraction of the emission or to image a more localized source than the gamma emission. Further research should include coincident UV and SWIR observations.