Imaging Alpha-Induced Radioluminescence Using the Digital Cherenkov Viewing Device

Alpha particles with a typical kinetic energy of 5 MeV have a range of approximately 4 cm in air. They ionize and excite nitrogen atoms and molecules by secondary electron impact. The de- excitation of these nitrogen species creates characteristic emission peaks in the UV and visible portions of the spectrum and is referred to as radioluminescence. The Digital Cherenkov Viewing Device (DCVD) is an International Atomic Energy Agency (IAEA) instrument designed for the observation and verification of spent nuclear fuel during underwater storage. Cherenkov radiation has a continuous wavelength distribution, and the Cherenkov radiation intensity is approximately inversely proportional to wavelength. This explains the bright blue color that is observed, but it is important to note that most Cherenkov radiation is in the ultraviolet (UV) portion of the spectrum. For this reason, the DCVD imager is optimized for very sensitive imaging in the UV. While the radioluminescence induced by alpha particles in air also produces a UV light signature, it is by a very different mechanism than Cherenkov radiation. However, the DCVD imager has many of the same attributes that a system designed to observe characteristic nitrogen UV light emissions over alpha emitters needs to have: low noise, high sensitivity to UV light and fast UV-compatible optics. These attributes suggest that the high-value DCVD imager, which is already in the IAEA inventory, might be adapted to extend its capability to alpha particle detection. The goal of this work is therefore to explore and enhance the capability of the DVCD system for alpha-induced radioluminescence imaging. This will include proof of concept measurements to determine the sensitivity of the instrument to detect alpha radiation, and possibly a technology demonstration to show the utility of the instrument in a nuclear facility environment. An effective alpha radiation imaging instrument could provide important safeguards verification opportunities to inspect engineering enclosures for process activities with alpha emitters, detect alpha contamination in a non-contact manner and potentially perform holdup measurements on alpha emitters. An added benefit could be that only a small incremental investment might be required to adapt the standard IAEA DCVD for this mission.