An air fluorescence imaging system for the detection of radiological contamination

On-site detection and measurement of the activity and extent of alpha (α) contamination presents a significant challenge to radiation detection personnel. Due to the short range of these particles, conventional detection techniques involve bringing a probe within a few centimetres of the suspect area. Performing a thorough survey of an area is a time consuming, painstaking, and potentially dangerous task, as personnel may be exposed to harmful radiation. Conventional detectors may have fragile Mylar windows which are highly prone to breakage. The instrumentation under development employs a novel approach: instead of detecting the radiation directly, it detects radiation-induced air fluorescence surrounding the contaminated area. Optical imaging is used to determine the spatial extent of the contamination, providing a much more rapid, accurate and robust tool for in-situ contamination measurements. A mobile, near-field, wide-angle, fast optical system has been designed and constructed to detect and image this radiation-induced air fluorescence. It incorporates large-area position-sensitive photo-multiplier tubes, UV filters, a specially constructed fast electronic shutter, and an aspherical phase mask to significantly increase the instrument's depth-of-field. First tests indicate that a 0.3 μCi α source can be detected in less than 10 seconds at a standoff distance of 1.5 meters.