New field-deployable image processing system for same-day analysis of nuclear track detectors

Nuclear Track Detectors (NTDs) can be used for detecting alpha-emitting radiological contamination (e.g. Pu, Am, U, Th) on surfaces and in soils. The primary disadvantage of this approach for field screening applications is the time required for analysis of the detectors. A R and D team at ORNL has developed a prototype analysis system which is sufficiently compact to be deployed in a van or on-site laboratory. The complete system consists of etch/rinse tanks, optical microscope, stepping motors, CCD camera, frame-grabber, and an image analysis software package. In addition to conventional gross counting of etch pit densities, two new capabilities are under investigation. Alpha particles are emitted radially from hot particles, and therefore hot particles generate starburst clusters of tracks in a track detector with very characteristic patterns. The image analysis system can be configured to search for and analyze these patterns, yielding quantitative size distributions of hot particle contaminants. Using this approach, the presence of hot particles has been determined in soil samples from the Nevada Test Site and Johnston Atoll. The second capability involves identification of radiological contaminants. A group at the University of Bristol, UK, has demonstrated that detailed analysis of the size and shape of individual alpha tracks can lead to a determination of the energy of the alpha particle that generated the track. Alpha particles are emitted at discrete energies from different radioisotopes, and therefore inexpensive and fast alpha spectroscopy can be carried out to identify unknown alpha-emitting contaminants. Progress on optimizing the image analysis system for this application will be reported