Semi-automated,three-dimensional measurement of etched tracks in solid-state nuclear track detectors

We describe a new method for measuring the shapes and sizes of etched tracks in plastic or glass detectors, using a commercial digital image processing system. The method exploits the fact that in transmitted light any portion of the microscopic image of the track is in best focus when it is darkest. A minimization algorithm is used to produce a two-dimensional projected image of the three-dimensional etched track. The locus of points of maximum gradients in the image leads to a closed contour of the projected image. From this gradient image the profile, length and width of the conical etched track are automatically determined. The method is also applicable (a) to a track that penetrates a detector and has been etched until the cones from opposite surfaces are connected and (b) to a track with a curved profile due to a strongly slowing particle. The method is illustrated with measurements of tracks of 1 A GeV uranium ions in Tuffak polycarbonate and in CR-73 polycarbonate and of cosmic ray tracks in a CR-39 detector.