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We analyzed several CR39 detector foils which had been exposed to the cosmic radiation during the Spacelab 1 mission. Particle tracks in the CR39 were detected and measured by an automatic measuring system. Methods of separation of the tracks from background structures on the foil surface which were also detected by the system are discussed in this paper. Due to the low registration threshold of the CR39 we can measure minimum ionizing iron nuclei, which form a peak in the differential LET-spectrum. Thus we get a point of calibration for each measured detector foil. An example of a measured LET-spectrum is presented and discussed.

We developed a completely automatic scanning and measuring system for nuclear track detectors. The video pictures of particle tracks seen through a microscope are digitized and analyzed in real time by MC 68000 microprocessors. In this paper we present some new developments: The picture analysis software is extended to separate overlapping tracks and to measure elliptical tracks even if these are flawed by surface structures. A software autofocus, a faster hardware version based on the contrast and a modified commercial laser autofocus are now available. A new picture analysis system based on the faster 32-bit microprocessor MC 68020 will operate on two pictures of 1024 × 1024 pixels resident in memory together. This will allow three dimensional track measurements.