Cosmic ray LET-spectra investigated by automatic scanning and measuring of plastic nuclear track detectors

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.