Extended calibration of a CR39 nuclear track detector with 158 A GeV 207Pb ions

Six stacks of nuclear track detectors (CR39 and Makrofol) were exposed to 158 A GeV 207Pb ions at the CERN-SPS. The main purpose of the experiment was the calibration of the CR39 nuclear track detector used in a large area experimental search for magnetic monopoles at the Gran Sasso Laboratory (the MACRO experiment). Different targets (C, CH2, CR39, Cu and Pb) were used in order to study also the fragmentation properties of ultrarelativistic lead nuclei. The exposures were performed at normal incidence and at a density of about 2000 ions/cm2. The total number of lead ions in a stack was about 5.8×104. For the stack with the lead target, we measured the base area and the length of the etched cones. We obtain a unique calibration curve for the charge region 7≤Z≤83 combining the two types of measurements. Using the cone length method, we obtain a charge resolution σZ≃0.19e for Z=82 ions using a single measurement in one face of CR39.