Charge identification in CR-39 nuclear track detector using relativistic lead ion fragmentation

Three stacks of plastic CR-39 Nuclear Track Detectors (NTD) were exposed to 158 A GeV ²⁰⁷Pb ions at the CERN-SPS beam facility. The main purpose of this experiment was the calibration of the CR-39 for the search of atmospheric magnetic monopoles. Different targets (Al, Cu and Pb) were used to produce a large spectrum of charge ions for the purpose of calibration as well as the study of ultrarelativistic lead ion fragmentation. The exposure of each stack was performed at normal incidence with a fluence of about 1500 ion/cm ². The total number of lead ions in each spill was about 7.8×10 ⁴ and there were eight spills incident on each stack. For the stack with the Cu target, the lengths of etched cones on one face of the CR-39 were measured. From this measurement procedure, a new calibration curve has been generated for the extended charge region 63⩽ Z⩽83. The charge resolution ( σ_Z) achieved by this technique is ∼0.18 e-0.21 e.