Characteristics of the copolymerized CR-39/DAP track detector for the observation of ultra heavy nuclei in galactic cosmic rays

A new copolymer of CR-39 and DAP resin was developed for the selective detection of ultra heavy nuclei in galactic cosmic rays. The track registration sensitivity for heavy ions with various Z*/β was verified for copolymers mixing CR-39 (BARYOTRAK) with various concentrations of DAP using heavy ion beams at the HIMAC accelerator. In order to realize sufficient polymerization of CR-39/DAP copolymer, the optimum fabricating method was also verified by modifying the concentration of the initiator and temperature-time curing cycle for the copolymerization. CR-39 (BARYOTRAK) used for the base material of copolymerization has many advantages: 1) high uniformity of detector response, 2) extremely clear surface condition after etching, and 3) excellent charge and mass resolutions for heavy ions. The surface condition of the copolymer after etching is remarkably improved by using the BARYOTRAK monomer and its track registration sensitivity is controllable by changing the DAP concentration. However the detection threshold of the CR-39 (BARYOTRAK)/DAP copolymer is not yet satisfactory.