Study of nuclear-nuclear reaction by heavy primary cosmic ray

A balloon flight was made to observe the heavy primary cosmic ray and to study the nuclear-nuclear reaction. The incident energy of particles was 10 GeV to 1 TeV/nucleon. The flight was carried out on May 26, 1981, and continued for 5.25 hours at the altitude of 32.5 km. The detection system was an emulsion chamber which consists of 103 layers of nuclear plates and 16 CR-39 plastic detectors. The charge of heavy primary particles was determined by the CR-39 detectors. The automatic measuring system for the minor and the major axes of etch pits in CR-39 was designed and constructed. These systems are an edge tracking system and an area analyzer system. The charge distribution of particles was obtained from the major and the minor axes and the dip angles. The measured flux intensity of VH nuclei was about 1.7 x 10-1/m2.sec.str, which was in agreement with the other observed results for particles with the effective cut-off energy of 3.5 GeV/n. The collision cross-sections of various target nuclei with VH nuclei were obtained. The fragmentation probability of incident nuclei was also obtained. Development of a large area plastic emulsion chambers is in progress. (Kato, T.)