Balloon observation of medium energy cosmic gamma-ray

A gamma-ray telescope was developed to observe the cosmic gamma-ray with energy from 10 to 30 MeV. The telescope consisted of position sensitive multiwire proportional counters and an energy counter. The former counters were used to determine the trajectories of the electron-positron pairs produced by high energy gamma-ray, and the latter counter was used to measure the total energy of positron-electron pairs. This telescope was exposed to the 14.7 and 17.6 MeV gamma-rays emitted by the resonance reaction of lithium, and the energy calibration was made. The telescope was borne on a balloon and launched on September 25, 1979. Since the altitude of the balloon was as low as 24.5 km, cosmic gamma-ray was not able to be detected. The preliminary data of growth curves and the energy spectra of atmospheric gamma-ray were reported. (Yoshimori, M.)