Development of telescope for cosmic gamma ray in the vicinity of 10 MeV

Though the observations with the satellite SAS-II gave a number of informations on the origin and the GeV region of cosmic ray, only the energy spectra were obtained with about 10% energy resolution in the other energy region of more than 1 MeV and less than 8 MeV, and the information on the spatial distribution is scarcely obtained. The authors intend to grasp the flux of 10 to 30 MeV diffuse components from the high galactic latitude or to determine the flux and the rough spatial distribution of cosmic ray at the same energy from the galactic surface. From the result of the tests of the telescope with the cosmic ray on the earth surface, it was known that the position counter picked up noise. Accordingly, the counter was improved. On the efficiency of the telescope, Monte Carlo calculation was performed. From this result, the counter seemed to be usable in the range of ca. 15 MeV to 50 MeV, though the efficiency was too low for the detection of incident ray of 10 MeV or less. Since the gamma ray obtained by the (n, γ) reaction used last year as a telescope calibration source contained considerable background, it is planned to use 17.6 MeV γ-ray by the 7Li(p,γ)8Be reaction using a Van de Graaf accelerator for the calibration this year. (Wakatsuki, Y.)