Detection of nuclear gamma rays from the galactic center region

An experiment involving the balloon-altitude observation of the galactic center region was conducted on April 2, 1974. An actively collimated scintillation counter was used in the experiment. A gamma-ray power-law continuum with a spectral index of 2.78 was detected. Several spectral lines, superposed on the continuum, were detected for the first time. The spectral lines are due to positron annihilation and to nuclear gamma-rays.