GAMMA-RAY SPECTRAL OBSERVATIONS WITH YOHKOH

We present gamma-ray observations of the 1991 October 27, November 15, and December 3 flares with the Yohkoh gamma-ray and hard X-ray spectrometers. The October 27 flare(X6.1/3B)shows significant gamma-ray line emission, and the temporal evolution of the gamma-ray line-to-bremsstrahlung flux ratio indicates that protons and electrons were complicatedly accelerated during flare. The December 3 flare(X2.0/2B) shows a strong bremsstrahlung continuum extending to 10MeV. A line feature at 420keV was observed from the November 15 flare(X1.0/3B). This is most likely due to a compound of redshifted nuclear deexcitation lines of Be(429keV) and Li(478keV) resulting from He-He reactions. The spectral feature indicates that the accelerated He nuclei suffer strong pitch-angle scattering in the corona and from a downward-peaked distribution. Furthermore, the November 15 flare exhibits evidence of positron annihilation line at 511 keV. The positron production processes and the electron density of the annihilation region are discussed on the basis of the temporal characteristics of 511 keV line emission.