Ilan Roth University of California, Berkeley, CA, USA
The sun constitutes a source of energetic particles either via internal processes or through formation of interplanetary shocks. The common underlying feature of all acceleration processes is magnetic activity related to flares or coronal mass ejections. Comparison of other young stellar objects to our Sun some 4.5 billions years ago indicates a significantly more intense magnetic activity than at present, resulting, presumably, in more frequent acceleration of solar particles and in filling of the interplanetary medium by energetic ions. Of particular interest are the large enhancements of the energetic rare He-3 ions, heavy elements (mainly Fe and elements heavier than O) and their particular charge states. Recent measurements indicate that He-3 is seen not only associated to impulsive flares but also during periods of gradual events. The importance of these observations will be viewed in the context of the formation of rare radionuclides in the protosolar cloud. Since neither supernova nor bombardment by the main solar energetic particles can explain quantitatively the production of several short-lived radionuclides, it is postulated that reactions with the energetic rare isotopes which are ejected into the early solar nebula may explain the observations of the large abundances of radioactive, short-lived fossil elements in meteorites which were formed in the early solar system and solidified before most of the radionuclides decayed. Of particular interest are the measurements in Ca-Al inclusions of anomaly in the isotopic abundance of Mg-26 which is a decay product of the radioactive Al-26 (lifetime 1.1 Myears). The interaction with energetic He-3 may explain the 20-fold enhancement of the deduced Al-26/Al-27 ratio.