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B. Fields (U. of Illinois)
The observations of Be and B in extreme metal-poor Population II stars show that these elements have a Galactic (rather than cosmological) nucleosynthesis source. In particular, Be and B are probably made in one or more kinds of spallation processes, due to cosmic-ray interactions with the interstellar medium and neutrino interactions in supernovae. Consequently, the galactic chemical evolution of Be and B provides unique information about the origin and history of cosmic rays. However, the current data are equivocal about the nature of Be and B origin, as encoded in the primary or secondary (linear or quadratic) scaling with metallicity. The results a careful analysis of the trends among Be, B, Fe, and O are presented, with an emphasis on the importance of the halo star O/Fe relation for interpreting the Be-Fe and B-Fe trends. If O/Fe is constant, then an unconventional cosmic ray origin or component is needed in the early Galaxy. On the other hand, if O/Fe is not constant, as recent data suggest, then the data could indicate a standard cosmic ray origin, wherein the abundances of cosmic rays scale with those of the interstellar medium. Future observational tests are suggested which can distinguish several proposed scenarios of Li, Be, B, and cosmic ray origin.
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