Session 7 - Gas and Dust in the ISM.
Display session, Monday, June 10
Great Hall,

## [7.10] The Boron Isotope Ratio in Interstellar Space

S. R. Federman (U. Toledo), D. L. Lambert (U. Texas), J. A. Cardelli (Villanova), Y. Sheffer (U. Texas)

We derived the ^11B/^10B ratio along the sight lines toward two stars, \kappa Ori and \delta Sco, from spectra acquired with the Goddard High Resolution Spectrograph on HST. These interstellar ratios, which are the first determinations beyond the Solar System, were based on analysis of absorption from the weak resonance line of B \small II at 1362 ÅThe interstellar value obtained from our analysis is similar for the two sight lines -- namely, 4 \pm 1. The interstellar value agrees with the boron isotope ratio of 4.05 \pm 0.05 for the Solar System. Our findings are consistent with detailed models of light element nucleosynthesis, which include the effects of spallation from cosmic ray protons on interstellar CNO, from enhanced fluxes of low energy C and O nuclei on interstellar protons, and from neutrinos on ^12C during a supernova explosion. Particular models predict a constant isotope ratio from the time the Solar System formed to the present. Furthermore, our analysis of the B \small II line yielded an isotope shift of 13.7 \pm 3.5 mÅ\ which agrees with the shift of 13.3 mÅ\ obtained from large-scale quantal computations.