THE B-11 B-10 RATIO OF LOCAL INTERSTELLAR DIFFUSE CLOUDS/

The isotopic ratio B-11/B-10 of gas in diffuse interstellar clouds tow ard zeta Oph, kappa Ori, and delta Sco is measured using HST/Goddard H igh Resolution Spectrograph echelle spectra of the B Pi 1362 Angstrom line. To within the errors of measurement, the three lines of sight gi ve identical results for a mean value of B-11/B-10 = 3.4 +/- 0.7, a va lue quite similar to the solar system ratio of 4.05. These results sho w that the latter value is not highly anomalous and that a ratio highe r than 2.5, as predicted for boron produced from spallation reactions controlled by high-energy cosmic rays, most probably requires a genera l explanation. The observed ratio is consistent with additional boron production either by spallation by low-energy (''Orion'') cosmic rays or by neutrino-induced spallation of carbon in Type II supernovae. The total abundance of B in the diffuse clouds is a factor of 5 less than the meteoritic value. This depletion of B is consistent with that fou nd for Cu and Ga, two elements with a condensation temperature similar to B.