First Observation of the Neutron-Rich IsotopeB19

The particle stability of ${}_{}{}^{19}{}_{}{}^{}\mathrm{B}$ and the particle instability of ${}_{}{}^{18}{}_{}{}^{}\mathrm{B}$ are demonstrated. Light neutron-rich nuclei were searched for among the projectile fragments resulting from interactions of a $670A$- MeV ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$ beam in a 7.9-g/${\mathrm{cm}}^2$ Be target. A detector consisting of a magnetic spectrometer, threshold Cherenkov paddles, and scintillator paddles was used to determine the charge and mass of the projectile fragments.