Decay of the 2.34- and 2.71-MeV States of B

Abstract

Proton emission from ${\mathrm{B}}^9$ states at 2.34 and 2.71 MeV has been investigated by populating the states in the ${\mathrm{B}}^{10}({\mathrm{He}}^3,\alpha ){\mathrm{B}}^9$ reaction and by measuring $\alpha -p$ coincidences with a 2-dimensional pulse-height analyzer. The 2.34-MeV $J^{\pi }={\frac{5}{2}}^{-}$ level decays less than 0.5% by proton emission to the ground state of ${\mathrm{Be}}^8$, while the 2.71-MeV level decays nearly 100% by this route. The $1f$ proton reduced width of the 2.34-MeV level for the ground state of ${\mathrm{Be}}^8$ (in units of) $\frac{{\hslash }^2}{m{R}^2}$) is then less than ${5\times 10}^{-3\mathrm{}}$ when $R$ has the value 4.35 F. The co-incidence method clearly resolves the 2.71-MeV $J^{\pi }={\frac{5}{2}}^{+}$ state from the 2.34-MeV state and background, its excitation and width being 2.71±0.03 MeV and 0.71±0.06 MeV, respectively. These figures imply a $1d$ proton reduced width of the 2.71-MeV state for the ground state of ${\mathrm{Be}}^8$ of about 0.7.