Gamma-Ray Decay of the Bound Levels ofB12

Abstract

Particle-$\gamma$ and $\gamma -\gamma$ coincidence measurements on the ${\mathrm{B}}^{11}(d, p\gamma ){\mathrm{B}}^{12}$ reaction were performed to determine the decay schemes of the bound excited states of ${\mathrm{B}}^{12}$. Branching ratios for the decay of the second excited state (1.67 MeV) to the ground state and first excited state (0.953 MeV) were determined to be (96.8±0.5) and (3.2±0.5)%, respectively. The 2.62-MeV third excited state was found to decay to the ground state with a branch of (6±1)%, and also to the first and second excited states with branches of (80±3) and (14±3)%, respectively. The last two values are from a $\gamma -\gamma -\gamma$ coincidence measurement of the 2.62→1.67→0.95→0 triple cascade. Ge(Li) measurements of the 2.62→0.95 transition energy yield a value of 2620.8±1.2 keV for the excitation energy of the initial state. A lower limit on the ground-state decay of the 2.723-MeV level of >85% was determined from $p-\gamma$ coincidence measurements. These results are combined with previously available information on lifetimes, spins, and parities to permit a comparison with the shell-model predictions for the electromagnetic transitions connecting the bound levels of ${\mathrm{B}}^{12}$.