Gamma decay of high-spin states inTi47

Abstract

The compound nucleus reaction $^{45}\mathrm{Sc}(\ensuremath{\alpha},np\ensuremath{\gamma})^{47}\mathrm{Ti}$ was used to confirm the high spins of states, observed previously in the ($\ensuremath{\alpha},d$) reaction, by studying their $\ensuremath{\gamma}$ decay. Measurements of $\ensuremath{\gamma}$-$\ensuremath{\gamma}$ coincidences, $\ensuremath{\gamma}$-ray excitation functions, and $\ensuremath{\gamma}$-ray angular distributions for several target thicknesses have been performed. These measurements allowed us to determine the energies and the spins for some of the observed levels, as well as the branching ratios and the multipolarities for the emitted $\ensuremath{\gamma}$ rays. Lifetimes for a few states were deduced from the Doppler shifts which were exhibited in the angular distributions. Shell-model calculations were made assuming an inert $^{40}\mathrm{Ca}$ core and all active nucleons in the $1{f}_{\frac{7}{2}}$ shell. Agreement between the measured and calculated branching ratios and multipolarities is excellent for all the yrast levels, and even the lifetimes of these states are predicted rather well by the theory. For two other levels, at 2.684- and 3.289-MeV energy, disagreement between the measured and calculated $\ensuremath{\gamma}$ decay is observed. The lifetime of the lower of these two states was found to be unusually slow for an $M1$ transition. This result suggests that perhaps the earlier spin assignments for both states are wrong. For the 2.684-MeV state a spin of either ${\frac{7}{2}}^{+}$ or ${\frac{11}{2}}^{+}$ is in agreement with all the available experimental data.[NUCLEAR REACTIONS $^{45}\mathrm{Sc}(\ensuremath{\alpha},\mathrm{np}\ensuremath{\gamma})$, $E=23$ MeV; measured $\ensuremath{\gamma}$ spectra, $\ensuremath{\gamma}$-$\ensuremath{\gamma}$ coincidences. Deduced decay scheme, multipolarities, ${T}_{\frac{1}{2}}$, ${J}^{\ensuremath{\pi}}$. Shell-model calculations].