Measurement and significance ofΓγ/Γ for the 7117-keV4+level ofO18

The excited $4^{+}$ state at 7117 keV in ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ is studied via the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ ${(}^7$Li,pγ${)}^{18}$O reaction. We show that it is highly improbable that the state is energetically degenerate with a state of different decay properties and that its γ decay is consistent with previously reported values. We obtain a γ-branching fraction ${\mathrm{\Gamma }}_{\gamma }$/(${\mathrm{\Gamma }}_{\gamma }$+${\mathrm{\Gamma }}_{\mathrm{\alpha }}$)=0.561±0.013 which together with recent results for other decay properties gives a B(E2) value of 6.4±1.6 Wu for the 4p-2h intraband transition 7117 $4_2^{+}$→5260 $2_3^{+}$. Shell-model calculations in a full (0+2)ħω basis supplement a previous ${\mathrm{SU}}_3$-truncated (0+2)ħω calculation to the effect that the calculations result in a considerably more collective B(E2) value of >15 Wu for this transition leaving a rather puzzling discrepancy between experiment and theory.