Quadrupole-deformed and octupole collective bands in $^{228}$Ra

Spins and parities for collective states in $^{228}$Ra have been determined from conversion electron measurements with a mini-orange $\beta$-spectrometer. The fast-timing $\beta\gamma\gamma(t)$ method has been used to measure lifetimes of T$_{1/2}$=550(20) ps and 181(3) ps for the $2^{+}_{1}$ and $4^{+}_{1}$ members of the K=0$^{+}$ band, and T$_{1/2} \leqslant$ 7 ps and $\leqslant$ 6 ps for the $1^{-}_{1}$ and $3^{-}_1$ members of the K = $0^{-}$ band, respectively The quadrupole moments, $Q_{0}$ deduced from the B (E2; 2$_{1}^{+} \rightarrow 0_{1}^{+}$) and B (E2; 4$_{1}^{+} \rightarrow 2_1^{+}$) rates are in good agreement with the previously measured value and the systematics of the region. However, the B(E1) rates of $\geqslant$ 4 × 10$^{−4}$ e$^{2}$fm$^{2}$, which represent the first B(E1) measurements for this nucleus, are at least 25 times larger than the value previously suggested for $^{228}$Ra. The new results are consistent with the B(E1) rates recently measured for the neighbouring $^{227}$Ra and reveal octupole correlations in $^{228}$Ra.