The properties of ${K=0\mathrm{}}^{+}$ excitations in deformed and transitional nuclei have recently been of intense interest. We present results of a study of the deexcitations of the lowest excited $0^{+}$ state in ${}^{152}$Sm from the $\epsilon$-decay of ${}^{152}$Eu, yielding one of the few precisely known values of the branching ratio $R_{0g}^{\gamma }{=B(E2;2\mathrm{}}_{\gamma }^{+}\to 0_2^{+}{)/B(E2;2\mathrm{}}_{\gamma }^{+}\to 0_1^{+})$ =0.048(4), which is extraordinarily small. From $T_{1/2}{(2\mathrm{}}_{\gamma }^{+})$ we also obtain ${B(E2;2\mathrm{}}_{\gamma }^{+}\to 0_2^{+})$=0.17 W.u. Values of $R_{0g}^{\gamma }$ calculated in the interacting boson model (IBA) go to zero extremely rapidly, changing by orders of magnitude for a narrow range of parameter values. ${}^{152}$Sm is a rare case of a transitional nucleus that lands almost at the minimum. ${}^{152}$Sm and ${}^{154}$Gd are the only nuclei from $90<~N<~114$ where the $B\left(E2\mathrm{}\right)\mathrm{}$ values for all four transitions $2_{\gamma }^{+}\to 0_2^{+}$, $2_{\gamma }^{+}\to 0_1^{+}$, $0_2^{+}\to 2_1^{+}$, and $2_1^{+}\to 0_1^{+}$ are now known. In ${}^{152}$Sm these $B\left(E2\mathrm{}\right)\mathrm{}$ values span three orders of magnitude, from 144 to 0.17 W.u. and are reproduced to within a factor of 2–3 by the IBA. The rather strong ${B(E2;0\mathrm{}}_2^{+}\to 2_1^{+})$ value of 33 W.u. suggest that the $0_2^{+}$ level is an example of a good low energy $\beta$-vibration.

• Received 3 September 1997

DOI:https://doi.org/10.1103/PhysRevC.57.R1553