THE FIRST EXCITED 0(+) STATE IN SM-152

The properties of K=0(+) excitations in deformed and transitional nucl ei have recently been of intense interest. We present results of a stu dy of the deexcitations of the lowest excited 0(+) state in Sm-152 fro m the epsilon-decay of Eu-152, yielding one of the few precisely known values of the branching ratio R-og(gamma)=B(E2;2(gamma)(+) -->0(2)(+) )/B(E2;2(gamma)(+)-->0(1)(+)) =0.048(4), which is extraordinarily smal l. From T-1/2(2(gamma)(+)) we also obtain B(E2;2(gamma)(+) -->0(2)(+)) =0.17 W.u. Values of R-og(gamma) calculated in the interacting boson m odel (IBA) go to zero extremely rapidly, changing by orders of magnitu de for a narrow range of parameter values. Sm-152 is a rare case of a transitional nucleus that lands almost at the minimum. Sm-152 and Gd-1 54 are the only nuclei from 90 less than or equal to N less than or eq ual to 114 where the B(E2) values for all four transitions 2(gamma)(+) -->0(2)(+), 2(gamma)(+)-->0(1)(+), 0(2)(+)-->2(1)(+), and 2(1)(+)-->0( 1)(+) are now known. In Sm-152 these B(E2) values span three orders of magnitude, from 144 to 0.17 W.u. and are reproduced to within a facto r of 2-3 by the IBA. The rather strong B(E2;0(2)(+)-->-2(1)(+)) value of 33 W.u, suggest that the 0(2)(+) level is an example of a good low energy beta-vibration. [S0556-2813(98)50104-5].