Experimental investigation of the 02+ band in 154Sm as a β-vibrational band

A study of Sm-154 through gamma-ray and internal conversion electron coincidence measurements was performed using the Silicon And GErmanium spectrometer (SAGE). An upper limit for the rho(2)(E0; 2(2)(+) -> 2(1)(+)) and measurement of the rho(2) (E0; 4(2)(+) -> 4(1)(+)) monopole transitions strengths were determined. The extracted transition strength for each is significantly lower than that predicted by either the Bohr and Mottelson beta-vibration description or the interacting boson model. Hence, the long standing interpretation of these states as a collective band built on the 0(2)(+) state, which is conventionally assigned as a Bohr and Mottelson beta vibration is questionable. (C) 2014 The Authors. Published by Elsevier B.V.