Experimental investigation of the 02+ band in Sm154 as a β-vibrational band

A study of Sm154 through γ  -ray and internal conversion electron coincidence measurements was performed using the Silicon And GErmanium spectrometer (SAGE). An upper limit for the ρ2(E0;22+→21+) and measurement of the ρ2(E0;42+→41+) monopole transitions strengths were determined. The extracted transition strength for each is significantly lower than that predicted by either the Bohr and Mottelson β  -vibration description or the interacting boson model. Hence, the long standing interpretation of these states as a collective band built on the 02+ state, which is conventionally assigned as a Bohr and Mottelson β vibration is questionable.