Search for one-phonon mixed-symmetry states in the radioactive nucleus 140Nd

Low-spin excited states of 140Nd have been studied via the 140Ce(3He,3n)140Nd reaction. The data show that one of the candidates for the one-phonon mixed symmetry state of 140Nd, namely the 2+3 state at 2140 keV with an effective lifetime of 220(90) fs, exhibits a fast M1 decay to the 2+1 state. Thus this state can be considered, at least, as a fragment of the one-phonon MSS of 140Nd. This is the first example where mixed symmetry character is tentatively assigned to a state of an unstable nucleus from the mass A∼140 region based on the data on absolute M1 transition rates. However, the data are not conclusive on whether this decay exhausts the total M1 strength or whether the one-phonon mixed symmetry state of 140Nd is fragmented.