Using a method whereby molecular and atomic ions are independently selected, an isobarically pure beam of ${}^{70}\mathrm{Se}$ ions was postaccelerated to an energy of 206 MeV using REX-ISOLDE. Coulomb-excitation yields for states in the beam and target nuclei were deduced by recording deexcitation $\gamma$ rays in the highly segmented MINIBALL $\gamma$-ray spectrometer in coincidence with scattered particles in a silicon detector. At these energies, the Coulomb-excitation yield for the first $2^{+}$ state is expected to be strongly sensitive to the sign of the spectroscopic quadrupole moment through the nuclear reorientation effect. Experimental evidence is presented here for a prolate shape for the first $2^{+}$ state in ${}^{70}\mathrm{Se}$, reopening the question over whether there are, as reported earlier, deformed oblate shapes near to the ground state in the light selenium isotopes.

• Received 17 August 2006

DOI:https://doi.org/10.1103/PhysRevLett.98.072501