Investigation of dipole excitations inCe142using resonant photon scattering

Abstract

A photon scattering experiment with bremsstrahlung has been performed on the vibrational nucleus $^{142}\mathrm{Ce}$ up to a photon endpoint energy of $4.1\phantom{\rule{0.3em}{0ex}}\text{MeV}$. Fourteen dipole excitations have been observed between 2.1 and $3.9\phantom{\rule{0.3em}{0ex}}\text{MeV}$, five of them for the first time. A candidate for the ${1}^{\ensuremath{-}}$ dipole member of the recently proposed quintuplet of negative parity ${({2}_{1,\text{ms}}^{+}\ensuremath{\bigotimes}{3}_{1}^{\ensuremath{-}})}^{({J}^{\ensuremath{-}})}$, involving the ${2}_{1,\text{ms}}^{+}$ isovector quadrupole excitation in the valence shell, has been identified. This exotic ${1}_{\text{ms}}^{\ensuremath{-}}$ state has been predicted within the $sdf$-IBM-2 and is expected to be accessible to photon scattering measurements. Solely one of nine $J=1$ states in the energy region of interest shows a decay pattern compatible with the model predictions for the ${1}_{\text{ms}}^{\ensuremath{-}}$ state.