Two-phonon character of the lowest electric dipole excitation in142Nd and in other nuclei near shell closures

A resonant inelastic proton scattering experiment was carried out to investigate the $\ensuremath{\gamma}$ decay of the lowest lying 1${}^{\ensuremath{-}}$ state in the $N$=82 nucleus ${}^{142}$Nd. A very high sensitivity for the detection of the $\ensuremath{\gamma}$ rays was achieved by combining the Osiris Cube array with a Euroball Cluster detector. The observed $\ensuremath{\gamma}$ decay of the dipole excitation is a direct proof of the dominant two-phonon character of the lowest 1${}^{\ensuremath{-}}$ state in this nucleus. A survey of the branching ratios in the magic neutron number $N$=82 region and the energy systematics of candidates for two phonon 1${}^{\ensuremath{-}}$ states in other nuclei in the vicinity of various shell closures point to a high degree of harmonicity of the (2${}^{+}\ensuremath{\bigotimes}{3}^{\ensuremath{-}})$ coupling.