Evidence for radiative coupling of the pygmy dipole resonance to excited states

Abstract

The photoabsorption cross section and ground-state branching ratio of ${}^{142}$Nd were measured using quasimonoenergetic $\ensuremath{\gamma}$-ray beams at several beam energies. Two peaks corresponding to the pygmy dipole resonance (PDR) were identified. The branching ratios were compared to statistical-model calculations. We found that the Brink hypothesis is violated, and that the branching ratios are only reproduced by introducing a possible new decay mode of the observed PDR.