Low-lyingE1,M1, andE2strength distributions inXe124,126,128,129,130,131,132,134,136: Systematic photon scattering experiments in the mass region of a nuclear shape or phase transition

Abstract

Systematic nuclear resonance fluorescence (NRF) experiments on all nine stable (seven even-even and two odd-mass) Xe isotopes have been performed at the bremsstrahlung facility of the 4.3-MV Stuttgart Dynamitron accelerator. For the first time thin-walled, high-pressure gas targets (about 70 bar) with highly enriched target material were used in NRF experiments. Precise excitation energies, transition strengths, spins, and decay branching ratios were obtained for numerous states, most of them previously unknown. The systematics of the observed $E1$ two-phonon excitations (${2}^{+}\ensuremath{\bigotimes}{3}^{\ensuremath{-}}$) and $M1$ excitations to ${1}^{+}$ mixed-symmetry states in the even-even isotopes are discussed with respect to the new critical point symmetry E(5). The fragmentation of these fundamental dipole excitation modes in the odd-mass isotopes $^{129,131}\mathrm{Xe}$ is shown and discussed. In the even-even nuclei several low-lying $E2$ excitations were observed.