Spectroscopy of excited states in234U and search for a two-phonon state in234U

Abstract

Excited states of the isotope ${}^{234}$U were studied employing the one-neutron transfer reaction ${}^{235}\mathrm{U}{(d,t)}^{234}$U at a beam energy of 11 MeV. The reaction channel was selected by an identification of the outgoing tritons in a $\ensuremath{\Delta}E$-$E$ measurement. In coincidence with the tritons, $\ensuremath{\gamma}$ rays were also detected with the highly efficient MINIBALL spectrometer. Based on the analysis of $\ensuremath{\gamma}\ensuremath{\gamma}$ coincidence data, the level scheme of ${}^{234}$U was extended. The 4${}^{+}$ state at an energy of 1886.7 keV provides evidence for a possible two-phonon $\ensuremath{\gamma}\ensuremath{\gamma}$ excitation, which is based on three $\ensuremath{\gamma}$ transitions from this state to the $\ensuremath{\gamma}$ vibrational band. However, this state is populated with a high cross section via the one-neutron transfer reaction, which is not expected for a highly collective excitation. The situation is compared to other known cases from the rare-earth region and to the neighboring isotone ${}^{232}$Th, which so far is the only known case for a two-phonon excitation in the actinide region.