Identification of multi-phononγ-vibrational bands in odd-Z105Nb

Background: The odd-$Z$ ${}^{105}$Nb nucleus is located in the $A=100$ neutron-rich region. The study of multi-phonon vibrational band structures is important for understanding nuclear structure in this region.Purpose: To search for multi-phonon $\ensuremath{\gamma}$-vibrational bands in ${}^{105}$Nb.Methods: The high spin states of ${}^{105}$Nb have been studied by measuring the prompt $\ensuremath{\gamma}$ rays emitted in the spontaneous fission of ${}^{252}$Cf. The data analysis is carried out using triple- and four-fold $\ensuremath{\gamma}$ coincidence methods.Results: A new level scheme of ${}^{105}$Nb is established. The yrast band has been confirmed, and three new collective bands have been identified. Compared with previous results, a total of 14 new levels and 36 new $\ensuremath{\gamma}$ transitions are observed. Two bands built on 625.9 keV and 1231.9 keV levels are proposed as one-phonon- and two-phonon $\ensuremath{\gamma}$-vibrational bands, respectively. The evidences for supporting assignments of the multi-phonon $\ensuremath{\gamma}$-vibrational bands have been discussed. Triaxial projected shell model calculations for the $\ensuremath{\gamma}$-vibrational band structures are found in good agreement with the experimental data, thus further supporting the $\ensuremath{\gamma}$-vibrational interpretations for the experimental results in ${}^{105}$Nb.Conclusions: The one-phonon- and two-phonon $\ensuremath{\gamma}$-vibrational bands have been identified in ${}^{105}$Nb. Our results provide new data to systematically understand the characteristics of the multi-phonon $\ensuremath{\gamma}$-vibrational bands in the $A=100$ neutron-rich region.