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First observation of multi-phonon $γ$-vibrations in an odd-odd nuclear system

E. H. Wang, M. Abushawish, J. H. Hamilton, A. Navin, S. Bhattacharyya, J. Dudouet, G. H. Bhat, J. A. Sheikh, S. Jehangir, S. Y. Wang, S. Sun, B. Qi, M. Rejmund, A. Lemasson, Y. H. Kim, E. Clement, F. Didierjean, R. Y. Dong, G. Duchene, B. Jacquot, C. F. Jiao, Y. X. Luo, C. Michelagnoli, A. V. Ramayya, J. O. Rasmussen, C. Schmitt, O. Stezowski, W. Z. Xu, H. Zhang, S. J. Zhu

Abstract

The identification of the first multi-phonon $γ$-vibrational bands in an odd-odd neutron-rich nucleus of the nuclear chart is presented. These high spin structures of hard to access $^{104}_{41}$Nb$_{63}$, produced in fission, were studied by combining a spectrometer with isotopic resolution coupled to a $γ$-ray tracking array and independently high-fold $γ$ coincidence measurements. Triaxial Projected Shell Model calculations for the high-spin states are in good agreement with the measured observables for the yrast, one-phonon and two-phonon $γ$ bands. The possibility of an oblate shape of an isomeric state and coexistence of triaxial and oblate configurations are investigated from the decay of the 141 keV isomer. The present work illustrates the robustness of vibration excitations in the presence of odd valence proton and neutron as well as the possibly coexisting shapes beyond the $N=60$ transitional region.

First observation of multi-phonon $γ$-vibrations in an odd-odd nuclear system

Abstract

The identification of the first multi-phonon -vibrational bands in an odd-odd neutron-rich nucleus of the nuclear chart is presented. These high spin structures of hard to access Nb, produced in fission, were studied by combining a spectrometer with isotopic resolution coupled to a -ray tracking array and independently high-fold coincidence measurements. Triaxial Projected Shell Model calculations for the high-spin states are in good agreement with the measured observables for the yrast, one-phonon and two-phonon bands. The possibility of an oblate shape of an isomeric state and coexistence of triaxial and oblate configurations are investigated from the decay of the 141 keV isomer. The present work illustrates the robustness of vibration excitations in the presence of odd valence proton and neutron as well as the possibly coexisting shapes beyond the transitional region.
Paper Structure (1 section, 4 figures)

This paper contains 1 section, 4 figures.

Table of Contents

  1. Acknowledgements

Figures (4)

  • Figure 1: Level scheme of $^{104}$Nb. New transitions and levels are labeled in red. For the excitation energy of band 7, x is either 0 or 8.7 keV. Half-lives of the ground state and the 10 keV isomer are taken from NUBASE2020 Kon20.
  • Figure 2: The $\gamma$-ray spectra from (a) gate on 157/185 keV; (b) gate on 656 keV; (c) gate on 157/714/245 keV; (d) gate on 157/714/318 keV; (e) gate on 656/532 keV; (f) delayed singles, inset decay curve; (g) gate on 168/441/557 keV; (h) gate on 207/319/410 keV. The single gate and delayed singles are from $^{238}$U induced fission data, while the double and triple gates are from $^{252}$Cf data. New transitions are labeled with *. Fission partner La transitions are labeled with p. Contamination is labeled with c.
  • Figure 3: (a) Angular momentum alignment $I_x$ and (b) kinematic moments of inertia $J^{(1)}$ as a function of rotational frequency $\hbar\omega$ for the 0, 1 and 2 phonon $\gamma$-vibrational bands in $^{104}$Nb. The corresponding TPSM calculations are shown as continuous lines.
  • Figure 4: Energy levels and $B(M1)/B(E2)$ ratios for the 0, 1 and 2 phonon $\gamma$-vibrational bands in $^{104}$Nb as a function of spin. The corresponding TPSM calculations are shown as continuous lines (see text).