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Open Access Publications from the University of California

Rotational band structure in Mg 32

  • Author(s): Crawford, HL
  • Fallon, P
  • Macchiavelli, AO
  • Poves, A
  • Bader, VM
  • Bazin, D
  • Bowry, M
  • Campbell, CM
  • Carpenter, MP
  • Clark, RM
  • Cromaz, M
  • Gade, A
  • Ideguchi, E
  • Iwasaki, H
  • Langer, C
  • Lee, IY
  • Loelius, C
  • Lunderberg, E
  • Morse, C
  • Richard, AL
  • Rissanen, J
  • Smalley, D
  • Stroberg, SR
  • Weisshaar, D
  • Whitmore, K
  • Wiens, A
  • Williams, SJ
  • Wimmer, K
  • Yamamato, T
  • et al.

There is significant evidence supporting the existence of deformed ground states within the neutron-rich N≈20 neon, sodium, and magnesium isotopes that make up what is commonly called the "island of inversion." However, the rotational band structures, which are a characteristic fingerprint of a rigid nonspherical shape, have yet to be observed. In this work, we report on a measurement and analysis of the yrast (lowest lying) rotational band in Mg32 up to spin I=6+ produced in a two-step projectile fragmentation reaction and observed using the state-of-the-art γ-ray tracking detector array, GRETINA (γ-ray energy tracking in-beam nuclear array). Large-scale shell-model calculations using the SDPF-U-MIX effective interaction show excellent agreement with the new data. Moreover, a theoretical analysis of the spectrum of rotational states as a function of the pairing gap, together with cranked-shell-model calculations, provides intriguing evidence for a reduction in pairing correlations with increased angular momentum, also in line with the shell-model results.

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