Physics Letters B (Nov 2022)

Experimental observation of the M1 scissors mode in 254No

  • F.L. Bello Garrote,
  • A. Lopez-Martens,
  • A.C. Larsen,
  • I. Deloncle,
  • S. Péru,
  • F. Zeiser,
  • P.T. Greenlees,
  • B.V. Kheswa,
  • K. Auranen,
  • D.L. Bleuel,
  • D.M. Cox,
  • L. Crespo Campo,
  • F. Giacoppo,
  • A. Görgen,
  • T. Grahn,
  • M. Guttormsen,
  • T.W. Hagen,
  • L. Harkness-Brennan,
  • K. Hauschild,
  • G. Henning,
  • R.-D. Herzberg,
  • R. Julin,
  • S. Juutinen,
  • T.A. Laplace,
  • M. Leino,
  • J.E. Midtbø,
  • V. Modamio,
  • J. Pakarinen,
  • P. Papadakis,
  • J. Partanen,
  • T. Renstrøm,
  • K. Rezynkina,
  • M. Sandzelius,
  • J. Sarén,
  • C. Scholey,
  • S. Siem,
  • J. Sorri,
  • S. Stolze,
  • J. Uusitalo

Journal volume & issue
Vol. 834
p. 137479

Abstract

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We present the first experimental evidence of the scissors mode in the superheavy nucleus 254No produced in the 208Pb(48Ca, 2nγ))254No reaction. The spectrum of γ rays emitted by the excited 254No nuclei shows an enhanced γ-ray yield for transition energies of ≈2.5 MeV. By measuring the linear polarization properties of the emitted γ rays, we confirm that the transitions in the enhancement region are predominantly of magnetic-dipole character, characteristic for the scissors mode. To further characterize the enhanced γ-ray yield, simulations of the electromagnetic decay of 254No were performed. The observed enhancement is reproduced by including an M1 component in the γ strength function with total strength B(M1↑)=11.8(19)μN2. This is in good agreement with the integrated M1 strength from sum-rule estimates and new calculations within the quasi-particle random-phase approximation presented here. Our results provide a stringent test of phenomenological formulae for the scissors mode currently used in stellar nucleosynthesis calculations. We find that those formulae are not satisfactory, and we recommend using sum-rule estimates assuming a rigid-body moment of inertia instead for describing the scissors mode in superheavy nuclei.

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