Deformation effects on the structures of the N=7 halo nuclei Furong Xu, Junchen Pei School of Physics, Peking University

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Deformation effects on the structures of the N7
halo nucleiFurong Xu, Junchen PeiSchool of
Physics, Peking University

1. Introduction
2. Calculations for the N7 isotones
3. Summary

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I. Introduction
Parity inversion

• H.D. Wilkinson and D.E. Ablburger,
• Phys. Rev. 113, 563 (1959)
• From the observedßdecay of 11Be, the nucleus
• might have an ½ ground state.
• In the next year, Talmi and Unna demonstrated
  that this possibility with shell-model
  systematics
• Later on, the levels of ½ and ½- states were
  well established experimentally.
• e.g. J.P. Deutsch et al., PLB 268, 178 (1968)

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mean-field scheme of neutron levels

½211
2s1/2
5/2202
1d5/2
½
3/2211
N8
½220
½-
1p1/2
½-101
3/2-101
1p3/2
½-110
ß20.3
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• In 1991, reaction cross section of 11Be was
  measured to suggest neutron-halo
• M. Fukuda et al., PLB 268, 339 (1991)
• Parity inversion ( ½, ½-), halo structure, very
  strong E1 transition from ½- to ½ states.
• interesting!
• In the past 15 years, a lot of works on 11Be
• Projected Hartree-Fock, Skyme-Hartree-Fock,
  Variational shell model, coupled channel, RMF

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Variational shell model (configuration mixing
calculations) T. Otsuka, N. Fukunishi, H. Sagawa,
PRL70, 1385(1993)
Mean field valid? very large ß2
deformation? 10Be, ß2 0.67 from B(E2, 2?0)52
(6) e2fm2 ?
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II. Investigation of the N7 isotones
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• Deformed SHF with the adiabatic blocking of the
• odd neutron.
• Blocking ½ 220 (the lowest level in sd shell)
• ½
• Blocking ½-101 (the highest level in p shell)
• ½-

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surface pairing
volume-pairing
mixture-pairing
Surface pairing component is important for exotic
nuclei J. Dobaczewski et al., EPJA 8, 59 (2000).
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Very flat minima very soft shapes
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• Deformations
• All ½- states have spherical shapes
• For the ½ state
• 11Be ß2 0.98
• 13C ß2 0.5
• 15O ß2 0.0
• 9He

Very soft shapes
Significant vibrational effect Core-vibration
mixture Energy could be sensitive to the
effects, but density would not
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To understand halo structure

• Calculate ltl2gt
• If 1d5/2 (l2), ltl2gt6, halo?
• 9He 11Be 13C
• ltl2gt 0.2 2.6 3.7 mixture of
  2s1/2

halo
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mean-field scheme of neutron levels

½211
2s1/2
5/2202
mixing
1d5/2
½
3/2211
N8
½220
½-
1p1/2
½-101
3/2-101
1p3/2
½-110
ß20.3
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33 A MeV Expt.
Cal.11Be12C 1.56 1.983 11Be27Al
2.27 2.734 13C12C 1.36 1.434
13C27Al 1.91 1.717 790 A MeV 11Be12C
0.942 1.156 11Be27Al 1.38 1.68
Glauber-model calculations of cross sections for
11Be (1/2)
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Summary

• For N7 isotones, the ½state may polarize the
  nuclei to be largely deformed.
• Mean-field calculations cannot understand the
  parity inversion that would be beyond mean field.
• Other properties, such as halo structure, can be
  obtained by mean field models.
• To be published in Nucl. Phys. A

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Thank you