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

I. Introduction H.D. Wilkinson and D.E. Ablburger, Parity inversion H.D. Wilkinson and D.E. Ablburger, Phys. Rev. 113, 563 (1959); From the observedβdecay 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)

mean-field scheme of neutron levels ½+[211] 2s1/2 5/2+[202] 1d5/2 ½+ 3/2+[211] N=8 ½+[220] ½- 1p1/2 ½-[101] 3/2-[101] 1p3/2 ½-[110] β2=0.3

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…

Variational shell model (configuration mixing calculations) T. Otsuka, N. Fukunishi, H. Sagawa, PRL70, 1385(1993) Mean field valid? very large β2 deformation? 10Be, β2 ~ 0.67 from B(E2, 2+→0+)=52 (6) e2fm2 ?

II. Investigation of the N=7 isotones

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-

surface pairing volume-pairing mixture-pairing Surface pairing component is important for exotic nuclei J. Dobaczewski et al., EPJA 8, 59 (2000).

Very flat minima very soft shapes SHF without pairing X.Li and P.-H.Heenen, PRC 54,1617(1996) Very flat minima very soft shapes

晕态

All ½- states have spherical shapes; For the ½+ state: 11Be: β2 ~ 0.98 Deformations All ½- states have spherical shapes; For the ½+ state: 11Be: β2 ~ 0.98 13C: β2 ~ 0.5 15O: β2 ~ 0.0 9He: Very soft shapes Significant vibrational effect; Core-vibration mixture; Energy could be sensitive to the effects, but density would not

To understand halo structure: Calculate <l2> If 1d5/2 (l=2), <l2>=6, halo? 9He 11Be 13C <l2>: 0.2 2.6 3.7 mixture of 2s1/2 halo

mean-field scheme of neutron levels ½+[211] 2s1/2 5/2+[202] mixing 1d5/2 ½+ 3/2+[211] N=8 ½+[220] ½- 1p1/2 ½-[101] 3/2-[101] 1p3/2 ½-[110] β2=0.3

Glauber-model calculations of cross sections for the 1/2+ state 33 A MeV Expt. Cal. 11Be+12C 1.56 1.983 11Be+27Al 2.27 2.734 13C+12C 1.36 1.434 13C+27Al 1.91 1.717 790 A MeV 11Be+12C 0.942 1.156 11Be+27Al 1.38 1.68

Summary For N=7 isotones, the ½＋state 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.

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