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Structure of exotic nuclei by large-scale shell model calculations

Structure of exotic nuclei by large-scale shell model calculations. Yutaka Utsuno （宇都野 穣） Japan Atomic Energy Agency Collaborators Takaharu Otsuka (Tokyo/RIKEN) Takahiro Mizusaki (Senshu) Michio Honma (Aizu). 6 th China-Japan Joint Nuclear Physics Symposium May 16-20, 2006, Shanghai.

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Structure of exotic nuclei by large-scale shell model calculations

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  1. Structure of exotic nucleiby large-scale shell modelcalculations Yutaka Utsuno （宇都野 穣） Japan Atomic Energy Agency Collaborators Takaharu Otsuka (Tokyo/RIKEN) Takahiro Mizusaki (Senshu) Michio Honma (Aizu) 6th China-Japan Joint Nuclear Physics Symposium May 16-20, 2006, Shanghai

  2. Exotic structure in N~20 • Disappearance of the N=20 magic number • Example: Large B(E2) in 32Mg • “Island of inversion”: conventionally standard picture • Normal (0p0h) vs. intruder (2p2h) • Restricted to nine nuclei over N=20 • Not necessarily meaning the collapse of the N=20 shell gap 20 E.K. Warburton et al., Phys. Rev. C 41, 1147 (1990).

  3. Mapping of the “island” from the moments of Na isotopes • Extensive Monte Carlo shell model (MCSM) study • The onset of the intruder dominance must occur at N=19. 19 Y. Utsuno et al., Phys. Rev. C 70, 044315 (2004).

  4. Implication to the shell structure difference in correlation energy “SDPF-M” interaction d3/2 largest smaller Earlier onset needs narrower N=20 shell gap. d5/2 Strongly attractive T=0 d3/2-d5/2monopole interaction provides uswith a unified shell evolution including the appearance of a new N=16 magic number (Ozawa et al.).

  5. Shell evolution from the viewpoint of interaction Spin-isospin dependence Tensor interaction T. Otsuka, T. Suzuki, R. Fujimoto, H. Grawe, and Y. Akaishi, Phys. Rev. Lett. 95, 232502 (2005). T. Otsuka, R. Fujimoto, Y. Utsuno, B.A. Brown, M. Honma, and T. Mizusaki, Phys. Rev. Lett. 87, 082502 (2001). Works also between different l-orbits (making other shells change?) Primarily works within the same l-orbits (highly related to N=20 shell breaking)

  6. From N~20 to N~28 region • Our previous model space: not sufficient to describe the N~28 region (upper pf orbits are lacking) • SDPF-M interaction: phenomenological treatment for the monopole interaction by shifting 0.3 MeV for the d3/2-d5/2 channel from USD • Extending the model space to the full sd-pf shell • Shell evolution with high predictive power • First stage: cross shell interaction

  7. Monopole of T=0 tensor (in MeV) • Tensor of GXPF1 (an empirically good interaction) is very close to p+r. • Much weaker for potential interactions on the market (MK and FPD6) • p+r is adopted as the T=0 tensor part (no free parameters).

  8. Tensor monopole interaction in sd shell (in MeV) • The tensor in USD is weaker than p+r by 1/2. • The difference supports the need for the modification in T=0 d3/2-d5/2 monopole adopted in the SDPF-M interaction. • An sd-pf interaction with a proper tensor interaction appears to make it possible to give a unified picture about the isoscalar shell evolution in the region. • What about effect on the N=28 shell closure?

  9. 42Si: a new magic nucleus? • Various theoretical predictions • shell model: spherical or weakly deformed • Skyrme HF(B): soft ranging from spherical to oblate • Gogny: oblate • RMF: oblate • Most theoretical works pay attention to the neutron shell structure (related to loosely bound p orbit). • Effect of the proton shell? • “evidence” for magic nucleus • low gamma-ray spectra in 43P • large Z=14 shell gap? • small cross section of two-protonknockout (44S to 42Si) • different deformation? • No direct measurement such as 2+ has not been published.

  10. Cross shell interaction with a proper tensor force • T=0 monopole compared to MK (in MeV) f7 Vf7d3 vs. Vf7d5 d3 (Z=14 magic) d5 p3 Vd3f7 vs. Vd3p3 f7 d3 (N=28 magic) This can affect the structure of a proposed magic nucleus 4214Si28. # present: a new cross shell interaction with (T=0) p+r as the tensor part

  11. Evolution of the proton shell from N=20 to 28 • The Nature paper (J. Fridmann et al, Nature 435, 922 (2005)) claims that the observation of a 184 keV gamma-ray in 43P is a strong evidence for the magicity of the 42Si core. • odd-even N=28 isotones for Z=15, 17, 19: sensitive to the s.p. state

  12. Even-even N=28 isotones (ep, en)=(1.3e, 0.5e) which is the same as USD’s

  13. A prediction for “magic” 42Si • Spherical minimum is very close in energy to the oblate deformed state • The 2+ level is thus sensitive to the N=28 shell gap.(Only a few hundred keV smaller gap makes the level lower than 1 MeV) • Further lower 2+ ? (report by Azaiez and Dombradi at SENUF06.) ~2 MeV by MK

  14. Summary • According to a systematic shell-model study around N=20, the shell evolution from stable to unstable nuclei must occur from the electromagnetic moment etc. • Its origin, i.e., the strong dependence of the monopole interaction on spin/isospin, can be quantitatively accounted for by the tensor force. • Using a proper tensor interaction as the shell-model interaction, we have started to construct a full sd-pf shell model interaction. • The proton shell evolution about d3/2 and s1/2 is reproduced in a natural way and it significantly affects the magic structure in 42Si.

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