Transcript スライド 1 - 上海应用物理研究所

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)
6th China-Japan Joint Nuclear Physics Symposium May 16-20, 2006, Shanghai
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).
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).
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-d5/2 monopole interaction provides us
with a unified shell evolution including the appearance of a new
N=16 magic number (Ozawa et al.).
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).
Primarily works within the same l-orbits
(highly related to N=20 shell breaking)
Works also between different l-orbits
(making other shells change?)
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
Monopole of T=0 tensor
GXPF1
p+r
i
j
MK
KB
KB3
FPD6
f7
f7
0.223
0.210
0.080
0.176
0.202
0.071
f7
p3
0.036
0.035
0.013
0.047
0.047
0.012
f7
f5
-0.335
-0.315
-0.120
-0.265
-0.303
-0.107
f7
p1
-0.073
-0.070
-0.026
-0.095
-0.095
-0.023
p3
p3
0.092
0.150
0.064
0.070
0.070
-0.002
p3
f5
-0.048
-0.046
-0.017
-0.063
-0.063
-0.016
p3
p1
-0.229
-0.376
-0.160
-0.174
-0.174
0.005
f5
f5
0.382
0.360
0.137
0.302
0.346
0.122
f5
p1
0.097
0.093
0.034
0.126
0.126
0.031
p1
p1
0.306
0.501
0.213
0.232
0.232
-0.008
(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).
Tensor monopole interaction in
sd shell
USD
p+r
i
j
Kuo
SDPOTA
d5
d5
+0.36
+0.69
+0.72
+0.26
d5
d3
-0.30
-0.57
-0.60
-0.22
d3
d3
+0.17
+0.33
+0.34
+0.13
(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?
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
1. low gamma-ray spectra in 43P
• large Z=14 shell gap?
2. small cross section of two-proton
knockout (44S to 42Si)
• different deformation?
No direct measurement such as 2+
has not been published.
Cross shell interaction with a
proper tensor force
• T=0 monopole compared to MK (in MeV)
Vf7d3 vs. Vf7d5
(Z=14 magic)
central
LS
tensor
total
MK
+0.04
+0.01 -0.19
-0.14
present
+0.13
+0.01 -0.52
-0.38
f7
d3
d5
p3
Vd3f7 vs. Vd3p3
(N=28 magic)
central
LS
tensor
total
MK
-0.41
-0.03
-0.09
-0.53
present
-0.37
-0.04
-0.24
-0.65
d3
f7
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
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
Even-even N=28 isotones
(ep, en)=(1.3e, 0.5e) which is the same as USD’s
A prediction for “magic”
42Si
~2 MeV by MK
• 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.)
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.