1 di-neutron correlation in soft octupole excitations of medium-mass nuclei near drip-line y....
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1
Di-Neutron Correlation in Soft Octupole Excitations of Mediu
m-Mass Nuclei near Drip-Line
Y. Serizawa and M. Matsuo
Niigata Univ.
2
Introduction
- Hyperspherical harmonics method
- 3-body model
- HFBO, Ca, Ni: Matsuo et al., PRC71 (2005) 064326.
11Li: Bertsch, Esbensen, Ann.Phys.209(1991)327.
6He, 11Li, 24O: Hagino, Sagawa, PRC72(2005)044321.
6He, 11Li: Zhukov et al., Phys.Rep.231(1993)151.
The di-neutron correlation has been discussed with various theoretical approaches.
9Li
neutron halo
n n
84Ni
11Li
3
Motivation
Di-Neutron correlation appears in soft dipole excitations of medium-mass nuclei near drip-line. M. Matsuo et al., PRC71(2005)064326.
We investigate the pairing effect in the soft octupole excitations of medium-mass nuclei near the neutron drip-line.
Purpose:
Does the di-neutron correlation appears in the other multipole excitations?
Motivation:
I. Hamamoto et al., PRC64, 024313 (2001),
X.R. Zhou et al., NPA723, 375 (2003).- Study by using continuum RPA:
4
MethodM. Matsuo NPA696, 371 (2001).
- Both continuum and pairing are treated in descriptions of excited states.
- Appropriate to study the di-neutron dynamics.
We use the continuum QRPA.
5
Model Hamiltonian
ph channel pp channel
Mean-field selfconsistent HF potential with Skyrme force SLy4 Density-dependent
delta int. QRPA residual int.
Skyrme force with Landau-Migdal approx.(t0 and t3 term are exactly treated)
)()/)(1)(1(2
),(
00
ji rrrPV
jiV
Mixed pairing
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IS Octupole Strength Functions
IS neutron proton
(1) The low-lying octupole state (corresponds to the sharp peak)
arrows: 1, 2-neutron threshold
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IS Octupole Strength Functions
arrows: 1, 2-neutron thresholdIS neutron proton
(2) The neutron mode (corresponds to the broad bump)
- is seem to be peculiar to near-drip-line nuclei. - develops as we approach the drip line.
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Dominant ph collective surface vibrational mode
Transition Densities
Full
No dynamical pairing
0)(ˆ)(ˆ
)(2
2
rrir
rr ph
0)(ˆ)(ˆ
)(2
2
rrir
rPr pp
Neutron-pair transition density
ph transition density
Significant tail in pp channel Large effect of dynamical pairing
(1)(2)
84Ni(2)
(1)
9
lcut for transition densities
l/1Ol=9
l=7
l=13
Full (l=17)
No dynamical
l=11
The high-l orbits essentially contribute to the neutron-pair transition density.
Di-neutron correlation appears in soft octupole excitations.
l=1584Ni
10
Neutron-number dependence
The di-neutron correlation is more significant as we approarch the neutron drip line.
11
Comparison with Soft Dipole Excitations
l=7
full
No dynamical
l=5
…
dipoleoctupole 84NiT
rans
ition
den
sitie
s [a
rb.u
nit]
The di-neutron correlation is more clear in the soft dipole excitations.
12
Model Dependences
Di-neutron correlation appears more significant as shallower Fermi level.
Features of the di-neutron correlation are sensitive to depth of Fermi surface.
13
Summary
The di-neutron correlation appears in the soft octupole excitations.
By using the continuum QRPA method, we investigate the soft octupole excitations of medium-mass nuclei near the neutron drip line.
Result:
- The di-neutron correlation is less clear than the soft dipole excitations.
- The di-neutron correlation is more significant as we approarch the neutron drip line.
- The features of the di-neutron correlation are sensitive to depth of the Fermi surface.
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