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

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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:

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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.

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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

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Neutron-number dependence

The di-neutron correlation is more significant as we approarch the neutron drip line.

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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.

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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.

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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.