Correlation between neutron skin thickness and R np for neutron-rich nuclei

2010 年赤峰第十三届全国核结构研讨会暨第九次全国“核结构与量子力学”专题讨论会

Correlation between neutron skin thickness and Rnp for neutr

on-rich nuclei

孙小艳方德清马余刚蔡翔舟陈金根郭威田文栋

王宏伟曹喜光傅瑶周培张国强

2010 年 07 月 25 日


outline

Introduction

Analytic Method & Important Results

Summary and Conclusions

1


The availability of high intensity radioactive beams facilitates the exploration of the nuclei far from stab-ility line.

Neutron-rich nucleus are considered to have a neutron skin thickness.

Experimental data on neutron skin thickness is important to the study of Nuclear physics and astrophysics.

Difficult to accurately determine the neutron skin thickness.

Find some experimental observables to extract the neutro

n skin thickness.

PART I Introduction

.

β

Why are we interested in neutron skin thickness ?

2

2010 年赤峰第十三届全国核结构研讨会暨第九次全国“核结构与量子力学”专题讨论会 3


PART Ⅱ Analytic Method & Important Results

QMD IQMD

Classical in essence. However, many important quantum features are included

Reasonably including isospin degrees of freedom in the mean field ,two-body collision, and Pauli blocking

Description of the model

Initialization

Mean field

Two-body collisions

Pauli blocking4


Each nucleon is represented by a coherent state of a Gaussian wave packet

Through a Wigner transformation, the one-body phase space distribution function for N-distinguishable particles is given by:

The propagation of nucleons under the self-consistently generated mean field is governed by Hamiltonian equations of motion:

5


The density of neutron and proton is different.

The Droplet Model:

(1). Initialization

is the normalization constant.

Ci is the half density radius of neutron or proton

Ri is the equivalent sharp surface radius of neutron and proton.

fi is introduced by us to adjust the diffuseness parameter.

0iρ

Monte carlo sampling method to get the initial coordinate of nucleons

6


The momentum distribution of nucleons is generated bymeans of the local Fermi gas approximation:

Monte carlo sampling method to get the initial momentum coordinate of nucleons

The binding energies and root mean square (rms) radii of the initial configuration for the colliding nuclei are required to be stable.

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(2). Mean field

α = −356 MeV, β = 303 MeV ， γ = 1.17

8


(3). Coalescence model

a) relative momentum smaller than p0= 300 MeV/c

b) relative distance smaller than R0= 3.5 fm

then coalescence to one cluster

(4). Rnp and neutron skin thickness δnp

Rnp=Yn/Yp

Yn : yield of neutrons

Yp : yield of protons

9


The collision processes of some Ca and Ni isotopes with 12C target at 50AMeV are simulated using the IQMD model.

Important Results

The evolution time dependence of Rnp for 50Ca+12C at 50AMeV

Rnp is stable after 150 fm/c

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Strong correlation between neutron skin thickness and Rnp for 54 Ca at peripheral collision

11


Different range of kinetic energy to see the correlation between neutron skin thickness and Rnp for 54Ca ， stronger correlation for Ken>40MeV

12


Correlation between neutron skin thickness and Rnp for

50 52 54 56 Ca and 60 62 64 66 68 70 Ni

Physics letter B 682(2010)396-400

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We have calculated Rnp from some Ni and Ca isotopes induced reactions using IQMD, the results show that Rnp has strong correlation with neutron skin thickness δnp

Rnp may be used as an experimental observable to extract δnp for neutron-rich nuclei

PART III Summary & Conclusion

14


Thank You

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Correlation between neutron skin thickness and R np for neutron-rich nuclei