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Chemical instability in heavy ion collisions at high and intermediate energies

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### Chemical instability in heavy ion collisions at high and intermediate energies

Z.Q. Feng(冯兆庆), W.F. Li(李文飞),

Z.Y. Ming(明照宇), L.W. Chen(陈列文),

F. S. Zhang (张丰收)

Institute of Low Energy Nuclear Physics

Beijing Normal University

Tel: 010-6220 8252

Fax: 010-6223 1765

E-mail: [email protected]

Outline

1 Introduction

2 Isospin dependent quantum molecular dynamics model

3 Isospin effects in nuclear multifragmentation

4 Chemical and mechanical instabilities

5 Conclusions and perspectives

1 Introduction

Experimental status

p(1GeV)+Kr, Xe, Ag, 1984

excited nuclei(4 detector)

Aladin, Au (600 MeV/nucl.) +X

<MIMF> Zbound

Miniball, Xe (30 MeV/nucl.)+X

<NIMF> NC, NLC, NN

Indra, Ar(32-95 MeV/nucl.)+X

Xe(25-50 MeV/nucl.)+X

etc.

Nuclear Multifragmentation, Zhang and Ge, Science Press, 1998

Isospin effects in nuclear multifragmentation

induced by radioactive ion beams (RIB facilities)

GANIL, GSI, MSU, Riken, IMP,

induced by stable nuclei with large neutron excesses(Accelerator with ECR source)

MSU, 1996-1998

112,124Sn(40MeV/nucl.)+112,124Sn

isospin effects in multifragmentation

58Fe(45-105 MeV/nucl.)+58Fe,

58Ni(45-105 MeV/nucl.)+58Ni,

disappearance of isospin effects in multifragmentation

Physical indications and challenges

0, T > 0, >0

E(, T, ) = ?

Important to production of RIB &Neutron Stars !!!

G. J. Kunde et al., 112,124Sn(40MeV/nucl.)+112,124Snisospin effects in multifragmentation,<NN>~NC ,<NIMF>~NC, <NIMF>~NN

G. J. Kunde et al., isospin effects in multifragmentation224,248100X(*=1.3-10 MeV), <NIMF>~NN ,<NIMF>~NC, <NIMF>~NLC, EES model

G. Kortemeyer et al.Percolation model just regenerate the isospin effects in the relationship of <NIMF> ~NN, but not for <NIMF> ~ NC

M. L. Miller et al. Disappearance of isospin dependence of multifragmentation prooduction58Fe(Ni)+58Fe(Ni), at 45-105 MeV/n

2 Isospin dependent quantum molecular dynamics model

Quantum molecular dynamics model (QMD)

The QMD model represents the many body state of the system and thus contains correlation effects to all orders.In QMD, nucleon i is represented by a Gaussian form of wave function.

After performing Wigner transformations, the density distribution of nucleon i is:

From QMD model & IQMD model

mean field (corresponds to interactions)

Uloc : density dependent potential

UYuk: Yukawa (surface) potential

UCoul: Coulomb energy

USym: symmetry energy

UMD: momentum dependent interaction

two-body collisions

Cugnon’s parameterization:

np =nn= pp

Experimental data:

NN is isospin dependent,

for Ebeam < 300 MeV/nucl.,

np 3nn=3pp

Pauli blocking:

the Pauli blocking of n and p is treated separately

Initialization:

in real space: the radial position of n and p are sampled by using MC method according to the n and p radial density distribution calculated from SHF (or RMF) theory

in momentum space: local Fermi momentum is given by

Coalescence model:

physics:

ri-rj R0, pi-pj P0

R0=3.5 fm, P0=300 MeV/c

geometry:

Rrms 1.14 A1/3

reality:

comparing the isotope calculated with the nuclear data sheets

3 Isospin effects in nuclear multifragmentation

4 analyzing

b=1, 2, 3, 4, 5, 6, 7, 8, 9, 10 fm

the number events is proportional to b

statistics: t 200 fm/c, the charge distribution have been stable. One selects fragments over t=200-400 fm/c

Charge distributions at t=200, 400 fm/c, and the average <NZ> over t=200-400 fm/c

Average n multiplicity <NN>, as a function of charged-particle multiplicity NC

Averaged number of IMF <NIMF>as a function of NC, NLC, and NN (4 analyzing)

Averaged number of IMF <NIMF>as a function of NC, NLC,and NN (4 pre equilibrium emissions)

Chapter 10:“Isospin-Dependent Quantum Molecular Dynamics

Model and Its Applications in Heavy Ion Collisions,”

Isospin Physics in Heavy Ion Collisions at Intermediate Energies,

ed. By Li and Schrode, Nova Science Publishers Inc.，New York,2001

Averaged number of MF <NIMF>as a function of Zbound (4 and 4 pre-equilibrium emissions)Averaged number of MF <NIMF>as a function of Zbound (4 and 4 pre-equilibrium emissions)

Chapter 10:“Isospin-Dependent Quantum Molecular Dynamics

Model and Its Applications in Heavy Ion Collisions,”

Isospin Physics in Heavy Ion Collisions at Intermediate Energies,

ed. by Li and Schrode, Nova Science Publishers Inc，New York,2001

4 Chemical and mechanical instabilities

- (E/ T),0
- thermodynamical instability
- (P/ )T,<0
- mechanical instability
- (volume, surface, Coulomb instabilities)
- (n/ )P,T<0
- chemical instability

Averaged number of IMF <NIMF>as a function of NC and Zbound (4 pre-equilibrium emissions)

Isotopic distributions of Li, Be, Ne and Na for central collisions at 40 and 100 MeV/nucl.

Isotopic distributions of Ne (A=17 ~32) for central collisions at 40 and 100 MeV/nucl.

---------- 112Sn+112Sn

_______ 124Sn+124Sn

mechanical or/and chemical instabilities ?

mechanical or/and chemical instabilities ?

5 Conclusions and perspectives

Theoratical Models

phenomenological :

expanding evaporating model

percolation model

statistical multifragmentation model

microscopic:

isospin dependent quantum molecular dynamics model

Boltzmann-like model, such as IBL

isospin dependent far from equilibrium model

Experimental

signals of chemical instability

isospin effects in multifragmentation

propose more physical observable

sensitive to chemical instability ?

nuclear reactions induced byradioactive ion beams

neutron-rich

neutron-poor

n-halo nuclei

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