Dynamics effect and evolution of isoscaling on the Quantum Molecular Dynamics model

Wendong TIAN, Yugang MA, Xiangzhou CAI, Jingen CHEN, Jinhui CHEN,Deqing FANG, Wei GUO, Chunwang MA, Guoliang MA, Wenqing SHEN, Kun WA

NG, Yibin WEI, Tingzhi YAN, Chen ZHONG and Jiaxu ZUO

Shanghai Institute of Applied Physics, Chinese Academy of SciencesP. O. Box 800-204, Shanghai 201800

Massimo Papa, Aldo BonaseraIstituto Nazionale di Fisica Nucleare,Laboratori Nazionali del Sud, Catania,Italy

CCAST-----ISOSPIN PHYSICS AND

LIQUID GAS PHASE TRANSITION

Outline

IsoscalingMotivationCoMD modelCalculation and DiscussionSummary

Isoscaling?

If two reactions, 1 and 2, have the same temperature butdi®erent isospin asymmetry, for example, the ratio of aspeci¯c isotope yields with neutron and proton number Nand Z obtained from system 2 and system 1 have been ob-served to exhibit isoscaling, i.e., exponential dependenceof the form:

)exp(),(

),(),(

1

221 ZNC

ZNY

ZNYZNR

where and are the scaling parameters and C is anoverall normalization constant, with the convention of that the neutron and proton composition of reaction 2 is more neutron-rich than that of reaction 1.

Tsang M B, Friedman W A, Gelbke C K et al 2001 Phys. Rev. Lett. 86 5023

Motivation

Experiment final products, cold,

light and few evidence on heavy fragments

Theory Statistical model

primary productsfinal products

Dynamical

only the hot products,

same behavior but different values

no dynamical effect shown

Mixed of different time emission fragments

CoMd modelSame principle as QMD considering the isospin effectSome constraints added 1.occupation probability of particle was constrained to f1

in every time step

2. short computation time

3. grounding state consider the isospin degree

4. test the stabability of the ground state to 1000s fm/c

Present simulation 25MeV/A b=1 40Ca+40Ca, 48Ca+48Ca

Time: 100fm/c ~ 600fm/c with time step =40fm/c

Parameters extracted from the simulation

Source Biggest fragment

Fragment Only those emitted from source of previous moment

State of the source keep relative stable

Temperature light particle spectra

(in the rest frame of the source)

Neutron, Proton, deutron,

Triton, and Alpha

Tf=140fm/c

Surface emission:

YS(ERFS)=C·ERFS1/2·exp[-(ERFS-VC)/T]

Volumn emission:

YV(ERFS)=C’·ERFS·exp[-(ERFS-VC)/T]

Combination of surface and volumn emission:

Y(ERFS)=[C1·ERFS1/2+C2·ERFS]·exp[-(ERFS-VC)/T]

Neutron Deutron Alpha

ERFS

TemperatureT=70fm/c

T=220fm/c

T=400fm/c

n, p

Neutron and proton Chemical potential differences between two reactions:

=n/T n= T

=p/T p= T

T

AZ

AZ

Csym

2

2

2

2

1

14

<Z1/A1>2 and <Z2/A2>2 :

Mean value of the parent nuclei

After Evaporation Process

Ex=Einc-m-Q

E*=factor*Exfactor=0.5

Light fragment:do change too much for the light fragment(a little lower than before evaporation, or say it having same value with T=600fm/c)

Heavy fragments:Higher than before evaporation

Summary:Confirmation of the isoscaling in CoMD dynamical modelDouble values obtained of and as in our another IQMD model calculation of the light particles does not change with the evolution time(within the fluctuations), so does the imtermediate fragments(here we only see the light source), but the heavy ones or the residues increase a lot with its mass increasingNo obvious dynamcal behavior of the isoscaling observered, at different evolution time, we find alomost the same , for both light fragmets and heavy source, values vary much than , and the residue values change a lot beyond the fluctuation

>>> do no varies with the reaction time, has a little differentThe derived Csym of the light products and IMF, from the observation is differ from the program input, but increase with the mass increase for the heavy residue

More Works:Check of the Csym, the reason causes the Csym deviaration from the input parameterEvaporation decay of the hot products, gemini program will be consideredSystimatic simulation of the isoscaling dynamicsIsotopic effect from other observations should be analyzed, study the isotopic effect in furtherThe density dependence of isoscaling parametersExcitation energy dependence of the isoscaling parameters