Transcript 幻灯片 1 - 上海应用物理研究所

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
WANG, Yibin WEI, Tingzhi YAN, Chen ZHONG and Jiaxu ZUO
Shanghai Institute of Applied Physics, Chinese Academy of Sciences
P. O. Box 800-204, Shanghai 201800
Massimo Papa, Aldo Bonasera
Istituto Nazionale di Fisica Nucleare,Laboratori Nazionali del Sud, Catania,Italy
CCAST-----ISOSPIN PHYSICS AND
LIQUID GAS PHASE TRANSITION
Outline
Isoscaling
Motivation
CoMD model
Calculation and Discussion
Summary
Isoscaling?
If two reactions, 1 and 2, have the same temperature but
di®erent isospin asymmetry, for example, the ratio of a
speci¯c isotope yields with neutron and proton number N
and Z obtained from system 2 and system 1 have been observed to exhibit isoscaling, i.e., exponential dependence
of the form:
Y2 ( N , Z )
R21 ( N , Z ) 
 C exp(N  Z )
Y1 ( N , Z )
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 productsfinal products
Dynamical
only the hot products,
same behavior but different values
no dynamical effect shown
Mixed of different time emission fragments
CoMd model
Same principle as QMD considering the isospin effect
Some constraints added
1.occupation probability of particle was constrained to f1
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
Temperature
Neutron
Deutron
Alpha
T=70fm/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:
T=220fm/c
Y(ERFS)=[C1·ERFS1/2+C2·ERFS]·exp[-(ERFS-VC)/T]
T=400fm/c
ERFS
n, p
Neutron and proton Chemical potential
differences between two reactions:
=n/T  n= T
=p/T  p= T
 Z
4Csym  1
 A1

2
Z2

A2
2



T
<Z1/A1>2 and <Z2/A2>2 :
Mean value of the parent nuclei
After Evaporation
Process
Ex=Einc-m-Q
E*=factor*Ex
factor=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 model
Double 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 increasing
No 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
different
The 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 parameter
Evaporation decay of the hot products, gemini
program will be considered
Systimatic simulation of the isoscaling dynamics
Isotopic effect from other observations should be
analyzed, study the isotopic effect in further
The density dependence of isoscaling parameters
Excitation energy dependence of the isoscaling
parameters