1. The document discusses gamma-ray pre-equilibrium emission from 40Ca+48Ca and 40Ca+46Ti collisions at energies ranging from 10-25 MeV/A. 2. CoMD calculations are able to provide a unified description of pre-equilibrium phenomena by evaluating the average fluctuating dynamics. 3. The parameter φch, which represents the ratio between average and fluctuating dynamics, is found to change rapidly when multifragmentation processes occur, indicating a change in the fundamental properties of hot reaction sources.

1. Sez.-CT
GDR pre-equilibrium emission 40Ca+48Ca,46Ti at 25 MeV/A
S.Tudisco EPL 58 (5), 811(2003)
M.Papa et al, PRC 68., 034606 (2003)
F.Amorini et al PRC 69, 014608(2004)
Fusion-Incomplete Fusion Dissipative binary processes
Extra yield at 10 MeV

2. GDR pre-equilibrium emission 40Ca+48Ca,46Ti at 10 MeV/A
M.Papa et al, submitted to PRC
Dissipative binary processes study of kinematical coincidence

3. Z=14-22 Elab<160 MeV
40Ca+46Ti
40Ca+46Ti
γ-1f γ-2f 40Ca+48Ca

4. CoMD calculations
TKEL-angular and charge distrib.
b-window→ pre-eq γ Yield

5. How we can generate the coherent Sez.-
contribution?
CT
A simple picture the “Molecular Dipole”
The average ensemble in an harmonic mean field
The initial conditions for the GDR mode
At the contact D1≈D2 ≈0
n
p
N1/Z1≠N2/Z2
if
If Y=0 NO coherent contribution

6. Sez.-CT
Coherent contribution Incoherent contribution
(ensemble average) a) Collective
b) Microscopic incoherent
Mean field approach Statistical models
Fully N-body dynamical approach for 1000 fm/c

7. Υ-ray average multiplicity in Sez.-CT
Semi classical Approximation
The Larmor formula
Fourier Transform

8. b=0 fm E/A 25 MeV Sez.-CT
Langevin prediction for
the total system
∗Prediction in the loc. Time
equil. hypothesis
• Prediction according to a
full CoMD approach
g~12
M.Papa et al, PRC 68(2003) 034606

9. We have also high energy Sez.-CT
bremsstrahlung contribution
We have to study the
1. We need to define T at long time
local time
2. We need to separate the
spectral properties of
incoherent Microscopic contribution

10. Sez.-CT
High energy results
Multifragmentation
of the hot
source

11. M.Papa et al, PRC 50 MeV/A b=0 fm Sez.-CT
68(2003) 024612
∗
•
α obtained from the fit procedure
Very small
or Coherent
contribution

12. Something is changed in the fundamental
properties of the formed hot sources….
Degree of collectivity-Degree of coherence as function of t

13. A new observable related to the properties
of the dipolar γ-ray emission in different reaction
mechanisms has been measured
- Φch represents the ratio between the average and fluctuating dynamics.
For N-body approaches able to evaluate the two contributions in a self
consistent way, this parameter should be rather robust with respect some model
ansatz: semiclassical approximaton, occupation numbers…….
- On the other hand and we can expect that Φch can depend
on the dynamics (Forces) governing the equilibration
Process.
From the experiments
Фch(12MeV)=0.6±0.15 10 MeV/A Binary. proc.
Фch(10 MeV)=0.3±0.07 25 MeV/A Inc. fusion.proc.

14. Collectivity and Coherence for the total system
limiting energy for the collective motion
M.Papa et al, PRC 68(2003) 024612,
Black: rather smooth
behaviour
40Ca + 48Ca Central Collisions
Red:it contains the
Ambiguity related
to the experimental
*10 selections of 1
equilibrated source
Green:high sensitivi
Φc(0,tm) ty, related to the
Φc(0,tf)
natural time selection
Φch(0,tf)
performed by the
dynamic through
memory effects.

15. CoMD calculations
TKEL-angular and charge distrib.
b-window→ pre-eq γ Yield

16. γ-Pre-equilibrium effects and “Isospin-Equlibration”
M.Papa et al Sub. PRC
Invariant with respect to
secondary statistical emission
processes

17. Conclusive remarks Sez.-CT
1. An unified description of the pre-equilibrium phenomenon
(fluctuating average dynamics) has been obtained throgh ComD
calculations 2.
2. The fluctuation predicted by the model are in agreement with
Cascade calculations at 25 MeV/A by using g≈12.
2. φch rapidly change when the multifragmentation processes set
in. (much more than φc)
3. The pre-equilibrium extra-yield it is strictly related to the
isospin equilibration process throgh a quasy-resonant mechanisms.