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Pisa, February 24-26 2005
E. De Filippo (INFN Catania)
for the REVERSE / ISOSPIN collaboration
Time sequence and isoscaling in neck
fragmentation
 Fragments production in peripheral collisions: isospin
dependence in neck formation
 The Reverse experiment with CHIMERA detector
 Characterization of dynamical emitted light fragments in
ternary events: time scale and time sequence
 Comparison with BNV calculations
 Isoscaling in “neck” fragmentation ?
 CONCLUSIONS AND OUTLOOK (Chimera upgrading)
At the Fermi energy, in binary dissipative collisions, an emission
component of fragments and light particles is centered between quasiprojectile and quasi-target-velocity.
Fragments can have several origin: they can be emitted sequentially
from (eventually equilibrated) projectile-like or target-like source or
promptly (dynamical emission) during the first stage of the reaction.
V. Baran et al. Nucl. Phys. A730 (2004) 329
Evolution of the
density contour plot at
6 fm in the reaction
124Sn + 64Ni at 35
A.MeV: the formation
of a neck-like
structure brought
after 100-160 fm/c to
a ternary event with
the appearance of
dynamical emitted
IMFs.
Neck fragmentation and isospin degree of freedom
E( , I )  E( , I  0)  Esym (  )I
2
Looking for a constraint to the density
dependence of EOS asymmetry term
N Z
I
A
Asymmetry
124Sn
Nucl Phys. A703, 603 (2002)
I=0.2
NEUTRONS
Asy-stiff
PROTONS
Asy-soft
Depending upon the shape of
symmetry potential around 0
neutron/proton diffusion
effects and a neutron
enrichment of the neck
region could be induced
(isospin fractionation).
The CHIMERA detector and Reverse experiment
1192 Si-CsI(Tl)
Telescopes
Beam
TARGET
30°
176°
REVERSE Experiment: 688 Telescopes,
forward part.
2002/2003- CHIMERA-Isospin 1192 telescopes
1°
124Sn
+ 64Ni,27Al
112Sn + 58Ni
35 A.MeV
1m
30°
Experimental Methods:
E(Si)-E(CsI(tl)): CHARGE, ISOTOPES
E(Si) –TOF(Si) VELOCITY - MASS
PULSE SHAPE in CsI(Tl)
p,d,t,3He,4He,.6,7,..Li,… Zlight<5
1°
TERNARY EVENTS SELECTION
p/pbeam> 0.6
Z1+Z2+Z3 ~ ZTOT
PLF
TLF
IMF

P
  pi
Ptot . i 1,n

Pbeam
To get insight the different mechanisms of
IMFs production we have selected in the
Vpar-Charge bi-dimensional plot three
regions where PLFs, TLFs and IMFs can be
easily separated:
BASIC CHARACTERISTICS OF SELECTED EVENTS
Parallel velocity distribution for Z=4,6,12,18 IMFs in
coincidence with projectile-like fragment (PLF) and
target-like fragment in ternary events.
BNV
IMFs mechanism production: REDUCED VELOCITY PLOT*
We have constructed event-by-event the relative velocity of IMF
respect to TLF (ry) and of IMF respect to the PLF (rx).
PLF
TLF
Vr1
Vr2
IMF
Relative velocities were normalized to the
relative velocity for a Coulomb repulsion
between fragments of charge Z1,Z2 (Vviola)
2 * EC

Z1Z 2
EC  0.755 1/ 3
 7.3
1/ 3
A1  A2
Plotting the two reduced relative velocity (rx) versus (ry) in a bidimensional plot different scenarios can be disentangle: for example
sequential decay from PLF (TLF) should be represented by a distribution
around rx=1 (ry=1).
On the contrary simultaneous values of rx and ry larger than one can
support a non-statistical origin for these fragments.
*E. De Filippo, A. Pagano, J. Wilczyński et al. (Isospin collaboration), to be published Phys. Rev. C
Events close to diagonal correspond to a prompt ternary division
while those approaching a ratio ~ 1 correspond to a sequential
emission from PLF or TLF respectively.
1 40 fm/c
Points are calculated in a simple
kinematical simulation assuming that IMFs
separate from projectile (square) or from
target (circle) after a time interval of 40, 80
and 120 fm/c elapsed from the primary
binary separation of the projectile from the
target at t=0.
2 80 fm/c
Prompt
3 120 fm/c
3
2
1
1
2
3
Results of BNV transport model for IMFs emission
probability from neck region for different impact
parameters (V. Baran et al. Nucl. Phys. A730 329, 2004).
REDUCED VELOCITY PLOTS:
Note: BNV model
accounts only for the
“prompt” component
of IMF’s
BNV
ISOSCALING FROM THE RATIO OF ISOTOPE YIELDS
112Sn+112Sn
and 124Sn+124Sn
50 A.MeV (MSU data)
R21= Y2(N,Z)/Y1(N,Z) =
C exp(N + Z)
M.B. Tsang et al. Phys. Rev. C64, 054615
For two systems having a different isospin asimmetry, the ratio of
isotope yields with Z protons and N neutrons obtained from sistem 2
(neutron rich) and system 1 (neutron poor) has been found to follow a
significative scaling (exponential dependence) where  and  are
scaling parameters.
A signal of phase transition: Isospin distillation
Isoscaling in central collisions
  n, 2 

R21 ( N , Z ) 
 C 

Y112 Sn  58 Ni ( N , Z )
  n ,1 
Y124 Sn  64 Ni ( N , Z )
N
Z
  p, 2 

  Cˆ nN ˆ Zp
 
 p ,1 
112Sn+58Ni
and 124Sn+64Ni at 35 AMeV
ˆ n  1.56  0.02
Central collisions
CHIMERA-REVERSE experiment
ˆ p  0.63  0.01
   0.44  0.01
   -0.47  0.02
C  1.03  0.03
Entrance channel values
N P T A P T 2
ˆ n 
 1.08
N P T A P T 1
ˆ p 
E. Geraci et al., Nucl. Phys. A732 (2004) 173
Z P  T
Z P  T
A P  T 2
A P  T 1
 0.90
Neutron
enrichment in the
gas phase
Gating the reduced plot for light IMFs:
ISOSCALING OF ISOTOPIC DISTRIBUTIONS
We have started a study upon isoscaling signal for
peripheral collisions and neck fragmentations. Infact also if
isoscaling relation can be derived assuming chemical and
thermal equilibrium, this is not a necessary condition to
observe this signal.
exp(-0.61*Z)
exp(0.61*N)
For the IMFs
sequential
emission
from
projectile-like
source a nice
fit is observed
with =0.61
and =-0.61
parameter’s
values.
For the neck region the isoscaling signal seems to
be yet present also if the quality of the exp(N) fit is
poor, especially for heavier IMFs.
exp(0.53*N)
This study can be interesting for the future prosecution
of data analysis because isoscaling parameters could
be sensitive to the density dependence of EOS as
shown by dynamical calculations.
exp(-0.40*Z)
IDENTIFICATION IN
CHIMERA
124Sn+64Ni
CHIMERAPS-UPGRADING (2005-2006)
Method: rise time measurement for Pulse shape application
35 A.MeV
Si PA Amp
Split
CFD30% Start TAC
Charge
E
T
TDC
RiseTime ~ Stop-Start
a
CFD90% Stop TAC
mass(*)
QDC
Standard ‘’CHIMERA LINE’’
Charge and mass
for light Ions
upgrading
Results: charge identification up Z 15
With ~ 4 MeV/A energy threshold for particle
stopped in silicon detector
40Ar+12C
Present threshold for charge
identification  10 A.MeV
(*) charge for particle stopped in silicon
detector is reconstructed by EPAX formula
20 A.MeV
+ TOF
A, Z
Conclusions and Outlook
We have studied with the forward part of the CHIMERA detector the
124Sn
+ 64Ni and 112Sn + 58Ni at 35 A.MeV.
Fragments produced in semi-peripheral ternary reactions have been
investigated. The analysis method gives the possibility to evaluate the
time scale of the process. Comparison, for light IMFs ions, with BNV
calculations supports the scenario of dynamical production of IMFs in
the overlapping zone (neck) between target and projectile nuclei.
Isospin effects, in particular of isoscaling signal are under study.
Sistematic evaluation of isoscaling parameters with proper source
selection are important quantities for testing symmetry energy density
dependence of EOS in asymmetric nuclear matter.
The Chimera detector will be upgrated and the combination of
pulse-shape analysis and time-of-flight measurements in Silicon
detectors will increase the capability of fragment identification in
mass and charge: this is important not only for the prosecution of
the isospin physics studies with stable beams but of course also
for future planning of experiments with exotic beams.
The REVERSE – ISOSPIN COLLABORATION
INFN, Sezione di Catania and Dipartimento di Fisica e Astronomia, Università di Catania, Italy
INFN, Sezione di Milano and Instituto di Fisica Cosmica, CNR, Milano,Italy
INFN, Laboratori Nazionali del Sud and Dipartimento di Fisica e Astronomia, Università di Catania, Italy
INFN, Gruppo Collegato di Messina and Dipartimento di Fisica, Università di Messina, Italy
INFN, Sezione di Milano and Dipartimento di Fisica Università di Milano, Italy
Institute for Physics and Nuclear Engineering, Bucharest, Romania
Institute of Physics, University of Silesia, Katowice, Poland
M. Smoluchowski Institute of Physics, Jagellonian University, Cracow, Poland
Institute de Physique Nucl´eaire, IN2P3-CNRS and Université Paris-Sud, Orsay, France
LPC, ENSI Caen and Université de Caen, France
INFN, Sezione di Bologna and Dipartimento di Fisica, Università di Bologna, Italy
Saha Institute of Nuclear Physics, Kolkata, India
GANIL, CEA, IN2P3-CNRS, Caen, France,
H. Niewodniczanski Institute of Nuclear Physics, Cracow, Poland
DAPNIA/SPhN,CEA-Saclay, France
IPN, IN2P3-CNRS and Université Claude Bernard, Lyon, France
Institute of Modern Physics, Lanzhou, China
Institute of Experimental Physics, Warsaw University, Warsaw, Poland
INFN, Sezione Napoli and Dipartimento di Fisica, Università di Napoli
Institute for Nuclear Studies, Swierk/Warsaw, Poland