workshop pisa nuclei esotici

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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)

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At the Fermi energy, in binary dissipative
collisions, an emission component of fragments
and light particles is centered between
quasi-projectile 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.
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.
V. Baran et al. Nucl. Phys. A730 (2004) 329
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Neck fragmentation and isospin degree of freedom
Looking for a constraint to the density
dependence of EOS asymmetry term
Asymmetry
124Sn I0.2
NEUTRONS
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).
Asy-stiff
PROTONS
Nucl Phys. A703, 603 (2002)
Asy-soft
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The CHIMERA detector and Reverse experiment
Beam
1192 Si-CsI(Tl) Telescopes
REVERSE Experiment 688 Telescopes, forward part.
2002/2003- CHIMERA-Isospin 1192 telescopes
124Sn 64Ni,27Al 112Sn 58Ni

35 A.MeV
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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,
Zlightlt5
1
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TERNARY EVENTS SELECTION
p/pbeamgt 0.6 Z1Z2Z3 ZTOT
PLF
TLF
IMF
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
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BASIC CHARACTERISTICS OF SELECTED EVENTS
Parallel velocity distribution for Z4,6,12,18
IMFs in coincidence with projectile-like fragment
(PLF) and target-like fragment in ternary events.
BNV
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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).
Relative velocities were normalized to the
relative velocity for a Coulomb repulsion between
fragments of charge Z1,Z2 (Vviola)
Plotting the two reduced relative velocity (rx)
versus (ry) in a bi-dimensional plot different
scenarios can be disentangle for example
sequential decay from PLF (TLF) should be
represented by a distribution around rx1
(ry1).
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. Wilczynski et al.
(Isospin collaboration), to be published Phys.
Rev. C
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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.
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 t0.
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).
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REDUCED VELOCITY PLOTS
Note BNV model accounts only for the prompt
component of IMFs
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Angular distributions alignment characteristics
Out-of-plane angular distributions for the
dynamical (gate 1) and statistical (gate 2)
components these last are more concentrated in
the reaction plane.
?plane is the angle, projected into the reaction
plane, between the direction defined by the
relative velocity of the CM of the system PLF-IMF
to TLF and the direction defined by the relative
velocity of PLF to IMF
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ISOSCALING FROM THE RATIO OF ISOTOPE YIELDS
112Sn112Sn and 124Sn124Sn 50 A.MeV (MSU
data)
R21 Y2(N,Z)/Y1(N,Z) C exp(?N ?Z)
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.
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A signal of phase transition Isospin
distillation
Isoscaling in central collisions
112Sn58Ni and 124Sn64Ni at 35 AMeV Central
collisions CHIMERA-REVERSE experiment
Neutron enrichment in the gas phase
E. Geraci et al., Nucl. Phys. A732 (2004) 173
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Gating the reduced plot for light IMFs
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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.
For the IMFs sequential emission from
projectile-like source a nice fit is observed
with ?0.61 and ?-0.61 parameters values.
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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.
Preliminary data
exp(-0.40Z)
exp(0.53N)
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.
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CHIMERAPS-UPGRADING (2005-2006) Method rise time
measurement for Pulse shape application
IDENTIFICATION IN CHIMERA
124Sn64Ni 35 A.MeV
TDC
CFD30 Start TAC
Si PA Amp Split
Charge
RiseTime Stop-Start
T
a
E
mass()
CFD90 Stop TAC
QDC
Standard CHIMERA LINE
upgrading
Charge and mass for light Ions
Results charge identification up Z ?15 With 4
MeV/A energy threshold for particle stopped in
silicon detector
40Ar12C 20 A.MeV
TOF
Present threshold for charge identification ? 10
A.MeV
A, Z
() charge for particle stopped in silicon
detector is reconstructed by EPAX formula
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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.
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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 Nucleaire, 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
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END
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IMFs CHARGE DISTRIBUTION
The charge distribution of the IMFs fall down
exponentially exp(aZ). Result of BNV
calculations (normalized to Z6) are compared
with the experimental distribution. Sequential
decay stage is not present in the calculation.
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Angular distributions angle definitions
In fission studies it is useful to interpret the
data by assuming a proper system of reference
the one associated with the Fissioning
nucleus see A. Stefanini et al., Z.Phys. A351
(1995) 167
HF
z
In the neck fragmentation studies we can adopt
the same reference frame to study the alignment
configuration between PLF-IMF-TLF
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SEMI-PERIPHERAL EVENT SELECTION
M?6
7? M?12
Semi-peripheral collisions, roughly selected by
requiring that the multiplicity of charged
particles is less than 7. Coincidence between
projectile-like fragments (PLF) and remnants of
the target nucleus (TLF) amount to about 10 of
the selected events.
Mgt12