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E. De Filippo (INFN Catania) for the REVERSE / ISOSPIN collaboration

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

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E. De Filippo (INFN Catania) for the REVERSE / ISOSPIN collaboration

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  1. 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)

  2. 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

  3. Neck fragmentation and isospin degree of freedom Looking for a constraint to the density dependence of EOS asymmetry term Asymmetry 124Sn I=0.2 NEUTRONS Depending upon theshape 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

  4. TARGET 30° 176° 1° 1m 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 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°

  5. TERNARY EVENTS SELECTION p/pbeam> 0.6 Z1+Z2+Z3 ~ 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:

  6. 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

  7. PLF TLF Vr2 Vr1 IMF 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 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

  8. Prompt 3 1 40 fm/c 2 1 2 80 fm/c 1 2 3 120 fm/c 3 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 t=0. 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).

  9. BNV REDUCED VELOCITY PLOTS: Note: BNV model accounts only for the “prompt” component of IMF’s

  10. M.B. Tsang et al. Phys. Rev. C64, 054615 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) 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.

  11. A signal of phase transition: Isospin distillation Isoscaling in central collisions 112Sn+58Ni and 124Sn+64Ni at 35 AMeV Central collisions CHIMERA-REVERSE experiment Neutron enrichment in the gas phase E. Geraci et al., Nucl. Phys. A732 (2004) 173

  12. Gating the reduced plot for light IMFs:

  13. exp(-0.61*Z) exp(0.61*N) 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 parameter’s values.

  14. 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(-0.40*Z) 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.

  15. CHIMERAPS-UPGRADING (2005-2006) Method: rise time measurement for Pulse shape application IDENTIFICATION IN CHIMERA 124Sn+64Ni 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 40Ar+12C 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

  16. 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.

  17. The REVERSE – ISOSPIN COLLABORATION INFN, Sezione di Catania and Dipartimento di Fisica e Astronomia, Università diCatania, ItalyINFN, Sezione di Milano and Instituto di Fisica Cosmica, CNR, Milano,ItalyINFN, Laboratori Nazionali del Sud and Dipartimento di Fisica e Astronomia,Università di Catania, ItalyINFN, Gruppo Collegato di Messina and Dipartimento di Fisica, Università di Messina,ItalyINFN, Sezione di Milano and Dipartimento di Fisica Università di Milano, ItalyInstitute for Physics and Nuclear Engineering, Bucharest, RomaniaInstitute of Physics, University of Silesia, Katowice, PolandM. Smoluchowski Institute of Physics, Jagellonian University, Cracow, PolandInstitute de Physique Nucl´eaire, IN2P3-CNRS and Université Paris-Sud, Orsay, FranceLPC, ENSI Caen and Université de Caen, FranceINFN, Sezione di Bologna and Dipartimento di Fisica, Università di Bologna, ItalySaha Institute of Nuclear Physics, Kolkata, IndiaGANIL, CEA, IN2P3-CNRS, Caen, France, H. Niewodniczanski Institute of Nuclear Physics, Cracow, PolandDAPNIA/SPhN,CEA-Saclay, FranceIPN, IN2P3-CNRS and Université Claude Bernard, Lyon, FranceInstitute of Modern Physics, Lanzhou, ChinaInstitute of Experimental Physics, Warsaw University, Warsaw, PolandINFN, Sezione Napoli and Dipartimento di Fisica, Università di NapoliInstitute for Nuclear Studies, Swierk/Warsaw, Poland

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