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XII Nuclear Physics Workshop Marie and Pierre Curie Nuclear Structure and Low Energy Reactions September 21-25, 2005 Kazimierz Dolny, Poland. Dynamical fission in Sn induced reaction s at 35 A . MeV CHIMERA-ISOSPIN Collaboration (*) (*) presented by Paolo Russotto INFN CT-LNS.

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## Dynamical fission in Sn induced reaction s at 35 A . MeV CHIMERA-ISOSPIN Collaboration (*)

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**XII Nuclear Physics Workshop Marie and Pierre Curie Nuclear**Structure and Low Energy Reactions September 21-25, 2005 Kazimierz Dolny, Poland Dynamical fission in Sn induced reactions at 35 A.MeV CHIMERA-ISOSPIN Collaboration(*) (*) presented by Paolo Russotto INFN CT-LNS**E.De Filippo et al., Phys. Rev. C 71, 064604 (2005)**100Mo + 100Mo at 19 A.MeV A.A. Stefanini et al., Z. Phys. A351 (1995) 167 Analysed systems 124Sn+64Ni at 35 A.Mev neutron rich 112Sn+58Ni at 35 A.Mev neutron poor Phenomenon Fission of projectile like fragments (PLF) in peripheral and semi-peripheral reaction Competition Statistical “slow” equilibrated fission Vs “Dynamical” “fast” non-equilibrated fission**6He**Li 4He H.I. 3He t d p DE-E Z,E PSD LCP The CHIMERA detector Beam REVERSE Experiment: 688 Telescopes, forward part. (2000-2002) 2003/2004- CHIMERA-ISOSPIN 1192 telescopes TARGET 176° REVERSE Forward part 30° 1° 30° 1m 1° • good angular resolution • identification in mass and/or charge of the detected particles • low detection threshold and high dynamical range in energy • direct velocitymeasurement (TOF) DE-TOF M,E**AH/AL Mass asymmetries**NOTE:Z2F=37-57 Zproj log scale The lighter fragments are emitted preferentially backwards in the PLF reference system, i.e., towards the target nucleus: DynamicalFission E2F = kinetic energy of the two fragments Centrality of collision Coulomb ring < Vbeam = 8 cm/ns Well defined PLF source: sequential scattering of PLF followed by its splitting into 2 fragments. 2 < multiplicity < 7 (peripheral reactions)Data Analysis focused on two heaviest fragments**In-plane () and out-of-plane () angles definition[A.A.**Stefanini et al., Z.Phys. A 351(1995)167]] Note:VLpar>4 cm/ns Angular distribution are not forward/backward symmetric. fast process Time interval between the two steps much shorter than PLF rotational time In the neutron rich system the Dynamical effects are stronger than in the neutron poor system**DYN/TOT [%]**Time estimation Time interval between collision and PLF splitting: 100-300 fm/c Asymmetric cases (outside Coulomb ring) shortest time scale: 40-120 fm/c E.De Filippo et al., Phys. Rev. C 71, 064604 (2005) V.Baran et al., Nucl. Phys. A730, 329 (2004) E.De Filippo et al., Phys. Rev. C 71, 044602 (2005) Difference: ??? no modelsnor simulations capable of describing Dynamical fission**Conclusion**• Analysed system 124Sn+64Ni at 35 A.Mev • 112Sn+58Ni at 35 A.Mev • Peripheral and semi-peripheral reactions are basically binary:PLF+TLF • We have analysed the sequential splitting of PLF in two fragments of comparable masses • In 20-80% of cases we have observed a fast non-equilibrated dynamical fission of PLF (100<t<300 fm/c): this process is one or two order of magnitude faster than equilibrated fission • In the neutron rich system the Dynamical effects are stronger (+1030%) than in the neutron poor system • We are not able to explain the reason of this difference because we have no models nor simulations capable of describing Dynamical fission • Further analysis and theoretical model are required!!**COLLABORAZIONE ISOSPIN**E. De Filippob, A. Paganob, E. Piaseckic, F. Amorinia, A. Anzalonea, L. Auditored, V. Barana, I. Berceanue, J. Blicharskaf, J. Brzychczykg, A. Bonaseraa, B. Borderieh, R. Bougaulti, M. Brunoj, G. Cardellab, S. Cavallaroa, M.B. Chatterjeek, A. Chbihil, M. Colonnaa, M. D'Agostinoj, R. Dayrasm, M. Di Toroa, J. Franklandl, E. Galicheth, W. Gawlikowiczg, E. Geracij, F. Giustolisia, A. Grzeszczukf, P. Guazzonin, D. Guineto, M. Iacono-Mannoa, S. Kowalskif, E. La Guidaraa, G. Lanzanob, G. Lanzalonea, N. Le Neindreh, S. Lip, S. Lo Nigroa, C. Maiolinoa, Z. Majkag, M. Papab, M. Petrovicie, S. Pirroneb, R. Planetag, G. Politib, A. Pope, F. Portoa, M.F. Riveth, E. Rosatoq, F. Rizzoa, S. Russon, P.Russottoa M. Sassin, K. Schmidte, K. Siwek-Wilczynskac, I. Skwirac, M.L. Sperdutoa, J. C. Steckmeyeri, L. Swiderskic, A. Trifiròd, M. Trimarchid, G. Vanninij, M. Vigilanteq, J.P. Wieleczkol, J. Wilczynskir, H. Wup, Z. Xiaop, L. Zettan, and W. Zipperf a) INFN, Laboratori Nazionali del Sud and Dipartimento di Fisica e Astronomia, Università di Catania, Italy b) INFN, Sezione di Catania and Dipartimento di Fisica e Astronomia, Università di Catania, Italy c) Institute of Experimental Physics, Warsaw University, Warsaw, Poland d) INFN, Gruppo Collegato di Messina and Dipartimento di Fisica, Università di Messina, Italy e) Institute for Physics and Nuclear Engineering, Bucharest, Romania f) Institute of Physics, University of Silesia, Katowice, Poland g) M. Smoluchowski Institute of Physics, Jagellonian University, Cracow, Poland h) Institute de Physique Nucléaire, IN2P3 and Université Paris-Sud, Orsay, France i) LPC, Ensi Caen and Université de Caen, France j) INFN, Sezione di Bologna and Dipartimento di Fisica, Università di Bologna, Italy k) Saha Institute Of Nuclear Physics, Kolkata, India l) GANIL, CEA, IN2P3, Caen, France m) DAPNIA/SPhn, CEA-Saclay,France n) INFN, Sezione di Milano and Dipartimento di Fisica, Università di Milano, Italy o) IPN, IN2P3-CNRS and Université Claude Bernard, Lyon, France p) Institute of Modern Physics, Lanzhou, China q) INFN, Sezione di Napoli and Dipartimento di Fisica, Università di Napoli, Italy r) A. Soltan Institute for Nuclear Studies, Swierk/Warsaw, Poland**Relative velocities between two fragments normalized to**velocity resulting from Coulomb repulsionViola Systematics [D.J. Hinde et al., Nucl. Phys. A472, 318 (1987)] Note:VLpar>4 cm/ns <Vratio> larger then 1 (+20%) in plane dynamical region The velocity field of various parts of the PLF did not attain equilibrium as in statistical fission**out=90°**in-plane emission**Exponentially decreasing distribution: dynamical**Flat distribution: statistical Dyn: -30°< plane <45° Eq: -130°<plane<-90° and -90°<plane<130° NOTE: TLF’s fragments have been cut off; VLpar >4cm/ns.**Dyn: -30° < plane< 45°**Eq: -130° < plane< -90° and -90° <plane <130°**Outside Coulomb ring and largest asymmetries neck**emission [E.De Filippo et al., Phys. Rev. C 71, 044602 (2005)] log scale NOTE: Angular coverage 1°<lab< 30°**Data Analysis focused on two heaviest fragments**Conditions 2 < multiplicity < 7 (peripheral reactions) 30<ZTOT<80 and Z2F>15 NOTE:in the highest asymmetry ZL> 9 AH/AL Mass asymmetries log scale Low velocity and Z2F >Zproj Target remnants E2Fperipherality VLpar>4 cm/ns and Z2F Zproj PLF splitting into 2 main fragments**AH/AL Mass asymmetries**log scale E2Fperipherality**How to select peripherality in both system to compare**them???????? Angular coverage 1°<lab< 30° no Energy Transverse lcp, no Total Kinetic Energy Loss (TKEL) E2FTKEL and centrality of the collision The global variables show a similar behaviour for both system Selection of same percentage of events inthe E2F distribution**Example:velocity of the source of the two heaviest fragments****DYN/TOT [%]**(124Sn+64Ni) – (112Sn+58Ni)

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