XII Nuclear Physics Workshop Marie and Pierre Curie

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. Me. V CHIMERA-ISOSPIN Collaboration(*) presented by Paolo Russotto INFN CT-LNS

Analysed systems 124 Sn+64 Ni at 35 A. Mev neutron rich 112 Sn+58 Ni at 35 A. Mev neutron poor E. De Filippo et al. , Phys. Rev. C 71, 064604 (2005) Phenomenon Fission of projectile like fragments (PLF) in peripheral and semi-peripheral reaction Competition Statistical “slow” equilibrated fission Vs “Dynamical” “fast” non-equilibrated fission 100 Mo + 100 Mo at 19 A. Me. V A. A. Stefanini et al. , Z. Phys. A 351 (1995) 167

The CHIMERA detector Beam TARGET 176° REVERSE Forward part 30° REVERSE Experiment: 688 Telescopes, forward part. (2000 -2002) 2003/2004 - CHIMERA-ISOSPIN 1192 telescopes 1° 30° 6 He 4 He Li 1 m H. I. 3 He t d p 1° PSD LCP • good angular resolution • identification in mass and/or charge of the detected particles • low detection threshold and high dynamical range in energy DE-TOF M, E DE-E • direct velocity measurement (TOF) Z, E

2 < multiplicity < 7 (peripheral reactions) Data Analysis focused on two heaviest fragments AH/AL Mass asymmetries NOTE: Z 2 F=37 -57 Zproj Centrality of collision E 2 F = kinetic energy of the two fragments log scale The lighter fragments are emitted preferentially backwards in the PLF reference system, i. e. , towards the target nucleus: Dynamical Fission Coulomb ring < Vbeam = 8 cm/ns Well defined PLF source: sequential scattering of PLF followed by its splitting into 2 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

Difference: ? ? ? no models nor simulations capable of describing Dynamical fission 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. A 730, 329 (2004) E. De Filippo et al. , Phys. Rev. C 71, 044602 (2005)

Conclusion Analysed system 124 Sn+64 Ni at 35 A. Mev 112 Sn+58 Ni 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 (+10 30%) 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, IN 2 P 3 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, IN 2 P 3, Caen, France m) DAPNIA/SPhn, CEA-Saclay, France n) INFN, Sezione di Milano and Dipartimento di Fisica, Università di Milano, Italy o) IPN, IN 2 P 3 -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 repulsion Viola Systematics [D. J. Hinde et al. , Nucl. Phys. A 472, 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

Dyn: -30°< plane <45° Exponentially decreasing distribution: dynamical Eq: -130°< plane<-90° and -90°< plane<130° Flat distribution: statistical NOTE: TLF’s fragments have been cut off; VLpar >4 cm/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 Z 2 F>15 NOTE: in the highest asymmetry ZL> 9 AH/AL Mass asymmetries log scale Target remnants VLpar>4 cm/ns and Z 2 F Zproj PLF splitting into 2 main fragments E 2 F peripherality Low velocity and Z 2 F >Zproj

AH/AL Mass asymmetries log scale E 2 F peripherality

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) E 2 F TKEL and centrality of the collision The global variables show a similar behaviour for both system Selection of same percentage of events in the E 2 F distribution

Example: velocity of the source of the two heaviest fragments

DYN/TOT [%] (124 Sn+64 Ni) – (112 Sn+58 Ni)