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Physical Review C 86 (2012) 014610
Correlations between emission timescale of fragments and isospin dynamics in $^{124}$Sn+$^{64}$Ni and $^{112}$Sn+$^{58}$Ni reactions at 35 AMeV
E. De Filippo, A. Pagano, P. Russotto, F. Amorini, A. Anzalone, L. Auditore, V. Baran, I. Berceanu, B. Borderie1, R. Bougault2, M. Bruno, T. Cap, G. Cardella, S. Cavallaro, M. B. Chatterjee, A. Chbihi3, M. Colonna, M. D'Agostino, R. Dayras4, M. Di Toro, J. Frankland3, E. Galichet1, W. Gawlikowicz, E. Geraci, A. Grzeszczuk, P. Guazzoni, S. Kowalski, E. La Guidara, G. Lanzalone, G. Lanzanò, N. Le Neindre2, I. Lombardo, C. Maiolino, M. Papa, E. Piasecki, S. Pirrone, R. Planeta, G. Politi, A. Pop, F. Porto, M. F. Rivet1, F. Rizzo, E. Rosato, K. Schmidt, K. Siwek-Wilczynska, I. Skwira-Chalot, A. Trifirò, M. Trimarchi, G. Verde, M. Vigilante, J. P. Wieleczko3, J. Wilczynski, L. Zetta, W. Zipper

We present a new experimental method to correlate the isotopic composition of intermediate mass fragments (IMF) emitted at mid-rapidity in semi-peripheral collisions with the emission timescale: IMFs emitted in the early stage of the reaction show larger values of $<$N/Z$>$ isospin asymmetry, stronger angular anisotropies and reduced odd-even staggering effects in neutron to proton ratio $<$N/Z$>$ distributions than those produced in sequential statistical emission. All these effects support the concept of isospin "migration", that is sensitive to the density gradient between participant and quasi-spectator nuclear matter, in the so called neck fragmentation mechanism. By comparing the data to a Stochastic Mean Field (SMF) simulation we show that this method gives valuable constraints on the symmetry energy term of nuclear equation of state at subsaturation densities. An indication emerges for a linear density dependence of the symmetry energy.
1 :  IPNO - Institut de Physique Nucléaire d'Orsay
2 :  LPCC - Laboratoire de Physique Corpusculaire de Caen
3 :  GANIL - Grand Accélérateur National d'Ions Lourds
4 :  IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers (ex DAPNIA)
Dynamique et thermodynamique nucléaire
Physique/Physique Nucléaire Expérimentale
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