Isospin Dependence of Incomplete Fusion Reactions at25  MeV/Nucleon

Abstract

40 Ca+ 40,48 Ca, 46 Ti reactions at 25 MeV/A have been studied using the 4π CHIMERA detector. An isospin effect on the competition between incomplete fusion and dissipative binary reaction mechanisms has been observed. The probability of producing a compound system is observed to be lower in the case of N≈Z colliding systems as compared to the case of reactions induced on the more neutron rich 48 Ca target. Predictions based on CoMD-II calculations show that the competition between fusion-like and dissipative reactions, for the selected centrality, can strongly constraint the parameterization of symmetry energy and its density dependence in the nuclear equation of state.Pacs: 21.65. Ef, 21.65.Mn, 25.70.Jj, 25.70.Lm Collisions between heavy ions with different neutronproton asymmetries offer a unique opportunity to study the equation of state (EOS) of asymmetric nuclear matter [1][2][3][4]. Accessing the density dependence of the symmetry energy has recently attracted the interest of the community due to its implications in both nuclear physics and astrophysics of neutron stars [2,5,6]. The isotopic composition of fragments produced in multifragmentation phenomena is being extensively studied at intermediate beam energies (E/A=20-100 MeV) bearing important information on the symmetry energy [7]. One aspect not yet fully investigated is represented by the effect of the isospin asymmetry on the fate of hot nuclear systems. The combined effects of the symmetry energy and of the repulsive Coulomb interaction can significantly affect the reaction mechanism and the rate of production of hot compound nuclei in heavy-ion reactions at low and intermediate energies [8][9]. The isospin N/Z-asymmetry can also play an important role in opening different decay channels for a hot nuclear system once this has been produced. In this respect, the limiting temperature of a nucleus is expected to depend on both its mass and its isotopic composition [10][11][12]. Experimentally, the observation of small isotopic effects on the temperatures of projectile spectators in relativistic heavy-ion collisions have been interpreted as a signal of no isospin dependence of nuclear limiting temperatures [13]. At lower beam energies, a mass and N/Z-asymmetry dependence in limiting temperatures have been explored by studying the population of the Giant Dipole Resonance (GDR) at high excitation energies [14]. A small difference in the limiting GDR excitation energy has been observed when comparing a symmetric N~Z system to a neutron rich system [15]. All these findings stimulate attempts to link N/Z effects on measured observables to the nuclear symmetry energy and its density dependence in the equation of state.In this work we explore isospin effects in heavy residue (HR) remnants produced in incomplete fusion reactions between projectile and targets with different N/Z asymmetries. The results on the competition between incomplete fusion and binary dissipative mechanisms are compared to simulations performed with a microscopic mode...

Isospin effects and symmetry energy studies with INDRA

“…And also by the results from the competition between dissipative mechanisms for Ca induced reactions on Ca and Ti at 25 A MeV [42], compared with a CoMD simulation. Results from Sn+Sn at 35 and 50 A MeV presented in reference [43] (several isospin dependent variables), compared to an improved quantum molecular dynamics model, ImQMD, plead for an asy-softer EOS.…”

Probing the momentum-dependent symmetry potential via nuclear collective flows

“…Contribution sources of the symmetry energy usually come from three parts, namely the kinetic energy part, density-dependent part, and momentum-dependent part. Until now, much of the theoretical research [1][2][3][4][5][6][7][8][9][10][11][12][13][14] and experimental data [7,9,[15][16][17][18][19] have been used to constrain the symmetry energy; for the recent reviews, see Refs. [21][22][23][24][25].…”

Symmetry energy effects on fusion cross sections

“…From the comparison of the total areas for the two systems we can also estimate isospin effects on the total fusion cross section, with a larger value in the more neutron-rich case, as also recently observed in fusion reactions with Ar + Ni [27] and Ca + Ca isotopes [28]. We note that this effect is also slightly dependent on the symmetry term: The total fusion cross section for the more neutron-rich system is 10% larger in the Asysoft calculation and about 7% in the Asystiff case.…”