Generation and division of excitation energy in heavy-ion collisions studied by measuring charged-particle survival fractions

Abstract

Generation and division of excitation energy in heavy-ion collisions studied by measuring chargedparticle survival fractions.

Angular Momentum Sharing in Dissipative Collisions

“…The observed correlation between the total number of emitted nucleons and the net mass transfer indicates a non-equilibrium excitation energy partition between the reaction products, with an excess of excitation being deposited in the fragment which gains nucleons. Similar conclusions had been drawn by other authors [12][13][14][15][16], but remained quite controversial. Although the existence of such correlations is compatible, by itself, with a nucleon exchange picture, the fact that they are largely independent of the degree of inelasticity [11,15] is difficult to understand within the present versions of the stochastic nucleon exchange model and deserves new investigation.…”

Direct Experimental Evidence of Nonequilibrium Energy Sharing in Dissipative Collisions

“…The determination of the microscopic mechanism of energy dissipation and energy partition between the reaction partners of a dissipative collision has been a controversial subject of debate in the past years [1][2][3][4][5][6][7][8][9][10][11][12] (for a review see [13]). The excitation energy sharing presents an evolution with the inelasticity of the reaction: in quasi-elastic events the two reaction partners reseparate with almost equal excitation energies, but with increasing dissipation there is a trend towards equilibrium partition (i.e.…”

“…These experimental findings can be explained by models [14] which describe the evolution of many macroscopic observables by means of stochastic exchanges of single nucleons between the interacting nuclei. More refined experiments [4,7,10] claimed that the excitation energy division is correlated with the net mass transfer, with an excess of excitation being deposited in the fragment which gains nucleons. Moreover, the strength of this experimental correlation seems to be largely independent of the degree of inelasticity [10] and this latter result seems difficult to understand within a stochastic nucleon exchange picture.…”

Evidence for a nonequilibrated dinuclear system in dissipative collisions at 19 MeV/nucleon

“…In many cases, and not only at bombarding energies greater than 10 MeV/nucleon, the lack of equilibrium is accompanied by features which cannot be explained within the framework of the NEM. In particular, some recent experiments [6,[8][9][10][11][12][13][14] show a dependence of the energy partition on the net nucleon flow, which is not predicted by the nucleon exchange models. This dependence is at present a matter of debate and its evidence is controversial.…”

“…The first is expected to be more appropriate at small energy losses, and the second at large energy losses, when deformations are more developed. In order to verify, as in recent attempts [11][12][13]26], whether incoherent processes alone are able to explain the observed strong correlation with the net mass drift, a simple calculation was performed. It is based on a nucleon exchange mechanism in energy space Fission probabilities vs TKEL/Z^TOT for fragments of mass A^=i \20 and 100 produced in the present symmetric collision '"^Sn-h'^^Sn (diamonds) and in the previously studied '^MoH-'^Mo at 18.7 MeV/nucleon (squares), respectively.…”