Dissipative quantum dynamics in low-energy collisions of complex nuclei

Abstract

Model calculations that include the effects of irreversible, environmental couplings on top of a coupled-channels dynamical description of the collision of two complex nuclei are presented. The Liouville-von Neumann equation for the time evolution of the density matrix of a dissipative system is solved numerically providing a consistent transition from coherent to decoherent (and dissipative) dynamics during the collision. Quantum decoherence and dissipation are clearly manifested in the model calculations. Energy dissipation, due to the irreversible decay of giant-dipole vibrational states of the colliding nuclei, is shown to result in a hindrance of quantum tunneling and fusion.

Investigating energy dissipation through nucleon transfer reactions

“…The ΔZ = -2 channel is more probable than the ΔZ = -1 channel over the entire energy range considered here. A closer examination of the Carbon isotopes produced in this reaction suggests that the dominant contribution is due to transfer of an alpha particle, with the vast majority of these events being identified with 14 C, as shown in figure 10. This result is very similar to that obtained in the 18 O + 204 Pb reaction (as seen in figure 10), supporting the idea that the importance of this channel is due to the intrinsic properties of the 18 O nucleus.…”

“…The physical origin of this phenomenon has been extensively sought [11][12][13], but no convincing explanation capable of consistently describing fusion above and below the Coulomb barrier has been forthcoming. Several theoretical explanations have been put forward-Amongst other mechanisms, energy dissipation [14,15] and transfer processes [16] in heavy ion collisions have been suggested to play a part in the observed suppression of fusion cross sections in many systems below the Coulomb barrier. The inclusion of dissipative couplings in fusion models has been shown to potentially account for the hindrance effect [14].…”

“…Several theoretical explanations have been put forward-Amongst other mechanisms, energy dissipation [14,15] and transfer processes [16] in heavy ion collisions have been suggested to play a part in the observed suppression of fusion cross sections in many systems below the Coulomb barrier. The inclusion of dissipative couplings in fusion models has been shown to potentially account for the hindrance effect [14]. It is therefore of interest to study how energy is dissipated in low-energy transfer reactions, and particularly how this differs depending on the transfer process in question.…”

Theoretical study of fusion reactions 32S + 94,96Zr and 40Ca + 94,96Zr and quadrupole deformation of 94Zr

“…The study of fusion reaction mechanism is also of fundamental importance for understanding the synthesis of superheavy elements, properties of weakly bound nuclei, and symmetry energy of the nuclear equation of state [8][9][10][11][12][13][14][15][16][17] Up to now, lots of important information about fusion dynamics at energies near the Coulomb barrier, especially at sub-barrier energies, are obtained through experimental and theoretical studies, such as the fusion hindrance phenomenon at extreme low energies-a steep falloff of the fusion cross sections [18][19][20][21][22][23], the role of the neutron transfer effect in the fusion [24][25][26][27], the breakup effect on the fusion reactions process [28][29][30][31][32][33][34][35], etc..…”

Formulae for partial widths derived from the Lindblad equation

“…Resonances, or meta-stable states, play a crucial role in several physical phenomena -ranging from solid state physics [1][2][3][4] and plasma physics [5,6] via atomic and molecular physics [7][8][9][10] to nuclear physics [11,12]. The population of such states are frequently assumed to follow an exponential decay law.…”