Energy partition in near-barrier strongly damped collisionsNi58+

Abstract

Neutron spectra from the inverse-kinematics reaction '"Ni+ "Pb at F~"s/A =6.65 Me.V have been measured in coincidence with nickel-like fragments.Neutron emission patterns for net pickup and stripping channels have been analyzed in terms of sequentia1 evaporation from fully accelerated projectilelike and targetlike fragments. As at higher energies, these patterns suggest an absence of appreciable correlations between net mass transfer and excitation energy division for strongly damped collisions, at the present near-barrier energy. The overall multiplicities, as well as energy spectra and angular distributions of neutrons, are well reproduced by simulation calculations, assuming an energy division always in favor of the heavy fragment.

Excitation energy division in 51V+197Au collisions 75 MeV above the barrier

“…4c), the temperature equilibrium (solid line) is approached for a broad range of charge numbers except for the values of Z close to the entrance channel Z = 23 and Z = 79 where the kinetic energies are far from being fully relaxed. Thus, our new experiments have yielded results that are consistent with results obtained for the similar reaction 58 Ni + 208 Pb at about 80 MeV above the barrier [9]. Note that the data in Figs.…”

“…In contrast to the conclusions drawn in our work, the observed neutron spectra were found to be compatible with the assumption that the Pb-like fragment receives most of the total excitation energy independent of the direction and magnitude of the net mass transfer. It was argued [9] that their observations could not be reconciled with those of Keller et al [5] but appeared consistent with the trends established at higher bombarding energies. The failure to reproduce our results was not associated with the fact that the center-of-mass energy was as much as 80 MeV above the barrier but with the fact that the evaluation of our radiochemical data "relies on unproven assumptions on the time scale of charge density equilibration in damped reactions" [9].…”

“…It was argued [9] that their observations could not be reconciled with those of Keller et al [5] but appeared consistent with the trends established at higher bombarding energies. The failure to reproduce our results was not associated with the fact that the center-of-mass energy was as much as 80 MeV above the barrier but with the fact that the evaluation of our radiochemical data "relies on unproven assumptions on the time scale of charge density equilibration in damped reactions" [9]. We have presented detailed arguments against this criticism in [10]: There is solid evidence for strong correlations between neutron and proton exchanges imposed on the system by the steep gradients of the potential energy surface [11].…”

“…The purpose of the present work is to follow the bombarding energy dependence of the excitation energy sharing in the 51 V + 197 Au reaction further by increasing the bombarding energy to E cm = B + 75 MeV. This corresponds closely to the bombarding energy in excess of the barrier (80 MeV) used in the work of Chatterjee et al [9]. This should allow us to check whether completely different methods -the measurement of neutron multiplicities in the 58 Ni + 208 Pb reaction [9] and radiochemical experiments in the 51 V + 197 Au reaction -arrive at consistent results if the bombarding energies in excess of the barrier are close to each other.…”

“…Chatterjee et al [9] studied the probability for cold-donor fragment production by measuring exclusive energy spectra of neutrons from the similar system 58 Ni + 208 Pb in coincidence with Ni-like fragments at "near-barrier energies". In contrast to the conclusions drawn in our work, the observed neutron spectra were found to be compatible with the assumption that the Pb-like fragment receives most of the total excitation energy independent of the direction and magnitude of the net mass transfer.…”