Nucleon exchange in the absence of strong driving forces: The reactionCa238atE

Abstract

Mass number, atomic number, energy, and angular distributions have been measured for the projectile-like fragments from the damped reaction ' U+ 'Ca at E~,b =425 MeV. Correlations in the measured two-dimensional probability distribution P ( A, Z) are discussed along with the general dissipative features of the damped reaction mechanism. The first and second moments of the observed atomic and mass number distributions are compared with those of other asymmetric reaction systems. Although the ' U+ Ca system is highly asymmetric, its potential energy surface in the vicinity of the injection point has a nearly zero gradient resulting in a negligible drift in the proton number. The proton drifts observed in reactions of "U with five different projectiles vary systematically with the potential gradient. The mass and charge data are compared with quantitative predictions by a dynamical reaction model based on nucleon exchange. The theoretical model gives a reasonable account of the mass and charge distributions for the "U+"'Ca reaction but fails systematically to predict experimental drifts when the driving forces are large.

How to extend the chart of nuclides?

“…The asymmetric systems 16 48 Ca + 238 U reaction, a large mass variance is observed along with a small change in the mean mass number of the light fragment, but it is not the case in the 40 Ca + 238 U reaction [67,68].…”

“…During formation and evolution of the DNS, there is continuous redistribution of nucleons, excitation energy and angular momentum between the two nuclei. The equilibrium between proton and neutron numbers occurs very fast in collisions of light nuclei and continuously proceeds in reactions with heavy nuclei [66][67][68][69]. As it evolves, the DNS can pass with some probability through any macroscopic configuration allowed by the conservation laws for particle number, charge and total energy.…”

“…The dots are the experimental data of Refs. [67,68]. The calculated results [205] are shown by lines W and Ta targets.…”

“…19 exemplarily the results for 40 Ca + 238 U (340 MeV) and 48 Ca + 238 U (425 MeV) collisions. The experimental data [67,68] are compared with DNS model calculations [205]. The calculations were performed for the angular momenta close to the critical value J crit being characteristic of DIC.…”

Isoscaling of heavy projectile residues andN/Zequilibration in peripheral heavy-ion collisions below the Fermi energy

“…Extensive work in deep-inelastic heavy-ion collisions at low energies (E/A<10 MeV, for a review see, e.g., [22,23]) provided insight into the relevant reaction mechanisms [24][25][26][27][28][29]. At these energies, the collisions are of binary character involving a transient dinuclear complex.…”