Constrained-phase-space approach to spin alignment in deep-inelastic heavy-ion collisions

Abstract

A constrained-phase-space description of equilibrium in the angular momentum degrees of freedom is used to calculate the spin alignment in deep-inelastic heavy-ion reactions. The phase space is constructed by considering the internal degrees of freedom of the excited fragments and the conservation of angular momentum; the constraint which reflects the reaction dynamics is derived from the classical sticking condition. For several cases of mass-asymmetric heavy-ion reactions, the measured alignments are quantitatively reproduced. It is found that the alignment depends most sensitively on the initial angular momentum and on the fragment deformation at separation so that alignment data are useful to determine these quantities. Angular correlations of sequential-fission fragments from deep-inelastic reactions are also calculated. In the considered example, the measured in-plane anisotropy is explained as mainly resulting from the restrictions, imposed by the experimental setup, on the orientations of the orbital angular momenta in the entrance and exit channels.