Tracking the dissipation of energy and angular momentum in central collisions between Ag and 40Ar of 7, 17, 27, and 34 MeV/nucleon.

Abstract

A 4\ensuremath{\pi} charged-particle multidetector has been used to study the reaction $^{40}\mathrm{Ar}$${+}^{\mathrm{nat}}$Ag from 280--1356 MeV. Charged-particle multiplicity distributions show a low-multiplicity group associated with peripheral collisions and a high-multiplicity group associated with central collisions. Average multiplicities for central collisions increase with increasing projectile energy, indicating ever-increasing collision violence. Angular distributions of emitted protons are essentially isotropic for \ensuremath{\theta}\ensuremath{\ge}80\ifmmode^\circ\else\textdegree\fi{} in a reference frame characterized by the empirical systematics of linear momentum transfer (i.e., \ensuremath{\approxeq}100% to \ensuremath{\approxeq}70% from 7--34 MeV/nucleon). Spectra of these protons at side angles are evaporationlike in shape and indicate relative effective temperatures of 3, 6, 8, and 12 MeV for beam energies of 7, 17, 27, and 34A MeV, respectively. Azimuthal angular correlations between various particle pairs are consistent with spin-driven emission from emitter sources of reasonable spin values. In short, these results support a classical picture of extensively thermalized emitter nuclei even for initial excitation energies of \ensuremath{\approxeq}5 MeV per system nucleon and spins of \ensuremath{\ge}100\ensuremath{\Elzxh}.