Studies of intermediate-mass fragment emission in the 3He+natAg, 197Au reactions between 0.48 and 3.6 GeV.

Abstract

Intermediate-mass fragments formed in reactions of $^{3}\mathrm{He}$ ions with $^{\mathrm{nat}}\mathrm{Ag}$ and $^{197}\mathrm{Au}$ targets have been studied at five energies between 0.48 and 3.6 GeV. Inclusive measurements show that as the bombarding energy increases, there is a strong enhancement in fragment cross sections and a trend toward isotropic angular distributions. Between 0.90 and 1.8 GeV, a change in the emission mechanism is suggested by (1) kinetic energy spectra with high-energy tails that become distinctly flatter, (2) a broadening of the spectral Coulomb peaks toward lower energies, and (3) charge distributions that become constant, exhibiting a power-law exponent \ensuremath{\tau}\ensuremath{\approxeq}2.0. Exclusive studies of the $^{3}\mathrm{He}$${+}^{\mathrm{nat}}$Ag system at 0.90 and 3.6 GeV detected multifragment events with multiplicities up to four. The probability for high-multiplicity events increases about 40-fold between 0.90 and 3.6 GeV. At both energies, the kinetic energy spectra depend on multiplicity, especially when triggering on backward-emitted fragments. For multiplicity three events, a rapidity analysis of the data at 3.6 GeV is consistent with a single, relatively low source velocity, ${\mathit{v}}_{\mathit{S}}$\ensuremath{\approxeq}0.4 cm/ns. The data are compared with predictions of a coplanarity-sphericity calculation, the sequential statistical decay code GEMINI, and a hybrid intranuclear cascade/percolation model.