Decay patterns of target-like and projectile-like nuclei produced in Kr-84+Au-197, U-nat reactions at E/A=150 MeV

The reactions Kr-84+Au-197 and Kr-84+U-nat were studied at an incident energy of E/A = 150 MeV employing the large-volume neutron multiplicity meter ORION, The observed correlations between the atomic number of projectile-like nuclei (PLN) and neutron multiplicity indicate large deposits of excitation energies in the primary fragments, Angular correlations between fragments from the fission of target-like nuclei (TLN) and secondary PLN show a memory of the reaction plane. No indications for spin effects were found in the TLN-fission fragment distribution

Formation and decay of hot nuclei in 475 MeV, 2 GeV proton- and 2 GeV He-3-induced reactions on Ag, Bi, An, and U

The formation and decay of hot nuclei generated in the interaction of light projectiles (475 MeV and 2 GeV protons and 2 GeV He-3) on a series of targets (Ag-107, Au-197, Bi-209, and U-238) are studied with an apparatus combining the efficient detection of neutrons in 4 pi sr and an accurate characterization of light charged particles, intermediate-mass fragments (IMF's), and fission fragments. A two-step approach with an intranuclear cascade process for modeling the initial off-equilibrium phase of the collision followed by a classical step-by-step evaporation-including fission competition-is used to reproduce the data. It is inferred from the model, which is found to reproduce several data sensitive to heat, that nuclei with temperatures exceeding T =5 MeV are produced for a sizable part of the events, thus giving the opportunity to study the behavior of hot nuclei free from strong collective excitations which generally accompany nucleus-nucleus collisions. Most of the observed features related to particle emission or more specifically to particle evaporation are rather well accounted for by the model calculation. The evaporationlike IMF emission is generally rather weak, and does not show any rapid onset at the highest excitation energies as would have been expected in a genuine thermal multifragmentation process. Binary fission of the U-like target is shown to be a fairly probable channel at most excitation energies. Some of the characteristics of the fission channel are satisfactorily reproduced, but not all. [S0556-2813(98)02605-3]