REACTION MECHANISMS FOR THE DISASSEMBLY OF 40-MEV/NUCLEON LANTHANUM (BREAK-UP, TEMPERATURE, FRAGMENTATION, EVAPORATION, SOURCE)

The reaction mechanisms responsible for the production of light charged particles and heavy fragments have been investigated for a 5560-MeV lanthanum beam from the Lawrence Berkeley Laboratory BEVALAC incident on targets of La, ('27)Al and ('197)Au. The inclusive kinetic energy spectra of particles with Z = 1 to 5 are characteristic of sequential emission from projectile-like fragments (PLF). Coincidence measurements between light charged particles (LCP) and heavy fragments indicate that the LCP's are predominately emitted from fragments with Z < 30. Alpha-to-proton ratios for very forward angles in the laboratory are greater than predicted using evaporation models. Possible explanations for these ratios may be kinematic focussing and/or emission from sources (Z < 16) which favor the emission of alpha-particles.;The energy spectra of heavy residual fragments show features associated with reaction mechanisms of low and intermediate energy reactions (binary and multi-body final states). For fragments detected at near-grazing angles, the energy spectra evolve from narrow fragmentation-like distributions, at charges closest to Z = 57, to more damped distributions below Z = 30. Momentum widths for detected fragments below Z = 30 suggest sequential break up from a primary fragment. Charge distributions at small angles (6(DEGREES)) are consistent with current models for multifragmentation. Charge distributions for a larger laboratory angle (28(DEGREES)) show significant yields for Z between 5 (detector threshold) and 16. This corresponds to the mass region where mildly excited primary fragments favor alpha-particle emission. Products at 28(DEGREES) may be dominated by harder or more central collisions in contrast to lower angle (6(DEGREES)) products which contain contributions from a range of impact parameters.