Splintering central collisions: Systematics of momentum and energy deposition for(17–115)AMeV40

Abstract

Measurements are reported for fragment masses and velocities from the reactions (17-115)A MeV 40 ArϩCu, Ag, and Au. Charged particle multiplicities were used to select the most violent reactions, and systematics are reported for the momentum and energy deposition. These reactions are fusionlike for Շ44A MeV 40 Ar with a large fraction of momentum and energy deposition in the heavy nuclear system. However, for տ44A MeV 40 Ar, a majority of the projectile energy and momentum is carried away by a multibody spray of light ejectiles and only a minority is deposited in the heavy nucleus. Nevertheless heavy composite systems are formed with up to 9-12 MeV per source nucleon for 115A MeV 40 Ar.

Balance of Mass, Momentum, and Energy in Splintering Central Collisions forA40rup to 115 MeV/Nucleon

“…Energy and time-of-flight signals from these detectors provided mass determinations (resolution 5%-10%) for fragments of A $ 10. As described in [1] we use these data to characterize the heaviest fragment in terms of its mass and longitudinal velocity; experimental details are given there. For data acquisition a minimum of two hits were required for 18 ± , u , 162 ± (thresholds 17 and 12 MeV for 1 H and 4 He)…”

“…Thin targets of Cu, Ag, or Au were bombarded, and charged ejectiles were detected from ϳ0.5 ± 162 ± in the 4p array [1,[5][6][7]]. An important aspect of this experiment was the use of 45 Si detectors (ϳ3 cm 3 3 cm 3 140 mm) mounted ഠ70 cm from the target in front of 45 plastic telescopes at polar angles of 3 ± 18 ± .…”

“…For such high deposition energies, statistical multifragmentation models predict much more extensive nuclear disassembly than is observed. Central collisions between mass asymmetric heavy nuclei of ϳ͑10 100͒A MeV deposit substantial amounts of energy into a core nuclear system, e.g., for ϳ100A MeV 40 Ar 1 Ag one finds *1 GeV (or ϳ10 MeV͞nucleon [1]). One expects that the addition of energy to a nuclear system will cause it to expand in size and ultimately lead to its disassembly, but we do not yet have a systematic picture of the evolution from nuclear evaporative decay to such disassembly [2].…”

“…As in [1] we select violent central collisions via the highest 15% of the multiplicity distributions and require that each event include $75% of the system charge and $70% of the incident momentum. We group the various ejectiles into two components: (a) an isotropic component in the frame of the heaviest fragment, and (b) a forward-directed component in this frame [3,4].…”

“…However, for beam energies of *44A MeV, the forwardpeaked components dominate, and the momentum is widely spread over many ejectile types. For this reason the term splintering central collisions was introduced [1].…”