Preequilibrium emission in central collisions of the mass-symmetric system 40Ar+40Ca at 20 MeV/u

Light-particle emission versus evaporation residue formation in collisions of40Ar onnatCa at 30 MeV/u

“…The present investigation extends earlier studies [1][2][3] on PE light-particle emission in the system 4~ + 4~ to higher energies. We focus on events where an ER is formed.…”

“…The nucleon exchange transport model (NETM), on the other hand, overestimates the peaking along the beam axis. There seems to be a systematic trend with energy in the NETM predictions for the system 4~ + 4~ whereas the anisotropy of the predicted PE angular distribution is overestimated at 30 MeV/u bombarding energy, it is in line with experiment at 20 MeV/u [1] but too weak at still lower energies [3]. The steepness of the PE angular distribution is strongly affected by two-body collisions which are especially responsible for particle emission off the beam axis.…”

“…In the experiments with lower incident energies [1,3] a hot moving source parametrization with two maxwellian-shaped distributions successfully described the measured double differential neutron multiplicities in a consistent manner at all angles and enabled the decomposition of the spectra into an equilibrium (EQ) and a preequilibrium (PE) component. The following parametrization was taken (all quantities in the c.m.…”

“…The measured neutron angular distribution is compared in Fig. 5 with model calculations which successfully reproduced differential preequilibrium cross sections at lower energied [1,3]: the quantal phase-space model (QPSM) [11] and the (modified) nucleon exchange transport model (NETM) [19]. Both models are free of adjustable parameters.…”

“…From the calculation it was deduced that the PE stage is over after a rather short time, t~20 fm/c, in which fast nucleons on the average underwent about 2 collisions prior to escape [1,12]. ii) ER mass and element distributions can be satisfactorily explained by the emission of only neutrons and light charged particles with Z < 2, in both the preequilibrium and subsequent evaporative stages of the reaction.…”