Abstract:
Aiming to develop a systematics in the pre-compound emission process and to get its driving
parameters, a sensitive analysis of the measured excitation functions for (α, n) reaction channel on target
nuclei viz., 139La, 159Tb, 181Ta, 197Au and 203Tl has been performed with codes pace4 and alice at
low projectile energies, where the compound nucleus process is dominant. The code pace4 considers only
compound nucleus emission, while the alice code takes into account both compound and pre-compound
emissions. The observed enhancement in experimental excitation functions in the tail portion of energies
as compared to calculations performed with code pace4 may be attributed to the contribution from
pre-compound emission. Further, the calculations performed with the alice code confirm the significant
contribution of the pre-compound emission. The effect of various pre-compound parameters on measured
excitation functions has also been studied. The energy dependent yield of the pre-compound contribution
over the compound nucleus emission for neutron emission channels is deduced in terms of pre-compound
fraction “FPCN ” which gives a good systematics on such process. The developed systematics in α-induced
reactions on target nuclei reflects that the pre-compound process is governed by the excitation energy
available with the nucleons at the surface of the composite systems. Furthermore, the mass number of the
target nuclei may also play an important role in the pre-compound process at low projectile energies.
