Systematics of the 14N + 159Tb reaction between 6 and 22 MeV/u:(III). The production of fast α-particles

Employing the results from inclusive and particle-KX-ray coincidence measurements for the 14N + 159Tb reaction between 6 and 22 MeV/u the cross sections of α-particles are decomposed into three components. These are (i) α-particles evaporated from the target-like nucleus, (ii) α-particles in coincidence with projectile-like fragments (PLF's) with Z ⩾ 3 and most likely resulting from sequential decay of excited primary fragments, and (iii) α-particles from processes in which only (fast) light particles with Z ⩽ 2 are emitted. The average number of α-particles emitted per collision increases with beam energy for each of the three components, whereas the total cross section tends to level off. The channels in which only light particles are emitted are found to be the major source of the large cross section of fast α-particles at forward angles. From γ-ray multiplicity data it is deduced that these channels involve a significantly larger excitation of the heavy residual nucleus (inelasticity) than the (quasi-elastic) channels in which a PLF with Z ⩾ 3 is emitted. However, from the near beam velocities of the α-particles it must be concluded that they are emitted prior to the attainment of full energy damping.