Fusion-fission and neutron-evaporation-residue cross-sections in 40Ar- and 50Ti-induced fusion reactions

Evidence for quasi-fission in40Ar+208Pb collisions near the coulomb-barrier

“…For the intermediate system 4~176 this new systematics [15] predicts an extra-push energy for formation of a compound nucleus inside the true fission saddle point of the order of 10 MeV. This is at variance with work by G/iggeler et al [20], who concluded on the basis of cross sections for fusion-evaporation residues [20] and for fission [22] that the 4~ Pb reactions did not show any evidence for an extra push.…”

“…The number of partial waves contributing to the region of fission-like products is inferred from the measured cross section [22]. Tl is the transmission coefficient for partial wave I.…”

Hindrance of fusion in central collisions of heavy, symmetric nuclear systems

“…The barrier transmission was taken into account by using the Hill-Wheeler extype. This procedure was found to give reasonable results for asymmetric systems [11]. Recently, however, experimental evidence has been accumulated that the assumption of a Hill-Wheeler-type barriertransmission is not valid for massive systems [12,13].…”

“…In the present work w(E*,l) was determined from the neutronevaporation-residue cross sections of the corresponding asymmetric reactions of which one example is shown in Fig. la for 4~176 For this purpose the measured excitation functions [11] for symmetric fragmentation for the systems 4~ _[_ 176,178, 18OHf ~ 169Tm were described by a slightly adjusted one-dimensional barrier-penetration model including dynamical fluctuations of the barrier [12], which were associated with low-energy excitations of the reaction partners and few-nucleon transfer processes in the early reaction stage [18,19]. The extracted barriers V, had already been shown in [11] to fit rather well into the systematics of a large body of fusion data of light and medium-heavy systems.…”

“…In order to extract the fusion probability from the evaporation-residue cross sections for the nearly symmetric systems, we used the experimental results [11,16] for the fusion reactions 4~ + 176'178'18~ 169Tm which lead to the same compound nuclei as obtained with the heavy projectiles. In the following, for brevity, we will discuss neutronevaporation-residue cross sections exclusively.…”