Jl. Barreto et al., SEARCH FOR ENTRANCE CHANNEL EFFECTS IN THE DECAY OF THE YB-164 COMPOUND NUCLEUS AT E-ASTERISK-APPROXIMATE-TO-54 MEV, Physical review. C. Nuclear physics, 48(6), 1993, pp. 2881-2894
The existence of entrance channel effects in the decay of 164Yb, form
ed at E almost-equal-to 54 MeV in the reactions O-16 + Sm-148 and 64N
i + Mo-100 is investigated. Evaporation residue cross sections, entry
state gamma-ray fold distributions as well as energy and angular distr
ibutions of exit-channel selected charged particles were obtained for
each reaction, using 4pi detection systems for both particles and gamm
a rays. In the 64Ni-induced reaction, the center-of-mass alpha-particl
e angular distributions were found to be symmetric around 90-degrees i
ndicating emission from a fully equilibrated compound nucleus. However
, the corresponding angular distributions in the O-16-induced reaction
show a forward component which exclusively affects the population of
the alphaxn residue channels. The gamma-ray fold distributions for the
alphaxn and xn channels show differences depending on the entrance ch
annel as reported previously for similar systems. These differences ca
n be understood in terms, of contributions from the equilibrium decay
of incompletely fused O-16 with Sm-148 and the mapping of the compound
nucleus spin distributions, obtained from realistic fusion models, to
the evaporation residue gamma-ray fold distributions. It is concluded
that the initial population of the compound nucleus is the only reaso
n for the observed differences in the decay of 164Yb populated in the
se reactions.