9 research outputs found
Statistical Analysis of Composite Spectra
We consider nearest neighbor spacing distributions of composite ensembles of
levels. These are obtained by combining independently unfolded sequences of
levels containing only few levels each. Two problems arise in the spectral
analysis of such data. One problem lies in fitting the nearest neighbor spacing
distribution to the histogram of level spacings obtained from the data. We show
that the method of Bayesian inference is superior to this procedure. The second
problem occurs when one unfolds such short sequences. We show that the
unfolding procedure generically leads to an overestimate of the chaoticity
parameter. This trend is absent in the presence of long-range level
correlations. Thus, composite ensembles of levels from a system with long-range
spectral stiffness yield reliable information about the chaotic behavior of the
system.Comment: 26 pages, 3 figures; v3: changed conclusions, appendix adde
Fusion and Binary-Decay Mechanisms in the Cl+Mg System at E/A 8 MeV/Nucleon
Compound-nucleus fusion and binary-reaction mechanisms have been investigated
for the Cl+Mg system at an incident beam energy of E= 282
MeV. Charge distributions, inclusive energy spectra, and angular distributions
have been obtained for the evaporation residues and the binary fragments.
Angle-integrated cross sections have been determined for evaporation residues
from both the complete and incomplete fusion mechanisms. Energy spectra for
binary fragment channels near to the entrance-channel mass partition are
characterized by an inelastic contribution that is in addition to a fully
energy damped component. The fully damped component which is observed in all
the binary mass channels can be associated with decay times that are comparable
to, or longer than the rotation period. The observed mass-dependent cross
sections for the fully damped component are well reproduced by the fission
transition-state model, suggesting a fusion followed by fission origin. The
present data cannot, however, rule out the possibility that a long-lived
orbiting mechanism accounts for part or all of this yield.Comment: 41 pages standard REVTeX file, 14 Figures available upon request -
Discrete structures in fusion-barrier distributions for vibrational nuclei
We obtain a closed-form expression for the distribution of fusion barriers
for vibrational nuclei using a generalization of Dasso, Landowne, and
Winther's model, which represents the nuclear surface vibrations as a number
of harmonic oscillators, and allows the excitation of an arbitrary number of
phonons in the target and/or projectile. We find that this expression is in
reasonable agreement with the average trends of the empirical distributions
for the fusion of with , and
, but fails to reproduce the double peaking of the
distribution for the target. Only when we restrict the
number of excited phonons to a limited number, we are able to reproduce such
discrete structures. We show that limiting the number of coupled channels,
particularly in the case of strong coupling, increases the spacings between
the channel eigenvalues that determine the positions of the peaks of the
barrier distribution and modifies their heights