17,843 research outputs found
Effects of geometric constraints on the nuclear multifragmentation process
We include in statistical model calculations the facts that in the nuclear
multifragmentation process the fragments are produced within a given volume and
have a finite size. The corrections associated with these constraints affect
the partition modes and, as a consequence, other observables in the process. In
particular, we find that the favored fragmenting modes strongly suppress the
collective flow energy, leading to much lower values compared to what is
obtained from unconstrained calculations. This leads, for a given total
excitation energy, to a nontrivial correlation between the breakup temperature
and the collective expansion velocity. In particular we find that, under some
conditions, the temperature of the fragmenting system may increase as a
function of this expansion velocity, contrary to what it might be expected.Comment: 16 pages, 5 figure
Statistical multifragmentation model with discretized energy and the generalized Fermi breakup. I. Formulation of the model
The Generalized Fermi Breakup recently demonstrated to be formally equivalent
to the Statistical Multifragmentation Model, if the contribution of excited
states are included in the state densities of the former, is implemented. Since
this treatment requires the application of the Statistical Multifragmentation
Model repeatedly on the hot fragments until they have decayed to their ground
states, it becomes extremely computational demanding, making its application to
the systems of interest extremely difficult. Based on exact recursion formulae
previously developed by Chase and Mekjian to calculate the statistical weights
very efficiently, we present an implementation which is efficient enough to
allow it to be applied to large systems at high excitation energies. Comparison
with the GEMINI++ sequential decay code shows that the predictions obtained
with our treatment are fairly similar to those obtained with this more
traditional model.Comment: 8 pages, 6 figure
Constraints on the density dependence of the symmetry energy
Collisions involving 112Sn and 124Sn nuclei have been simulated with the
improved Quantum Molecular Dynamics transport model. The results of the
calculations reproduce isospin diffusion data from two different observables
and the ratios of neutron and proton spectra. By comparing these data to
calculations performed over a range of symmetry energies at saturation density
and different representations of the density dependence of the symmetry energy,
constraints on the density dependence of the symmetry energy at sub-normal
density are obtained. Results from present work are compared to constraints put
forward in other recent analysis.Comment: 8 pages, 4 figures,accepted for publication in Phy. Rev. Let
Nuclear isotope thermometry
We discuss different aspects which could influence temperatures deduced from
experimental isotopic yields in the multifragmentation process. It is shown
that fluctuations due to the finite size of the system and distortions due to
the decay of hot primary fragments conspire to blur the temperature
determination in multifragmentation reactions. These facts suggest that caloric
curves obtained through isotope thermometers, which were taken as evidence for
a first-order phase transition in nuclear matter, should be investigated very
carefully.Comment: 9 pages, 7 figure
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