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