Formation of hot heavy nuclei in supernova explosions

We point out that during the supernova II type explosion the thermodynamical condition of stellar matter between the protoneutron star and the shock front corresponds to the nuclear liquid-gas phase coexistence region, which can be investigated in nuclear multifragmentation reactions. We have demonstrated, that neutron-rich hot heavy nuclei can be produced in this region. The production of these nuclei may influence dynamics of the explosion and contribute to the synthesis of heavy elements.Comment: 6 pages with 4 figure

Production of Neutron-rich Heavy Residues and the Freeze-out Temperature in the Fragmentation of Relativistic 238U Projectiles Determined by the Isospin Thermometer

Isotope yields of heavy residues produced in collisions of 238U with lead at 1AGeV show indications for a simultaneous break-up process. From the average N-over-Z ratio of the final residues up to Z = 70, the average limiting temperature of the break-up configuration at freeze out was determined to T approximately 5 MeV using the isospin-thermometer method. Consequences for the understanding of other phenomena in highly excited nuclear systems are discussed.Comment: 22 pages, 9 figures, accepted by Nucl. Phys.

Isotopic composition of fragments in multifragmentation of very large nuclear systems: effects of the chemical equilibrium

Studies on the isospin of fragments resulting from the disassembly of highly excited large thermal-like nuclear emitting sources, formed in the ^{197}Au + ^{197}Au reaction at 35 MeV/nucleon beam energy, are presented. Two different decay systems (the quasiprojectile formed in midperipheral reactions and the unique source coming from the incomplete fusion of projectile and target in the most central collisions) were considered; these emitting sources have the same initial N/Z ratio and excitation energy (E^* ~= 5--6 MeV/nucleon), but different size. Their charge yields and isotopic content of the fragments show different distributions. It is observed that the neutron content of intermediate mass fragments increases with the size of the source. These evidences are consistent with chemical equilibrium reached in the systems. This fact is confirmed by the analysis with the statistical multifragmentation model.Comment: 9 pages, 4 ps figure

Mass Parameterizations and Predictions of Isotopic Observables

We discuss the accuracy of mass models for extrapolating to very asymmetric nuclei and the impact of such extrapolations on the predictions of isotopic observables in multifragmentation. We obtain improved mass predictions by incorporating measured masses and extrapolating to unmeasured masses with a mass formula that includes surface symmetry and Coulomb terms. We find that using accurate masses has a significant impact on the predicted isotopic observables.Comment: 12 pages, 4 figure

Tracing the evolution of the symmetry energy of hot nuclear fragments from the compound nucleus towards multifragmentation

The evolution of the symmetry energy coefficient of the binding energy of hot fragments with increasing excitation is explored in multifragmentation processes following heavy-ion collisions below the Fermi energy. In this work, high-resolution mass spectrometric data on isotopic distributions of projectile-like fragments from collisions of 25 MeV/nucleon 86Kr and 64Ni beams on heavy neutron-rich targets are systematically compared to calculations involving the Statistical Multifragmentation Model. The study reveals a gradual decrease of the symmetry energy coefficient from 25 MeV at the compound nucleus regime (E*/A < 2 MeV) towards 15 MeV in the bulk multifragmentation regime (E*/A > 4 MeV). The ensuing isotopic distributions of the hot fragments are found to be very wide and extend towards the neutron drip-line. These findings may have important implications to the composition and evolution of hot astrophysical environments, such as core-collapse supernova.Comment: 5 pages, 4 figures, submitted to Phys. Rev.

Limits of complete equilibration of fragments produced in central Au on Au collisions at intermediate energies

Experimental data related to fragment production in central Au on Au collisions were analyzed in the framework of a modified statistical model which considers cluster production both prior and at the equilibrated stage. The analysis provides limits to the number of nucleons and to the temperature of the equilibrated source. The rather moderate temperatures obtained from experimental double-yield ratios of d,t,3He and 4He are in agreement with the model calculations. A phenomenological relation was established between the collective flow and the chemical temperature in these reactions. It was shown that dynamical mechanisms of fragment production, e.g. coalescence, dominate at high energies. It is demonstrated that coalescence may be consistent with chemical equilibrium between the produced fragments. The different meaning of chemical and kinetic temperatures is discussed.Comment: 13 pages, 10 figures, accepted at EPJ

Calculation of the number of partitions with constraints on the fragment size

This article introduces recursive relations allowing the calculation of the number of partitions with constraints on the minimum and/or on the maximum fragment size

Multifragmentation of charge asymmetric nuclear systems

The multifragmentation of excited spherical nuclear sources with various N/Z ratios and fixed mass number is studied within dynamical and statistical models. The dynamical model treats the multifragmentation process as a final stage of the growth of density fluctuations in unstable expanding nuclear matter. The statistical model makes a choice of the final multifragment configuration according to its statistical weight at a global thermal equilibrium. Similarities and differences in the predictions of the two models on the isotopic composition of the produced fragments are presented and the most sensitive observable characteristics are discussed.Comment: 15 pages, 8 figure

Comparative Study of Multifragmentation of Gold Nuclei Induced by Relativistic Protons, 4^4He, and 12^{12}C

Multiple emission of intermediate-mass fragments has been studied for the collisions of p, $^4$He and $^{12}$C on Au with the $4\pi$ setup FASA. The mean IMF multiplicities (for the events with at least one IMF) are saturating at the value of $2.2\pm0.2$ for the incident energies above 6 GeV. The observed IMF multiplicities cannot be described in a two-stage scenario, a fast cascade followed by a statistical multifragmentation. Agreement with the measured IMF multiplicities is obtained by introducing an intermediate phase and modifying empirically the excitation energies and masses of the remnants. The angular distributions and energy spectra from the p-induced collisions are in agreement with the scenario of ``thermal'' multifragmentation of a hot and diluted target spectator. In the case of $^{12}$C+Au(22.4 GeV) and $^4$He(14.6 GeV)+Au collisions, deviations from a pure thermal break-up are seen in the energy spectra of the emitted fragments, which are harder than those both from model calculations and from the measured ones for p-induced collisions. This difference is attributed to a collective flow.Comment: 33 pages 15 figures, accepted in Nucl. Phys.

Comparisons of Statistical Multifragmentation and Evaporation Models for Heavy Ion Collisions

The results from ten statistical multifragmentation models have been compared with each other using selected experimental observables. Even though details in any single observable may differ, the general trends among models are similar. Thus these models and similar ones are very good in providing important physics insights especially for general properties of the primary fragments and the multifragmentation process. Mean values and ratios of observables are also less sensitive to individual differences in the models. In addition to multifragmentation models, we have compared results from five commonly used evaporation codes. The fluctuations in isotope yield ratios are found to be a good indicator to evaluate the sequential decay implementation in the code. The systems and the observables studied here can be used as benchmarks for the development of statistical multifragmentation models and evaporation codes.Comment: To appear on Euorpean Physics Journal A as part of the Topical Volume "Dynamics and Thermodynamics with Nuclear Degrees of Freedo