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Abstract This review article takes stock of the progress made in understanding the phase transition in hot nuclei and highlights the coherence of observed signatures. [ABSTRACT FROM AUTHOR]

High energy gamma-rays from the 116 Sn + 24 Mg reaction at 23 A MeV were measured using the MEDEA detector at LNS – INFN Catania. Combining this new data with previous measurements yields a detailed view of the quenching of the Giant Dipole Resonance as a function of excitation energy in nuclei of mass A in the range 120 ÷ 132 . The transition towards the disappearance of the dipole strength, which occurs around 230 MeV excitation energy, appears to be remarkably sharp. Current phenomenological models give qualitative explanations for the quenching but cannot reproduce its detailed features. [ABSTRACT FROM AUTHOR]

A universal decay law (UDL) for light cluster decay of excited nuclei is formulated by fitting the UDL half-lives to those evaluated within an excitation energy-dependent double folding model (DFM). The half-lives are evaluated within a preformed cluster model. The excitation energy dependence is introduced both in the energy of the emitted cluster and in the interaction potential through the density distributions of the interacting nuclei. The half-lives are found to decrease when the difference between the excitation energies of the parent and daughter nuclei, Δ E ⁎ > 0, increases, with the reduction being a few orders of magnitude for higher values of Δ E ⁎. This can be of importance for nucleosynthesis calculations of heavy elements formed in extremely hot environments, as well as in highly energetic heavy-ion collisions. The UDL for excited nuclei is used to provide an estimate of the enhancement in the cluster decay rates of thermally excited nuclei such as those produced in r-process nucleosynthesis. [ABSTRACT FROM AUTHOR]

Abstract: The thermal evolution of the energies and free energies of a set of spherical and near-spherical nuclei spanning the whole periodic table are calculated in the subtracted finite-temperature Thomas–Fermi framework with the zero-range Skyrme-type KDE0 and the finite-range modified Seyler–Blanchard interaction. The calculated energies are subjected to a global fit in the spirit of the liquid-drop model. The extracted parameters in this model reflect the temperature dependence of the volume symmetry and surface symmetry coefficients of finite nuclei, in addition to that of the volume and surface energy coefficients. The temperature dependence of the surface symmetry energy is found to be very substantial whereas that of the volume symmetry energy turns out to be comparatively mild. [Copyright &y& Elsevier]

Abstract: The multipole response of nuclei at temperatures is studied using a self-consistent finite-temperature RPA (random phase approximation) based on relativistic energy density functionals. Illustrative calculations are performed for the isoscalar monopole and isovector dipole modes and, in particular, the evolution of low-energy excitations with temperature is analyzed, including the modification of pygmy structures. Both for the monopole and dipole modes, in the temperature range additional transition strength appears at low energies due to thermal unblocking of single-particle orbitals close to the Fermi level. A concentration of dipole strength around 10 MeV excitation energy is predicted in 60,62Ni. The principal effect of finite temperature on low-energy strength that is already present at zero temperature, e.g. in 68Ni and 132Sn, is the spreading of this structure to even lower energy and the appearance of states that correspond to thermally unblocked transitions. [Copyright &y& Elsevier]

Abstract: The process of nuclear multifragmentation leads to thermodynamic conditions akin to those encountered in the collapse/explosion of massive stars. Thus, the knowledge obtained from studying multifragmentation may be applied to describe matter distribution in supernova. Along these lines, the present study focuses on the symmetry energy of hot fragments produced in the multifragmentation of neutron-rich systems following collisions near the Fermi energy. The experiments consist of high-resolution mass spectrometric measurements of the isotopic and velocity distributions of heavy projectile fragments. The data were systematically compared to calculations with the Statistical Multifragmentation Model (SMM). The study indicates a gradual decrease of the symmetry energy coefficient from the standard value of ∼25MeV in the compound nucleus regime (E ∗/A <2MeV) towards ∼15MeV in the bulk multifragmentation regime (E ∗/A >4MeV). The isotopic distributions of the hot fragments are very wide and extend towards or beyond the neutron drip-line. These findings may have important implications to the composition and evolution of hot astrophysical environments, such as core-collapse supernova and the course of the ensuing nucleosynthesis processes, such as the r-process. [Copyright &y& Elsevier]

Abstract: The expansion of an isolated hot spherical nucleus with excitation energy and its caloric curve are studied in a thermodynamic model with the force as the nuclear effective two-body interaction. The calculated results are shown to compare well with the recent experimental data from energetic nuclear collisions. The fluctuations in temperature and density are also studied. They are seen to build up very rapidly beyond an excitation energy of . Volume-conserving quadrupole deformation in addition to expansion indicates, however, nuclear disassembly above an excitation energy of . [Copyright &y& Elsevier]