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We study primary and secondary reactions induced by 600 MeV proton beams in monolithic cylindrical targets made of natural tungsten and uranium by using Monte Carlo simulations with the Geant4 toolkit [1–3]. Bertini intranuclear cascade model, Binary cascade model and IntraNuclear Cascade Liège (INCL) with ABLA model [4] were used as calculational options to describe nuclear reactions. Fission cross sections, neutron multiplicity and mass distributions of fragments for 238U fission induced by 25.6 and 62.9 MeV protons are calculated and compared to recent experimental data [5]. Time distributions of neutron leakage from the targets and heat depositions are calculated.
The present limits of the upper part of the nuclear map are rather close to the beta stability line while the unexplored area of heavy neutron rich nuclides (also those located along the neutron closed shell N = 126 to the right hand side of the stability line) is extremely important for nuclear astrophysics investigations and, in particular, for the understanding of the r-process of astrophysical nucleogenesis. For elements with Z > 100 only neutron deficient isotopes (located to the left of the stability line) have been synthesized so far. The “north-east” area of the nuclear map can be reached neither in fusion–fission reactions nor in fragmentation processes widely used nowadays for the production of new nuclei. Multi-nucleon transfer processes in near barrier collisions of heavy ions seem to be the only reaction mechanism allowing us to produce and explore neutron rich heavy nuclei including those located at the superheavy island of stability. Neutron capture process can be also considered as an alternative method for the production of long-lived neutron rich superheavy nuclei. Strong neutron fluxes might be provided by nuclear reactors and nuclear explosions in laboratory frame and by supernova explosions in nature.
Short range particle repulsion is rather important property of the hadronic and nuclear matter equations of state. We present a novel equation of state which is based on the virial expansion for the multicomponent mixtures with hard-core repulsion. In addition to the hard-core repulsion taken into account by the proper volumes of particles, this equation of state explicitly contains the surface tension which is induced by another part of the hard-core repulsion between particles. At high densities the induced surface tension vanishes and the excluded volume treatment of hard-core repulsion is switched to its proper volume treatment. Possible applications of this equation of state to a description of hadronic multiplicities measured in A+A collisions, to an investigation of the nuclear matter phase diagram properties and to the neutron star interior modeling are discussed.
A novel approach to identify the geometrical (anti)clusters formed by the Polyakov loops of the same sign and to study their properties in the lattice SU(2) gluodynamics is developed. The (anti)cluster size distributions are analyzed for the lattice coupling constant β ∈ 2 [2:3115; 3]. The found distributions are similar to the ones existing in 2- and 3-dimensional Ising systems. Using the suggested approach, we explain the phase transition in SU(2) gluodynamics at β = 2.52 as a transition between two liquids during which one of the liquid droplets (the largest cluster of a certain Polyakov loop sign) experiences a condensation, while another droplet (the next to the largest cluster of opposite Polyakov loop sign) evaporates. The clusters of smaller sizes form two accompanying gases, which behave oppositely to their liquids. The liquid drop formula is used to analyze the distributions of the gas (anti)clusters and to determine their bulk, surface and topological parts of free energy. Surprisingly, even the monomer multiplicities are reproduced with high quality within such an approach. The behavior of surface tension of gaseous (anti)clusters is studied. It is shown that this quantity can serve as an order parameter of the deconfinement phase transition in SU(2) gluodynamics. Moreover, the critical exponent β of surface tension coefficient of gaseous clusters is found in the upper vicinity of critical temperature. Its value coincides with the one found for 3-dimensional Ising model within error bars. The Fisher topological exponent τ of (anti)clusters is found to have the same value 1:806±0:008, which agrees with an exactly solvable model of the nuclear liquid-gas phase transition and disagrees with the Fisher droplet model, which may evidence for the fact that the SU(2) gluodynamics and the model are in the same universality class.
We present a novel equation of state which is based on the virial expansion for the multicomponent mixtures with hard core repulsion. The suggested equation of state explicitly contains the surface tension which is induced by particle interaction. At high densities such a surface tension vanishes and in this way it switches the excluded volume treatment of hard core repulsion to its eigen volume treatment. The great advantage of the developed model is that the number of equations to be solved is two and it does not depend on the number of independent hard-core radii. Using the suggested equation of state we obtained a high quality fit of the hadron multiplicities measured at AGS, SPS, RHIC and ALICE energies and studied the properties of the nuclear matter phase diagram. It is shown the developed equation of state is softer than the gas of hard spheres and remains causal up to the several normal nuclear densities. Therefore, it could be applied to the neutron star interior modeling.
We study the impact of nonequilibrium effects on the relevant signals within a chiral fluid dynamics model including explicit propagation of the Polyakov loop. An expanding heat bath of quarks is coupled to the Langevin dynamics of the order parameter fields. The model is able to describe relaxational processes, including critical slowing down and the enhancement of soft modes near the critical point. At the first-order phase transition we observe domain formation and phase coexistence in the sigma and Polyakov loop field leading to a significant amount of clumping in the energy density. This effect gets even more pronounced if we go to systems at finite baryon density. Here the formation of high-density clusters could provide an important observable signal for upcoming experiments at FAIR and NICA.We conclude that improving our understanding of dynamical symmetry breaking is important to give realistic estimates for experimental observables connected to the QCD phase transition.
The biological effects of energetic heavy ions are attracting increasing interest for their applications in cancer therapy and protection against space radiation. The cascade of events leading to cell death or late effects starts from stochastic energy deposition on the nanometer scale and the corresponding lesions in biological molecules, primarily DNA. We have developed experimental techniques to visualize DNA nanolesions induced by heavy ions. Nanolesions appear in cells as “streaks” which can be visualized by using different DNA repair markers. We have studied the kinetics of repair of these “streaks” also with respect to the chromatin conformation. Initial steps in the modeling of the energy deposition patterns at the micrometer and nanometer scale were made with MCHIT and TRAX models, respectively.
Background: In this interdisciplinary project, the biological effects of heavy ions are compared to those of X-rays using tissue slice culture preparations from rodents and humans. Advantages of this biological model are the conservation of an organotypic environment and the independency from genetic immortalization strategies used to generate cell lines. Its open access allows easy treatment and observation via live-imaging microscopy. Materials and methods: Rat brains and human brain tumor tissue are cut into 300 micro m thick tissue slices. These slices are cultivated using a membrane-based culture system and kept in an incubator at 37°C until treatment. The slices are treated with X-rays at the radiation facility of the University Hospital in Frankfurt at doses of up to 40 Gy. The heavy ion irradiations were performed at the UNILAC facility at GSI with different ions of 11.4 A MeV and fluences ranging from 0.5–10 x 106 particles/cm². Using 3D-confocal microscopy, cell-death and immune cell activation of the irradiated slices are analyzed. Planning of the irradiation experiments is done with simulation programs developed at GSI and FIAS. Results: After receiving a single application of either X-rays or heavy ions, slices were kept in culture for up to 9d post irradiation. DNA damage was visualized using gamma H2AXstaining. Here, a dose-dependent increase and time-dependent decrease could clearly be observed for the X-ray irradiation. Slices irradiated with heavy ions showed less gamma H2AX-positive cells distributed evenly throughout the slice, even though particles were calculated to penetrate only 90–100 micro m into the slice. Conclusions: Single irradiations of brain tissue, even at high doses of 40 Gy, will result neither in tissue damage visible on a macroscopic level nor necrosis. This is in line with the view that the brain is highly radio-resistant. However, DNA damage can be detected very well in tissue slices using gamma H2AX-immuno staining. Thus, slice cultures are an excellent tool to study radiation-induced damage and repair mechanisms in living tissues.
We argue that Clustering in heavy ion collisions could be the missing element in resolving the socalled HBT puzzle, and briefly discuss the different physical situations where clustering could be present. We then propose a method by which clustering in heavy ion collisions could be detectedin a model-independent way.
We develop a 1+1 dimensional hydrodynamical model for central heavy-ion collisions at ultrarelativistic energies. Deviations from Bjorken's scaling are taken into account by implementing finite-size profiles for the initial energy density. The calculated rapidity distributions of pions, kaons and antiprotons in central Au+Au collisions at the c.m. energy 200 AGeV are compared with experimental data of the BRAHMS Collaboration. The sensitivity of the results to the choice of the equation of state, the parameters of initial state and the freeze-out conditions is investigated. The best fit of experimental data is obtained for a soft equation of state and Gaussian-like initial profiles of the energy density.