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Öğe A comparative study of statistical models for nuclear equation of state of stellar matter(ELSEVIER, 2013) Buyukcizmeci, N.; Botvina, A. S.; Mishustin, I. N.; Ogul, R.; Hempel, M.; Schaffner-Bielich, J.; Thielemann, F. -K.We compare three different statistical models for the equation of state (EOS) of stellar matter at sub-nuclear densities and temperatures (0.5-10 MeV) expected to occur during the collapse of massive stars and supernova explosions. The models introduce the distributions of various nuclear species in nuclear statistical equilibrium, but use somewhat different nuclear physics inputs. It is demonstrated that the basic thermodynamical quantities of stellar matter under these conditions are similar, except in the region of high densities and low temperatures. We demonstrate that mass and isotopic distributions have considerable differences related to the different assumptions of the models on properties of nuclei at these stellar conditions. Overall, the three models give similar trends, but the details reflect the uncertainties related to the modeling of medium effects, such as the temperature and density dependence of surface and bulk energies of heavy nuclei, and the nuclear shell structure effects. We discuss importance of new physics inputs for astrophysical calculations from experimental data obtained in intermediate energy heavy-ion collisions, in particular, the similarities of the conditions reached during supernova explosions and multifragmentation reactions. (c) 2013 Elsevier B.V. All rights reserved.Öğe INVESTIGATING THE ISOTOPIC EFFECTS IN NUCLEAR FRAGMENTATION(POLISH ACAD SCIENCES INST PHYSICS, 2011) Buyukcizmeci, N.; Bulut, F.; Erdogan, M.; Imal, H.; Ogul, R.; Botvina, A. S.; Mishustin, I. N.Modifications for symmetry energy coefficients of nuclear matter at freeze-out density are investigated on the basis of the Statistical Multifragmentation Model (SMM). In order to compare our predictions with MSU experimental data we consider the fragmentation of the projectiles (124)Sn and (112)Sn which were also used for the MSU experiments, and of the projectiles (124)Sn La and (107)Sn used for the ALADIN experiments. Comparing our results with the experimental data, it is confirmed that a significant reduction of the symmetry term coefficient is found necessary to reproduce the mean < N >/Z values of light fragments.Öğe Isospin-dependent multifragmentation of relativistic projectiles(AMER PHYSICAL SOC, 2011) Ogul, R.; Botvina, A. S.; Atav, U.; Buyukcizmeci, N.; Mishustin, I. N.; Adrich, P.; Aumann, T.The N/Z dependence of projectile fragmentation at relativistic energies has been studied with the ALADIN forward spectrometer at the GSI Schwerionen Synchrotron (SIS). Stable and radioactive Sn and La beams with an incident energy of 600 MeV per nucleon have been used in order to explore a wide range of isotopic compositions. For the interpretation of the data, calculations with the statistical multifragmentation model for a properly chosen ensemble of excited sources were performed. The parameters of the ensemble, representing the variety of excited spectator nuclei expected in a participant-spectator scenario, are determined empirically by searching for an optimum reproduction of the measured fragment-charge distributions and correlations. An overall very good agreement is obtained. The possible modification of the liquid-drop parameters of the fragment description in the hot freeze-out environment is studied, and a significant reduction of the symmetry-term coefficient is found necessary to reproduce the mean neutron-to-proton ratios < N >/Z and the isoscaling parameters of Z <= 10 fragments. The calculations are, furthermore, used to address open questions regarding the modification of the surface-term coefficient at freeze-out, the N/Z dependence of the nuclear caloric curve, and the isotopic evolution of the spectator system between its formation during the initial cascade stage of the reaction and its subsequent breakup.Öğe Isotopic Yields and Symmetry Energy in Nuclear Multifragmentation Reactions(Iop Publishing Ltd, 2012) Buyukcizmeci, N.; Imal, H.; Ogul, R.; Botvina, A. S.; Mishustin, I. N.Isotopic yields of light intermediate mass fragments (Z 8) were studied with data from the MSU experiments for central collisions of 124 Sn + 124 Sn and 112Sn+112Sn at E/A = 50 MeV. Within the statistical multifragmentation model, microcanonical Markov-chain calculations were performed with the aim to reproduce experimental elemental and isotopic distributions. The effects of varying liquid-drop parameters of hot fragments formed inside the freeze-out volume on charge and isotopic distributions are demonstrated. It is seen that the isotopic distributions of these fragments are very sensitive to the variation of the symmetry energy of fragments. Comparing our results with the experimental data, it is seen that a significant reduction of the symmetry term coefficient leads to better reproduction of the isotopic distributions. Comparison with other statistical calculations has been made. This is in agreement with previous conclusions obtained from the interpretation of both central and peripheral heavy ion collisions.Öğe Modification of surface energy in nuclear multifragmentation(AMER PHYSICAL SOC, 2006) Botvina, A. S.; Buyukcizmeci, N.; Erdogan, M.; Lukasik, J.; Mishustin, I. N.; Ogul, R.; Trautmann, W.Within the statistical multifragmentation model we study modifications of the surface and symmetry energy of primary fragments in the freeze-out volume. The ALADIN experimental data on multifragmentation obtained in reactions induced by high-energy projectiles with different neutron richness are analyzed. We have extracted the isospin dependence of the surface energy coefficient at different degrees of fragmentation. We conclude that the surface energy of hot fragments produced in multifragmentation reactions differs from the values extracted for isolated nuclei at low excitation. At high fragment multiplicity, it becomes nearly independent of the neutron content of the fragments.Öğe Role of bulk energy in nuclear multifragmentation(AMER PHYSICAL SOC, 2008) Buyukcizmeci, N.; Botvina, A. S.; Mishustin, I. N.; Ogul, R.Because of thermal expansion and residual interactions, hot nuclear fragments produced in multifragmentation reactions may have nucleon density lower than the equilibrium density of cold nuclei. In terms of a liquid-drop model this effect can be taken into account by reducing the bulk energy of fragments. We study the influence of this change on fragment yields and isotope distributions within the framework of the statistical multifragmentation model. Similarities and differences with previously discussed modifications of symmetry and surface energies of nuclei are analyzed.Öğe TABULATED EQUATION OF STATE FOR SUPERNOVA MATTER INCLUDING FULL NUCLEAR ENSEMBLE(IOP PUBLISHING LTD, 2014) Buyukcizmeci, N.; Botvina, A. S.; Mishustin, I. N.This is an introduction to the tabulated database of stellar matter properties calculated within the framework of the Statistical Model for Supernova Matter (SMSM). The tables present thermodynamical characteristics and nuclear abundances for 31 values of baryon density (10(-8) < rho/rho(0) < 0.32, rho(0) = 0.15 fm(-3) is the normal nuclear matter density), 35 values of temperature (0.2MeV < T < 25 MeV), and 28 values of electron-to-baryon ratio (0.02 < Y-e < 0.56). The properties of stellar matter in beta equilibrium are also considered. The main ingredients of the SMSM are briefly outlined, and the data structure and content of the tables are explained.Öğe Towards the Equation of State for Dense Stellar Matter(IOP PUBLISHING LTD, 2010) Buyukcizmeci, N.; Botvina, A. S.; Mishustin, I. N.; Ogul, R.The thermal nuclear multifragmentation reaction can be used to investigate the nuclear liquid-gas phase coexistence region and its relation to the astrophysical processes such as the collapse of massive stars, and the supernova type-II explosions. We have performed some calculations to estimate stellar equation of state (EOS) on the basis of statistical multifragmentation model.
