R. Keser

Vanderbilt University, Nashville, Michigan, United States

Are you R. Keser?

Claim your profile

Publications (14)16.63 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present results for calculating fusion cross-sections using a new microscopic approach based on a time-dependent density-constrained DFT calculations. The theory is implemented by using densities and other information obtained from TDDFT time-evolution of the nuclear system as constraint on the density for DFT calculations.
    The European Physical Journal Conferences 02/2014; 66.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The density-constrained time-dependent Hartree-Fock (DC-TDHF) theory is a fully microscopic approach for calculating heavy-ion interaction potentials and fusion cross sections below and above the fusion barrier. We discuss recent applications of DC-TDHF method to fusion of light and heavy neutron-rich systems.
    10/2013;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We perform a study of 16O+16O fusion at above and below the interaction barrier energies using three-dimensional time-dependent Hartree-Fock (TDHF) calculations at above-barrier energies and density-constrained TDHF calculations for the entire energy range. We discuss the variations of the experimental data at above the barrier energies. Calculations reasonably reproduce the observed energy-dependent broad oscillations in the fusion excitation functions. These oscillations result from overcoming L-dependent fusion barriers. The role of the coupling to low-lying octupole states is also discussed.
    Physical Review C 08/2013; 88(2). · 3.72 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We perform a study of $^{16}$O+$^{16}$O fusion at above and below the interaction barrier energies using three-dimensional time-dependent Hartree-Fock (TDHF) calculations at above barrier energies and density-constrained TDHF calculations for the entire energy range. We discuss the variations of the experimental data at above the barrier energies. Calculations reasonably reproduce the observed energy-dependent broad oscillations in the fusion excitation functions. These oscillations result from overcoming $L$-dependent fusion barriers. The role of the coupling to low-lying octupole states is also discussed.
    06/2013;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The density-constrained time-dependent Hartree-Fock (DC-TDHF) theory is a fully microscopic approach for calculating heavy-ion interaction potentials and fusion cross sections below and above the fusion barrier. We discuss recent applications of DC-TDHF method to fusion of light and heavy systems.
    AIP Conference Proceedings. 08/2012; 1491(1).
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We study heavy-ion fusion reactions at energies near the Coulomb barrier, in particular with neutron-rich radioactive ion beams. Dynamic microscopic calculations are carried out on a three-dimensional lattice using the Density-Constrained Time-Dependent Hartree-Fock (DC-TDHF) method. New results are presented for the $^{132}$Sn+$^{40}$Ca system which are compared to $^{132}$Sn+$^{48}$Ca studied earlier. Our theoretical fusion cross-sections agree surprisingly well with recent data measured at HRIBF. We also study the near- and sub-barrier fusion of $^{24,16}$O on $^{12}$C which is important to determine the composition and heating of the crust of accreting neutron stars.
    Journal of Physics Conference Series 08/2012; 420(1).
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Marine fish is an important daily diet item for the people of Turkey. The Black Sea Region of Turkey was contaminated by the Chernobyl accident in 1986, a comprehensive study was planned and carried out to determine the radioactivity levels ((226)Ra, (232)Th, (40)K and (137)Cs) and heavy metal concentrations (As, Mn, Fe, Cr, Ni, Zn, Cu and Pb) in four of the most common fish species: Engraulis encrasicholus (anchovy), Oncorhynchus mykiss (trout), Trachurus mediterranus (bluefin) and Merlangius merlangus (whiting) samples collected from eight stations in the Black Sea Region of Turkey during 2010. The dose due to consumption of fish by the public was estimated and it was shown that this dose imposes no threat to human healthy. The concentrations of heavy metal are below the daily intake recommended by the international organizations.
    Chemosphere 04/2012; 87(4):356-61. · 3.14 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigate the fusion barriers for reactions involving Ca isotopes $\mathrm{^{40}Ca}+\mathrm{^{40}Ca}$, $\mathrm{^{40}Ca}+\mathrm{^{48}Ca}$, and $\mathrm{^{48}Ca}+\mathrm{^{48}Ca}$ using the microscopic time-dependent Hartree-Fock theory coupled with a density constraint. In this formalism the fusion barriers are directly obtained from TDHF dynamics. We also study the excitation of the pre-equilibrium GDR for the $\mathrm{^{40}Ca}+\mathrm{^{48}Ca}$ system and the associated $\gamma$-ray emission spectrum. Fusion cross-sections are calculated using the incoming-wave boundary condition approach. We examine the dependence of fusion barriers on collision energy as well as on the different parametrizations of the Skyrme interaction.
    Physical Review C 02/2012; 85(4). · 3.72 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Rize in Turkey was contaminated by the Chernobyl accident in 1986. A comprehensive study was planned and carried out to determine the radioactivity levels and heavy metal concentrations in four food categories collected in Rize in 2008, 2009 and 2010. Tomato showed the highest concentration of (238) U, at 9.43 ± 0.128 Bq kg(-1) , whereas the lowest concentration of 0.20 ± 0.02 Bq kg(-1) was measured in aubergine samples. The highest concentration of (232) Th was measured at 3.22 ± 0.29 Bq kg(-1) in grape samples. (40) K was found to contribute the highest activity in all the food samples. The highest activity concentration of (137) Cs was 10.20 ± 4.19 Bq kg(-1) , for parsley. The average contribution range of each of the heavy metals to the dietary intake was 0.13-9.14, 0.27-34.63, 0.05-3.62, 0.11-14.97, 0.78-8.51 and 0.01-1.57 mg, respectively, for Mn, Fe, Cu, Zn, Ni and As. The range of radioactivity levels in food samples of the present study is of no risk to public health. Heavy metal concentrations of Mn, Fe, Cu, Zn, Ni and As obtained were far below the established values by FAO/WHO limits.
    Journal of the Science of Food and Agriculture 08/2011; 92(2):307-12. · 1.88 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this study, the activity concentrations of (232) Th, (238) U, (40) K and (137) Cs were measured in tea, cabbage, orange, kiwi and soil samples collected from different stations using gamma spectrometry with a high-purity germanium detector. The average activity concentrations of (232) Th, (238) U, (40) K and (137) Cs were found to be 8.2 ± 1.8, 17.3 ± 3.3, 465.8 ± 11.8 and 20.9 ± 3.8 Bq kg(-1) in food samples, and 72.4 ± 9.8, 51.1 ± 8.3, 229.3 ± 14.7 and 312.9 ± 11.5 Bq kg(-1) in farm soils, respectively. The internal effective dose to individuals and excess lifetime cancer risk from the consumption of the food type radioactivity ranged between 11.7 and 53.6 µSv y(-1) and between 0.05 × 10(-3) and 0.24 × 10(-3) , respectively. The annual external gamma effective dose and excess lifetime cancer risk in the farms due to soil radioactivity ranged between 94.1 and 139.8 µSv y(-1) and between 0.43 × 10(-3) and 0.64 × 10(-3) , respectively. The mean transfer factors of (232) Th, (238) U, (40) K and (137) Cs, from the soil to vegetables and fruit were 0.57, 0.32, 2.12 and 0.04, respectively. Annual effective gamma doses were found to be higher than the world's average in soil samples. The excess lifetime cancer risks were only found higher than the world's average in soil samples.
    Journal of the Science of Food and Agriculture 03/2011; 91(6):987-91. · 1.88 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Tea is one of the most popular beverages in the world. The Eastern Black Sea Region of Turkey is one of the main tea producers in Turkey and the fifth in the world. Thus, the chemical components in tea have received great interest because they are related to health. Since this region was contaminated by the Chernobyl accident in 1986, a comprehensive study was planned and carried out to determine the radioactivity level in the tea growing region. The activity concentrations of 232Th, 238U, 40K and 137Cs were measured in 29 black tea and one green tea samples from local Turkish markets using gamma spectrometry with an HpGe detector. The average activity concentration of 232Th, 226Ra, 40K and 137Cs were found 3.2 ± 0.6 Bq/kg, 6.4 ± 0.7 Bq/kg, 445.6 ± 17.8 Bq/kg and 42.0 ± 1.4 Bq/kg in tea samples, respectively.In addition, the concentration of five heavy metals including Fe, Mn, Zn, Cu and Pb were determined by inductively coupled plasma spectroscopy (ICP/OES) on tea samples. Among the investigated metals, Mn was the highest levels. The levels of manganese were in the range of 1850.75–292.65 μg/g (mean: 1286.35 ± 0.58 μg/g). Levels of Pb in the tea samples analyzed were below the detection limits. The concentrations of all elements for daily intake are below safety levels for human consumptions.Highlights► This study was determined the radioactivity and heavy metal levels in the tea. ► The heavy metal concentrations of all elements are below safety levels. ► The annual dose from the consumption of the tea samples were calculated.
    Food Control. 01/2011; 22(12):2065-2070.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Samsun city which is between the deltas where Yeşilırmak and Kızılırmak rivers run out, exists in the middle part of Black Sea's costal way. It is the biggest city of the Black Sea Region in terms of population, industry, trade, natural and cultural wealth. There is no information about radioactivity measurement reported in water samples in the Samsun province so far. For this reason, gross α and gross β activities of 19 different water samples collected from spring, river and tap waters in Samsun were determined. The instrumentation used to count the gross α and gross β activities was an α/β counter of the low background multiple detector type with 10 sample detectors (Berthold LB770). The average activity concentrations were 51.9mBq/l, 77.8mBq/l for gross α and gross β in tap water. The obtained results showed that, natural activity concentrations of α and β emitting radionuclides in drinking, spring and river water samples did not exceed WHO recommendations. For all samples the gross β activity is always higher than the gross α activity. The results obtained in this study indicate that the annual effective doses are below the WHO recommended reference level of 0.1mSv/y for all water samples.
    Desalination. 01/2011; 279(1):135-139.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The concentrations and distribution of natural and artificial radionuclides in sediment and water samples collected from Fırtına River in the Eastern Black Sea region of Turkey were investigated with an aim of evaluating the environmental radioactivity and radiation hazard. Natural gross α and gross β activities were determined for 21 different water samples, and the activity concentrations were obtained for 226Ra, 214Pb, 214Bi, 228Ac, 208Tl, 40K and 137Cs in 20 different sediment samples. The obtained results showed that natural gross α and gross β activity concentrations in water samples range from 12.4±3.4 to 66.2±9.2mBql−1 and from 27.9±3.3 to 133.3±4.1mBql−1, respectively. The mean activity concentrations were 32.6±3.8mBql−1 for gross α and 69.9±4.4mBql−1 for gross β. Generally, the gross β activities were higher than the corresponding gross α activities. The average concentrations of 238U and 232Th daughter products vary from 11 to 167Bqkg−1 and from 16 to 107Bqkg−1, respectively. The concentrations of 40K and 137Cs vary from 51 to 1,605Bqkg−1 and from 0.8 to 42Bqkg−1, respectively. Sediment characterization was also investigated using grain size, thin section and XRD analysis.
    Environmental Geology 09/2008; 55(7):1483-1491. · 1.13 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The natural radioactivity levels in soil and sediment samples of Firtina Valley have been determined. To our knowledge, there seems to be no information about radioactivity level in the Firtina Valley soils and sediments so far. For this reason, soil and sediment samples were collected along the Firtina Valley and analysis on the collected samples were carried out to determine 238U, 232Th, 40K and 137Cs radioisotopes using high purity germanium detector. The activity concentrations obtained for 226Ra, 214Pb, 214Bi, 228Ac, 208Tl, 40K and 137Cs are given in the unit of Bq/kg. The results have been compared with other radioactivity measurements in different country's soils and sediments. The radium equivalent activity (Raeq), the absorbed dose rate (D), the external hazard index (Hex), the annual gonadal dose equivalent (AGDE) and the annual effective dose equivalent (AEDE) were also calculated and compared with the international recommended values.
    Applied Radiation and Isotopes 12/2007; 65(11):1281-9. · 1.18 Impact Factor