J. B. Natowitz

Texas A&M University, College Station, Texas, United States

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Publications (237)612.93 Total impact

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    ABSTRACT: Cluster formation is a fundamental aspect of the equation of state (EOS) of warm and dense nuclear matter such as can be found in supernovae (SN). Similar matter can be studied in heavy-ion collisions (HIC). We use the experimental data of Qin et al. 2012 to test calculations of cluster formation and the role of in-medium modifications of cluster properties in SN EOSs. For the comparison between theory and experiment we use chemical equilibrium constants as the main observables. This reduces some of the systematic uncertainties and allows deviations from ideal gas behavior to be identified clearly. In the analysis, we carefully account for the differences between matter in SN and HIC. We find that, at the lowest densities, the experiment and all theoretical models are consistent with the ideal gas behavior. At higher densities ideal behavior is clearly ruled out and interaction effects have to be considered. The contributions of continuum correlations are of relevance in the virial expansion and remain a difficult problem to solve at higher densities. We conclude that at the densities and temperatures discussed mean-field interactions of nucleons, inclusion of all relevant light clusters, and a suppression mechanism of clusters at high densities have to be incorporated in the SN EOS.
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    ABSTRACT: We measured the average deuterium cluster size within a mixture of deuterium clusters and helium gas by detecting Rayleigh scattering signals. The average cluster size from the gas mixture was comparable to that from a pure deuterium gas when the total backing pressure and temperature of the gas mixture were the same as those of the pure deuterium gas. According to these measurements, the average size of deuterium clusters depends on the total pressure and not the partial pressure of deuterium in the gas mixture. To characterize the cluster source size further, a Faraday cup was used to measure the average kinetic energy of the ions resulting from Coulomb explosion of deuterium clusters upon irradiation by an intense ultrashort pulse. The deuterium ions indeed acquired a similar amount of energy from the mixture target, corroborating our measurements of the average cluster size. As the addition of helium atoms did not reduce the resulting ion kinetic energies, the reported results confirm the utility of using a known cluster source for beam-target-fusion experiments by introducing a secondary target gas.
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    ABSTRACT: Symmetry energy, temperature and density at the time of the intermediate mass fragment formation are determined in a self-consistent manner, using the experimentally reconstructed primary hot isotope yields and anti-symmetrized molecular dynamics (AMD) simulations. The yields of primary hot fragments are experimentally reconstructed for multifragmentation events in the reaction system $^{64}$Zn + $^{112}$Sn at 40 MeV/nucleon. Using the reconstructed hot isotope yields and an improved method, based on the modified Fisher model, symmetry energy values relative to the apparent temperature, $a_{sym}/T$, are extracted. The extracted values are compared with those of the AMD simulations, extracted in the same way as that for the experiment, with the Gogny interaction with three different density-dependent symmetry energy terms. $a_{sym}/T$ values change according to the density-dependent symmetry energy terms used. Using this relation, the density of the fragmenting system is extracted first. Then symmetry energy and apparent temperature are determined in a self consistent manner in the AMD model simulations. Comparing the calculated $a_{sym}/T$ values and those of the experimental values from the reconstructed yields, $\rho /\rho_{0} = 0.65 \pm 0.02 $, $a_{sym} = 23.1 \pm 0.6$ MeV and $T= 5.0 \pm 0.4$ MeV are evaluated for the fragmenting system experimentally observed in the reaction studied.
    Nuclear Physics A 09/2014; 933. DOI:10.1016/j.nuclphysa.2014.09.077 · 2.50 Impact Factor
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    ABSTRACT: The mass dependence of the transverse flow in the reactions of Ca-40 + Ca-40 at 35 MeV/nucleon has been determined for emitted isotopes with Z = 1 to 9. The observed flow is compared with that calculated using a constrained molecular dynamics (CoMD) simulation. With the application of the appropriate experimental filter, the general trend of the experimental mass-dependent flow is well reproduced by the simulation employing an effective interaction corresponding to a soft equation of state (K = 200 MeV). The CoMD events are further utilized to study the mechanism of generation of the mass-dependent flow. It is found that the mass-dependent flow is generated by the interplay between the thermal and collective motions under a momentum conservation in the fragmenting system. With the help of the collective-thermal-interplay model, the mass-dependent flow scaled by the reduced mass of fragments A/A(sys) is found to be almost independent of the size of the system.
    Physical Review C 07/2014; 90(1). DOI:10.1103/PhysRevC.90.014604 · 3.88 Impact Factor
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    ABSTRACT: Fermi energy heavy ion collisions provide a valuable tool to research nuclear reaction dynamics and the hot nuclear matter Equation of State (EOS) at sub/supra-normal densities. In this energy regime, multi-fragmentation becomes important and the ejected light particles and intermediate mass fragments (IMFs) with Z > 2 carry a great deal of information on the thermal and chemical evolution of the reaction system under investigation. Existing detectors [1] include those with excellent isotopic resolution with limited angular coverage or excellent geometric acceptance with moderate isotopic resolution. Much information has been extracted from experiments performed with these detectors [2–9]. Ideally, a detector array with both excellent isotopic resolution and with a nearly 4π angular coverage of discrete telescopes with a high granularity is desirable. NIMROD–ISiS at the Cyclotron Institute, TAMU, is designed for such purposes and provides a powerful detector array capable of both charged particle and neutron detection in one apparatus.
    07/2014; 24(3). DOI:10.1080/10619127.2014.883480
  • Physical Review C 07/2014; 90(1). DOI:10.1103/PhysRevC.90.019903 · 3.88 Impact Factor
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    ABSTRACT: Ternary fission yields in the reaction Pu-241(n(th), f) are calculated using a new model which assumes a nucleation-time-moderated chemical equilibrium in the low-density matter which constitutes the neck region of the scissioning system. The temperature, density, proton fraction, and fission time required to fit the experimental data are derived and discussed. A reasonably good fit to the experimental data is obtained. This model provides a natural explanation for the observed yields of heavier isotopes relative to those of the lighter isotopes, the observation of low proton yields relative to H-2 and H-3 yields, and the nonobservation of He-3, all features which are shared by similar thermal neutron-induced and spontaneous fissioning systems.
    Physical Review C 07/2014; 90(1). DOI:10.1103/PhysRevC.90.011601 · 3.88 Impact Factor
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    ABSTRACT: The characteristic properties of the hot nuclear matter existing at the time of fragment formation in the multifragmentation events produced in the reaction $^{64}$Zn + $^{112}$Sn at 40 MeV/nucleon are studied. A kinematical focusing method is employed to determine the multiplicities of evaporated light particles, associated with isotopically identified detected fragments. From these data the primary isotopic yield distributions are reconstructed using a Monte Carlo method. The reconstructed yield distributions are in good agreement with the primary isotope distributions obtained from AMD transport model simulations. Utilizing the reconstructed yields, power distribution, Landau free energy, characteristic properties of the emitting source are examined. The primary mass distributions exhibit a power law distribution with the critical exponent, $A^{-2.3}$, for $A \geq 15$ isotopes, but significantly deviates from that for the lighter isotopes. Landau free energy plots show no strong signature of the first order phase transition. Based on the Modified Fisher Model, the ratios of the Coulomb and symmetry energy coefficients relative to the temperature, $a_{c}/T$ and $a_{sym}/T$, are extracted as a function of A. The extracted $a_{sym}/T$ values are compared with results of the AMD simulations using Gogny interactions with different density dependencies of the symmetry energy term. The calculated $a_{sym}/T$ values show a close relation to the symmetry energy at the density at the time of the fragment formation. From this relation the density of the fragmenting source is determined to be $\rho /\rho_{0} = (0.63 \pm 0.03 )$. Using this density, the symmetry energy coefficient and the temperature of fragmenting source are determined in a self-consistent manner as $a_{sym} = (24.7 \pm 3.4) MeV$ and $T=(4.9 \pm 0.2)$ MeV.
    Physical Review C 05/2014; 90(4). DOI:10.1103/PhysRevC.90.044603 · 3.88 Impact Factor
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    ABSTRACT: The density and temperature of a fragmenting system in a multifragmentation process are evaluated in a self-consistent manner using ratios between the ratio of the symmetry energy coefficient relative to the temperature, a_{sym}/T, extracted from the fragment yields generated by antisymmetrized molecular dynamics (AMD) simulations for central collisions of ^{40}Ca + ^{40}Ca at 35 MeV/nucleon. The a_{sym}/T values are extracted from all isotope yields by an improved method based on the Modified Fisher Model (MFM). The ratios of a_{sym}/T obtained, using interactions with different density dependencies of the symmetry energy term, reflect the ratios of the symmetry energy at the density of fragment formation. Using this correlation, the density is found to be \rho/\rho_0 = 0.66 \pm 0.02. The symmetry energy values for each interaction are determined at this density. With these values, temperature values are extracted as a function of isotope mass A. The extracted temperature values are compared with those evaluated from the fluctuation thermometer with a radial flow correction.
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    ABSTRACT: Ternary fission yields in the reaction 241Pu(nth,f) are calculated using a new model which assumes a nucleation-time moderated chemical equilibrium in the low density matter which constitutes the neck region of the scissioning system. The temperature, density, proton fraction and fission time required to fit the experimental data are derived and discussed. A reasonably good fit to the experimental data is obtained. This model provides a natural explanation for the observed yields of heavier isotopes relative to those of the lighter isotopes, the observation of low proton yields relative to 2H and 3H yields and the non-observation of 3He, all features which are shared by similar thermal neutron induced and spontaneous fissioning systems.
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    ABSTRACT: The density and temperature of a fragmenting system in a multifragmentation process are evaluated in a self-consistent manner using ratios between the ratio of the symmetry energy coefficient relative to the temperature, a_{sym}/T, extracted from the fragment yields generated by antisymmetrized molecular dynamics (AMD) simulations for central collisions of ^{40}Ca + ^{40}Ca at 35 MeV/nucleon. The a_{sym}/T values are extracted from all isotope yields by an improved method based on the Modified Fisher Model (MFM). The ratios of a_{sym}/T obtained, using interactions with different density dependencies of the symmetry energy term, reflect the ratios of the symmetry energy at the density of fragment formation. Using this correlation, the density is found to be \rho/\rho_0 = 0.66 \pm 0.02. The symmetry energy values for each interaction are determined at this density. With these values, temperature values are extracted as a function of isotope mass A. The extracted temperature values are compared with those evaluated from the fluctuation thermometer with a radial flow correction.
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    ABSTRACT: We explored alpha clustering in 24Mg using the reaction 20Ne+α and the Thick Target Inverse Kinematics (TTIK) technique. 20Ne beams of energy 3.7 AMeV and 11 AMeV were delivered by the K150 cyclotron at Texas A&M; University. The reaction chamber was filled with 4He gas at a pressure sufficient to stop the beam before the detectors. The energy of the light reaction products was measured by three silicon detector telescopes. The time relative to the cyclotron radiofrequency was also measured. For the first time the TTIK method was used to study both single and multiple α-particle decays. New results were obtained on elastic resonant α scattering, as well as on inelastic processes leading to high excitation energy systems decaying by multiple α-particle emission. Preliminary results will be shown on events with α-multiplicity one and two.
    The European Physical Journal Conferences 02/2014; 66. DOI:10.1051/epjconf/20146603005
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    ABSTRACT: For the first time primary hot isotope distributions are experimentally reconstructed in intermediate heavy ion collisions and used with antisymmetrized molecular dynamics (AMD) calculations to determine density, temperature and symmetry energy coefficient in a self-consistent manner. A kinematical focusing method is employed to reconstruct the primary hot fragment yield distributions for multifragmentation events observed in the reaction system $^{64}$Zn + $^{112}$Sn at 40 MeV/nucleon.The reconstructed yield distributions are in good agreement with the primary isotope distributions of AMD simulations. The experimentally extracted values of the symmetry energy coefficient relative to the temperature, $a_{sym}/T$, are compared with those of the AMD simulations with different density dependence of the symmetry energy term.The calculated $a_{sym}/T$ values changes according to the different interactions. By comparison of the experimental values of $a_{sym}/T$ with those of alculations, the density of the source at fragment formation was determined to be $\rho /\rho_{0} = (0.63 \pm 0.03 )$. Using this density, the symmetry energy coefficient and the temperature are determined in a self-consistent manner as $a_{sym} = (23.5 \pm 1.5) MeV$ and $T=(5.1 \pm 0.1)$ MeV.
    Physical Review C 02/2014; 89(2). DOI:10.1103/PhysRevC.89.021601 · 3.88 Impact Factor
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    K. Hagel, J. B. Natowitz, G. Röpke
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    ABSTRACT: The symmetry energy of nuclear matter is a fundamental ingredient in the investigation of exotic nuclei, heavy-ion collisions and astrophysical phenomena. A recently developed quantum statistical (QS) approach that takes the formation of clusters into account predicts low density symmetry energies far above the usually quoted mean field limits. A consistent description of the symmetry energy has been developed that joins the correct low-density limit with values calculated from quasi-particle approaches valid near the saturation density. The results are confronted with experimental values for free symmetry energies and internal symmetry energies, determined at sub-saturation densities and temperatures below 10 MeV using data from heavy-ion collisions. There is very good agreement between the experimental symmetry energy values and those calculated in the QS approach
    European Physical Journal A 01/2014; 50(2). DOI:10.1140/epja/i2014-14039-4 · 2.42 Impact Factor
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    ABSTRACT: We report on experiments in which the Texas Petawatt laser irradiated a mixture of deuterium or deuterated methane clusters and helium-3 gas, generating three types of nuclear fusion reactions: D(d,^{3}He)n, D(d,t)p, and ^{3}He(d,p)^{4}He. We measured the yields of fusion neutrons and protons from these reactions and found them to agree with yields based on a simple cylindrical plasma model using known cross sections and measured plasma parameters. Within our measurement errors, the fusion products were isotropically distributed. Plasma temperatures, important for the cross sections, were determined by two independent methods: (1) deuterium ion time of flight and (2) utilizing the ratio of neutron yield to proton yield from D(d,^{3}He)n and ^{3}He(d,p)^{4}He reactions, respectively. This experiment produced the highest ion temperature ever achieved with laser-irradiated deuterium clusters.
    Physical Review E 09/2013; 88(3-1):033108. DOI:10.1103/PhysRevE.88.033108 · 2.31 Impact Factor
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    ABSTRACT: The plasma astrophysical S factor for the ^{3}He(d,p)^{4}He fusion reaction was measured for the first time at temperatures of few keV, using the interaction of intense ultrafast laser pulses with molecular deuterium clusters mixed with ^{3}He atoms. Different proportions of D_{2} and ^{3}He or CD_{4} and ^{3}He were mixed in the gas target in order to allow the measurement of the cross section for the ^{3}He(d,p)^{4}He reaction. The yield of 14.7 MeV protons from the ^{3}He(d,p)^{4}He reaction was measured in order to extract the astrophysical S factor at low energies. Our result is in agreement with other S factor parametrizations found in the literature.
    Physical Review Letters 08/2013; 111(8):082502. DOI:10.1103/PhysRevLett.111.082502 · 7.73 Impact Factor
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    ABSTRACT: Two different methods have been employed to determine the plasma temperature in a laser-cluster fusion experiment on the Texas Petawatt laser. In the first, the temperature was derived from time-of-flight data of deuterium ions ejected from exploding D_{2} or CD_{4} clusters. In the second, the temperature was measured from the ratio of the rates of two different nuclear fusion reactions occurring in the plasma at the same time: D(d,^{3}He)n and ^{3}He(d,p)^{4}He. The temperatures determined by these two methods agree well, which indicates that (i) the ion energy distribution is not significantly distorted when ions travel in the disassembling plasma; (ii) the kinetic energy of deuterium ions, especially the "hottest part" responsible for nuclear fusion, is well described by a near-Maxwellian distribution.
    Physical Review Letters 08/2013; 111(5):055002. · 7.73 Impact Factor
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    ABSTRACT: The diagnostics of particle flows in Inertial Confinement Fusion experiments is a delicate issue, due to the fast timescales and to the strong radiative electromagnetic contributions. This makes the discrimination of the different particles produced by the laser–plasma interaction not trivial, and requires the use of several diagnostic techniques. We describe here the diagnostics improvement in the ABC facility. They will provide more detailed analysis of microwave fields and particles originating from the interaction of laser with targets foreseen for future experiments.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 08/2013; 720:149–152. DOI:10.1016/j.nima.2012.12.013 · 1.32 Impact Factor
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    ABSTRACT: The experimental determination of freeze-out temperatures and densities from the yields of light elements emitted in heavy ion collisions is discussed. Results from different experimental approaches are compared with those of model calculations carried out with and without the inclusion of medium effects. Medium effects become of relevance for baryon densities above $\approx 5 \times 10^{-4}$ fm$^{-3}$. A quantum statistical (QS) model incorporating medium effects is in good agreement with the experimentally derived results at higher densities. A densitometer based on calculated chemical equilibrium constants is proposed.
    Physical Review C 05/2013; 88(2). DOI:10.1103/PhysRevC.88.024609 · 3.88 Impact Factor
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    ABSTRACT: The excitation energies of the primary hot isotopes in multifragmentation events are experimentally reconstructed in the reaction system 64Zn + 112Sn at 40 MeV/nucleon. A kinematical focusing method is employed to evaluate the multiplicities of the evaporated light particles associated with isotopically identified fragments with 3 � Z � 14. Angular distributions of the velocity spectra of light charged particles and neutrons associated with trigger isotopes are examined. A moving source fit is used to separate the kinematically correlated particles, evaporated from the parents of the detected isotopes, from the uncorrelated particles originating from other sources. The latter are evaluated experimentally relative to those in coincidence with the Li isotopes. A parameter, k, is used to adjust the yield of the uncorrelated particles for different trigger isotopes. For each experimentally detected isotope, the multiplicities, apparent temperatures, and k values for n, p, d, t, and α particles are extracted. Using the extracted values, the excitation energies of the primary hot isotopes are reconstructed employing a Monte Carlo method. The extracted excitation energies are in the range of 1 to 4 MeV/nucleon but show a significant decreasing trend as a function of A for a given Z of the isotopes. The results are compared with those of antisymmetrized molecular dynamics (AMD) and statistical multifragmentation model (SMM) simulations.While some of the experimental characteristics are predicted partially by each model, neither simulation reproduces the overall characteristics of the experimental results
    Physical Review C 04/2013; DOI:10.1103/PhysRevC.88.034605 · 3.88 Impact Factor

Publication Stats

3k Citations
612.93 Total Impact Points

Institutions

  • 1973–2014
    • Texas A&M University
      • Department of Chemistry
      College Station, Texas, United States
  • 2013
    • University of Texas at Austin
      • Department of Physics
      Austin, Texas, United States
  • 2009
    • Association for Molecular Pathology
      베서스다, Maryland, United States
  • 1994–2000
    • Alabama A & M University
      Huntsville, Alabama, United States
  • 1999
    • University of Padova
      • Department of Information Engineering
      Padua, Veneto, Italy
  • 1986–1992
    • Hope College
      • Department of Physics
      Holland, Michigan, United States
  • 1990
    • Texas A&M University System
      College Station, Texas, United States
  • 1987
    • Catholic University of Louvain
      • Institute of Nuclear Physics
      Louvain-la-Neuve, WAL, Belgium
  • 1983
    • Washington University in St. Louis
      • Department of Chemistry
      San Luis, Missouri, United States
  • 1982
    • Max Planck Institute for Nuclear Physics
      Heidelburg, Baden-Württemberg, Germany