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Christian G Iliadis - One of the best experts on this subject based on the ideXlab platform.

  • nuclear thermometers for classical novae
    The Astrophysical Journal, 2013
    Co-Authors: Lori Downen, Christian G Iliadis, J Jose, Sumner Starrfield
    Abstract:

    Classical novae are stellar explosions occurring in binary systems, consisting of a white dwarf and a main-sequence companion. Thermonuclear runaways on the surface of massive white dwarfs, consisting of oxygen and neon, are believed to reach peak temperatures of several hundred million kelvin. These temperatures are strongly correlated with the underlying white dwarf mass. The observational counterparts of such models are likely associated with outbursts that show strong spectral lines of neon in their shells (neon novae). The goals of this work are to investigate how useful elemental abundances are for constraining the peak temperatures achieved during these outbursts and determine how robust 'nova thermometers' are with respect to uncertain nuclear physics input. We present updated observed abundances in neon novae and perform a series of hydrodynamic simulations for several white dwarf masses. We find that the most useful thermometers, N/O, N/Al, O/S, S/Al, O/Na, Na/Al, O/P, and P/Al, are those with the steepest monotonic dependence on peak temperature. The sensitivity of these thermometers to Thermonuclear Reaction rate variations is explored using post-processing nucleosynthesis simulations. The ratios N/O, N/Al, O/Na, and Na/Al are robust, meaning they are minimally affected by uncertain rates. However, their dependence on peak temperature is relativelymore » weak. The ratios O/S, S/Al, O/P, and P/Al reveal strong dependences on temperature and the poorly known {sup 30}P(p, {gamma}){sup 31}S rate. We compare our model predictions to neon nova observations and obtain the following estimates for the underlying white dwarf masses: 1.34-1.35 M {sub Sun} (V838 Her), 1.18-1.21 M {sub Sun} (V382 Vel), {<=}1.3 M {sub Sun} (V693 CrA), {<=}1.2 M {sub Sun} (LMC 1990 no. 1), and {<=}1.2 M {sub Sun} (QU Vul).« less

  • the effects of Thermonuclear Reaction rate variations on 26al production in massive stars a sensitivity study
    Astrophysical Journal Supplement Series, 2011
    Co-Authors: Christian G Iliadis, Arthur E Champagne, Alessandro Chieffi, Marco Limongi
    Abstract:

    We investigate the effects of Thermonuclear Reaction rate variations on 26Al production in massive stars. The dominant production sites in such events were recently investigated by using stellar model calculations: explosive neon-carbon burning, convective shell carbon burning, and convective core hydrogen burning. Post-processing nucleosynthesis calculations are performed for each of these sites by adopting temperature-density-time profiles from recent stellar evolution models. For each profile, we individually multiplied the rates of all relevant Reactions by factors of 10, 2, 0.5, and 0.1, and analyzed the resulting abundance changes of 26Al. In total, we performed ≈900 nuclear Reaction network calculations. Our simulations are based on a next-generation nuclear physics library, called STARLIB, which contains a recent evaluation of Monte Carlo Reaction rates. Particular attention is paid to quantifying the rate uncertainties of those Reactions that most sensitively influence 26Al production. For stellar modelers our results indicate to what degree predictions of 26Al nucleosynthesis depend on currently uncertain nuclear physics input, while for nuclear experimentalists our results represent a guide for future measurements. We also investigate equilibration effects of 26Al. In all previous massive star investigations, either a single species or two species of 26Al were taken into account, depending on whether thermal equilibrium was achieved or not. These are two extreme assumptions, and in a hot stellar plasma the ground and isomeric states may communicate via γ-ray transitions involving higher-lying 26Al levels. We tabulate the results of our Reaction rate sensitivity study for each of the three distinct massive star sites referred to above. It is found that several current Reaction rate uncertainties influence the production of 26Al. Particularly important Reactions are 26Al(n,p)26Mg, 25Mg(α,n)28Si, 24Mg(n,γ)25Mg, and 23Na(α,p)26Mg. These Reactions should be prime targets for future measurements. Overall, we estimate that the nuclear physics uncertainty of the 26Al yield predicted by the massive star models explored here amounts to about a factor of three. We also find that taking the equilibration of 26Al levels explicitly into account in any of the massive star sites investigated here has only minor effects on the predicted 26Al yields. Furthermore, we provide for the interested reader detailed comments regarding the current status of certain Reactions, including 12C(12C,n)23Mg, 23Na(α,p)26Mg, 25Mg(α,n)28Si, 26Al m (p,γ)27Si, 26Al(n,p)26Mg, and 26Al(n,α)23Na.

  • charged particle Thermonuclear Reaction rates iii nuclear physics input
    Nuclear Physics, 2010
    Co-Authors: Christian G Iliadis, Arthur E Champagne, R Longland
    Abstract:

    Abstract The nuclear physics input used to compute the Monte Carlo Reaction rates and probability density functions that are tabulated in the second paper of this issue (Paper II) is presented. Specifically, we publish the input files to the Monte Carlo Reaction rate code RatesMC , which is based on the formalism presented in the first paper of this issue (Paper I). This data base contains overwhelmingly experimental nuclear physics information. The survey of literature for this review was concluded in November 2009.

  • new Reaction rate for o 16 p gamma f 17 and its influence on the oxygen isotopic ratios in massive agb stars
    Physical Review C, 2008
    Co-Authors: Christian G Iliadis, Maria Lugaro, Pierre Descouvemont, Carmen Angulo, Peter Mohr
    Abstract:

    The O-16(p, gamma)F-17 Reaction rate is revisited with special emphasis on the stellar temperature range of T=60-100 MK, important for hot bottom burning in asymptotic giant branch (AGB) stars. We evaluate existing cross-section data that were obtained since 1958 and, if appropriate, correct published data for systematic errors that were not noticed previously, including the effects of coincidence summing and updated effective stopping powers. The data are interpreted by using two different models of nuclear Reactions, that is, a potential model and R-matrix theory. A new astrophysical S factor and recommended Thermonuclear Reaction rates are presented. As a result of our work, the O-16(p, gamma)F-17 Reaction has now the most precisely known rate involving any target nucleus in the mass A >= 12 range, with Reaction rate errors of about 7% over the entire temperature region of astrophysical interest (T=0.01-2.5 GK). The impact of the present improved Reaction rate with its significantly reduced uncertainties on the hot bottom burning in AGB stars is discussed. In contrast to earlier results we find now that there is not clear evidence to date for any stellar grain origin from massive AGB stars.

  • nuclear physics of stars
    2007
    Co-Authors: Christian G Iliadis
    Abstract:

    Preface. 1 Aspects of Nuclear Physics and Astrophysics. 1.1 History. 1.2 Nomenclature. 1.3 Solar System Abundances. 1.4 Astrophysical Aspects. 1.4.1 General Considerations. 1.4.2 Hertzsprung-Russell Diagram. 1.4.3 Stellar Evolution of Single Stars. 1.4.4 Binary Stars. 1.5 Masses, Binding Energies, Nuclear Reactions, and Related Topics. 1.5.1 Nuclear Mass and Binding Energy. 1.5.2 Energetics of Nuclear Reactions. 1.5.3 Atomic Mass and Mass Excess. 1.5.4 Number Abundance, Mass Fraction, and Mole Fraction. 1.5.5 Decay Constant, Mean Lifetime, and Half-Life. 1.6 Nuclear Shell Model. 1.6.1 Closed Shells and Magic Numbers. 1.6.2 Nuclear Structure and Nucleon Configuration. 1.7 Nuclear Excited States and Electromagnetic Transitions. 1.7.1 Energy, Angular Momentum, and Parity. 1.7.2 Transition Probabilities. 1.7.3 Branching Ratio and Mixing Ratio. 1.7.4 Gamma-Ray Transitions in a Stellar Plasma. 1.7.5 Isomeric States and the Case of 26 Al. 1.8 Weak Interaction. 1.8.1 Weak Interaction Processes. 1.8.2 Energetics. 1.8.3 Beta-Decay Probabilities. 1.8.4 Beta-Decays in a Stellar Plasma. 2 Nuclear Reactions. 2.1 Cross Sections. 2.2 Reciprocity Theorem. 2.3 Elastic Scattering and Method of Partial Waves. 2.3.1 General Aspects. 2.3.2 Relationship Between Differential Cross Section and Scattering Amplitude. 2.3.3 The Free Particle. 2.3.4 Turning the Potential On. 2.3.5 Scattering Amplitude and Elastic Scattering Cross Section. 2.3.6 Reaction Cross Section. 2.4 Scattering by Simple Potentials. 2.4.1 Square-Well Potential. 2.4.2 Square-Barrier Potential. 2.4.3 Transmission Through the Coulomb Barrier. 2.5 Theory of Resonances. 2.5.1 General Aspects. 2.5.2 Logarithmic Derivative, Phase Shift, and Cross Section. 2.5.3 Breit-Wigner Formulas. 2.5.4 Extension to Charged Particles and Arbitrary Values of Orbital Angular Momentum. 2.5.5 R-Matrix Theory. 2.5.6 Experimental Tests of the One-Level Breit-Wigner Formula. 2.5.7 Partial and Reduced Widths. 2.6 Continuum Theory. 2.7 Hauser-Feshbach Theory. 3 Thermonuclear Reactions. 3.1 Cross Sections and Reaction Rates. 3.1.1 Particle-Induced Reactions. 3.1.2 Photon-Induced Reactions. 3.1.3 Abundance Evolution. 3.1.4 Forward and Reverse Reactions. 3.1.5 Reaction Rates at Elevated Temperatures. 3.1.6 Reaction Rate Equilibria. 3.1.7 Nuclear Energy Generation. 3.2 Nonresonant and Resonant Thermonuclear Reaction Rates. 3.2.1 Nonresonant Reaction Rates for Charged-Particle-Induced Reactions. 3.2.2 Nonresonant Reaction Rates for Neutron-Induced Reactions. 3.2.3 Nonresonant Reaction Rates for Photon-Induced Reactions. 3.2.4 Narrow-Resonance Reaction Rates. 3.2.5 Broad-Resonance Reaction Rates. 3.2.6 Electron Screening. 3.2.7 Total Reaction Rates. 4 Nuclear Physics Experiments. 4.1 General Aspects. 4.1.1 Charged-Particle Beams. 4.1.2 Neutron Beams. 4.2 Interaction of Radiation with Matter. 4.2.1 Interactions of Heavy Charged Particles. 4.2.2 Interactions of Photons. 4.2.3 Interactions of Neutrons. 4.3 Targets and Related Equipment. 4.3.1 Backings. 4.3.2 Target Preparation. 4.3.3 Contaminants. 4.3.4 Target Chamber and Holder. 4.4 Radiation Detectors. 4.4.1 General Aspects. 4.4.2 Semiconductor Detectors. 4.4.3 Scintillation Detectors. 4.4.4 Proportional Counters. 4.4.5 Microchannel Plate Detectors. 4.5 Nuclear Spectroscopy. 4.5.1 Charged-Particle Spectroscopy. 4.5.2 Gamma-Ray Spectroscopy. 4.5.3 Neutron Spectroscopy. 4.6 Miscellaneous Experimental Techniques. 4.6.1 Radioactive Ion Beams. 4.6.2 Activation Method. 4.6.3 Time-of-Flight Technique. 4.7 Background Radiation. 4.7.1 General Aspects. 4.7.2 Background in Charged-Particle Detector Spectra. 4.7.3 Background in &alpha -Ray Detector Spectra. 4.7.4 Background in Neutron Detector Spectra. 4.8 Yields and Cross Sections for Charged-Particle-Induced Reactions. 4.8.1 Nonresonant and Resonant Yields. 4.8.2 General Treatment of Yield Curves. 4.8.3 Measured Yield Curves and Excitation Functions. 4.8.4 Determination of Absolute Resonance Strengths and Cross Sections. 4.9 Transmissions, Yields, and Cross Sections for Neutron-Induced Reactions. 4.9.1 Resonance Transmission. 4.9.2 Resonant and Nonresonant Yields. 4.9.3 Effective Cross Section. 4.9.4 Measured Yields and Transmissions. 4.9.5 Relative and Absolute Cross Sections. 5 Nuclear Burning Stages and Processes. 5.1 Hydrostatic Hydrogen Burning. 5.1.1 pp Chains. 5.1.2 CNO Cycles. 5.1.3 Hydrostatic Hydrogen Burning Beyond the CNO Mass Region. 5.2 Explosive Hydrogen Burning. 5.2.1 Hot CNO Cycles. 5.2.2 Explosive Hydrogen Burning Beyond the CNO Mass Region. 5.3 Hydrostatic Helium Burning. 5.3.1 Helium-Burning Reactions. 5.3.2 Nucleosynthesis During Hydrostatic He Burning. 5.3.3 Other Helium-Burning Reactions. 5.4 Explosive Hydrogen-Helium Burning. 5.4.1 Breakout from the HCNO Cycles. 5.4.2 Network Calculations at Constant Temperature and Density. 5.4.3 Nucleosynthesis for Temperature-Density Profiles. 5.5 Advanced Burning Stages. 5.5.1 Carbon Burning. 5.5.2 Neon Burning. 5.5.3 Oxygen Burning. 5.5.4 Silicon Burning. 5.5.5 Nuclear Statistical Equilibrium and Freeze-Out. 5.6 Nucleosynthesis Beyond the Iron Peak. 5.6.1 The s-Process. 5.6.2 The r-Process. 5.6.3 The p-Process. 5.7 Origin of the Solar System Nuclides. Appendix. A Solutions of the Schrodinger Equation in Three Dimensions. A.1 Zero Orbital Angular Momentum and Constant Potential. A.2 Arbitrary Orbital Angular Momentum and Zero Potential. A.3 Arbitrary Orbital Angular Momentum and Coulomb Potential. B Quantum Mechanical Selection Rules. C Kinematics. C.1 Relationship of Kinematic Quantities in the Laboratory Coordinate System. C.2 Transformation Between Laboratory and Center-of-Mass Coordinate System. D Angular Correlations. D.1 General Aspects. D.2 Pure Radiations in a Two-Step Process. D.3 Mixed Radiations in a Two-Step Process. D.4 Three-Step Process with Unobserved Intermediate Radiation. D.5 Experimental Considerations. D.6 Concluding Remarks. E Constants, Data, Units, and Notation. E.1 Physical Constants and Data. E.2 Mathematical Expressions. E.3 Prefixes and Units. E.4 Physical Quantities. Color Plates. References. Index.

Arthur E Champagne - One of the best experts on this subject based on the ideXlab platform.

  • high intensity beam study of o 17 p γ f 18 and Thermonuclear Reaction rates for o 17 p
    Physical Review C, 2015
    Co-Authors: Arthur E Champagne, Christian Iliadis, Lori Downen, M Q Buckner, K J Kelly
    Abstract:

    Hydrogen burning of the oxygen isotopes takes place in low-mass stars, asymptotic giant branch stars, and classical novae. Observations of oxygen elemental and isotopic abundances in stellar spectra or in presolar grains provide strong constraints for stellar models if reliable Thermonuclear Reaction rates for hydrogen burning of oxygen are available. We present the results of a new measurement of the ${}^{17}\mathrm{O}{(p,\ensuremath{\gamma})}^{18}\mathrm{F}$ Reaction in the laboratory bombarding energy range of $170--530$ keV. The measurement is performed with significantly higher beam intensities (${I}_{\mathrm{max}}$ $\ensuremath{\approx}$ 2 mA) compared to previous work and by employing a sophisticated $\ensuremath{\gamma}$-ray coincidence spectrometer. We measured the cross section at much lower energies than previous in-beam experiments. We also apply a novel data-analysis technique that is based on the decomposition of different contributions to the measured pulse-height spectrum. Our measured strengths of the low-energy resonances amount to $\ensuremath{\omega}{\ensuremath{\gamma}}_{\mathrm{pres}}(193\phantom{\rule{0.16em}{0ex}}\mathrm{keV})=(1.86\ifmmode\pm\else\textpm\fi{}0.13)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ eV and $\ensuremath{\omega}{\ensuremath{\gamma}}_{\mathrm{pres}}(518\phantom{\rule{0.16em}{0ex}}\mathrm{keV})=(13.70\ifmmode\pm\else\textpm\fi{}0.96)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ eV. For the direct capture $S$ factor at zero energy, we find a value of ${S}_{\mathrm{DC}}^{\mathrm{pres}}(0)$ = $4.82\ifmmode\pm\else\textpm\fi{}0.41$ keV b. We also present new Thermonuclear rates for the ${}^{17}\mathrm{O}+p$ Reactions, taking into account all consistent results from previous measurements.

  • the effects of Thermonuclear Reaction rate variations on 26al production in massive stars a sensitivity study
    Astrophysical Journal Supplement Series, 2011
    Co-Authors: Christian G Iliadis, Arthur E Champagne, Alessandro Chieffi, Marco Limongi
    Abstract:

    We investigate the effects of Thermonuclear Reaction rate variations on 26Al production in massive stars. The dominant production sites in such events were recently investigated by using stellar model calculations: explosive neon-carbon burning, convective shell carbon burning, and convective core hydrogen burning. Post-processing nucleosynthesis calculations are performed for each of these sites by adopting temperature-density-time profiles from recent stellar evolution models. For each profile, we individually multiplied the rates of all relevant Reactions by factors of 10, 2, 0.5, and 0.1, and analyzed the resulting abundance changes of 26Al. In total, we performed ≈900 nuclear Reaction network calculations. Our simulations are based on a next-generation nuclear physics library, called STARLIB, which contains a recent evaluation of Monte Carlo Reaction rates. Particular attention is paid to quantifying the rate uncertainties of those Reactions that most sensitively influence 26Al production. For stellar modelers our results indicate to what degree predictions of 26Al nucleosynthesis depend on currently uncertain nuclear physics input, while for nuclear experimentalists our results represent a guide for future measurements. We also investigate equilibration effects of 26Al. In all previous massive star investigations, either a single species or two species of 26Al were taken into account, depending on whether thermal equilibrium was achieved or not. These are two extreme assumptions, and in a hot stellar plasma the ground and isomeric states may communicate via γ-ray transitions involving higher-lying 26Al levels. We tabulate the results of our Reaction rate sensitivity study for each of the three distinct massive star sites referred to above. It is found that several current Reaction rate uncertainties influence the production of 26Al. Particularly important Reactions are 26Al(n,p)26Mg, 25Mg(α,n)28Si, 24Mg(n,γ)25Mg, and 23Na(α,p)26Mg. These Reactions should be prime targets for future measurements. Overall, we estimate that the nuclear physics uncertainty of the 26Al yield predicted by the massive star models explored here amounts to about a factor of three. We also find that taking the equilibration of 26Al levels explicitly into account in any of the massive star sites investigated here has only minor effects on the predicted 26Al yields. Furthermore, we provide for the interested reader detailed comments regarding the current status of certain Reactions, including 12C(12C,n)23Mg, 23Na(α,p)26Mg, 25Mg(α,n)28Si, 26Al m (p,γ)27Si, 26Al(n,p)26Mg, and 26Al(n,α)23Na.

  • the effects of Thermonuclear Reaction rate variations on 26al production in massive stars a sensitivity study
    arXiv: Solar and Stellar Astrophysics, 2011
    Co-Authors: Arthur E Champagne, Alessandro Chieffi, Christian Iliadis, Marco Limongi
    Abstract:

    We investigate the effects of Thermonuclear Reaction rate variations on 26Al production in massive stars. The dominant production sites in such events were recently investigated by using stellar model calculations: explosive neon-carbon burning, convective shell carbon burning, and convective core hydrogen burning. Post-processing nucleosynthesis calculations are performed for each of these sites by adopting temperature-density-time profiles from recent stellar evolution models. For each profile, we individually multiplied the rates of all relevant Reactions by factors of 10, 2, 0.5 and 0.1, and analyzed the resulting abundance changes of 26Al. Our simulations are based on a next-generation nuclear physics library, called STARLIB, which contains a recent evaluation of Monte Carlo Reaction rates. Particular attention is paid to quantifying the rate uncertainties of those Reactions that most sensitively influence 26Al production. For stellar modelers our results indicate to what degree predictions of 26Al nucleosynthesis depend on currently uncertain nuclear physics input, while for nuclear experimentalists our results represent a guide for future measurements. We tabulate the results of our Reaction rate sensitivity study for each of the three distinct massive star sites referred to above. It is found that several current Reaction rate uncertainties influence the production of 26Al. Particularly important Reactions are 26Al(n,p)26Mg, 25Mg(alpha,n)28Si, 24Mg(n,gamma)25Mg and 23Na(alpha,p)26Mg. These Reactions should be prime targets for future measurements. Overall, we estimate that the nuclear physics uncertainty of the 26Al yield predicted by the massive star models explored here amounts to about a factor of 3.

  • charged particle Thermonuclear Reaction rates ii tables and graphs of Reaction rates and probability density functions
    Nuclear Physics, 2010
    Co-Authors: Arthur E Champagne, R Longland, Christian Iliadis, A. Coc, R. Fitzgerald
    Abstract:

    Abstract Numerical values of charged-particle Thermonuclear Reaction rates for nuclei in the A = 14 to 40 region are tabulated. The results are obtained using a method, based on Monte Carlo techniques, that has been described in the preceding paper of this issue (Paper I). We present a low rate, median rate and high rate which correspond to the 0.16, 0.50 and 0.84 quantiles, respectively, of the cumulative Reaction rate distribution. The meaning of these quantities is in general different from the commonly reported, but statistically meaningless expressions, “lower limit”, “nominal value” and “upper limit” of the total Reaction rate. In addition, we approximate the Monte Carlo probability density function of the total Reaction rate by a lognormal distribution and tabulate the lognormal parameters μ and σ at each temperature. We also provide a quantitative measure (Anderson–Darling test statistic) for the reliability of the lognormal approximation. The user can implement the approximate lognormal Reaction rate probability density functions directly in a stellar model code for studies of stellar energy generation and nucleosynthesis. For each Reaction, the Monte Carlo Reaction rate probability density functions, together with their lognormal approximations, are displayed graphically for selected temperatures in order to provide a visual impression. Our new Reaction rates are appropriate for bare nuclei in the laboratory. The nuclear physics input used to derive our Reaction rates is presented in the subsequent paper of this issue (Paper III). In the fourth paper of this issue (Paper IV) we compare our new Reaction rates to previous results.

  • charged particle Thermonuclear Reaction rates iii nuclear physics input
    Nuclear Physics, 2010
    Co-Authors: Christian G Iliadis, Arthur E Champagne, R Longland
    Abstract:

    Abstract The nuclear physics input used to compute the Monte Carlo Reaction rates and probability density functions that are tabulated in the second paper of this issue (Paper II) is presented. Specifically, we publish the input files to the Monte Carlo Reaction rate code RatesMC , which is based on the formalism presented in the first paper of this issue (Paper I). This data base contains overwhelmingly experimental nuclear physics information. The survey of literature for this review was concluded in November 2009.

Christian Iliadis - One of the best experts on this subject based on the ideXlab platform.

  • Thermonuclear Reaction rates and primordial nucleosynthesis
    Astrophys.J., 2020
    Co-Authors: Christian Iliadis, Alain Coc
    Abstract:

    Assuming the best numerical value for the cosmic baryonic density and the existence of three neutrino flavors, standard Big Bang nucleosynthesis is a parameter-free model. It is important to assess if the observed primordial abundances can be reproduced by simulations. Numerous studies have shown that the simulations overpredict the primordial 7Li abundance by a factor of compared to the observations. The discrepancy may be caused by unknown systematics in 7Li observations, poorly understood depletion of lithium in stars, errors in Thermonuclear rates that take part in the lithium and beryllium synthesis, or physics beyond the standard model. Here, we focus on the likelihood of a nuclear physics solution. The status of the key nuclear Reaction rates is summarized. Big Bang nucleosynthesis simulations are performed with the most recent Reaction rates, and the uncertainties of the predicted abundances are established using a Monte Carlo technique. Correlations between abundances and Reaction rates are investigated based on the metric of mutual information. The rates of four Reactions impact the primordial 7Li abundance: 3He(α,γ)7Be, d(p,γ)3He, 7Be(d,p)2α, and 7Be(n,p)7Li. We employ a genetic algorithm to search for simultaneous rate changes in these four Reactions that may account for all observed primordial abundances. When the search is performed for Reaction rate ranges that are much wider than recently reported uncertainties, no acceptable solutions are found. Based on the currently available evidence, we conclude that it is highly unlikely for the cosmological lithium problem to have a nuclear physics solution.

  • high intensity beam study of o 17 p γ f 18 and Thermonuclear Reaction rates for o 17 p
    Physical Review C, 2015
    Co-Authors: Arthur E Champagne, Christian Iliadis, Lori Downen, M Q Buckner, K J Kelly
    Abstract:

    Hydrogen burning of the oxygen isotopes takes place in low-mass stars, asymptotic giant branch stars, and classical novae. Observations of oxygen elemental and isotopic abundances in stellar spectra or in presolar grains provide strong constraints for stellar models if reliable Thermonuclear Reaction rates for hydrogen burning of oxygen are available. We present the results of a new measurement of the ${}^{17}\mathrm{O}{(p,\ensuremath{\gamma})}^{18}\mathrm{F}$ Reaction in the laboratory bombarding energy range of $170--530$ keV. The measurement is performed with significantly higher beam intensities (${I}_{\mathrm{max}}$ $\ensuremath{\approx}$ 2 mA) compared to previous work and by employing a sophisticated $\ensuremath{\gamma}$-ray coincidence spectrometer. We measured the cross section at much lower energies than previous in-beam experiments. We also apply a novel data-analysis technique that is based on the decomposition of different contributions to the measured pulse-height spectrum. Our measured strengths of the low-energy resonances amount to $\ensuremath{\omega}{\ensuremath{\gamma}}_{\mathrm{pres}}(193\phantom{\rule{0.16em}{0ex}}\mathrm{keV})=(1.86\ifmmode\pm\else\textpm\fi{}0.13)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ eV and $\ensuremath{\omega}{\ensuremath{\gamma}}_{\mathrm{pres}}(518\phantom{\rule{0.16em}{0ex}}\mathrm{keV})=(13.70\ifmmode\pm\else\textpm\fi{}0.96)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ eV. For the direct capture $S$ factor at zero energy, we find a value of ${S}_{\mathrm{DC}}^{\mathrm{pres}}(0)$ = $4.82\ifmmode\pm\else\textpm\fi{}0.41$ keV b. We also present new Thermonuclear rates for the ${}^{17}\mathrm{O}+p$ Reactions, taking into account all consistent results from previous measurements.

  • the effects of Thermonuclear Reaction rate variations on 26al production in massive stars a sensitivity study
    arXiv: Solar and Stellar Astrophysics, 2011
    Co-Authors: Arthur E Champagne, Alessandro Chieffi, Christian Iliadis, Marco Limongi
    Abstract:

    We investigate the effects of Thermonuclear Reaction rate variations on 26Al production in massive stars. The dominant production sites in such events were recently investigated by using stellar model calculations: explosive neon-carbon burning, convective shell carbon burning, and convective core hydrogen burning. Post-processing nucleosynthesis calculations are performed for each of these sites by adopting temperature-density-time profiles from recent stellar evolution models. For each profile, we individually multiplied the rates of all relevant Reactions by factors of 10, 2, 0.5 and 0.1, and analyzed the resulting abundance changes of 26Al. Our simulations are based on a next-generation nuclear physics library, called STARLIB, which contains a recent evaluation of Monte Carlo Reaction rates. Particular attention is paid to quantifying the rate uncertainties of those Reactions that most sensitively influence 26Al production. For stellar modelers our results indicate to what degree predictions of 26Al nucleosynthesis depend on currently uncertain nuclear physics input, while for nuclear experimentalists our results represent a guide for future measurements. We tabulate the results of our Reaction rate sensitivity study for each of the three distinct massive star sites referred to above. It is found that several current Reaction rate uncertainties influence the production of 26Al. Particularly important Reactions are 26Al(n,p)26Mg, 25Mg(alpha,n)28Si, 24Mg(n,gamma)25Mg and 23Na(alpha,p)26Mg. These Reactions should be prime targets for future measurements. Overall, we estimate that the nuclear physics uncertainty of the 26Al yield predicted by the massive star models explored here amounts to about a factor of 3.

  • charged particle Thermonuclear Reaction rates i monte carlo method and statistical distributions
    Nuclear Physics, 2010
    Co-Authors: R Longland, Christian Iliadis, A E Champagne, Joe Newton, C Ugalde
    Abstract:

    Abstract A method based on Monte Carlo techniques is presented for evaluating Thermonuclear Reaction rates. We begin by reviewing commonly applied procedures and point out that Reaction rates that have been reported up to now in the literature have no rigorous statistical meaning. Subsequently, we associate each nuclear physics quantity entering in the calculation of Reaction rates with a specific probability density function, including Gaussian, lognormal and chi-squared distributions. Based on these probability density functions the total Reaction rate is randomly sampled many times until the required statistical precision is achieved. This procedure results in a median (Monte Carlo) rate which agrees under certain conditions with the commonly reported recommended “classical” rate. In addition, we present at each temperature a low rate and a high rate, corresponding to the 0.16 and 0.84 quantiles of the cumulative Reaction rate distribution. These quantities are in general different from the statistically meaningless “minimum” (or “lower limit”) and “maximum” (or “upper limit”) Reaction rates which are commonly reported. Furthermore, we approximate the output Reaction rate probability density function by a lognormal distribution and present, at each temperature, the lognormal parameters μ and σ . The values of these quantities will be crucial for future Monte Carlo nucleosynthesis studies. Our new Reaction rates, appropriate for bare nuclei in the laboratory , are tabulated in the second paper of this issue (Paper II). The nuclear physics input used to derive our Reaction rates is presented in the third paper of this issue (Paper III). In the fourth paper of this issue (Paper IV) we compare our new Reaction rates to previous results.

  • charged particle Thermonuclear Reaction rates ii tables and graphs of Reaction rates and probability density functions
    Nuclear Physics, 2010
    Co-Authors: Arthur E Champagne, R Longland, Christian Iliadis, A. Coc, R. Fitzgerald
    Abstract:

    Abstract Numerical values of charged-particle Thermonuclear Reaction rates for nuclei in the A = 14 to 40 region are tabulated. The results are obtained using a method, based on Monte Carlo techniques, that has been described in the preceding paper of this issue (Paper I). We present a low rate, median rate and high rate which correspond to the 0.16, 0.50 and 0.84 quantiles, respectively, of the cumulative Reaction rate distribution. The meaning of these quantities is in general different from the commonly reported, but statistically meaningless expressions, “lower limit”, “nominal value” and “upper limit” of the total Reaction rate. In addition, we approximate the Monte Carlo probability density function of the total Reaction rate by a lognormal distribution and tabulate the lognormal parameters μ and σ at each temperature. We also provide a quantitative measure (Anderson–Darling test statistic) for the reliability of the lognormal approximation. The user can implement the approximate lognormal Reaction rate probability density functions directly in a stellar model code for studies of stellar energy generation and nucleosynthesis. For each Reaction, the Monte Carlo Reaction rate probability density functions, together with their lognormal approximations, are displayed graphically for selected temperatures in order to provide a visual impression. Our new Reaction rates are appropriate for bare nuclei in the laboratory. The nuclear physics input used to derive our Reaction rates is presented in the subsequent paper of this issue (Paper III). In the fourth paper of this issue (Paper IV) we compare our new Reaction rates to previous results.

R Longland - One of the best experts on this subject based on the ideXlab platform.

  • charged particle Thermonuclear Reaction rates i monte carlo method and statistical distributions
    Nuclear Physics, 2010
    Co-Authors: R Longland, Christian Iliadis, A E Champagne, Joe Newton, C Ugalde
    Abstract:

    Abstract A method based on Monte Carlo techniques is presented for evaluating Thermonuclear Reaction rates. We begin by reviewing commonly applied procedures and point out that Reaction rates that have been reported up to now in the literature have no rigorous statistical meaning. Subsequently, we associate each nuclear physics quantity entering in the calculation of Reaction rates with a specific probability density function, including Gaussian, lognormal and chi-squared distributions. Based on these probability density functions the total Reaction rate is randomly sampled many times until the required statistical precision is achieved. This procedure results in a median (Monte Carlo) rate which agrees under certain conditions with the commonly reported recommended “classical” rate. In addition, we present at each temperature a low rate and a high rate, corresponding to the 0.16 and 0.84 quantiles of the cumulative Reaction rate distribution. These quantities are in general different from the statistically meaningless “minimum” (or “lower limit”) and “maximum” (or “upper limit”) Reaction rates which are commonly reported. Furthermore, we approximate the output Reaction rate probability density function by a lognormal distribution and present, at each temperature, the lognormal parameters μ and σ . The values of these quantities will be crucial for future Monte Carlo nucleosynthesis studies. Our new Reaction rates, appropriate for bare nuclei in the laboratory , are tabulated in the second paper of this issue (Paper II). The nuclear physics input used to derive our Reaction rates is presented in the third paper of this issue (Paper III). In the fourth paper of this issue (Paper IV) we compare our new Reaction rates to previous results.

  • charged particle Thermonuclear Reaction rates ii tables and graphs of Reaction rates and probability density functions
    Nuclear Physics, 2010
    Co-Authors: Arthur E Champagne, R Longland, Christian Iliadis, A. Coc, R. Fitzgerald
    Abstract:

    Abstract Numerical values of charged-particle Thermonuclear Reaction rates for nuclei in the A = 14 to 40 region are tabulated. The results are obtained using a method, based on Monte Carlo techniques, that has been described in the preceding paper of this issue (Paper I). We present a low rate, median rate and high rate which correspond to the 0.16, 0.50 and 0.84 quantiles, respectively, of the cumulative Reaction rate distribution. The meaning of these quantities is in general different from the commonly reported, but statistically meaningless expressions, “lower limit”, “nominal value” and “upper limit” of the total Reaction rate. In addition, we approximate the Monte Carlo probability density function of the total Reaction rate by a lognormal distribution and tabulate the lognormal parameters μ and σ at each temperature. We also provide a quantitative measure (Anderson–Darling test statistic) for the reliability of the lognormal approximation. The user can implement the approximate lognormal Reaction rate probability density functions directly in a stellar model code for studies of stellar energy generation and nucleosynthesis. For each Reaction, the Monte Carlo Reaction rate probability density functions, together with their lognormal approximations, are displayed graphically for selected temperatures in order to provide a visual impression. Our new Reaction rates are appropriate for bare nuclei in the laboratory. The nuclear physics input used to derive our Reaction rates is presented in the subsequent paper of this issue (Paper III). In the fourth paper of this issue (Paper IV) we compare our new Reaction rates to previous results.

  • charged particle Thermonuclear Reaction rates iii nuclear physics input
    Nuclear Physics, 2010
    Co-Authors: Christian G Iliadis, Arthur E Champagne, R Longland
    Abstract:

    Abstract The nuclear physics input used to compute the Monte Carlo Reaction rates and probability density functions that are tabulated in the second paper of this issue (Paper II) is presented. Specifically, we publish the input files to the Monte Carlo Reaction rate code RatesMC , which is based on the formalism presented in the first paper of this issue (Paper I). This data base contains overwhelmingly experimental nuclear physics information. The survey of literature for this review was concluded in November 2009.

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  • Thermonuclear Reaction rates and primordial nucleosynthesis
    'American Astronomical Society', 2020
    Co-Authors: Iliadis Christian, Coc Alain
    Abstract:

    International audienceAssuming the best numerical value for the cosmic baryonic density and the existence of three neutrino flavors, standard Big Bang nucleosynthesis is a parameter-free model. It is important to assess if the observed primordial abundances can be reproduced by simulations. Numerous studies have shown that the simulations overpredict the primordial 7Li abundance by a factor of compared to the observations. The discrepancy may be caused by unknown systematics in 7Li observations, poorly understood depletion of lithium in stars, errors in Thermonuclear rates that take part in the lithium and beryllium synthesis, or physics beyond the standard model. Here, we focus on the likelihood of a nuclear physics solution. The status of the key nuclear Reaction rates is summarized. Big Bang nucleosynthesis simulations are performed with the most recent Reaction rates, and the uncertainties of the predicted abundances are established using a Monte Carlo technique. Correlations between abundances and Reaction rates are investigated based on the metric of mutual information. The rates of four Reactions impact the primordial 7Li abundance: 3He(α,γ)7Be, d(p,γ)3He, 7Be(d,p)2α, and 7Be(n,p)7Li. We employ a genetic algorithm to search for simultaneous rate changes in these four Reactions that may account for all observed primordial abundances. When the search is performed for Reaction rate ranges that are much wider than recently reported uncertainties, no acceptable solutions are found. Based on the currently available evidence, we conclude that it is highly unlikely for the cosmological lithium problem to have a nuclear physics solution

  • Hierarchical Bayesian Thermonuclear Rate for the $^7$Be(n,p)$^7$Li Big Bang Nucleosynthesis Reaction
    'American Astronomical Society', 2020
    Co-Authors: De Souza, Rafael S., Coc Alain, Kiat, Tan Hong, Iliadis Christian
    Abstract:

    International audienceBig Bang nucleosynthesis provides the earliest probe of standard model physics, at a time when the universe was less than 1000 seconds old. It determines the abundances of the lightest nuclides, which give rise to the subsequent history of the visible matter in the universe. This work derives new 7Be(n,p)7Li Thermonuclear Reaction rates based on all available experimental information. This Reaction sensitively impacts the primordial abundances of 7Be and 7Li during big bang nucleosynthesis. We critically evaluate all available data and disregard experimental results that are questionable. For the nuclear model, we adopt an incoherent sum of single-level, two-channel, R-matrix approximation expressions, which are implemented into a hierarchical Bayesian model, to analyze the remaining six data sets we deem most reliable. In the fitting of the data, we consistently model all known sources of uncertainty, including discrepant absolute normalizations of different data sets, and also take the variation of the neutron and proton channel radii into account, hence providing less biased estimates of the 7Be(n,p)7Li Thermonuclear rates. From the resulting posteriors, we extract R-matrix parameters (E r , , ) and derive excitation energies and partial and total widths. Our fit is sensitive to the contributions of the first three levels above the neutron threshold. Reaction rates were computed by integrating 10,000 samples of the reduced cross section. Our 7Be(n,p)7Li Thermonuclear rates have uncertainties between 1.5% and 2.0% at temperatures of ≤1 GK. We compare our rates to previous results and find that the 7Be(n,p)7Li rates most commonly used in big bang simulations have uncertainties that are too optimistic

  • Hierarchical Bayesian Thermonuclear Rate for the $^7$Be(n,p)$^7$Li Big Bang Nucleosynthesis Reaction
    'American Astronomical Society', 2020
    Co-Authors: De Souza, Rafael S., Coc Alain, Kiat, Tan Hong, Iliadis Christian
    Abstract:

    Big bang nucleosynthesis provides the earliest probe of standard model physics, at a time when the universe was less than a thousand seconds old. It determines the abundances of the lightest nuclides, which give rise to the subsequent history of the visible matter in the Universe. This work derives new $^7$Be(n,p)$^7$Li Thermonuclear Reaction rates based on all available experimental information. This Reaction sensitively impacts the primordial abundances of $^{7}$Be and $^7$Li during big bang nucleosynthesis. We critically evaluate all available data and disregard experimental results that are questionable. For the nuclear model, we adopt an incoherent sum of single-level, two-channel R-matrix approximation expressions, which are implemented into a hierarchical Bayesian model, to analyze the remaining six data sets we deem most reliable. In the fitting of the data, we consistently model all known sources of uncertainty, including discrepant absolute normalizations of different data sets, and also take the variation of the neutron and proton channel radii into account, hence providing less biased estimates of the $^7$Be(n,p)$^7$Li Thermonuclear rates. From the resulting posteriors, we extract R-matrix parameters ($E_r$, $\gamma^2_n$, $\gamma^2_p$) and derive excitation energies, partial and total widths. Our fit is sensitive to the contributions of the first three levels above the neutron threshold. Reaction rates were computed by integrating 10,000 samples of the reduced cross section. Our $^7$Be(n,p)$^7$Li Thermonuclear rates have uncertainties between 1.5% and 2.0% at temperatures of $\leq$1 GK. We compare our rates to previous results and find that the $^7$Be(n,p)$^7$Li rates most commonly used in big bang simulations have too optimistic uncertainties.Comment: 24 pages, 8 figures, ApJ in pres

  • Hierarchical Bayesian Thermonuclear Rate for the $^7$Be(n,p)$^7$Li Big Bang Nucleosynthesis Reaction
    HAL CCSD, 2020
    Co-Authors: De Souza, Rafael S., Coc Alain, Kiat, Tan Hong, Iliadis Christian
    Abstract:

    Big bang nucleosynthesis provides the earliest probe of standard model physics, at a time when the universe was between 100 seconds and 1000 seconds old. It determines the abundances of the lightest nuclides, which give rise to the subsequent history of the visible matter in the Universe. The present work derives new $^7$Be(n,p)$^7$Li Thermonuclear Reaction rates based on all available experimental information. This Reaction sensitively impacts the primordial abundances of $^{7}$Be and $^7$Li during big bang nucleosynthesis. For the nuclear model, we adopt an incoherent sum of single-level, two-channel R-matrix approximation expressions, which are implemented into a hierarchical Bayesian model, to analyze the remaining six data sets we deem most reliable. The nuclear structure of $^8$Be near the neutron threshold has also been evaluated to estimate appropriate prior densities for our analysis. In the fitting of the data, we consistently model all known sources of uncertainty and also take the variation of the neutron and proton channel radii into account, hence providing less biased estimates of the $^7$Be(n,p)$^7$Li Thermonuclear rates. From the resulting posteriors, we extract R-matrix parameters and derive excitation energies, partial and total widths. Our fit is sensitive to the contributions of the first three levels above the neutron threshold. Values of excitation energies and total widths for these states are in overall agreement with previous results, although our results have significantly smaller uncertainties. Our $^7$Be(n,p)$^7$Li Thermonuclear rates have uncertainties between 1.5% and 2.0% at temperatures of $\leq$1 GK. We compare our rates to previously published results and find that the $^7$Be(n,p)$^7$Li rates most commonly used in big bang simulations have too optimistic uncertainties

  • Thermonuclear Reaction Rate of $^{30}$Si(p,$\gamma$)$^{31}$P
    'American Physical Society (APS)', 2019
    Co-Authors: Dermigny John, Iliadis Christian, Champagne Art, Longland Richard
    Abstract:

    Silicon synthesis in high-temperature hydrogen burning environments presents one possible avenue for the study of abundance anomalies in globular clusters. This was suggested in a previous study, which found that the large uncertainties associated with the $^{30}$Si(p,$\gamma$)$^{31}$P Reaction rate preclude a firm understanding of the stellar conditions that give rise to the Mg-K anti-correlation observed in the globular cluster NGC 2419. In an effort to improve the Reaction rate, we present new strength measurements of the $E_r^{lab} = 435$ keV and $E_r^{lab} = 501$ keV resonances in $^{30}$Si(p,$\gamma$)$^{31}$P. For the former, which was previously unobserved, we obtain a resonance strength of $\omega\gamma = (1.28 \pm 0.25$) $\times 10^{-4}$ eV. For the latter, we obtain a value of $\omega\gamma = (1.88 \pm 0.14)$ $\times 10^{-1}$ eV, which has a smaller uncertainty compared to previously measured strengths. Based on these results, the Thermonuclear Reaction rate has been re-evaluated. The impact of the new measurements is to lower the Reaction rate by a factor of $\approx$10 at temperatures important to the study of NGC 2419. The rate uncertainty at these temperatures has also been reduced significantly.Comment: 27 pages, 7 figure