WorldWideScience

Sample records for astrophysical reaction rates

  1. The path to improved reaction rates for astrophysics

    International Nuclear Information System (INIS)

    Rauscher, T.

    2011-01-01

    This review focuses on nuclear reactions in astrophysics and, more specifically, on reactions with light ions (nucleons and α particles) proceeding via the strong interaction. It is intended to present the basic definitions essential for studies in nuclear astrophysics, to point out the differences between nuclear reactions taking place in stars and in a terrestrial laboratory, and to illustrate some of the challenges to be faced in theoretical and experimental studies of those reactions. The discussion revolves around the relevant quantities for astrophysics, which are the astrophysical reaction rates. The sensitivity of the reaction rates to the uncertainties in the prediction of various nuclear properties is explored and some guidelines for experimentalists are also provided. (author)

  2. Nuclear Data and Reaction Rate Databases in Nuclear Astrophysics

    Science.gov (United States)

    Lippuner, Jonas

    2018-06-01

    Astrophysical simulations and models require a large variety of micro-physics data, such as equation of state tables, atomic opacities, properties of nuclei, and nuclear reaction rates. Some of the required data is experimentally accessible, but the extreme conditions present in many astrophysical scenarios cannot be reproduced in the laboratory and thus theoretical models are needed to supplement the empirical data. Collecting data from various sources and making them available as a database in a unified format is a formidable task. I will provide an overview of the data requirements in astrophysics with an emphasis on nuclear astrophysics. I will then discuss some of the existing databases, the science they enable, and their limitations. Finally, I will offer some thoughts on how to design a useful database.

  3. Charged particle induced thermonuclear reaction rates: a compilation for astrophysics

    International Nuclear Information System (INIS)

    Grama, C.

    1999-01-01

    We report on the results of the European network NACRE (Nuclear Astrophysics Compilation of REaction rates). The principal reason for setting up the NACRE network has been the necessity of building up a well-documented and detailed compilation of rates for charged-particle induced reactions on stable targets up to Si and on unstable nuclei of special significance in astrophysics. This work is meant to supersede the only existing compilation of reaction rates issued by Fowler and collaborators. The main goal of NACRE network was the transparency in the procedure of calculating the rates. More specifically this compilation aims at: 1. updating the experimental and theoretical data; 2. distinctly identifying the sources of the data used in rate calculation; 3. evaluating the uncertainties and errors; 4. providing numerically integrated reaction rates; 5. providing reverse reaction rates and analytical approximations of the adopted rates. The cross section data and/or resonance parameters for a total of 86 charged-particle induced reactions are given and the corresponding reaction rates are calculated and given in tabular form. Uncertainties are analyzed and realistic upper and lower bounds of the rates are determined. The compilation is concerned with the reaction rates that are large enough for the target lifetimes shorter than the age of the Universe, taken equal to 15 x 10 9 y. The reaction rates are provided for temperatures lower than T = 10 10 K. In parallel with the rate compilation a cross section data base has been created and located at the site http://pntpm.ulb.ac.be/nacre..htm. (authors)

  4. Astrophysical Nuclear Reaction Rates in the Dense Metallic Environments

    Science.gov (United States)

    Kilic, Ali Ihsan

    2017-09-01

    Nuclear reaction rates can be enhanced by many orders of magnitude in dense and relatively cold astrophysical plasmas such as in white dwarfs, brown dwarfs, and giant planets. Similar conditions are also present in supernova explosions where the ignition conditions are vital for cosmological models. White dwarfs are compact objects that have both extremely high interior densities and very strong local magnetic fields. For the first time, a new formula has been developed to explain cross section and reaction rate quantities for light elements that includes not only the nuclear component but also the material dependence, magnetic field, and crystal structure dependency in dense metallic environments. I will present the impact of the developed formula on the cross section and reaction rates for light elements. This could have possible technological applications in energy production using nuclear fusion reactions.

  5. General properties of astrophysical reaction rates in explosive nucleosynthesis

    International Nuclear Information System (INIS)

    Rauscher, Thomas

    2013-01-01

    Fundamental differences in the prediction of reaction rates with intermediate and heavy target nuclei compared to the ones with light nuclei are discussed, with special emphasis on stellar modifications of the rates. Ground and excited state contributions to the stellar rates are quantified, deriving a linear weighting of excited state contributions despite of a Boltzmann population of the nuclear states. A Coulomb suppression effect of the excited state contributions is identified, acting against the usual Q-value rule in some reactions. The proper inclusion of experimental data in revised stellar rates is shown, containing revised uncertainties. An application to the s-process shows that the actual uncertainties in the neutron capture rates are larger than would be expected from the experimental errors alone. Sensitivities of reaction rates and cross sections are defined and their application in reaction studies is discussed. The conclusion provides a guide to experiment as well as theory on how to best improve the rates used in astrophysical simulations and how to assess their uncertainties.

  6. Improved predictions of nuclear reaction rates with the TALYS reaction code for astrophysical applications

    International Nuclear Information System (INIS)

    Goriely, S.; Hilaire, S.; Koning, A.J

    2008-01-01

    Context. Nuclear reaction rates of astrophysical applications are traditionally determined on the basis of Hauser-Feshbach reaction codes. These codes adopt a number of approximations that have never been tested, such as a simplified width fluctuation correction, the neglect of delayed or multiple-particle emission during the electromagnetic decay cascade, or the absence of the pre-equilibrium contribution at increasing incident energies. Aims. The reaction code TALYS has been recently updated to estimate the Maxwellian-averaged reaction rates that are of astrophysical relevance. These new developments enable the reaction rates to be calculated with increased accuracy and reliability and the approximations of previous codes to be investigated. Methods. The TALYS predictions for the thermonuclear rates of relevance to astrophysics are detailed and compared with those derived by widely-used codes for the same nuclear ingredients. Results. It is shown that TALYS predictions may differ significantly from those of previous codes, in particular for nuclei for which no or little nuclear data is available. The pre-equilibrium process is shown to influence the astrophysics rates of exotic neutron-rich nuclei significantly. For the first time, the Maxwellian- averaged (n, 2n) reaction rate is calculated for all nuclei and its competition with the radiative capture rate is discussed. Conclusions. The TALYS code provides a new tool to estimate all nuclear reaction rates of relevance to astrophysics with improved accuracy and reliability. (authors)

  7. Improved predictions of nuclear reaction rates for astrophysics applications with the TALYS reaction code

    International Nuclear Information System (INIS)

    Goriely, S.; Hilaire, S.; Koning, A.J.

    2008-01-01

    Nuclear reaction rates for astrophysics applications are traditionally determined on the basis of Hauser-Feshbach reaction codes, like MOST. These codes use simplified schemes to calculate the capture reaction cross section on a given target nucleus, not only in its ground state but also on the different thermally populated states of the stellar plasma at a given temperature. Such schemes include a number of approximations that have never been tested, such as an approximate width fluctuation correction, the neglect of delayed particle emission during the electromagnetic decay cascade or the absence of the pre-equilibrium contribution at increasing incident energies. New developments have been brought to the reaction code TALYS to estimate the Maxwellian-averaged reaction rates of astrophysics relevance. These new developments give us the possibility to calculate with an improved accuracy the reaction cross sections and the corresponding astrophysics rates. The TALYS predictions for the thermonuclear rates of astrophysics relevance are presented and compared with those obtained with the MOST code on the basis of the same nuclear ingredients for nuclear structure properties, optical model potential, nuclear level densities and γ-ray strength. It is shown that, in particular, the pre-equilibrium process significantly influences the astrophysics rates of exotic neutron-rich nuclei. The reciprocity theorem traditionally used in astrophysics to determine photo-rates is also shown no to be valid for exotic nuclei. The predictions obtained with different nuclear inputs are also analyzed to provide an estimate of the theoretical uncertainties still affecting the reaction rate prediction far away from the experimentally known regions. (authors)

  8. Measurements of astrophysical reaction rates for radioactive samples

    International Nuclear Information System (INIS)

    Koehler, P.E.; O'Brien, H.A.; Bowman, C.D.

    1987-01-01

    Reaction rates for both big-bang and stellar nucleosynthesis can be obtained from the measurement of (n,p) and (n,γ) cross sections for radioactive nuclei. In the past, large backgrounds associated with the sample activity limited these types of measurements to radioisotopes with very long half lives. The advent of the low-energy, high-intensity neutron source at the Los Alamos Neutron Scattering CEnter (LANSCE) has greatly increased the number of nuclei which can be studied. Results of (n,p) measurements on samples with half lives as short as fifty-three days will be given. The astrophysics to be learned from these data will be discussed. Additional difficulties are encountered when making (n,γ) rather than (n,p) measurements. However, with a properly designed detector, and with the high peak neutron intensities now available, (n,γ) measurements can be made for nuclei with half lives as short as several weeks. Progress on the Los Alamos (n,γ) cross-section measurement program for radioactive samples will be discussed. 25 refs., 3 figs., 1 tab

  9. Thermonuclear Reaction Rate Libraries and Software Tools for Nuclear Astrophysics Research

    International Nuclear Information System (INIS)

    Smith, Michael S.; Cyburt, Richard; Schatz, Hendrik; Smith, Karl; Warren, Scott; Ferguson, Ryan; Wiescher, Michael; Lingerfelt, Eric; Buckner, Kim; Nesaraja, Caroline D.

    2008-01-01

    Thermonuclear reaction rates are a crucial input for simulating a wide variety of astrophysical environments. A new collaboration has been formed to ensure that astrophysical modelers have access to reaction rates based on the most recent experimental and theoretical nuclear physics information. To reach this goal, a new version of the REACLIB library has been created by the Joint Institute for Nuclear Astrophysics (JINA), now available online at http://www.nscl.msu.edu/~nero/db. A complementary effort is the development of software tools in the Computational Infrastructure for Nuclear Astrophysics, online at nucastrodata.org, to streamline, manage, and access the workflow of the reaction evaluations from their initiation to peer review to incorporation into the library. Details of these new projects will be described

  10. Charged-particle induced thermonuclear reaction rates: a compilation for astrophysics

    International Nuclear Information System (INIS)

    Grama, Cornelia; Angulo, C.; Arnould, M.

    2000-01-01

    The rapidly growing wealth of nuclear data becomes less and less easily accessible to the astrophysics community. Mastering this volume of information and making it available in an accurate and usable form for incorporation into stellar evolution or nucleosynthesis models become urgent goals of prime necessity. we report on the results of the European network NACRE (Nuclear Astrophysics Compilation of REaction rates). The principal motivation for the setting-up of the NACRE network has been the necessity of building up a well-documented and detailed compilation of rates for charged-particle induced reactions on stable targets up to Si and on unstable nuclei of special significance in astrophysics. This work is meant to supersede the only existing compilation of reaction rates issued by Fowler and collaborators. The cross section data and/or resonance parameters for a total of 86 charged-particle induced reactions are given and the corresponding reaction rates are calculated and given in tabular form. When cross section data are not available in the whole needed range of energies, the theoretical predictions obtained in the framework of the Hauser-Feshbach model is used. Uncertainties are analyzed and realistic upper and lower bounds of the rates are determined. Reverse reaction rates and analytical approximations of the adopted rates are also provided. (authors)

  11. Charged-particle induced thermonuclear reaction rates: a compilation for astrophysics

    International Nuclear Information System (INIS)

    Grama, Cornelia

    1999-01-01

    The rapidly growing wealth of nuclear data becomes less and less easily accessible to the astrophysics community. Mastering this volume of information and making it available in an accurate and usable form for incorporation into stellar evolution or nucleosynthesis models become urgent goals of prime necessity. We report on the results of the European network NACRE (Nuclear Astrophysics Compilation of REaction rates). The principal motivation for the setting-up of the NACRE network has been the necessity of building up a well-documented and detailed compilation of rates for charged -particle induced reactions on stable targets up to Si and on unstable nuclei of special significance in astrophysics. This work is meant to supersede the only existing compilation of reaction rates issued by Fowler and collaborators. The cross section data and/or resonance parameters for a total of 86 charged-particle induced reactions are given and the corresponding reaction rates are calculated and given in tabular form. When cross section data are not available in the whole needed range of energies the theoretical predictions obtained in the framework of the Hauser-Feshbach model are used. Uncertainties are analyzed and realistic upper and lower bounds of the rates are determined. Reverse reaction rates and analytical approximations of the adopted rates are also provided. (author)

  12. Astrophysical reaction rate for α(αn,γ)9Be by photodisintegration

    International Nuclear Information System (INIS)

    Sumiyoshi, K.; Utsunomiya, H.; Goko, S.; Kajino, T.

    2002-01-01

    We study the astrophysical reaction rate for the formation of 9 Be through the three body reaction α(αn,γ). This reaction is one of the key reactions which could bridge the mass gap at A=8 nuclear systems to produce intermediate-to-heavy mass elements in alpha- and neutron-rich environments such as r-process nucleosynthesis in supernova explosions, s-process nucleosynthesis in asymptotic giant branch (AGB) stars, and primordial nucleosynthesis in baryon inhomogeneous cosmological models. To calculate the thermonuclear reaction rate in a wide range of temperatures, we numerically integrate the thermal average of cross sections assuming a two-steps formation through a metastable 8 Be, α+α[rlhar2] 8 Be(n,γ) 9 Be. Off-resonant and on-resonant contributions from the ground state in 8 Be are taken into account. As input cross section, we adopt the latest experimental data by photodisintegration of 9 Be with laser-electron photon beams, which covers all relevant resonances in 9 Be. Experimental data near the neutron threshold are added with γ-ray flux corrections and a new least-squares analysis is made to deduce resonance parameters in the Breit-Wigner formulation. Based on the photodisintegration cross section, we provide the reaction rate for α(αn,γ) 9 Be in the temperature range from T 9 =10 -3 to T 9 =10 1 (T 9 is the temperature in units of 10 9 K) both in the tabular form and in the analytical form for potential usage in nuclear reaction network calculations. The calculated reaction rate is compared with the reaction rates of the CF88 and the NACRE compilations. The CF88 rate, which is based on the photoneutron cross section for the 1/2 + state in 9 Be by Berman et al., is valid at T 9 >0.028 due to lack of the off-resonant contribution. The CF88 rate differs from the present rate by a factor of two in a temperature range T 9 ≥0.1. The NACRE rate, which adopted different sources of experimental information on resonance states in 9 Be, is 4-12 times

  13. Nuclear reactions in astrophysics

    International Nuclear Information System (INIS)

    Arnould, M.; Rayet, M.

    1990-01-01

    At all times and at all astrophysical scales, nuclear reactions have played and continue to play a key role. This concerns the energetics as well as the production of nuclides (nucleosynthesis). After a brief review of the observed composition of various objects in the universe, and especially of the solar system, the basic ingredients that are required in order to build up models for the chemical evolution of galaxies are sketched. Special attention is paid to the evaluation of the stellar yields through an overview of the important burning episodes and nucleosynthetic processes that can develop in non-exploding or exploding stars. Emphasis is put on the remaining astrophysical and nuclear physics uncertainties that hamper a clear understanding of the observed characteristics, and especially compositions, of a large variety of astrophysical objects

  14. Nuclear reactions in astrophysics

    International Nuclear Information System (INIS)

    Cardenas, M.

    1976-01-01

    It is revised the nuclear reactions which present an interest in astrophysics regarding the explanation of some problems such as the relative quantity of the elements, the structure and evolution of the stars. The principal object of the study is the determination of the experimental possibilities in the field of astrophysics, of an accelerator Van de Graaff's 700 KeV type. Two hundred nuclear reactions approximately, were found, and nothing or very little has been done in the intervals of energy which are of interest. Since the bombardment energies and the involved sections are low in some cases, there are real possibilities, for the largest number of stars to obtain important statistical data with the above mentioned accelerator, taking some necessary precautions. (author)

  15. Constraining astrophysical reaction rates: using the storage rings at FAIR/GSI

    Science.gov (United States)

    Langer, Christoph; Glorius, Jan; Slavkovská, Zuzana; Litvinov, Sergey; Litvinov, Yuri A.; Reifarth, René

    2018-01-01

    Ion optical calculations for a storage ring at the present GSI facility for direct proton-induced reactions relevant for different astrophysical processes are presented. As an example case, the 59Cu(p,γ) and 59Cu(p,α) reactions are shown. The branching of these two reactions is important in X-ray burst scenarios, since it determines the breakout out of the major 56Ni waiting point.

  16. Calculation of astrophysical S-factor and reaction rate in 12C(p, γ)13N reaction

    Science.gov (United States)

    Moghadasi, A.; Sadeghi, H.; Pourimani, R.

    2018-02-01

    The 12C(p, γ)13N reaction is the first process in the CNO cycle. Also it is a source of low-energy solar neutrinos in various neutrino experiments. Therefore, it is of high interest to gain data of the astrophysical S-factor in low energies. By applying Faddeev's method, we calculated wave functions for the bound state of 13N. Then the cross sections for resonance and non-resonance were calculated through using Breit-Wigner and direct capture cross section formulae, respectively. After that, we calculated the total S-factor and compared it with previous experimental data, revealing a good agreement altogether. Then, we extrapolated the S-factor in zero energy and the result was 1.32 ± 0.19 (keV.b). In the end, we calculated reaction rate and compared it with NACRE data.

  17. Large area isotopic silicon targets for astrophysical reaction rate studies in Si-26

    NARCIS (Netherlands)

    Greene, JP; Berg, GPA

    2005-01-01

    For measurements of stellar reaction rates of proton rich nuclei involving resonance levels just above threshold, targets of Si-28 were used in studies of the Si-21(He-4, He-6)Si-26 reaction using the Research Center for Nuclear Physics (RCNP) Ring Cyclotron at Osaka University. Resonance structure

  18. Astrophysical reaction rate for the neutron-generator reaction 13C(alpha,n)16O in asymptotic giant branch stars.

    Science.gov (United States)

    Johnson, E D; Rogachev, G V; Mukhamedzhanov, A M; Baby, L T; Brown, S; Cluff, W T; Crisp, A M; Diffenderfer, E; Goldberg, V Z; Green, B W; Hinners, T; Hoffman, C R; Kemper, K W; Momotyuk, O; Peplowski, P; Pipidis, A; Reynolds, R; Roeder, B T

    2006-11-10

    The reaction 13C(alpha,n) is considered to be the main source of neutrons for the s process in asymptotic giant branch stars. At low energies, the cross section is dominated by the 1/2+ 6.356 MeV subthreshold resonance in (17)O whose contribution at stellar temperatures is uncertain by a factor of 10. In this work, we performed the most precise determination of the low-energy astrophysical S factor using the indirect asymptotic normalization (ANC) technique. The alpha-particle ANC for the subthreshold state has been measured using the sub-Coulomb alpha-transfer reaction ((6)Li,d). Using the determined ANC, we calculated S(0), which turns out to be an order of magnitude smaller than in the nuclear astrophysics compilation of reaction rates.

  19. AN UPDATED 6Li(p, α)3He REACTION RATE AT ASTROPHYSICAL ENERGIES WITH THE TROJAN HORSE METHOD

    International Nuclear Information System (INIS)

    Lamia, L.; Spitaleri, C.; Sergi, M. L.; Pizzone, R. G.; Tumino, A.; La Cognata, M.; Tognelli, E.; Degl'Innocenti, S.; Prada Moroni, P. G.; Pappalardo, L.

    2013-01-01

    The lithium problem influencing primordial and stellar nucleosynthesis is one of the most interesting unsolved issues in astrophysics. 6 Li is the most fragile of lithium's stable isotopes and is largely destroyed in most stars during the pre-main-sequence (PMS) phase. For these stars, the convective envelope easily reaches, at least at its bottom, the relatively low 6 Li ignition temperature. Thus, gaining an understanding of 6 Li depletion also gives hints about the extent of convective regions. For this reason, charged-particle-induced reactions in lithium have been the subject of several studies. Low-energy extrapolations of these studies provide information about both the zero-energy astrophysical S(E) factor and the electron screening potential, U e . Thanks to recent direct measurements, new estimates of the 6 Li(p, α) 3 He bare-nucleus S(E) factor and the corresponding U e value have been obtained by applying the Trojan Horse method to the 2 H( 6 Li, α 3 He)n reaction in quasi-free kinematics. The calculated reaction rate covers the temperature window 0.01 to 2T 9 and its impact on the surface lithium depletion in PMS models with different masses and metallicities has been evaluated in detail by adopting an updated version of the FRANEC evolutionary code.

  20. Photonuclear reactions: astrophysical implications

    International Nuclear Information System (INIS)

    Nedorezov, V.G.

    2005-01-01

    Full text: Brief review on astrophysical aspects in photonuclear studies is presented. Main attention is paid on the two kind experiments. The first one was performed at ESRF by GRAAL collaboration using the back scattering laser photons technique to study light speed anisotropy with respect to the dipole of the Cosmic Microwave Background (CMB) radiation. This is a modern analog of the Michelson - Morley experiment. The results obtained are not only methologically different from those of the above mentioned experiments but also provide stronger constrains on the light speed anisotropy in CMB frame. Second subject is related to the electron scattering on exotic nuclei which can play significant role in explosive phenomena such as novae, supernovae and neutron stars. Such approach may be considered as the alternative to traditional low energy accelerator experiments. Exotic nuclei for these purposes can be obtained at CSI (ELISe project). The experiment is foreseen to be installed at the New Experimental Storage Ring (NESR) at RAIR where cooled secondary beams of radioactive ions will collide with an intense electron beam circulating in a small electron storage beam

  1. Low-energy enhancement of nuclear γ strength and its impact on astrophysical reaction rates

    Directory of Open Access Journals (Sweden)

    Larsen A. C.

    2014-03-01

    Full Text Available An unexpected enhancement in the low-energy part of the γ-strength function for light and medium-mass nuclei has been discovered at the Oslo Cyclotron Laboratory. This enhancement could lead to an increase in the neutron-capture rates up to two orders of magnitude for very exotic, neutron-rich nuclei. However, it is still an open question whether this structure persists when approaching the neutron drip line.

  2. Resonant thermonuclear reaction rate

    International Nuclear Information System (INIS)

    Haubold, H.J.; Mathai, A.M.

    1986-01-01

    Basic physical principles for the resonant and nonresonant thermonuclear reaction rates are applied to find their standard representations for nuclear astrophysics. Closed-form representations for the resonant reaction rate are derived in terms of Meijer's G-function. Analytic representations of the resonant and nonresonant nuclear reaction rates are compared and the appearance of Meijer's G-function is discussed in physical terms

  3. AN UPDATED {sup 6}Li(p, {alpha}){sup 3}He REACTION RATE AT ASTROPHYSICAL ENERGIES WITH THE TROJAN HORSE METHOD

    Energy Technology Data Exchange (ETDEWEB)

    Lamia, L.; Spitaleri, C.; Sergi, M. L. [Dipartimento di Fisica e Astronomia, Universita di Catania, I-95123 Catania (Italy); Pizzone, R. G.; Tumino, A.; La Cognata, M. [INFN-Laboratori Nazionali del Sud, I-95125 Catania (Italy); Tognelli, E.; Degl' Innocenti, S.; Prada Moroni, P. G. [Dipartimento di Fisica, Universita di Pisa, I-56127 Pisa (Italy); Pappalardo, L. [Dipartimento di Fisica e Scienze della Terra, Universita di Ferrara, I-44100 Ferrara (Italy)

    2013-05-01

    The lithium problem influencing primordial and stellar nucleosynthesis is one of the most interesting unsolved issues in astrophysics. {sup 6}Li is the most fragile of lithium's stable isotopes and is largely destroyed in most stars during the pre-main-sequence (PMS) phase. For these stars, the convective envelope easily reaches, at least at its bottom, the relatively low {sup 6}Li ignition temperature. Thus, gaining an understanding of {sup 6}Li depletion also gives hints about the extent of convective regions. For this reason, charged-particle-induced reactions in lithium have been the subject of several studies. Low-energy extrapolations of these studies provide information about both the zero-energy astrophysical S(E) factor and the electron screening potential, U{sub e} . Thanks to recent direct measurements, new estimates of the {sup 6}Li(p, {alpha}){sup 3}He bare-nucleus S(E) factor and the corresponding U{sub e} value have been obtained by applying the Trojan Horse method to the {sup 2}H({sup 6}Li, {alpha} {sup 3}He)n reaction in quasi-free kinematics. The calculated reaction rate covers the temperature window 0.01 to 2T{sub 9} and its impact on the surface lithium depletion in PMS models with different masses and metallicities has been evaluated in detail by adopting an updated version of the FRANEC evolutionary code.

  4. New high accuracy measurement of the O-17(p,alpha)N-14 reaction rate at astrophysical temperatures

    Czech Academy of Sciences Publication Activity Database

    Sergi, M. L.; Spitaleri, C.; La Cognata, M.; Coc, A.; Mukhamedzhanov, A.; Burjan, Václav; Cherubini, S.; Crucilla, V.; Gulino, M.; Hammache, F.; Hons, Zdeněk; Irgaziev, B.; Kiss, G.G.; Kroha, Václav; Lamia, L.; Pizzone, R. G.; Puglia, S. M. R.; Rapisarda, G. G.; Romano, S.; de Sereville, N.; Somorjai, E.; Tudisco, S.; Tumino, A.

    2010-01-01

    Roč. 82, č. 3 (2010), 032801/1-032801/5 ISSN 0556-2813 Institutional research plan: CEZ:AV0Z10480505 Keywords : ASYMPTOTIC GIANT BRANCH * CNO CYCLE * NUCLEAR ASTROPHYSICS Subject RIV: BG - Nuclear, Atomic and Molecular Physics, Colliders Impact factor: 3.416, year: 2010

  5. Coulomb dissociation studies for astrophysical thermonuclear reactions

    Energy Technology Data Exchange (ETDEWEB)

    Motobayashi, T [Dept. of Physics, Rikkyo Univ., Toshima, Tokyo (Japan)

    1998-06-01

    The Coulomb dissociation method was applied to several radiative capture processes of astrophysical interest. The method has an advantage of high experimental efficiency, which allow measurements with radioactive nuclear beams. The reactions {sup 13}N(p,{gamma}){sup 14}O and {sup 7}Be(p,{gamma}){sup 8}B are mainly discussed. They are the key reaction in the hot CNO cycle in massive stars and the one closely related to the solar neutrino problem, respectively. (orig.)

  6. New determination of the {sup 2}H(d,p){sup 3}H and {sup 2}H(d,n){sup 3}He reaction rates at astrophysical energies

    Energy Technology Data Exchange (ETDEWEB)

    Tumino, A.; Spartà, R.; Spitaleri, C.; Pizzone, R. G.; La Cognata, M.; Rapisarda, G. G.; Romano, S.; Sergi, M. L. [Laboratori Nazionali del Sud-INFN, Catania (Italy); Mukhamedzhanov, A. M. [Cyclotron Institute Texas A and M University-College Station, Texas (United States); Typel, S. [GSI Helmholtzzentrum für Schwerionenforschung GmbH-Theorie Darmstadt (Germany); Tognelli, E.; Degl' Innocenti, S.; Prada Moroni, P. G. [Dipartimento di Fisica, Università di Pisa, and INFN-Sezione di Pisa, Pisa (Italy); Burjan, V.; Kroha, V.; Hons, Z.; Mrazek, J.; Piskor, S. [Nuclear Physics Institute of ASCR-Rez near Prague (Czech Republic); Lamia, L., E-mail: tumino@lns.infn.it [Dipartimento di Fisica e Astronomia, Università degli Studi di Catania, Catania (Italy)

    2014-04-20

    The cross sections of the {sup 2}H(d,p){sup 3}H and {sup 2}H(d,n){sup 3}He reactions have been measured via the Trojan Horse method applied to the quasi-free {sup 2}H({sup 3}He,p {sup 3}H){sup 1}H and {sup 2}H({sup 3}He,n {sup 3}He){sup 1}H processes at 18 MeV off the proton in {sup 3}He. For the first time, the bare nucleus S(E) factors have been determined from 1.5 MeV, across the relevant region for standard Big Bang nucleosynthesis, down to the thermal energies of deuterium burning in the pre-main-sequence (PMS) phase of stellar evolution, as well as of future fusion reactors. Both the energy dependence and the absolute value of the S(E) factors deviate by more than 15% from the available direct data and existing fitting curves, with substantial variations in the electron screening by more than 50%. As a consequence, the reaction rates for astrophysics experience relevant changes, with a maximum increase of up to 20% at the temperatures of the PMS phase. From a recent primordial abundance sensitivity study, it turns out that the {sup 2}H(d,n){sup 3}He reaction is quite influential on {sup 7}Li, and the present change in the reaction rate leads to a decrease in its abundance by up to 10%. The present reaction rates have also been included in an updated version of the FRANEC evolutionary code to analyze their influence on the central deuterium abundance in PMS stars with different masses. The largest variation of about 10%-15% pertains to young stars (≤1 Myr) with masses ≥1 M {sub ☉}.

  7. New determination of the 2H(d,p)3H and 2H(d,n)3He reaction rates at astrophysical energies

    International Nuclear Information System (INIS)

    Tumino, A.; Spartà, R.; Spitaleri, C.; Pizzone, R. G.; La Cognata, M.; Rapisarda, G. G.; Romano, S.; Sergi, M. L.; Mukhamedzhanov, A. M.; Typel, S.; Tognelli, E.; Degl'Innocenti, S.; Prada Moroni, P. G.; Burjan, V.; Kroha, V.; Hons, Z.; Mrazek, J.; Piskor, S.; Lamia, L.

    2014-01-01

    The cross sections of the 2 H(d,p) 3 H and 2 H(d,n) 3 He reactions have been measured via the Trojan Horse method applied to the quasi-free 2 H( 3 He,p 3 H) 1 H and 2 H( 3 He,n 3 He) 1 H processes at 18 MeV off the proton in 3 He. For the first time, the bare nucleus S(E) factors have been determined from 1.5 MeV, across the relevant region for standard Big Bang nucleosynthesis, down to the thermal energies of deuterium burning in the pre-main-sequence (PMS) phase of stellar evolution, as well as of future fusion reactors. Both the energy dependence and the absolute value of the S(E) factors deviate by more than 15% from the available direct data and existing fitting curves, with substantial variations in the electron screening by more than 50%. As a consequence, the reaction rates for astrophysics experience relevant changes, with a maximum increase of up to 20% at the temperatures of the PMS phase. From a recent primordial abundance sensitivity study, it turns out that the 2 H(d,n) 3 He reaction is quite influential on 7 Li, and the present change in the reaction rate leads to a decrease in its abundance by up to 10%. The present reaction rates have also been included in an updated version of the FRANEC evolutionary code to analyze their influence on the central deuterium abundance in PMS stars with different masses. The largest variation of about 10%-15% pertains to young stars (≤1 Myr) with masses ≥1 M ☉ .

  8. Alpha resonant scattering for astrophysical reaction studies

    Energy Technology Data Exchange (ETDEWEB)

    Yamaguchi, H.; Kahl, D.; Nakao, T. [Center for Nuclear Study (CNS), University of Tokyo, RIKEN campus, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Wakabayashi, Y.; Kubano, S. [The Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Hashimoto, T. [Research Center for Nuclear Physics (RCNP), Osaka University, 10-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); Hayakawa, S. [Istituto Nazionale Fisica Nucleare - Laboratori Nazionali del Sud (INFN-LNS), Via S. Sofia 62, 95125 Catania (Italy); Kawabata, T. [Department of Physics, Kyoto University, Kita-Shirakawa, Kyoto 606-8502 (Japan); Iwasa, N. [Department of Physics, Tohoku University, Aoba, Sendai, Miyagi 980-8578 (Japan); Teranishi, T. [Department of Physics, Kyushu University, 6-10-1 Hakozaki, Fukuoka 812-8581 (Japan); Kwon, Y. K. [Institute for Basic Science, 70, Yuseong-daero 1689-gil, Yuseong-gu, Daejeon 305-811 (Korea, Republic of); Binh, D. N. [30 MeV Cyclotron Center, Tran Hung Dao Hospital, Hoan Kiem District, Hanoi (Viet Nam); Khiem, L. H.; Duy, N. G. [Institute of Physics, Vietnam Academy of Science and Technology, 18 Hong Quoc Viet, Nghia do, Hanoi (Viet Nam)

    2014-05-02

    Several alpha-induced astrophysical reactions have been studied at CRIB (CNS Radioactive Ion Beam separator), which is a low-energy RI beam separator at Center for Nuclear Study (CNS) of the University of Tokyo. One of the methods to study them is the α resonant scattering using the thick-target method in inverse kinematics. Among the recent studies at CRIB, the measurement of {sup 7}Be+α resonant scattering is discussed. Based on the result of the experiment, we evaluated the contributions of high-lying resonances for the {sup 7}Be(α,γ) reaction, and proposed a new cluster band in {sup 11}C.

  9. Alpha resonant scattering for astrophysical reaction studies

    International Nuclear Information System (INIS)

    Yamaguchi, H.; Kahl, D.; Nakao, T.; Wakabayashi, Y.; Kubano, S.; Hashimoto, T.; Hayakawa, S.; Kawabata, T.; Iwasa, N.; Teranishi, T.; Kwon, Y. K.; Binh, D. N.; Khiem, L. H.; Duy, N. G.

    2014-01-01

    Several alpha-induced astrophysical reactions have been studied at CRIB (CNS Radioactive Ion Beam separator), which is a low-energy RI beam separator at Center for Nuclear Study (CNS) of the University of Tokyo. One of the methods to study them is the α resonant scattering using the thick-target method in inverse kinematics. Among the recent studies at CRIB, the measurement of 7 Be+α resonant scattering is discussed. Based on the result of the experiment, we evaluated the contributions of high-lying resonances for the 7 Be(α,γ) reaction, and proposed a new cluster band in 11 C

  10. Astrophysical rate of O-15(alpha,gamma)Ne-19 via the (p, t) reaction in inverse kinematics

    NARCIS (Netherlands)

    Davids, B; van den Berg, AM; Dendooven, P; Fleurot, F; Hunyadi, M; de Huu, MA; Siemssen, RH; Wilschut, HW; Wortche, HJ; Hernanz, M; Jose, J; Rehm, KE; Wuosmaa, AH; Segel, RE

    A recoil coincidence technique has been applied to measure the alpha-decay branching ratios of near-threshold states in Ne-19. Populating these states using the (p,t) reaction in inverse kinematics, we detected the recoils and their decay products with 100% geometric efficiency using a magnetic

  11. Observation of low-lying resonances in the quasicontinuum of 195,196Pt and enhanced astrophysical reaction rates

    Directory of Open Access Journals (Sweden)

    Giacoppo F.

    2015-01-01

    Full Text Available An excess of strength on the low-energy tail of the giant dipole resonance recently has been observed in the γ-decay from the quasicontinuum of 195,196Pt. The nature of this phenomenon is not yet fully investigated. If this feature is present also in the γ-ray strength of the neutron-rich isotopes, it can affect the neutron-capture reactions involved in the formation of heavy-elements in stellar nucleosynthesis. The experimental level density and γ-ray strength function of 195,196Pt are presented together with preliminary calculations of the corresponding neutron-capture cross sections.

  12. Photoneutron Reaction Data for Nuclear Physics and Astrophysics

    Directory of Open Access Journals (Sweden)

    Utsunomiya Hiroaki

    2018-01-01

    Full Text Available We discuss the role of photoneutron reaction data in nuclear physics and astrophysics in conjunction with the Coordinated Research Project of the International Atomic Energy Agency with the code F41032 (IAEA-CRP F41032.

  13. Photoneutron Reaction Data for Nuclear Physics and Astrophysics

    Science.gov (United States)

    Utsunomiya, Hiroaki; Renstrøm, Therese; Tveten, Gry Merete; Gheorghe, Ioana; Filipescu, Dan Mihai; Belyshev, Sergey; Stopani, Konstantin; Wang, Hongwei; Fan, Gongtao; Lui, Yiu-Wing; Symochko, Dmytro; Goriely, Stephane; Larsen, Ann-Cecilie; Siem, Sunniva; Varlamov, Vladimir; Ishkhanov, Boris; Glodariu, Tudor; Krzysiek, Mateusz; Takenaka, Daiki; Ari-izumi, Takashi; Amano, Sho; Miyamoto, Shuji

    2018-05-01

    We discuss the role of photoneutron reaction data in nuclear physics and astrophysics in conjunction with the Coordinated Research Project of the International Atomic Energy Agency with the code F41032 (IAEA-CRP F41032).

  14. Nuclear data needs in nuclear astrophysics: Charged-particle reactions

    International Nuclear Information System (INIS)

    Smith, Michael S.

    2001-01-01

    Progress in understanding a diverse range of astrophysical phenomena - such as the Big Bang, the Sun, the evolution of stars, and stellar explosions - can be significantly aided by improved compilation, evaluation, and dissemination of charged-particle nuclear reaction data. A summary of the charged-particle reaction data needs in these and other astrophysical scenarios is presented, along with recommended future nuclear data projects. (author)

  15. Empirical estimation of astrophysical photodisintegration rates of 106Cd

    Science.gov (United States)

    Belyshev, S. S.; Kuznetsov, A. A.; Stopani, K. A.

    2017-09-01

    It has been noted in previous experiments that the ratio between the photoneutron and photoproton disintegration channels of 106Cd might be considerably different from predictions of statistical models. The thresholds of these reactions differ by several MeV and the total astrophysical rate of photodisintegration of 106Cd, which is mostly produced in photonuclear reactions during the p-process nucleosynthesis, might be noticeably different from the calculated value. In this work the bremsstrahlung beam of a 55.6 MeV microtron and the photon activation technique is used to measure yields of photonuclear reaction products on isotopically-enriched cadmium targets. The obtained results are compared with predictions of statistical models. The experimental yields are used to estimate photodisintegration reaction rates on 106Cd, which are then used in nuclear network calculations to examine the effects of uncertainties on the produced abundences of p-nuclei.

  16. Nuclear Reactions for Astrophysics and Other Applications

    Energy Technology Data Exchange (ETDEWEB)

    Escher, J E; Burke, J T; Dietrich, F S; Scielzo, N D; Ressler, J J

    2011-03-01

    Cross sections for compound-nuclear reactions are required for many applications. The surrogate nuclear reactions method provides an indirect approach for determining cross sections for reactions on unstable isotopes, which are difficult or impossible to measure otherwise. Current implementations of the method provide useful cross sections for (n,f) reactions, but need to be improved upon for applications to capture reactions.

  17. Direct reactions for nuclear structure and nuclear astrophysics

    International Nuclear Information System (INIS)

    Jones, Katherine Louise

    2014-01-01

    Direct reactions are powerful probes for studying the atomic nucleus. Modern direct reaction studies are illuminating both the fundamental nature of the nucleus and its role in nucleosynthetic processes occurring in the cosmos. This report covers experiments using knockout reactions on neutron-deficient fragmentation beams, transfer reactions on fission fragment beams, and theoretical sensitivity studies relating to the astrophysical r-process. Results from experiments on 108,106 Sn at the NSCL, and on 131 Sn at HRIBF are presented as well as the results from the nucleosynthesis study.

  18. Direct Reactions for Nuclear Structure and Nuclear Astrophysics

    Energy Technology Data Exchange (ETDEWEB)

    Jones, Katherine Louise [Univ. of Tennessee, Knoxville, TN (United States). Experimental Low-Energy Nuclear Physics Group

    2014-12-18

    Direct reactions are powerful probes for studying the atomic nucleus. Modern direct reaction studies are illuminating both the fundamental nature of the nucleus and its role in nucleosynthetic processes occurring in the cosmos. This report covers experiments using knockout reactions on neutron-deficient fragmentation beams, transfer reactions on fission fragment beams, and theoretical sensitivity studies relating to the astrophysical r-process. Results from experiments on 108,106Sn at the NSCL, and on 131Sn at HRIBF are presented as well as the results from the nucleosynthesis study.

  19. Thermonuclear reaction rates. III

    International Nuclear Information System (INIS)

    Harris, M.J.; Fowler, W.A.; Caughlan, G.R.; Zimmerman, B.A.

    1983-01-01

    Stellar thermonuclear reaction rates are revised and updated, adding a number of new important reaction rates. Several reactions with large negative Q-values are included, and examples of them are discussed. The importance of the decay rates for Mg-26(p,n) exp 26 Al and Al-26(n,p) exp 26 Mg for stellar studies is emphasized. 19 references

  20. Nuclear Astrophysics and Neutron Induced Reactions: Quasi-Free Reactions and RIBs

    International Nuclear Information System (INIS)

    Cherubini, S.; Spitaleri, C.; Crucilla, V.; Gulino, M.; La Cognata, M.; Lamia, L.; Pizzone, R. G.; Puglia, S.; Rapisarda, G. G.; Romano, S.; Sergi, M. L.; Coc, A.; Kubono, S.; Binh, D. N.; Hayakawa, S.; Wakabayashi, Y.; Yamaguchi, H.; Burjan, V.; Kroha, V.; De Sereville, N.

    2010-01-01

    The use of quasi-free reactions in studying nuclear reactions between charged particles of astrophysical interest has received much attention over the last two decades. The Trojan Horse Method is based on this approach and it has been used to study a number of reactions relevant for Nuclear Astrophysics. Recently we applied this method to the study of nuclear reactions that involve radioactive species, namely to the study of the 18 F+p→ 15 O+α process at temperatures corresponding to the energies available in the classical novae scenario. Quasi-free reactions can also be exploited to study processes induced by neutrons. This technique is particularly interesting when applied to reaction induced by neutrons on unstable short-lived nuclei. Such processes are very important in the nucleosynthesis of elements in the sand r-processes scenarios and this technique can give hints for solving key questions in nuclear astrophysics where direct measurements are practically impossible.

  1. New Determination of the H-2(d,p)H-3 and H-2(d,n)He-3 Reaction Rates at Astrophysical Energies

    Czech Academy of Sciences Publication Activity Database

    Tumino, A.; Sparta, R.; Spitaleri, C.; Mukhamedzhanov, A. M.; Typel, S.; Pizzone, R. G.; Tognelli, E.; Degl'Innocenti, S.; Burjan, Václav; Kroha, Václav; Hons, Zdeněk; La Cognata, M.; Lamia, L.; Mrázek, Jaromír; Piskoř, Štěpán; Moroni, P. G. P.; Rapisarda, G. G.; Romano, S.; Sergi, M. L.

    2014-01-01

    Roč. 785, č. 2 (2014), s. 96 ISSN 0004-637X R&D Projects: GA MŠk LC07050; GA ČR GAP203/10/0310 Institutional support: RVO:61389005 Keywords : nuclear reactions * nucleosynthesis * abundances * primordial nucleosynthesis * stars: pre-main sequence Subject RIV: BG - Nuclear, Atomic and Molecular Physics, Colliders Impact factor: 5.993, year: 2014

  2. Nuclear astrophysics with DRAGON at ISAC: the 21Na(p, γ)22Mg reaction

    International Nuclear Information System (INIS)

    D'Auria, J.M.

    2003-01-01

    The DRAGON facility at the new intense radioactive beams facility, ISAC, is now operational. It was built to perform studies of radiative alpha and proton capture reactions involving radioactive reactants, and of interest to nuclear astrophysics. The rate of the 21 Na(p, γ) 22 Mg reaction has been measured using inverse kinematics. Resonance strengths have been measured for states of importance for novae explosions. This report will summarize aspects of this study and its impact. (orig.)

  3. Neutron Thermal Cross Sections, Westcott Factors, Resonance Integrals, Maxwellian Averaged Cross Sections and Astrophysical Reaction Rates Calculated from the ENDF/B-VII.1, JEFF-3.1.2, JENDL-4.0, ROSFOND-2010, CENDL-3.1 and EAF-2010 Evaluated Data Libraries

    Science.gov (United States)

    Pritychenko, B.; Mughabghab, S. F.

    2012-12-01

    We present calculations of neutron thermal cross sections, Westcott factors, resonance integrals, Maxwellian-averaged cross sections and astrophysical reaction rates for 843 ENDF materials using data from the major evaluated nuclear libraries and European activation file. Extensive analysis of newly-evaluated neutron reaction cross sections, neutron covariances, and improvements in data processing techniques motivated us to calculate nuclear industry and neutron physics quantities, produce s-process Maxwellian-averaged cross sections and astrophysical reaction rates, systematically calculate uncertainties, and provide additional insights on currently available neutron-induced reaction data. Nuclear reaction calculations are discussed and new results are presented. Due to space limitations, the present paper contains only calculated Maxwellian-averaged cross sections and their uncertainties. The complete data sets for all results are published in the Brookhaven National Laboratory report.

  4. Charged-particle transfer reactions and nuclear astrophysics problems

    International Nuclear Information System (INIS)

    Artemov, S.V.; Yarmukhamedov, R.; Yuldashev, B.S.; Burtebaev, N.; Duysebaev, A.; Kadyrzhanov, K.K.

    2002-01-01

    In the report a review of the recent results of calculation of the astrophysical S-factors S(E) for the D(α, γ) 6 Li, 3 He(α, γ) 7 Be, 7 Be(p, γ) 8 Be, 12,13 C(p, γ) 13, 14 N and 12 C(p,γ) 16 O* reactions at extremely low energies E, including value E=0 , performed within the framework of a new method taking into account the additional information about the nuclear vertex constant (Nc) (or the respective asymptotic normalization coefficient) are presented. The required values of Nc can be obtained from an analysis of measured differential cross-sections of proton and α-particle transfer reactions (for example A( 3 He,d)B, 6 Li(d, 6 Li)d, 6 Li(α, 6 Li)α, 12 C( 6 Li, d) 16 O* etc.). A comparative analysis between the results obtained by different authors is also done. Taking into account an important role of the NVC's values for the nuclear astrophysical A(p, γ)B and A(α, γ)B reactions, a possibility of obtaining the reliable NVC values for the virtual decay B→A+p and B→A+α from the analysis of differential cross sections both sub- and above-barrier A( 3 He, d) and A( 6,7 Li, 2,3 H)B reactions is discussed in detail. In this line the use the isochronous cyclotron U-150 M, the 'DC-60' heavy ion machine and electrostatic charge-exchanging accelerator UKP-2-1 of Institute of Nuclear Physics of National Nuclear Center of the Republic of Kazakhstan for carrying out the needed experiments is considered and the possibility of the obtained data application for the astrophysical interest is also discussed

  5. Applications of Reaction Rate

    Science.gov (United States)

    Cunningham, Kevin

    2007-01-01

    This article presents an assignment in which students are to research and report on a chemical reaction whose increased or decreased rate is of practical importance. Specifically, students are asked to represent the reaction they have chosen with an acceptable chemical equation, identify a factor that influences its rate and explain how and why it…

  6. The astrophysical S factor for dd reaction at ultralow energies

    International Nuclear Information System (INIS)

    Bystritskii, Vit.M.; Bystritsky, V.M.; Grebenyuk, V.M.

    2001-01-01

    The experimental results of measurements of the astrophysical S factor for dd reaction at very low deuteron collision energies using liner plasma technique are presented. The experiment was fulfilled at the high-current generator of the High-Current Electronics Institute (Tomsk, Russia). The measured values of S factors for the deuteron collision energies 1.80, 2.06, and 2.27 keV are S dd = 114 ± 68, 64 ± 30, and 53 ± 16 keV b, respectively. The corresponding cross sections for dd reaction, described as a product of the barrier factor and measured astrophysical S factor are: σ dd n (E col = 1.80 keV) = (4.3 ± 2.6) x 10 -33 cm 2 ; σ dd n (E col = 2.06 keV) = (9.8 ± 4.6) x 10 -33 cm 2 ; σ dd n (E col = 2.27 keV) = (2.1 ± 0.6) x 10 -32 cm 2 [ru

  7. Studying astrophysical reactions with low-energy RI beams at CRIB

    Directory of Open Access Journals (Sweden)

    Yamaguchi H.

    2016-01-01

    Full Text Available Studies on nuclear astrophysics, nuclear structure, and other interests have been performed using the radioactive-isotope (RI beams at the low-energy RI beam separator CRIB, operated by Center for Nuclear Study (CNS, the University of Tokyo. A typical measurement performed at CRIB is the elastic resonant scattering with the inverse kinematics. One recent experiment was on the α resonant scattering with 7Li and 7Be beams. This study is related to the astrophysical 7Li/7Be(α,γ reactions, important at hot p-p chain and νp-process in supernovae. There have also been measurements based on other experimental methods. The first THM measurement using an RI beam has been performed at CRIB, to study the 18F(p, α15O reaction at astrophysical energies via the three body reaction 2H(18F, α15On. The 18F(p, α 15O reaction rate is crucial to understand the 511-keV γ-ray production in nova explosion phenomena, and we successfully evaluated the reaction cross section at novae temperature and below experimentally for the first time.

  8. Resonant elastic scattering, inelastic scattering and astrophysical reactions; Diffusion elastique resonante, diffusion inelastique et reactions astrophysiques

    Energy Technology Data Exchange (ETDEWEB)

    De Oliveira Santos, F. [Grand Accelerateur National d' Ions Lourds, UMR 6415, 14 - Caen (France)

    2007-07-01

    Nuclear reactions can occur at low kinetic energy. Low-energy reactions are characterized by a strong dependence on the structure of the compound nucleus. It turns out that it is possible to study the nuclear structure by measuring these reactions. In this course, three types of reactions are treated: Resonant Elastic Scattering (such as N{sup 14}(p,p)N{sup 14}), Inelastic Scattering (such as N{sup 14}(p,p')N{sup 14*}) and Astrophysical reactions (such as N{sup 14}(p,{gamma})O{sup 15}). (author)

  9. Influences of the astrophysical environment on nuclear decay rates

    International Nuclear Information System (INIS)

    Norman, E.B.

    1987-09-01

    In many astronomical environments, physical conditions are so extreme that nuclear decay rates can be significantly altered from their laboratory values. Such effects are relevant to a number of current problems in nuclear astrophysics. Experiments related to these problems are now being pursued, and will be described in this talk. 19 refs., 5 figs

  10. First Accurate Normalization of the $\\beta$-delayed $\\alpha$ Decay of $^{16}$N and Implications for the $^{12}$C$(\\alpha,\\gamma)^{16}$O Astrophysical Reaction Rate arXiv

    CERN Document Server

    Kirsebom, O.S.; Lica, R.; Munch, M.; Riisager, K.; Fynbo, H.O.U.; Borge, M.J.G.; Madurga, M.; Marroquin, I.; Andreyev, A.N.; Berry, T.A.; Christensen, E.R.; Fernández, P. Díaz; Doherty, D.T.; Van Duppen, P.; Fraile, L.M.; Gallardo, M.C.; Greenlees, P.T.; Harkness-Brennan, L.J.; Hubbard, N.; Huyse, M.; Jensen, J.H.; Johansson, H.; Jonson, B.; Judson, D.S.; Konki, J.; Lazarus, I.; Lund, M.V.; Marginean, N.; Marginean, R.; Perea, A.; Mihai, C.; Negret, A.; Page, R.D.; Pucknell, V.; Rahkila, P.; Sorlin, O.; Sotty, C.; Swartz, J.A.; Sørensen, H.B.; Törnqvist, H.; Vedia, V.; Warr, N.; De Witte, H.

    The $^{12}$C$(\\alpha,\\gamma)^{16}$O reaction plays a central role in astrophysics, but its cross section at energies relevant for astrophysical applications is only poorly constrained by laboratory data. The reduced $\\alpha$ width, $\\gamma_{11}$, of the bound $1^-$ level in $^{16}$O is particularly important to determine the cross section. The magnitude of $\\gamma_{11}$ is determined via sub-Coulomb $\\alpha$-transfer reactions or the $\\beta$-delayed $\\alpha$ decay of $^{16}$N, but the latter approach is presently hampered by the lack of sufficiently precise data on the $\\beta$-decay branching ratios. Here we report improved branching ratios for the bound $1^-$ level and for $\\beta$-delayed $\\alpha$ emission. In the case of the $\\beta$-delayed $\\alpha$ branch, we find a $5\\sigma$ deviation from the literature value. With our new branching ratios, the constraints imposed on $\\gamma_{11}$ by the $\\beta\\alpha$-decay and $\\alpha$-transfer data are of similar precision and, for the first time, in good agreement. Th...

  11. Semi empirical model for astrophysical nuclear fusion reactions of 1≤Z≤15

    International Nuclear Information System (INIS)

    Manjunatha, H.C.; Seenappa, L.; Sridhar, K.N.

    2017-01-01

    The fusion reaction is one of the most important reactions in the stellar evolution. Due to the complicated reaction mechanism of fusion, there is great uncertainty in the reaction rate which limits our understanding of various stellar objects. Low z elements are formed through many fusion reactions such as "4He+"1"2C→"1"6O, "1"2C+"1"2C→"2"0Ne+"4He, "1"2C+"1"2C→"2"3Na, "1"2C+"1"2C→"2"3Mg, "1"6O+"1"6O→"2"8Si+"4He, "1"2C+"1H→"1"3N and "1"3C+"4He→"1"6O. A detail study is required on Coulomb and nuclear interaction in formation of low Z elements in stars through fusion reactions. For astrophysics, the important energy range extends from 1 MeV to 3 MeV in the center of mass frame, which is only partially covered by experiments. In the present work, we have studied the basic fusion parameters such as barrier heights (V_B), positions (R_B), curvature of the inverted parabola (ħω_1) for fusion barrier, cross section and compound nucleus formation probability (P_C_N) and fusion process in the low Z element (1≤Z≤15) formation process. For each isotope, we have studied all possible projectile-target combinations. We have also studied the astrophysical S(E) factor for these reactions. Based on this study, we have formulated the semi empirical relations for barrier heights (V_B), positions (R_B), curvature of the inverted parabola and hence for the fusion cross section and astrophysical S(E) factor. The values produced by the present model compared with the experiments and data available in the literature. (author)

  12. Photonuclear reactions in astrophysical p-process: Theoretical calculations and experiment simulation based on ELI-NP

    Science.gov (United States)

    Xu, Yi; Luo, Wen; Balabanski, Dimiter; Goriely, Stephane; Matei, Catalin; Tesileanu, Ovidiu

    2017-09-01

    The astrophysical p-process is an important way of nucleosynthesis to produce the stable and proton-rich nuclei beyond Fe which can not be reached by the s- and r-processes. In the present study, the astrophysical reaction rates of (γ,n), (γ,p), and (γ,α) reactions are computed within the modern reaction code TALYS for about 3000 stable and proton-rich nuclei with 12 Infrastructure-Nuclear Physics (ELI-NP) facility is being developed, which will provide the great opportunity to experimentally study the photonuclear reactions in p-process. Simulations of the experimental setup for the measurements of the photonuclear reactions 96Ru(γ,p) and 96Ru(γ,α) are performed. It is shown that the experiments of photonuclear reactions in p-process based on ELI-NP are quite promising.

  13. Thermonuclear F-19(p,alpha(0))O-16 reaction rate

    Czech Academy of Sciences Publication Activity Database

    He, J. J.; Lombardo, I.; Dell'Aquila, D.; Xu, Yi; Zang, L. Y.; Liu, W. P.

    2018-01-01

    Roč. 42, č. 1 (2018), č. článku 015001. ISSN 1674-1137 Institutional support: RVO:61389005 Keywords : asymptotic giant branch (AGB) star * nucleosynthesis * astrophysical S factor * cross section * reaction rate Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics OBOR OECD: Astronomy (including astrophysics,space science) Impact factor: 5.084, year: 2016

  14. Alpha-induced reaction cross section measurements on 151Eu for the astrophysical γ-process

    International Nuclear Information System (INIS)

    Gyuerky, Gy.; Elekes, Z.; Farkas, J.; Fueloep, Zs.; Halasz, Z.; Kiss, G.G.; Somorjai, E.; Szuecs, T.; Gueraya, R.T.; Oezkana, N.

    2010-01-01

    could be determined separately. The obtained results are compared with the predictions of the statistical model code NON-SMOKER WEB version v5.8.1 which is widely used in γ-process network calculations. It is found that the calculations overestimate the cross sections by about a factor of two. A sensitivity analysis shows that this discrepancy is caused by the inadequate description of the α+nucleus channel. A factor of two reduction of the reaction rate of 151 Eu(α, γ) 155 Tb in γ-process network calculations with respect to theoretical rates using the standard optical potential by McFadden and Satchler (1966) is recommended. Further details of the experiment, the data analysis and the astrophysical discussion can be found in [3].

  15. S-factor for radiative capture reactions for light nuclei at astrophysical energies

    Science.gov (United States)

    Ghasemi, Reza; Sadeghi, Hossein

    2018-06-01

    The astrophysical S-factors of thermonuclear reactions, including radiative capture reactions and their analysis in the frame of different theoretical models, are the main source of nuclear processes. We have done research on the radiative capture reactions importance in the framework of a potential model. Investigation of the reactions in the astrophysical energies is of great interest in the aspect of astrophysics and nuclear physics for developing correct models of burning and evolution of stars. The experimental measurements are very difficult and impossible because of these reactions occurrence at low-energies. In this paper we do a calculation on radiative capture astrophysical S-factors for nuclei in the mass region A theoretical methods.

  16. What Is a Reaction Rate?

    Science.gov (United States)

    Schmitz, Guy

    2005-01-01

    The definition of reaction rate is derived and demonstrations are made for the care to be taken while using the term. Reaction rate can be in terms of a reaction property, the extent of reaction and thus it is possible to give a definition applicable in open and closed systems.

  17. Cross section measurements of proton capture reactions on Se isotopes relevant to the astrophysical p process

    Science.gov (United States)

    Foteinou, V.; Harissopulos, S.; Axiotis, M.; Lagoyannis, A.; Provatas, G.; Spyrou, A.; Perdikakis, G.; Zarkadas, Ch.; Demetriou, P.

    2018-03-01

    Cross sections of proton capture reactions on 74Se, 78Se, and 80Se have been measured at incident beam energies from 2 to 6 MeV, 1.7 to 3 MeV, and 1.5 to 3.5 MeV, respectively. In the case of Se,8078, cross sections were obtained from in-beam γ -angular distribution measurements, whereas for the 74Se isotope they were derived from off-beam activity measurements. The measured cross sections were compared with calculations performed with the nuclear reaction code talys (version 1.6). A good agreement between theory and experiment was found. Astrophysical S factors and reaction rates deduced from the experimental and calculated cross sections were also compared and the impact of different nuclear ingredients in the calculations on the reaction rates was investigated. It was found that, for certain combinations of nuclear input models, the reaction rates obtained at temperatures relevant to p -process nucleosynthesis differ by a factor 2 at the most, differences that are well within the acceptable deviations of calculated p -nuclei abundances and observations.

  18. BAYESIAN ESTIMATION OF THERMONUCLEAR REACTION RATES

    Energy Technology Data Exchange (ETDEWEB)

    Iliadis, C.; Anderson, K. S. [Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3255 (United States); Coc, A. [Centre de Sciences Nucléaires et de Sciences de la Matière (CSNSM), CNRS/IN2P3, Univ. Paris-Sud, Université Paris–Saclay, Bâtiment 104, F-91405 Orsay Campus (France); Timmes, F. X.; Starrfield, S., E-mail: iliadis@unc.edu [School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-1504 (United States)

    2016-11-01

    The problem of estimating non-resonant astrophysical S -factors and thermonuclear reaction rates, based on measured nuclear cross sections, is of major interest for nuclear energy generation, neutrino physics, and element synthesis. Many different methods have been applied to this problem in the past, almost all of them based on traditional statistics. Bayesian methods, on the other hand, are now in widespread use in the physical sciences. In astronomy, for example, Bayesian statistics is applied to the observation of extrasolar planets, gravitational waves, and Type Ia supernovae. However, nuclear physics, in particular, has been slow to adopt Bayesian methods. We present astrophysical S -factors and reaction rates based on Bayesian statistics. We develop a framework that incorporates robust parameter estimation, systematic effects, and non-Gaussian uncertainties in a consistent manner. The method is applied to the reactions d(p, γ ){sup 3}He, {sup 3}He({sup 3}He,2p){sup 4}He, and {sup 3}He( α , γ ){sup 7}Be, important for deuterium burning, solar neutrinos, and Big Bang nucleosynthesis.

  19. Measurement of reaction rates of interest in stellar structure and evolution

    International Nuclear Information System (INIS)

    Terrasi, F.; D''Onofrio, A.; Campajola, L.; Imbriani, G.; Gialanella, L.; Greife, U.; Rolfs, C.; Strieder, F.; Trautvetter, H.P.; Roca, V.; Romano, M.; Straniero, O.

    1998-01-01

    Accurate determinations of reaction rates at astrophysical energies are very important in stellar structure and evolution studies. The cases of two key reactions, namely 7 Be(p,γ) 8 B and 12 C(α,γ) 16 O are discussed, both from the point of view of their astrophysical interest and of the experimental difficulties in the measurement of their cross section. (orig.)

  20. Nuclear effects on bremsstrahlung neutrino rates of astrophysical interest

    International Nuclear Information System (INIS)

    Stoica, Sabin; Horvath, J.E.

    2002-01-01

    We calculate in this work the rates for the neutrino pair production by nucleon-nucleon bremsstrahlung taking into account the full contribution from a nuclear one-pion-exchange potential. It is shown that if the temperatures are low enough (T≤20 MeV), the integration over the nuclear part can be done for the general case, ranging from the completely degenerate (D) to the nondegenerate (ND) regime. We find that the inclusion of the full nuclear contribution enhances the neutrino pair production by nn and pp bremsstrahlung by a factor of about 2 in both the D and ND limits when compared with previous calculations. This result may be relevant for the physical conditions of interest in the semitransparent regions near the neutrinosphere in type II supernovae, cooling of neutron stars, and other astrophysical situations

  1. Determination by transfer reaction of alpha widths in fluorine for astrophysical interest

    International Nuclear Information System (INIS)

    Oliveira Santos, F. de

    1995-04-01

    The nucleosynthesis of fluorine is not known. Several astrophysical models predict the alpha radiative capture onto N 15 as the main fluorine production reaction. In the expression of the reaction rate, one parameter is missing: the alpha width of the resonance on the E = 4.377 MeV level in fluorine. A direct measurement is excluded due to the very low cross-section expected. We have determined this alpha width using a transfer reaction followed by analyses with FR-DWBA (Finite Range Distorted Wave Born Approximation) in a simple cluster alpha model. This experiment was carried out with a Li 7 beam with E = 28 MeV onto a N 15 gas target. The 16 first levels were studied. Spectroscopic factors were extracted for most of them. Alpha widths for unbound levels were determined. Many alpha width were compared with known values from direct reaction and the differences lie within the uncertainty range (factor 2). The alpha width for the E = 4.377 MeV level was determined (Γ α = 1.5*10 -15 MeV), its value is about 60 times weaker than the used value. The influence of our new rate was studied in AGB (Asymptotic Giant Branch) stars during thermal pulses. In this model the alteration is sensitive. (author)

  2. Rates of Thermonuclear Reactions in Dense Plasmas

    International Nuclear Information System (INIS)

    Tsytovich, V.N.; Bornatici, M.

    2000-01-01

    The problem of plasma screening of thermonuclear reactions has attracted considerable scientific interest ever since Salpeter's seminal paper, but it is still faced with controversial statements and without any definite conclusion. It is of relevant importance to thermonuclear reactions in dense astrophysical plasmas, for which charge screening can substantially affect the reaction rates. Whereas Salpeter and a number of subsequent investigations have dealt with static screening, Carraro, Schafer, and Koonin have drawn attention to the fact that plasma screening of thermonuclear reactions is an essentially dynamic effect. In addressing the issue of collective plasma effects on the thermonuclear reaction rates, the first critical overview of most of the work carried out so far is presented and the validity of the test particle approach is assessed. In contrast to previous investigations, we base our description on the kinetic equation for nonequilibrium plasmas, which accounts for the effects on the rates of thermonuclear reactions of both plasma fluctuations and screening and allows one to analyze explicitly the effects of the fluctuations on the reaction rates. Such a kinetic formulation is more general than both Salpeter's approach and the recently developed statistical approaches and makes it possible to obtain a more comprehensive understanding of the problem. A noticeable result of the fluctuation approach is that the static screening, which affects both the interaction and the self-energy of the reacting nuclei, does not affect the reaction rates, in contrast with the results obtained so far. Instead, a reduction of the thermonuclear reaction rates is obtained as a result of the effect of plasma fluctuations related to the free self-energy of the reacting nuclei. A simple physical explanation of the slowing down of the reaction rates is given, and the relation to the dynamically screened test particle approach is discussed. Corrections to the reaction rates

  3. The Trojan Horse method for nuclear astrophysics: Recent results for direct reactions

    International Nuclear Information System (INIS)

    Tumino, A.; Gulino, M.; Spitaleri, C.; Cherubini, S.; Romano, S.; Cognata, M. La; Pizzone, R. G.; Rapisarda, G. G.; Lamia, L.

    2014-01-01

    The Trojan Horse method is a powerful indirect technique to determine the astrophysical factor for binary rearrangement processes A+x→b+B at astrophysical energies by measuring the cross section for the Trojan Horse (TH) reaction A+a→B+b+s in quasi free kinematics. The Trojan Horse Method has been successfully applied to many reactions of astrophysical interest, both direct and resonant. In this paper, we will focus on direct sub-processes. The theory of the THM for direct binary reactions will be shortly presented based on a few-body approach that takes into account the off-energy-shell effects and initial and final state interactions. Examples of recent results will be presented to demonstrate how THM works experimentally

  4. The Trojan Horse method for nuclear astrophysics: Recent results for direct reactions

    Energy Technology Data Exchange (ETDEWEB)

    Tumino, A.; Gulino, M. [Laboratori Nazionali del Sud, Istituto Nazionale di Fisica Nucleare, Catania, Italy and Università degli Studi di Enna Kore, Enna (Italy); Spitaleri, C.; Cherubini, S.; Romano, S. [Laboratori Nazionali del Sud, Istituto Nazionale di Fisica Nucleare, Catania, Italy and Dipartimento di Fisica e Astronomia, Università di Catania, Catania (Italy); Cognata, M. La; Pizzone, R. G.; Rapisarda, G. G. [Laboratori Nazionali del Sud, Istituto Nazionale di Fisica Nucleare, Catania (Italy); Lamia, L. [Dipartimento di Fisica e Astronomia, Università di Catania, Catania (Italy)

    2014-05-09

    The Trojan Horse method is a powerful indirect technique to determine the astrophysical factor for binary rearrangement processes A+x→b+B at astrophysical energies by measuring the cross section for the Trojan Horse (TH) reaction A+a→B+b+s in quasi free kinematics. The Trojan Horse Method has been successfully applied to many reactions of astrophysical interest, both direct and resonant. In this paper, we will focus on direct sub-processes. The theory of the THM for direct binary reactions will be shortly presented based on a few-body approach that takes into account the off-energy-shell effects and initial and final state interactions. Examples of recent results will be presented to demonstrate how THM works experimentally.

  5. The Trojan Horse method for nuclear astrophysics: Recent results on resonance reactions

    Energy Technology Data Exchange (ETDEWEB)

    Cognata, M. La; Pizzone, R. G. [Laboratori Nazionali del Sud, Istituto Nazionale di Fisica Nucleare, Catania (Italy); Spitaleri, C.; Cherubini, S.; Romano, S. [Dipartimento di Fisica e Astronomia, Università di Catania, Catania, Italy and Laboratori Nazionali del Sud, Istituto Nazionale di Fisica Nucleare, Catania (Italy); Gulino, M.; Tumino, A. [Kore University, Enna, Italy and Laboratori Nazionali del Sud, Istituto Nazionale di Fisica Nucleare, Catania (Italy); Lamia, L. [Dipartimento di Fisica e Astronomia, Università di Catania, Catania (Italy)

    2014-05-09

    Nuclear astrophysics aims to measure nuclear-reaction cross sections of astrophysical interest to be included into models to study stellar evolution and nucleosynthesis. Low energies, < 1 MeV or even < 10 keV, are requested for this is the window where these processes are more effective. Two effects have prevented to achieve a satisfactory knowledge of the relevant nuclear processes, namely, the Coulomb barrier exponentially suppressing the cross section and the presence of atomic electrons. These difficulties have triggered theoretical and experimental investigations to extend our knowledge down to astrophysical energies. For instance, indirect techniques such as the Trojan Horse Method have been devised yielding new cutting-edge results. In particular, I will focus on the application of this indirect method to resonance reactions. Resonances might dramatically enhance the astrophysical S(E)-factor so, when they occur right at astrophysical energies, their measurement is crucial to pin down the astrophysical scenario. Unknown or unpredicted resonances might introduce large systematic errors in nucleosynthesis models. These considerations apply to low-energy resonances and to sub-threshold resonances as well, as they may produce sizable modifications of the S-factor due to, for instance, destructive interference with another resonance.

  6. The Trojan Horse method for nuclear astrophysics: Recent results on resonance reactions

    International Nuclear Information System (INIS)

    Cognata, M. La; Pizzone, R. G.; Spitaleri, C.; Cherubini, S.; Romano, S.; Gulino, M.; Tumino, A.; Lamia, L.

    2014-01-01

    Nuclear astrophysics aims to measure nuclear-reaction cross sections of astrophysical interest to be included into models to study stellar evolution and nucleosynthesis. Low energies, < 1 MeV or even < 10 keV, are requested for this is the window where these processes are more effective. Two effects have prevented to achieve a satisfactory knowledge of the relevant nuclear processes, namely, the Coulomb barrier exponentially suppressing the cross section and the presence of atomic electrons. These difficulties have triggered theoretical and experimental investigations to extend our knowledge down to astrophysical energies. For instance, indirect techniques such as the Trojan Horse Method have been devised yielding new cutting-edge results. In particular, I will focus on the application of this indirect method to resonance reactions. Resonances might dramatically enhance the astrophysical S(E)-factor so, when they occur right at astrophysical energies, their measurement is crucial to pin down the astrophysical scenario. Unknown or unpredicted resonances might introduce large systematic errors in nucleosynthesis models. These considerations apply to low-energy resonances and to sub-threshold resonances as well, as they may produce sizable modifications of the S-factor due to, for instance, destructive interference with another resonance

  7. Reaction rate of propene pyrolysis.

    Science.gov (United States)

    Han, Peipei; Su, Kehe; Liu, Yan; Wang, Yanli; Wang, Xin; Zeng, Qingfeng; Cheng, Laifei; Zhang, Litong

    2011-10-01

    The reaction rate of propene pyrolysis was investigated based on the elementary reactions proposed in Qu et al., J Comput Chem 2009, 31, 1421. The overall reaction rate was developed with the steady-state approximation and the rate constants of the elementary reactions were determined with the variational transition state theory. For the elementary reaction having transition state, the vibrational frequencies of the selected points along the minimum energy path were calculated with density functional theory at B3PW91/6-311G(d,p) level and the energies were improved with the accurate model chemistry method G3(MP2). For the elementary reaction without transition state, the frequencies were calculated with CASSCF/6-311G(d,p) and the energies were refined with the multireference configuration interaction method MRCISD/6-311G(d,p). The rate constants were evaluated within 200-2000 K and the fitted three-parameter expressions were obtained. The results are consistent with those in the literatures in most cases. For the overall rate, it was found that the logarithm of the rate and the reciprocal temperature have excellent linear relationship above 400 K, predicting that the rate follows a typical first-order law at high temperatures of 800-2000 K, which is also consistent with the experiments. The apparent activation energy in 800-2000 K is 317.3 kJ/mol from the potential energy surface of zero Kelvin. This value is comparable with the energy barriers, 365.4 and 403.7 kJ/mol, of the rate control steps. However, the apparent activation energy, 215.7 kJ/mol, developed with the Gibbs free energy surface at 1200 K is consistent with the most recent experimental result 201.9 ± 0.6 kJ/mol. Copyright © 2011 Wiley Periodicals, Inc.

  8. Coulomb dissociation reactions on molybdenum isotopes for astrophysics applications

    Energy Technology Data Exchange (ETDEWEB)

    Ershova, Olga

    2012-03-09

    Within the present work, photodissociation reactions on {sup 100}Mo, {sup 93}Mo and {sup 92}Mo isotopes were studied by means of the Coulomb dissociation method at the LAND setup at GSI. As a result of the analysis of the present experiment, integrated Coulomb excitation cross sections of the {sup 100}Mo({gamma},n), {sup 100}Mo({gamma},2n), {sup 93}Mo({gamma},n) and {sup 92}Mo({gamma},n) reactions were determined. A second important topic of the present thesis is the investigation of the efficiency of the CsI gamma detector. The data taken with the gamma calibration sources shortly after the experiment were used for the investigation. In addition, a test experiment in refined conditions was conducted within the framework of this thesis. Numerous GEANT3 simulations of the detector were performed in order to understand various aspects of its performance. As a result, the efficiency of the detector was determined to be approximately a factor of 2 lower than the efficiency expected from the simulation. (orig.)

  9. Nuclear astrophysics: Recent results on CNO-cycle reactions and AGB nucleosynthesis

    International Nuclear Information System (INIS)

    La Cognata, M.

    2011-01-01

    Nuclear astrophysics aims to measure nuclear-reaction cross sections of astrophysical interest to be included into models to study stellar evolution and nucleosynthesis. Low energies, < 100 keV, are requested for this is the window where these processes are more effective. Two effects have prevented to achieve a satisfactory knowledge of the relevant nuclear processes, namely the Coulomb barrier exponentially suppressing the cross section and the presence of atomic electrons. These difficulties have triggered theoretical and experimental investigations to extend our knowledge down to astrophysical energies. For instance, indirect techniques such as the Trojan Horse Method and new experimental facilities such as deep underground laboratories have been devised yielding new cutting-edge results.

  10. Microscopic (n,γ) rates with astrophysical relevance near the N = 50 neutron core

    International Nuclear Information System (INIS)

    Dutta, Saumi; Gangopadhyay, G.; Bhattacharyya, Abhijit

    2016-01-01

    The weak s-process component, that takes place in He core and C-burning shell of massive stars, produces elements in the mass range 56 < A < 90 from iron up to Sr-Y-Mo region. Neutron capture rates are crucial in the study of weak s-process nucleosynthesis via classical or model-based network calculations. The nuclei in the vicinity of shell closures have very small capture cross sections and hence, act as bottlenecks to the reaction chain. The (n,γ) rates of s-only isotopes are crucial to test the validity of local approximation. Precise neutron capture rates have also consequences for s-process branching analysis that can predict various constraints about the astrophysical medium. The neutron capture rates are also important for p-process study. The rates of the (γ, n) reactions can be deduced from (n,γ) rates via detailed balance. The nuclei, for which experimental data do not exist, a good theoretical model can predict the values

  11. New Improved Indirect Measurement of the F-19(p, alpha)O-16 Reaction at Energies of Astrophysical Relevance

    Czech Academy of Sciences Publication Activity Database

    Indelicato, I.; La Cognata, M.; Spitaleri, C.; Burjan, Václav; Cherubini, S.; Gulino, M.; Hayakawa, S.; Hons, Zdeněk; Kroha, Václav; Lamia, L.; Mazzocco, M.; Mrázek, Jaromír; Pizzone, R. G.; Romano, S.; Strano, E.; Torresi, D.; Tumino, A.

    2017-01-01

    Roč. 845, č. 1 (2017), č. článku 19. ISSN 0004-637X Institutional support: RVO:61389005 Keywords : nuclear reactions * nucleosynthesis * abundances Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics OBOR OECD: Astronomy (including astrophysics,space science) Impact factor: 5.533, year: 2016

  12. Measurement of reaction rates of interest in stellar structure and evolution

    Energy Technology Data Exchange (ETDEWEB)

    Terrasi, F; D` Onofrio, A [Dipt. di Scienze Ambientali, Seconda Univ. di Napoli, Caserta (Italy); [INFN, Napoli (Italy); Campajola, L; Imbriani, G [INFN, Napoli (Italy); [Dipt. di Scienze Fisiche, Univ. Federico II, Napoli (Italy); Gialanella, L [INFN, Napoli (Italy); [Dipt. di Scienze Fisiche, Univ. Federico II, Napoli (Italy); [Inst. fuer Experimentalphysik III, Ruhr-Univ. Bochum, Bochum (Germany); Greife, U; Rolfs, C; Strieder, F; Trautvetter, H P [Inst. fuer Experimentalphysik III, Ruhr-Univ. Bochum, Bochum (Germany); Roca, V; Romano, M [INFN, Napoli (Italy); [Dipt. di Scienze Fisiche, Univ. Federico II, Napoli (Italy); Straniero, O [Osservatorio Astronomico di Collurania, Teramo (Italy)

    1998-06-01

    Accurate determinations of reaction rates at astrophysical energies are very important in stellar structure and evolution studies. The cases of two key reactions, namely {sup 7}Be(p,{gamma}){sup 8}B and {sup 12}C({alpha},{gamma}){sup 16}O are discussed, both from the point of view of their astrophysical interest and of the experimental difficulties in the measurement of their cross section. (orig.)

  13. New Improved Indirect Measurement of the {sup 19}F( p , α ){sup 16}O Reaction at Energies of Astrophysical Relevance

    Energy Technology Data Exchange (ETDEWEB)

    Indelicato, I.; La Cognata, M.; Spitaleri, C.; Cherubini, S.; Gulino, M.; Lamia, L.; Pizzone, R. G.; Romano, S.; Tumino, A. [INFN, Laboratori Nazionali del Sud, Catania (Italy); Burjan, V.; Hons, Z.; Kroha, V.; Mrazek, J. [Nuclear Physics Institute of ASCR, Rez near Prague (Czech Republic); Hayakawa, S. [RIKEN, CNS, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Mazzocco, M.; Strano, E.; Torresi, D., E-mail: indelicato@lns.infn.it [INFN, Sezione di Padova, Padova (Italy)

    2017-08-10

    Fluorine abundance determination is of great importance in stellar physics to understand s-elements production and mixing processes in asymptotic giant branch (AGB) stars. Up to now, theoretical models overproduce F abundances in AGB stars with respect to the observed values, thus calling for further investigation of the reactions involving fluorine. In particular, the {sup 19}F( p , α ){sup 16}O reaction is the main destruction channel of fluorine at the bottom of the convective envelope in AGB stars, an H-rich environment where it can experience temperatures high enough to determine its destruction, owing to additional mixing processes. In this paper the Trojan horse method (THM) was used to extract the {sup 19}F( p , α {sub 0}){sup 16}O S-factor in the energy range of astrophysical interest ( E {sub cm} ≈ 0–1 MeV). This is the most relevant channel at the low temperatures (few 10{sup 7} K) characterizing the bottom of the convective envelope, according to current knowledge. A previous indirect experiment using the THM has observed three resonances in the energy regions below E {sub cm} ≈ 450 keV. These energies correspond to typical AGB temperatures, thus implying a significant increase in the reaction rate. Statistics are scarce for performing an accurate separation between resonances, preventing one from drawing a quantitative conclusion about their total widths and spin parities. Before THM measurement, only extrapolations were available below about 500 keV, showing a non-resonant behavior that sharply contradicts the trend of the astrophysical factor at higher energies. A new experiment has been performed to verify the measured TH astrophysical factor and to perform more accurate spectroscopy of the involved resonances.

  14. Nuclear astrophysics: An application of nuclear physics

    International Nuclear Information System (INIS)

    Fueloep, Z.

    2005-01-01

    Nuclear astrophysics, a fruitful combination of nuclear physics and astrophysics can be viewed as a special application of nuclear physics where the study of nuclei and their reactions are motivated by astrophysical problems. Nuclear astrophysics is also a good example for the state of the art interdisciplinary research. The origin of elements studied by geologists is explored by astrophysicists using nuclear reaction rates provided by the nuclear physics community. Due to the high interest in the field two recent Nuclear Physics Divisional Conferences of the European Physical Society were devoted to nuclear astrophysics and a new conference series entitled 'Nuclear Physics in Astrophysics' has been established. Selected problems of nuclear astrophysics will be presented emphasizing the interplay between nuclear physics and astrophysics. As an example the role of 14 N(p,r) 15 O reaction rate in the determination of the age of globular clusters will be discussed in details

  15. Experimental studies of keV energy neutron-induced reactions relevant to astrophysics and nuclear physics

    Energy Technology Data Exchange (ETDEWEB)

    Shima, T.; Kii, T.; Kikuchi, T.; Okazaki, F.; Kobayashi, T.; Baba, T.; Nagai, Y. [Tokyo Inst. of Tech. (Japan). Faculty of Science; Igashira, M.

    1997-03-01

    Nuclear reactions induced by keV energy neutrons provide a plenty of informations for studies of both astrophysics and nuclear physics. In this paper we will show our experimental studies of neutron- induced reactions of light nuclei in the keV energy region by means of a pulsed keV neutron beam and high-sensitivity detectors. Also we will discuss astrophysical and nuclear-physical consequences by using the obtained results. (author)

  16. Investigating resonances above and below the threshold in nuclear reactions of astrophysical interest and beyond

    Energy Technology Data Exchange (ETDEWEB)

    La Cognata, M., E-mail: lacognata@lns.infn.it [Laboratori Nazionali del Sud - INFN, Catania (Italy); Kiss, G. G. [ATOMKI, Debrecen (Hungary); Mukhamedzhanov, A. M. [Cyclotron Institute, Texas A& M University, College Station, Texas (United States); Spitaleri, C. [Laboratori Nazionali del Sud - INFN, Catania (Italy); Department of Physics and Astronomy, University of Catania, Catania (Italy); Trippella, O. [Sezione di Perugia - INFN, Perugia (Italy)

    2015-10-15

    Resonances in nuclear cross sections dramatically change their trends. Therefore, the presence of unexpected resonances might lead to unpredicted consequences on astrophysics and nuclear physics. In nuclear physics, resonances allow one to study states in the intermediate compound systems, to evaluate their cluster structure, for instance, especially in the energy regions approaching particle decay thresholds. In astrophysics, resonances might lead to changes in the nucleosynthesis flow, determining different isotopic compositions of the nuclear burning ashes. For these reasons, the Trojan Horse method has been modified to investigate resonant reactions. Thanks to this novel approach, for the first time normalization to direct data might be avoided. Moreover, in the case of sub threshold resonances, the Trojan Horse method modified to investigate resonances allows one to deduce the asymptotic normalization coefficient, showing the close connection between the two indirect approaches.

  17. Reaction rates for neutrino processes

    International Nuclear Information System (INIS)

    Shalitin, D.

    1978-01-01

    Some integrals involved in neutrino processes are evaluated by transformation to a special system of reference - usually to the center of mass system (CM). Rather simple analytic expressions are obtained for reaction rates and, though less simple, for moments. An interesting result thus obtained is for an isotropic interaction (in CM) of a neutrino with a monoenergetic isotropic gas of extreme relativistic electrons: it is found that the probability of the scattered neutrino to have energy in a certain range is independent of this energy. (Auth.)

  18. Investigating the astrophysical 22Ne(p, γ23Na and 22Mg(p, γ23Al reactions with a multi-channel scattering formalism

    Directory of Open Access Journals (Sweden)

    Fraser P. R.

    2014-03-01

    Full Text Available The reaction 22Ne(p, γ23Na is key to the NeNa cycle of stellar nucleogenesis, and better understanding of the 22Mg(p, γ23Al reaction is needed to understand the 22Na puzzle in ONe white dwarf novae. We aim to study these reactions using a multi-channel algebraic scattering (MCAS formalism for low-energy nucleon-nucleus scattering, recently expanded to investigate radiative capture. As a first step towards this goal, we here calculate the energy levels of the mass-23 (Ne, Mg, Na, Al nuclei. This is not only because the resonant structure of these nuclei are related to the astrophysical -rates of interest, but also because the interaction parameters determined for describing the energy levels are an integral part of the future calculation of the astrophysical reactions when using the MCAS scheme.

  19. Nuclear Reaction Data File for Astrophysics (NRDF/A) in Hokkaido University Nuclear Reaction Data Center

    International Nuclear Information System (INIS)

    Kato, Kiyoshi; Kimura, Masaaki; Furutachi, Naoya; Makinaga, Ayano; Togashi, Tomoaki; Otuka, Naohiko

    2010-01-01

    The activities of the Japan Nuclear Reaction Data Centre is explained. The main task of the centre is data compilation of Japanese nuclear reaction data in collaboration of the International Network of Nuclear Reaction Data Centres. As one of recent activities, preparation of a new database (NRDF/A) and evaluation of astronuclear reaction data are reported. Collaboration in the nuclear data activities among Asian countries is proposed.

  20. Astrophysical S factor for the 15N(p,γ)16O reaction

    International Nuclear Information System (INIS)

    Mukhamedzhanov, A. M.; La Cognata, M.; Kroha, V.

    2011-01-01

    The R-matrix approach has proved to be very useful in extrapolating the astrophysical factor down to astrophysically relevant energies, since the majority of measurements are not available in this region. However, such an approach has to be critically considered when no complete knowledge of the reaction model is available. To get reliable results in such cases one has to use all the available information from independent sources and, accordingly, fix or constrain variations of the parameters. In this paper we present a thorough R-matrix analysis of the 15 N(p,γ) 16 O reaction, which provides a path from the CN cycle to the CNO bi-cycle and CNO tri-cycle. The measured astrophysical factor for this reaction is dominated by resonant capture through two strong J π =1 - resonances at E R =312 and 962 keV and direct capture to the ground state. Recently, a new measurement of the astrophysical factor for the 15 N(p,γ) 16 O reaction has been published [P. J. LeBlanc et al., Phys. Rev. C 82, 055804 (2010)]. The analysis has been done using the R-matrix approach with unconstrained variation of all parameters including the asymptotic normalization coefficient (ANC). The best fit has been obtained for the square of the ANC C 2 =539.2 fm -1 , which exceeds the previously measured value by a factor of ≅3. Here we present a new R-matrix analysis of the Notre Dame-LUNA data with the fixed within the experimental uncertainties square of the ANC C 2 =200.34 fm -1 . Rather than varying the ANC we add the contribution from a background resonance that effectively takes into account contributions from higher levels. Altogether we present ten fits, seven unconstrained and three constrained. For the unconstrained fit with the boundary condition B c =S c (E 2 ), where E 2 is the energy of the second level, we get S(0)=39.0±1.1 keVb and normalized χ-tilde 2 =1.84, i.e., the result which is similar to LeBlanc et al. From all our fits we get the range 33.1≤S(0)≤40.1 keVb which

  1. Light elements burning reaction rates at stellar temperatures as deduced by the Trojan Horse measurements

    Energy Technology Data Exchange (ETDEWEB)

    Lamia, L. [Dipartimento di Fisica e Astronomia, Università degli Studi di Catania, Catania (Italy); Spitaleri, C. [Dipartimento di Fisica e Astronomia, Università degli Studi di Catania, Catania, Italy and INFN-Laboratori Nazionali del Sud, Catania (Italy); La Cognata, M.; Palmerini, S.; Sergi, M. L. [INFN-Laboratori Nazionali del Sud, Catania (Italy); Puglia, S. M. R. [INFN-Laboratori Nazionali del Sud, Catania, Italy and Dipartimento di Fisica e Astronomia, Università degli Studi di Catania, Catania (Italy)

    2015-02-24

    Experimental nuclear astrophysics aims at determining the reaction rates for astrophysically relevant reactions at their Gamow energies. For charged-particle induced reactions, the access to these energies is usually hindered, in direct measurements, by the presence of the Coulomb barrier between the interacting particles or by electron screening effects, which make hard the determination of the bare-nucleus S(E)-factor of interest for astrophysical codes. The use of the Trojan Horse Method (THM) appears as one of the most suitable tools for investigating nuclear processes of interest for astrophysics. Here, in view of the recent TH measurements, the main destruction channels for deuterium ({sup 2}H), for the two lithium {sup 6,7}Li isotopes, for the {sup 9}Be and the one for the two boron {sup 10,11}B isotopes will be discussed.

  2. Origin of a maximum of the astrophysical S factor in heavy-ion fusion reactions at deep subbarrier energies

    Science.gov (United States)

    Hagino, K.; Balantekin, A. B.; Lwin, N. W.; Thein, Ei Shwe Zin

    2018-03-01

    The hindrance phenomenon of heavy-ion fusion cross sections at deep subbarrier energies often accompanies a maximum of an astrophysical S factor at a threshold energy for fusion hindrance. We argue that this phenomenon can naturally be explained when the fusion excitation function is fitted with two potentials, with a larger (smaller) logarithmic slope at energies lower (higher) than the threshold energy. This analysis clearly suggests that the astrophysical S factor provides a convenient tool to analyze the deep subbarrier hindrance phenomenon, even though the S factor may have a strong energy dependence for heavy-ion systems unlike that for astrophysical reactions.

  3. The fluorine destruction in stars: First experimental study of the 19F(p,α)16O reaction at astrophysical energies

    International Nuclear Information System (INIS)

    La Cognata, M.; Mukhamedzhanov, A.; Spitaleri, C.; Indelicato, I.; Aliotta, M.; Burjan, V.; Cherubini, S.; Coc, A.; Gulino, M.; Hons, Z.; Kiss, G. G.; Kroha, V.; Lamia, L.; Mrazek, J.; Palmerini, S.; Piskor, S.; Pizzone, R. G.; Puglia, S. M. R.; Rapisarda, G. G.; Romano, S.

    2012-01-01

    The 19 F(p,α) 16 O reaction is an important fluorine destruction channel in the proton-rich outer layers of asymptotic giant branch (AGB) stars and it might also play a role in hydrogendeficient post-AGB star nucleosynthesis. So far, available direct measurements do not reach the energy region of astrophysical interest (E cm ∼ 300 keV), because of the hindrance effect of the Coulomb barrier. The Trojan Horse (TH) method was thus used to access this energy region, by extracting the quasi-free contribution to the 2 H( 19 F,α 16 O)n reaction. The TH measurement of the α 0 channel, which is the dominant one at such energies, shows the presence of resonant structures not observed before that cause an increase of the reaction rate at astrophysical temperatures up to a factor of 1.7, with potential important consequences for stellar nucleosynthesis.

  4. The astrophysical S-factor for dd-reactions at keV-energy range

    International Nuclear Information System (INIS)

    Bystritskii, V.; Bystritsky, V.; Chaikovsky, S.

    2001-01-01

    The experimental results of measurements of the astrophysical S-factor for dd-reaction at keV-energy range collision energies using liner plasma technique are presented. The experiments were carried out at the high current generator of the Institute of High-Current Electronics in Tomsk, Russia. The measured values of the S-factors for the deuteron collision energies 1.80, 2.06 and 2.27 keV are S dd =(114±68), (64±30), (53±16) b x keV, respectively. The corresponding cross sections for dd-reactions, described as a product of the barrier factor and measured astrophysical S-factor, are σ dd n (E col =1.80 keV)=(4.3±2.6) x 10 -33 cm 2 ; σ dd n (E col =2.06 keV)=(9.8±4.6) x 10 -33 cm 2 ; σ dd n (E col =2.27 keV)=(2.1±0.6) x 10 -32 cm 2 . (orig.) [de

  5. Recent progress in ab-initio studies of nuclear reactions of astrophysical interest with A ≤ 3

    Science.gov (United States)

    Marcucci, Laura E.

    2018-03-01

    We review the most recent theoretical studies of nuclear reactions of astrophysical interest involving few-nucleon systems. In particular, we focus on the consequences for the solar neutrino fluxes of the recent determination for the astrophysical S-factor of the proton weak capture by proton, and on the radiative capture of protons by deuterons in the energy range of interest for Big Bang Nucleosynthesis.

  6. E1-forbidden transition rates in ions of astrophysical interest

    International Nuclear Information System (INIS)

    Träbert, E

    2014-01-01

    Transition rates in atomic systems may appear to be of little importance in steady-state plasmas that are observed at great distances from Earth. However, some of the transition rates compete with collision rates, and in these cases certain line intensity ratios are affected and can serve as remote indicators of density. In the low-density environments of stellar coronae and planetary nebulae, the transition rates of interest are mostly spin-forbidden E1 decays, higher-multipole order transitions (M1, E2, M2, M3), and hyperfine-induced transitions. On Earth, measurements of the long upper level lifetimes of these atomic systems require the use of ion traps. A fair number of test cases with lifetimes in the range from nanoseconds to many seconds have been treated successfully, and the evolution of calculations along with the experimental progress is notable. A new generation of cold ion traps is expected to extend the atomic lifetime measurements on multiply charged ions into the range of many minutes. (paper)

  7. Indirect Study of the (2)H(d,p)(3)H and (2)H(d,n)(3)He Reactions at Astrophysical Energies via the Trojan Horse Method

    Czech Academy of Sciences Publication Activity Database

    Tumino, A.; Spitaleri, C.; Mukhamedzhanov, A.; Typel, S.; Aliotta, M.; Burjan, Václav; Del Santo, M. G.; Kiss, G.G.; Kroha, Václav; Hons, Zdeněk; La Cognata, M.; Lamia, L.; Mrázek, Jaromír; Pizzone, R. G.; Piskoř, Štěpán; Rapisarda, G. G.; Romano, S.; Sergi, M. L.; Sparta, R.

    2011-01-01

    Roč. 50, 1-4 (2011), s. 323-325 ISSN 0177-7963. [21st European Conference on Few-Body Problems in Physics Location. Salamanca, 30.08.2010-03092010] R&D Projects: GA ČR GAP203/10/0310 Institutional research plan: CEZ:AV0Z10480505 Keywords : CROSS-SECTIONS * REACTION-RATES * COMPILATION * D+D Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 1.438, year: 2011

  8. The astrophysical S-factor for the dd-reaction at ultralow energies

    International Nuclear Information System (INIS)

    Bystritskij, V.M.; Grebenyuk, V.M.; Parzhitskij, S.S.

    1999-01-01

    The experimental results for measurements of the astrophysical S-factor for dd-reaction at very low deuteron collision energies using liner plasma technique are presented. The experiment was fulfilled at the high current generator of the High-Current Electronics Institute, Tomsk, Russia. The measured values of S-factor for the deuteron collision energies: 2.27, 2.06, and 1.8 keV are: S dd = (53 ± 16), (64 ± 30), (114 ±68)b · keV, respectively. The corresponding dd cross sections described as a product of the barrier factor and measured astrophysical S-factor are: σ dd n (E col = 1.8 keV) = (4.3 ± 2.6) · 10 -33 cm 2 ; σ dd n (E col = 2.06 keV) = (9.8 ± 4.6) · 10 -33 cm 2 ; σ dd n (E col = 2.27 keV) = (2.1 ±0.6) · 10 -32 cm 2

  9. Nuclear transfer reaction measurements at the ESR-for the investigation of the astrophysical O-15(alpha,gamma)Ne-19 reaction

    NARCIS (Netherlands)

    Doherty, D. T.; Woods, P. J.; Litvinov, Yu A.; Najafi, M. Ali; Bagchi, S.; Bishop, S.; Bo, M.; Brandau, C.; Davinson, T.; Dillmann, I.; Estrade, A.; Egelhof, P.; Evdokimov, A.; Gumberidze, A.; Heil, M.; Lederer, C.; Litvinov, S. A.; Lotay, G.; Kalantar-Nayestanaki, N.; Kiselev, O.; Kozhuharov, C.; Kroell, T.; Mahjour-Shafei, M.; Mutterer, M.; Nolden, F.; Petridis, N.; Popp, U.; Reifarth, R.; Rigollet, C.; Roy, S.; Steck, M.; Stoehlker, Th; Streicher, B.; Trotsenko, S.; von Schmid, M.; Yan, X. L.; Zamora, J. C.

    Astrophysical x-ray bursts are thought to be a result of thermonuclear explosions on the atmosphere of an accreting neutron star. Between these bursts, energy is thought to be generated by the hot CNO cycles. The O-15(alpha,gamma)Ne-19 reaction is one reaction that allows breakout from these CNO

  10. Nuclear transfer reaction measurements at the ESR-for the investigation of the astrophysical O-15(alpha,gamma)Ne-19 reaction

    NARCIS (Netherlands)

    Doherty, D. T.; Woods, P. J.; Litvinov, Yu A.; Najafi, M. Ali; Bagchi, S.; Bishop, S.; Bo, M.; Brandau, C.; Davinson, T.; Dillmann, I.; Estrade, A.; Egelhof, P.; Evdokimov, A.; Gumberidze, A.; Heil, M.; Lederer, C.; Litvinov, S. A.; Lotay, G.; Kalantar-Nayestanaki, N.; Kiselev, O.; Kozhuharov, C.; Kroell, T.; Mahjour-Shafei, M.; Mutterer, M.; Nolden, F.; Petridis, N.; Popp, U.; Reifarth, R.; Rigollet, C.; Roy, S.; Steck, M.; Stoehlker, Th; Streicher, B.; Trotsenko, S.; von Schmid, M.; Yan, X. L.; Zamora, J. C.

    2015-01-01

    Astrophysical x-ray bursts are thought to be a result of thermonuclear explosions on the atmosphere of an accreting neutron star. Between these bursts, energy is thought to be generated by the hot CNO cycles. The O-15(alpha,gamma)Ne-19 reaction is one reaction that allows breakout from these CNO

  11. Nuclear astrophysics at DRAGON

    International Nuclear Information System (INIS)

    Hager, U.

    2014-01-01

    The DRAGON recoil separator is located at the ISAC facility at TRIUMF, Vancouver. It is designed to measure radiative alpha and proton capture reactions of astrophysical importance. Over the last years, the DRAGON collaboration has measured several reactions using both radioactive and high-intensity stable beams. For example, the 160(a, g) cross section was recently measured. The reaction plays a role in steady-state helium burning in massive stars, where it follows the 12C(a, g) reaction. At astrophysically relevant energies, the reaction proceeds exclusively via direct capture, resulting in a low rate. In this measurement, the unique capabilities of DRAGON enabled determination not only of the total reaction rates, but also of decay branching ratios. In addition, results from other recent measurements will be presented

  12. Future coordinated researches by Argonne (USA), Tashkent (Uzbekistan) and Almaty (Kazakhstan) nuclear centres on the nuclear reactions and astrophysics

    International Nuclear Information System (INIS)

    Artemov, S.V.; Yarmukhamedov, R.; Yuldashev, B.S.; Burtebaev, N.; Kadyrzhanov, K.K.; Rehm, K.E.

    2004-01-01

    An actual problem of modern nuclear physics and astrophysics is realistic evaluation of astrophysical S-factors and rates of the nuclear reactions, which are responsible for the energy generation and nucleosynthesis in Universe. The essential progress in understanding of these processes has been made in the last decade. Those are the discovery of neutrino oscillations, obtaining new precise data on the reactions cross sections at rather low energies, development of methods of extrapolation to the stellar energy region. Nevertheless, the available experimental data close to stellar energies are very poor especially for unstable particles interactions, and uncertainties remain rather remarkable. It leads to large errors when measured data are extrapolated to astrophysical important super low energy region. The experimental possibilities for improvement the accuracy of the data using 'indirect' measurements are discussed. One of them is based on the peripheral character of charged particles interaction at low energy in which the asymptotical normalization coefficients (ANC) of overlapping functions are used for extrapolation. In this case the differential cross-section of the particle transfer reaction is expressed via the product of ANCs squares of participating particles. Their values may be obtained from the peripheral reactions at larger energies where the accuracy of measurement is higher. From this point of view the particle transfer A(x,y)B reactions are the most preferable, where (x,y) are ( 13 N, 12 C) or ( 17 F, 16 O) (proton transfer) and ( 13 C, 12 C) or ( 17 O, 16 O) (neutron transfer). We should know firstly the ANCs for 13 C→ 12 C+n ( 17 O→ 16 O+n) and 13 N→ 12 C+p ( 17 F→ 16 O+p) systems, and all other ANCs B→ A+p(n) are expressed through these values. The nucleon separation energies ε N are relatively small for these nuclei (ε 13N → 12C+p =1.943 MeV; ε 17F → 16O+p =0.6003 MeV; ε 13C → 12C+n =4.946 MeV and ε 17O → 16O+n =4.143 Me

  13. Reaction rate of 24Mg(p,γ)25Al

    International Nuclear Information System (INIS)

    Powell, D.C.; Iliadis, C.; Champagne, A.E.; Grossmann, C.A.; Hale, S.E.; Hansper, V.Y.; McLean, L.K.

    1999-01-01

    The proton-capture reaction on 24 Mg has been investigated in the bombarding energy range of E p =0.2-1.7 MeV. Resonance properties (strengths, branching ratios and lifetimes) of low-energy resonances have been measured. From the experimental results, accurate proton partial widths, γ-ray partial widths and total widths (Γ p , Γ γ , and Γ) have been deduced. The present experimental information establishes the 24 Mg+p reaction rates over the temperature range T=0.02-2.0 GK with statistical uncertainties of 5% to 21%. Our recommended reaction rates deviate from previous estimates by 18% to 45%. Based on our results, we can rule out the recent suggestion that the total width of the E R =223 keV resonance has a significant influence on the reaction rates. We also discuss several effects that might give rise to systematic uncertainties in the reaction rates. The astrophysical implications for hydrogen burning of 24 Mg at low stellar temperatures are presented

  14. Study of astrophysically important resonant states in 26Si by the 28Si(4He,6He)26Si reaction

    Science.gov (United States)

    Kwon, Young Kwan; Lee, C. S.; Moon, J. Y.; Lee, J. H.; Kim, J. Y.; Kubono, S.; Iwasa, N.; Inafiki, K.; Yamaguchi, H.; He, J. J.; Saito, A.; Wakabayashi, Y.; Fukijawa, H.; Amadio, G.; Khiem, L. H.; Tanaka, M.; Chen, A.; Kato, S.

    PoS(NIC-IX)024 , b, H. Yamaguchia, J. J. Hea , A. Saitoa , Y. Wakabayashia, H. Fujikawaa, G. The emission of 1.809 MeV gamma-ray from the first excited state of 26 Mg followed by beta- decay of 26 Al in its ground state (denoted as 26 Alg.s. ) has been identified by gamma-ray telescopes such the Compton Gamma-Ray Observatory (CGRO) [1]. To resolve controversy over the pos- sible sources of the observational 1.809 MeV gamma-rays, one needs accurate knowledge of the production rate of 26 Al. The 25 Al(p,γ)26Si reaction which is the competition reaction for produc- tion of 26 Alg.s. is one of the important subjects to be investigated. In this work, the astrophysically important 26 Si states above the proton threshold were studied via the 28 Si(4 He,6 He)26 Si reaction. We have preformed an angular distribution measurement using the high resolution QDD spectro- graph (PA) at Center for Nuclear Study (CNS), University of Tokyo. The experimental results and data analysis will be presented.

  15. Bare astrophysical S(E)-factor for the 6Li(d, α)4He and 7Li(p, α)4He reactions at astrophysical energies

    International Nuclear Information System (INIS)

    Pizzone, R.G.; Spitaleri, C.; Lattuada, M.; Musumarra, A.; Pellegriti, M.G.; Romano, S.; Tumino, A.; Cherubini, S.; Figuera, P.; Miljanic, D.; Rolfs, C.; Typel, S.; Wolter, H.H.; Castellani, V.; Degl'Innocenti, S.; Imperio, A.

    2003-01-01

    The Trojan Horse Method has been applied to study the 7 Li(p, α) 4 He and 6 (Li(d, α) 4 He reactions through the 7 Li(d, αα)n and 6 Li( 6 Li, αα) 4 He three body processes, respectively. The electron screening potential deduced from these experiments is much larger than the adiabatic approximation prediction for both cases; the systematic discrepancy between data and theoretical predictions is thus confirmed. Astrophysical implications of these measurements are also discussed

  16. Reaction Order Ambiguity in Integrated Rate Plots

    Science.gov (United States)

    Lee, Joe

    2008-01-01

    Integrated rate plots are frequently used in reaction kinetics to determine orders of reactions. It is often emphasised, when using this methodology in practice, that it is necessary to monitor the reaction to a substantial fraction of completion for these plots to yield unambiguous orders. The present article gives a theoretical and statistical…

  17. Nuclear Astrophysics Experiments at CIAE

    International Nuclear Information System (INIS)

    Liu Weiping; Li Zhihong; Bai Xixiang; Lian Gang; Guo Bing; Zeng, Sheng; Yan Shengquan; Wang Baoxiang; Shu Nengchuan; Wu Kaisu; Chen Yongshou

    2005-01-01

    This paper describes nuclear astrophysical studies using the unstable ion beam facility GIRAFFE. We measured the angular distributions for some low energy reactions, such as 7 Be(d, n) 8 B, 11 C(d, n) 12 N, 8 Li(d, n) 9 Be and 8 Li(d, p) 9 Li in inverse kinematics, and indirectly derived the astrophysical S-factors or reaction rates of 7 Be(p, γ) 8 B, 11 C(p, γ) 12 N, 8 Li(n, γ) 9 Li at astrophysically relevant energies

  18. Measurement of inertial confinement fusion reaction rate

    International Nuclear Information System (INIS)

    Peng Xiaoshi; Wang Feng; Tang Daorun; Liu Shenye; Huang Tianxuan; Liu Yonggang; Xu Tao; Chen Ming; Mei Yu

    2011-01-01

    Fusion reaction rate is an important parameter for measuring compression during the implosion in inertial confinement fusion experiment. We have developed a system for fusion reaction history measurement with high temporal resolution. The system is composed of plastic scintillator and nose cone, optical system and streak camera. We have applied this system on the SG-III prototype for fusion reaction rate measuring. For the first time, fusion reaction rate history have been measured for deuterium-tritium filled targets with neutrons yields about 10 10 . We have analyzed possible influence factor during fusion reaction rate measuring. It indicates that the instrument measures fusion reaction bang time at temporal resolutions as low as 30 ps.(authors)

  19. Nuclear astrophysics data at ORNL

    International Nuclear Information System (INIS)

    Smith, M.S.; Blackmon, J.C.

    1998-01-01

    There is a new program of evaluation and dissemination of nuclear data of critical importance for nuclear astrophysics within the Physics Division of Oak Ridge National Laboratory. Recent activities include determining the rates of the important 14 O(α,p) 17 F and 17 F(p,γ) 18 Ne reactions, disseminating the Caughlan and Fowler reaction rate compilation on the World Wide Web, and evaluating the 17 O(p,α) 14 N reaction rate. These projects, which are closely coupled to current ORNL nuclear astrophysics research, are briefly discussed along with future plans

  20. Reaction rate of hydrolysis of iodine

    International Nuclear Information System (INIS)

    Miyake, Yoshikazu; Eguchi, Wataru; Adachi, Motonari

    1979-01-01

    Absorption rates of dilute iodine vapor contained in air by aqueous mixtures of sodium hydroxide and boric acid were measured using a laminar liquid jet column absorber at 298 K. Absorption rates in this system are controlled by a series of complex reactions taking place in the liquid phase. The reaction rate constant of iodine hydrolysis in the aqueous phase was determined from the absorption rates observed under the conditions that the base-catalytic hydrolysis reaction of iodine can be considered to be irreversible and that other reactions can be neglected. The absorption rates calculated theoretically with the rate constant value obtained above were in good accordance with the whole experimental data observed for a wide range of experimental conditions. (author)

  1. REACLIB: A Reaction Rate Library for the Era of Collaborative Science

    Science.gov (United States)

    Meisel, Zachary

    2008-10-01

    Thermonuclear reaction rates and weak decay rates are of great importance to modern nuclear astrophysics. They are critical in the study of many topics such as Big Bang Nucleosynthesis, X-ray bursts, Supernovae, and S-process element formation, among others. The Joint Institute for Nuclear Astrophysics (JINA) has been created to increase connectivity amongst nuclear astrophysicists in our modern age of highly collaborative science. Within JINA there has been an effort to create a frequently updated and readily accessible database of thermonuclear reactions and weak decay rates. This database is the REACLIB library, which can be accessed at the web address: http://www.nscl.msu.edu/˜nero/db/. Here I will discuss the JINA REACLIB Project, including a new procedure to fit reaction rates as a function of temperature that takes full advantage of physicality. With these updated reaction rates, astrophysical modelers will no longer have to worry about the adverse effects of using obsolete reaction rate libraries lacking physical behavior.

  2. Differential neutrino rates and emissivities from the plasma process in astrophysical systems

    International Nuclear Information System (INIS)

    Ratkovic, Sasa; Iyer Dutta, Sharada; Prakash, Madappa

    2003-01-01

    The differential rates and emissivities of neutrino pairs from an equilibrium plasma are calculated for the wide range of density and temperature encountered in astrophysical systems. New analytical expressions are derived for the differential emissivities which yield total emissivities in full agreement with those previously calculated. The photon and plasmon pair production and absorption kernels in the source term of the Boltzmann equation for neutrino transport are provided. The appropriate Legendre coefficients of these kernels, in forms suitable for multi-group flux-limited diffusion schemes are also computed

  3. Recent Progresses in Ab-Initio Studies of Low-Energy Few-Nucleon Reactions of Astrophysical Interest

    Science.gov (United States)

    Marcucci, Laura E.

    2017-03-01

    We review the most recent theoretical studies of nuclear reactions of astrophysical interest involving few-nucleon systems. In particular, we focus on the radiative capture of protons by deuterons in the energy range of interest for Big Bang Nucleosynthesis. Related to this, we will discuss also the most recent calculation of tritium β -decay. Two frameworks will be considered, the conventional and the chiral effective field theory approach.

  4. Nuclear astrophysics deep underground the case of the 15N(p,γ)16O reaction at LUNA

    CERN Document Server

    Mazzocchi, Chiara

    2010-01-01

    Measuring nuclear reactions of astrophysical interest at the relevant energies is not always possible on the Earth’s surface because of the cosmic-ray background that dominates the spectra. The LUNA collaboration exploits the lowbackground enviroment of Gran Sasso National Laboratory to study these reactions at or close to the Gamow peak. The latest experimental efforts included the measurement of the 15N(p,γ)16O at beam energies between 77 and 350 keV. The status of these measurements is summarised in this contribution.

  5. Trojan Horse Method and RIBs: The {sup 18}F(p,{alpha}){sup 15}O reaction at astrophysical energies

    Energy Technology Data Exchange (ETDEWEB)

    Cherubini, S.; Gulino, M.; Rapisarda, G. G.; Spitaleri, C.; La Cognata, M.; Lamia, L.; Kubono, S.; Yamaguchi, H.; Hayakawa, S.; Wakabayashi, Y.; Iwasa, N.; Kato, S.; Komatsubara, H.; Teranishi, T.; Coc, A.; De Sereville, N.; Hammache, F. [Dipartimento di Fisica ed Astronomia, Universita di Catania and INFN-LNS, Catania (Italy); INFN-LNS, Catania (Italy) and UniKORE, Enna (Italy)

    2012-11-12

    The abundance of {sup 18}F in Nova explosions is an important issue for the understanding of this astrophysical phenomenon. For this reason it is necessary to study the nuclear reactions that produce or destroy this isotope in novae. Among these latter processes, the {sup 18}F(p,{alpha}){sup 15}O is one of the main {sup 18}F destruction channels. We report here on the preliminary results of the first experiment that applies the Trojan Horse Method to a Radioactive Ion Beam induced reaction. The experiment was performed using the CRIB apparatus of the Center for Nuclear Study of The Tokyo University.

  6. Trojan Horse Method and RIBs: The 18F(p,α)15O reaction at astrophysical energies

    International Nuclear Information System (INIS)

    Cherubini, S.; Gulino, M.; Rapisarda, G. G.; Spitaleri, C.; La Cognata, M.; Lamia, L.; Kubono, S.; Yamaguchi, H.; Hayakawa, S.; Wakabayashi, Y.; Iwasa, N.; Kato, S.; Komatsubara, H.; Teranishi, T.; Coc, A.; De Séréville, N.; Hammache, F.

    2012-01-01

    The abundance of 18 F in Nova explosions is an important issue for the understanding of this astrophysical phenomenon. For this reason it is necessary to study the nuclear reactions that produce or destroy this isotope in novae. Among these latter processes, the 18 F(p,α) 15 O is one of the main 18 F destruction channels. We report here on the preliminary results of the first experiment that applies the Trojan Horse Method to a Radioactive Ion Beam induced reaction. The experiment was performed using the CRIB apparatus of the Center for Nuclear Study of The Tokyo University.

  7. The fluorine destruction in stars: First experimental study of the {sup 19}F(p,{alpha}){sup 16}O reaction at astrophysical energies

    Energy Technology Data Exchange (ETDEWEB)

    La Cognata, M.; Mukhamedzhanov, A.; Spitaleri, C.; Indelicato, I.; Aliotta, M.; Burjan, V.; Cherubini, S.; Coc, A.; Gulino, M.; Hons, Z.; Kiss, G. G.; Kroha, V.; Lamia, L.; Mrazek, J.; Palmerini, S.; Piskor, S.; Pizzone, R. G.; Puglia, S. M. R.; Rapisarda, G. G.; Romano, S. [INFN-LNS, Catania (Italy); Cyclotron Institute, Texas A and M University, College Station, Texas (United States); University of Catania and INFN-LNS, Catania (Italy); and others

    2012-11-12

    The {sup 19}F(p,{alpha}){sup 16}O reaction is an important fluorine destruction channel in the proton-rich outer layers of asymptotic giant branch (AGB) stars and it might also play a role in hydrogendeficient post-AGB star nucleosynthesis. So far, available direct measurements do not reach the energy region of astrophysical interest (E{sub cm}{approx} 300 keV), because of the hindrance effect of the Coulomb barrier. The Trojan Horse (TH) method was thus used to access this energy region, by extracting the quasi-free contribution to the {sup 2}H({sup 19}F,{alpha}{sup 16}O)n reaction. The TH measurement of the {alpha}{sub 0} channel, which is the dominant one at such energies, shows the presence of resonant structures not observed before that cause an increase of the reaction rate at astrophysical temperatures up to a factor of 1.7, with potential important consequences for stellar nucleosynthesis.

  8. Rates of the main thermonuclear reactions

    International Nuclear Information System (INIS)

    Abramovich, S.N.; Guzhovskii, B.Ya.; Dunaeva, S.A.; Fomushkin, E.F.

    1992-01-01

    The data on the cross sections of main thermonuclear reactions have been estimated with an account of the latest experimental results in a form of S-factor spline presentation. Based on this estimation, the reates of these reactions in 0.0001-1 MeV temperature range in the supposition of Maxwell distribution of relative velocities have been computed. The Maxwell-Boltzmann averaged -factors were calculated according to the table values of the reaction rates. Then the -factors were approximated with the 3 order spline-function. The necessity of the account of electron shielding and intramolecular movement at low temperatures is discussed (orig.)

  9. Nuclear astrophysics

    International Nuclear Information System (INIS)

    Lehoucq, Roland; Klotz, Gregory

    2015-11-01

    Astronomy deals with the position and observation of the objects in our Universe, from planets to galaxies. It is the oldest of the sciences. Astrophysics is the study of the physical properties of these objects. It dates from the start of the 20. century. Nuclear astrophysics is the marriage of nuclear physics, a laboratory science concerned with the infinitely small, and astrophysics, the science of what is far away and infinitely large. Its aim is to explain the origin, evolution and abundance of the elements in the Universe. It was born in 1938 with the work of Hans Bethe, an American physicist who won the Nobel Prize for physics in 1967, on the nuclear reactions that can occur at the center of stars. It explains where the incredible energy of the stars and the Sun comes from and enables us to understand how they are born, live and die. The matter all around us and from which we are made, is made up of ninety-two chemical elements that can be found in every corner of the Universe. Nuclear astrophysics explains the origin of these chemical elements by nucleosynthesis, which is the synthesis of atomic nuclei in different astrophysical environments such as stars. Nuclear astrophysics provides answers to fundamental questions: - Our Sun and the stars in general shine because nuclear reactions are taking place within them. - The stars follow a sequence of nuclear reaction cycles. Nucleosynthesis in the stars enables us to explain the origin and abundance of elements essential to life, such as carbon, oxygen, nitrogen and iron. - Star explosions, in the form of supernovae, disperse the nuclei formed by nucleosynthesis into space and explain the formation of the heaviest chemical elements such as gold, platinum and lead. Nuclear astrophysics is still a growing area of science. (authors)

  10. Back Reaction And Local Cosmological Expansion Rate

    CERN Document Server

    Geshnizjani, G; Geshnizjani, Ghazal; Brandenberger, Robert

    2002-01-01

    We calculate the back reaction of cosmological perturbations on a general relativistic variable which measures the local expansion rate of the Universe. Specifically, we consider a cosmological model in which matter is described by a single field. We analyze back reaction both in a matter dominated Universe and in a phase of scalar field-driven chaotic inflation. In both cases, we find that the leading infrared terms contributing to the back reaction vanish when the local expansion rate is measured at a fixed value of the matter field which is used as a clock, whereas they do not appear to vanish if the expansion rate is evaluated at a fixed value of the background time. We discuss possible implications for more realistic models with a more complicated matter sector.

  11. Effective dynamics along given reaction coordinates, and reaction rate theory.

    Science.gov (United States)

    Zhang, Wei; Hartmann, Carsten; Schütte, Christof

    2016-12-22

    In molecular dynamics and related fields one considers dynamical descriptions of complex systems in full (atomic) detail. In order to reduce the overwhelming complexity of realistic systems (high dimension, large timescale spread, limited computational resources) the projection of the full dynamics onto some reaction coordinates is examined in order to extract statistical information like free energies or reaction rates. In this context, the effective dynamics that is induced by the full dynamics on the reaction coordinate space has attracted considerable attention in the literature. In this article, we contribute to this discussion: we first show that if we start with an ergodic diffusion process whose invariant measure is unique then these properties are inherited by the effective dynamics. Then, we give equations for the effective dynamics, discuss whether the dominant timescales and reaction rates inferred from the effective dynamics are accurate approximations of such quantities for the full dynamics, and compare our findings to results from approaches like Mori-Zwanzig, averaging, or homogenization. Finally, by discussing the algorithmic realization of the effective dynamics, we demonstrate that recent algorithmic techniques like the "equation-free" approach and the "heterogeneous multiscale method" can be seen as special cases of our approach.

  12. The 152Sm(p,n) reaction and its astrophysical importance

    International Nuclear Information System (INIS)

    Pohl, Moritz

    2014-01-01

    Within the nucleosynthetic processes of the slow neutron-capture reaction network (called the s process) the so called branching points, unstable isotopes where different nuclear reactions are competing, are important to understand. For modeling and calculating the nucleosynthesis and compare the resulting abundances to the observed ones, it is indispensable to know the branching ratios as well as the corresponding cross sections. A great challenge in measuring those rates in experiments may be the radioactivity of the isotopes involved, which can make it nearly impossible to manufacture the needed targets. In addition, in stellar environments the excited states of isotopes can be in equilibrium with the ground state, affecting the half-lives and the branching ratios significantly. The isotope 152 Eu is such a branching point, with neutron captures and β-decays competing. Those challenges were approached in the s405 experiment performed at the GSI Helmholtzzentrum fuer Schwerionenforschung GmbH: the challenge the challenge of the radioactivity can be approached by experiments carried out in inverse kinematics with radioactive beams, solving the problem of unstable targets. Also a reversed reaction was used to access the excited states of the studied isotope. The performed 152 Sm(p,n) 152 Eu is a pioneering attempt to use those methods on heavy ions. The (p,n) reaction was used as a substitute for electron capture, the focus lies on reactions with low-momentum transfers, resulting in the emission of low-energy neutrons. The new developed low-energy detector array LENA was put to test for the fist time in the s405 experiment.

  13. Few-Body Problems in Experimental Nuclear Astrophysics

    DEFF Research Database (Denmark)

    Fynbo, H.O.U.

    2013-01-01

    The 3α-reaction is one of the key reactions in nuclear astrophysics. Since it is a three-body reaction direct measurement is impossible, and therefore the reaction rate must be estimated theoretically. In this contribution I will discuss uncertainties in this reaction rate both at very low...

  14. Nuclear transfer reaction measurements at the ESR—for the investigation of the astrophysical 15O(α,γ)19Ne reaction

    International Nuclear Information System (INIS)

    Doherty, D T; Woods, P J; Davinson, T; Estrade, A; Lotay, G; Litvinov, Yu A; Brandau, C; Dillmann, I; Egelhof, P; Evdokimov, A; Gumberidze, A; Heil, M; Litvinov, S A; Kiselev, O; Najafi, M Ali; Bagchi, S; Kalantar-Nayestanaki, N; Bishop, S; Bo, M; Lederer, C

    2015-01-01

    Astrophysical x-ray bursts are thought to be a result of thermonuclear explosions on the atmosphere of an accreting neutron star. Between these bursts, energy is thought to be generated by the hot CNO cycles. The 15 O(α,γ) 19 Ne reaction is one reaction that allows breakout from these CNO cycles and into the rp-process to fuel outbursts. The reaction is expected to be dominated by a single 3/2 + resonance at 4.033 MeV in 19 Ne, however, limited information is available on this key state. This work reports on a pioneering study of the 20 Ne(p,d) 19 Ne reaction, performed in inverse kinematics at the experimental storage ring (ESR) as a means of accessing the astrophysically important 4.033 MeV state in 19 Ne. The unique, background free, high luminosity conditions of the storage ring were utilized for this, the first transfer reaction performed at the ESR. The results of this pioneering test experiment are presented along with suggestions for future measurements at storage ring facilities. (paper)

  15. Cross section of α-induced reactions on iridium isotopes obtained from thick target yield measurement for the astrophysical γ process

    Directory of Open Access Journals (Sweden)

    T. Szücs

    2018-01-01

    Full Text Available The stellar reaction rates of radiative α-capture reactions on heavy isotopes are of crucial importance for the γ process network calculations. These rates are usually derived from statistical model calculations, which need to be validated, but the experimental database is very scarce. This paper presents the results of α-induced reaction cross section measurements on iridium isotopes carried out at first close to the astrophysically relevant energy region. Thick target yields of 191Ir(α,γ195Au, 191Ir(α,n194Au, 193Ir(α,n196mAu, 193Ir(α,n196Au reactions have been measured with the activation technique between Eα=13.4 MeV and 17 MeV. For the first time the thick target yield was determined with X-ray counting. This led to a previously unprecedented sensitivity. From the measured thick target yields, reaction cross sections are derived and compared with statistical model calculations. The recently suggested energy-dependent modification of the α+nucleus optical potential gives a good description of the experimental data.

  16. Nuclear reactions in AGB nucleosynthesis: the 19F(α, p22Ne at energies of astrophysical relevance

    Directory of Open Access Journals (Sweden)

    D’Agata G.

    2017-01-01

    Full Text Available The abundance of 19F in the universe is strictly related to standard and extra-mixing processes taking place inside AGB-stars, that are considered to be the most important sites for its production. Nevertheless the way in which it is destroyed is far from being well understood. For this reason we studied the 19F(α,p22Ne reaction, that is supposed to be the main destruction channel in the Helium-rich part of the star. In this experiment, the reaction has been studied in the energy range of relevance for astrophysics (0÷1 MeV via the Trojan Horse Method (THM, using the three-body reaction 6Li(19F,p22Ned.

  17. Measurement of the 13C(α,n)16O reaction at astrophysical energies using the Trojan Horse Method. Focus on the -3 keV subthreshold resonance

    International Nuclear Information System (INIS)

    La Cognata, M.; Spitaleri, C.; Guardo, G.L.; Puglia, S.M.R.; Romano, S.; Sparta, R.; Trippella, O.; Kiss, G.G.; Rogachev, G.V.; Avila, M.; Koshchiy, E.; Kuchera, A.; Santiago, D.; Mukhamedzhanov, A.M.; Lamia, L.

    2014-01-01

    Most of the nuclei in the mass range 90 ≤ A ≤ 208 are produced through the so-called s-process, namely through a series of neutron capture reactions on seed nuclei followed by β-decays. The 13 C(α,n) 16 O reaction is the neutron source for the main component of the s-process. It is active inside the helium-burning shell of asymptotic giant branch stars, at temperatures ≤ 10 8 K, corresponding to an energy interval of 140 - 230 keV. In this region, the astrophysical S (E)-factor is dominated by the -3 keV sub-threshold resonance due to the 6.356 MeV level in 17 O. Direct measurements could not soundly establish its contribution owing to the cross section suppression at astrophysical energies determined by the Coulomb barrier between interacting nuclei. Indirect measurements and extrapolations yielded inconsistent results, calling for further investigations. The Trojan Horse Method turns out to be very suited for the study of the 13 C(α,n) 16 O reaction as it allows us to access the low as well as the negative energy region, in particular in the case of resonance reactions. We have applied the Trojan Horse Method to the 13 C( 6 Li; n 16 O)d quasi-free reaction. By using the modified R-matrix approach, the asymptotic normalization coefficient (C(O(1/2+),α 13 C)] 2 of the 6.356 MeV level has been deduced as well as the n-partial width, allowing to attain an unprecedented accuracy for the 13 C(α,n) 16 O astrophysical factor. A preliminary analysis of a partial data set has lead to (C(O(1/2+),α 13 C)] 2 = (6.7-0.6+0.9) fm -1 , slightly larger than the values in the literature, determining a 13 C(α,n) 16 O reaction rate in agreement with the most results in the literature at ∼ 10 8 K, with enhanced accuracy thanks to this innovative approach. (authors)

  18. Neutron Capture Reactions on Fe and Ni Isotopes for the Astrophysical s-process

    Energy Technology Data Exchange (ETDEWEB)

    Lederer, C., E-mail: claudia.lederer@ed.ac.uk [University of Vienna, Faculty of Physics, 1090 Vienna (Austria); Johann-Wolfgang-Goethe Universität, 60438 Frankfurt (Germany); Giubrone, G. [Instituto de Física Corpuscular, CSIC-Universidad de Valencia, 46071 Valencia (Spain); Massimi, C. [Dipartimento di Fisica, Università di Bologna, and Sezione INFN di Bologna, 40100 Bologna (Italy); Žugec, P. [Department of Physics, Faculty of Science, University of Zagreb, 10002 Zagreb (Croatia); Barbagallo, M.; Colonna, N. [Istituto Nazionale di Fisica Nucleare, 70125 Bari (Italy); Domingo-Pardo, C. [Instituto de Física Corpuscular, CSIC-Universidad de Valencia, 46071 Valencia (Spain); Guerrero, C. [European Organization for Nuclear Research (CERN), CH-1211 Geneva (Switzerland); Gunsing, F. [Commissariat à l' Énergie Atomique (CEA) Saclay – Irfu, 91191 Gif-sur-Yvette (France); Käppeler, F. [Karlsruhe Institute of Technology, Campus Nord, Institut für Kernphysik, 76021 Karlsruhe (Germany); Tain, J.L. [Instituto de Física Corpuscular, CSIC-Universidad de Valencia, 46071 Valencia (Spain); Altstadt, S. [Johann-Wolfgang-Goethe Universität, 60438 Frankfurt (Germany); Andrzejewski, J. [Uniwersytet Łódzki, 90131 Lodz (Poland); Audouin, L. [Centre National de la Recherche Scientifique/IN2P3 – IPN, 91406 Orsay (France); Bécares, V. [Centro de Investigaciones Energeticas Medioambientales y Tecnológicas (CIEMAT), 28040 Madrid (Spain); Bečvář, F. [Faculty of Mathematics and Physics, Charles University, CZ-180 00 Prague (Czech Republic); and others

    2014-06-15

    Neutron capture cross sections in the keV neutron energy region are the key nuclear physics input to study the astrophysical slow neutron capture process. In the past years, a series of neutron capture cross section measurements has been performed at the neutron time-of-flight facility n{sub T}OF at CERN focussing on the Fe/Ni mass region. Recent results and future developments in the neutron time-of-flight technique are discussed.

  19. Pycnonuclear reaction rates for binary ionic mixtures

    Science.gov (United States)

    Ichimaru, S.; Ogata, S.; Van Horn, H. M.

    1992-01-01

    Through a combination of compositional scaling arguments and examinations of Monte Carlo simulation results for the interparticle separations in binary-ionic mixture (BIM) solids, we have derived parameterized expressions for the BIM pycnonuclear rates as generalizations of those in one-component solids obtained previously by Salpeter and Van Horn and by Ogata et al. We have thereby discovered a catalyzing effect of the heavier elements, which enhances the rates of reactions among the lighter elements when the charge ratio exceeds a critical value of approximately 2.3.

  20. Experimental study of the 6Li(d,α)4He reaction and its astrophysical implications via the Trojan Horse Method

    International Nuclear Information System (INIS)

    Pizzone, R.G.; Aliotta, M.; Pellegriti, M.G.; Spitaleri, C.; Blagus, S.; Milin, M.; Miljanic, D.; Rendic, D.; Soic, N.; Zadro, M.; Cherubini, S.; Figuera, P.; Romano, S.; Lattuada, M.; Zappala, R. A.

    2000-01-01

    The 6 Li(d,α) 4 He reaction, whose astrophysical importance is connected to the primordial nucleosynthesis in the framework of the Inhomogeneous Big Bang, has been studied by using the Trojan Horse Method (THM). We derive and discuss the cross section and the astrophysical S(E)-factor for E cm =0.025-0.7 MeV. Results are compared with data from a direct measurement

  1. Rate coefficient for the reaction N + NO

    Science.gov (United States)

    Fox, J. L.

    1994-01-01

    Evidence has been advanced that the rate coefficient for the reaction N + NO right arrow N2 + O has a small positive temperature dependence at the high temperatures (900 to 1500 K) that prevail in the terrestrial middle and upper thermosphere by Siskind and Rusch (1992), and at the low temperatures (100 to 200 K) of the Martian lower thermosphere by Fox (1993). Assuming that the rate coefficient recommended by the Jet Propulsion Laboratory evaluation (DeMore et al., 1992) is accurate at 300 K, we derive here the low temperature value of the activation energy for this reaction and thus the rate coefficient that best fits the Viking 1 measured NO densities. We find that the fit is acceptable for a rate coefficient of about 1.3 x 10(exp -10)(T/300)(exp 0.5)exp(-400/T) and better for a value of about 2.5 x 10(exp -10)(T/300)(exp 0.5)exp(-600/T)cu cm/s.

  2. Indirect methods in nuclear astrophysics

    International Nuclear Information System (INIS)

    Bertulani, C.A.; Shubhchintak; Mukhamedzhanov, A.; Kadyrov, A. S.; Kruppa, A.; Pang, D. Y.

    2016-01-01

    We discuss recent developments in indirect methods used in nuclear astrophysics to determine the capture cross sections and subsequent rates of various stellar burning processes, when it is difficult to perform the corresponding direct measurements. We discuss in brief, the basic concepts of Asymptotic Normalization Coefficients, the Trojan Horse Method, the Coulomb Dissociation Method, (d,p), and charge-exchange reactions. (paper)

  3. Nuclear reaction rates and the nova outburst

    International Nuclear Information System (INIS)

    Starrfield, S.G.; Iliadis, C.

    2000-01-01

    In this paper we examined the consequences of improving the nuclear reaction library on our simulations of TNRs on 1.25M, WD and 1.35M, WDS. We have found that the changes in the rates have affected the nucleosynthesis predictions of our calculations but not, to any great extent, the gross features. In addition, we have used a lower mass accretion rate than in our previous studies in order to accrete (and eject) more material. This has, as expected, caused the peak values of some important parameters to increase over our previous studies at the same WD mass. However, because some important reaction rates have declined in the new compilation this has not increased the abundances for nuclei above aluminum and, in fact, they have declined while the abundances of both 26 Al and 27 Al have increased at both WD masses. In contrast, the abundance of 22 Na has declined at both WD masses over the values predicted in our earlier work. This has important implications with respect to predictions of the observability of novae with INTEGRAL

  4. Reaction rate calculations via transmission coefficients

    International Nuclear Information System (INIS)

    Feit, M.D.; Alder, B.J.

    1985-01-01

    The transmission coefficient of a wavepacket traversing a potential barrier can be determined by steady state calculations carried out in imaginary time instead of by real time dynamical calculations. The general argument is verified for the Eckart barrier potential by a comparison of transmission coefficients calculated from real and imaginary time solutions of the Schroedinger equation. The correspondence demonstrated here allows a formulation for the reaction rate that avoids difficulties due to both rare events and explicitly time dependent calculations. 5 refs., 2 figs

  5. Investigations of astrophysically interesting nuclear reactions by the use of gas target techniques

    Energy Technology Data Exchange (ETDEWEB)

    Hammer, J W [Inst. fuer Strahlenphysik, Univ. Stuttgart, Stuttgart (Germany)

    1998-06-01

    A brief review of the common properties of windowless and recirculating gas targets is presented. As example the Stuttgart gas target facility Rhinoceros in the extended and in the supersonic jet mode with its properties and techniques is explained, also with respect to gas purification techniques. Furthermore several typical experiments from the field of nuclear astrophysics with characteristic results are described (D({alpha},{gamma}){sup 6}Li, {sup 15}N({alpha},{gamma}){sup 19}F, {sup 16}O(p,{gamma}){sup 17}F, {sup 16}O({alpha},{gamma}){sup 20}Ne, {sup 20}Ne({alpha},{gamma}){sup 24}Mg, {sup 21}Ne({alpha},n){sup 24}Mg, {sup 18}O({alpha},n){sup 21}Ne, {sup 17}O({alpha},n){sup 20}Ne). In several cases the experimental sensitivity could be raised by up to a factor of 10{sup 6}. (orig.)

  6. Trojin horse method for indirect measurement of astrophysic S factor

    International Nuclear Information System (INIS)

    Fu Yuanyong; Zhou Shuhua; Li Chengbo; Wen Qungang

    2014-01-01

    The nuclear reaction rates in the astrophysical environment are indispensable input parameters in different astrophysics theories, and play important roles in understanding the astrophysical nuclear synthesis and the evolution of the universe. However, at the astrophysical temperature, the nuclear reactions proceed at very low energies. Due to the Coulomb barrier the reaction cross sections are very small, so that the direct measurement is almost impossible. The Trojin horse theory provides a useful method to measure indirectly the low energy two body cross sections by measuring the suitable three body reactions. Some approximations are applied in the theory to get convenient formula. This paper introduces the Trojin horse theory and its application in astrophysics nuclear reactions. (authors)

  7. Measurement of the d({sup 26}Al{sup m},p){sup 27}Al reaction for nuclear astrophysics

    Energy Technology Data Exchange (ETDEWEB)

    Roeder, B.T.; Trache, L.; Iacob, V.E.; McCleskey, M.; Simmons, E.; Spiridon, A.; Tribble, R.E. [Texas A and M Univ., TX (United States); Davinson, T.; Lotay, G.; Woods, P.J. [University of Edinburgh (United Kingdom); La Cognata, M.; Pizzone, R.G.; Rapisarda, G.G.; Sparta, R.; Spitaleri, C. [Istituto Nazionale di Fisica Nucleare (LNS/INFN), Catania (Italy). Lab. Nazionali del Sud

    2012-07-01

    Full text: The detection of gamma rays from the decay of the {sup 26}Al ground state in the galaxy gives evidence that nucleosynthesis is occurring in present-day stars, but its origin is not yet clear. This implies that reactions involving {sup 26}Al are important for astrophysical processes. In a recent experiment at the Cyclotron Institute at Texas A and M University, reactions with the ground state and isomeric state of {sup 26}Al were investigated with the Texas A and M-Edinburgh-Catania Silicon detector Array (TECSA). TECSA is a collaborative effort to build a high-efficiency detector Si array useful for measuring reactions of interest for nuclear astrophysics and nuclear structure. The array consists of up to 16 Micron Semiconductor YY1 detectors that are each 300 μm thick. Each detector has 16 annular ring sectors to measure the energy and the scattering angle of the detected particles. Using TECSA, we measured d({sup 26}Al{sup g},p){sup 27}Al and d({sup 26}Al{sup m},p){sup 27}Al with a {sup 26}Al secondary beam prepared in-flight with the MARS spectrometer. First, the composition of the {sup 26}Al beam was determined by measuring the ratio of beta-decays to {sup 26}Al ions produced. It was found that at different spectrometer rigidities, beams of 2/3 isomer to ground state ratio or vice-versa could be obtained. Then, in the second part of the experiment, angular distributions were measured for both reactions at backward angles with TECSA. The protons were measured in TECSA in coincidence with timing signals from the beam detected by a scintillator and with the cyclotron radio-frequency. Details of the experiment and preliminary results from the analysis of the d({sup 26}Al{sup m},p){sup 27}Al and d({sup 26}Al{sup g},p){sup 27}Al data will be presented. They will give information about the proton capture reactions {sup 26}Al{sup m}(p,γ){sup 27}Si and {sup 26}Al{sup g}(p,γ){sup 27}Si taking place in stars. (author)

  8. Recent results in nuclear astrophysics

    Energy Technology Data Exchange (ETDEWEB)

    Coc, Alain; Kiener, Juergen [CNRS/IN2P3 et Universite Paris Sud 11, UMR 8609, Centre de Sciences Nucleaires et de Sciences de la Matiere (CSNSM), Orsay Campus (France); Hammache, Fairouz [CNRS/IN2P3 et Universite Paris Sud 11, UMR 8608, Institut de Physique Nucleaire d' Orsay (IPNO), Orsay Campus (France)

    2015-03-01

    In this review, we emphasize the interplay between astrophysical observations, modeling, and nuclear physics laboratory experiments. Several important nuclear cross sections for astrophysics have long been identified, e.g., {sup 12}C(α, γ){sup 16}O for stellar evolution, or {sup 13}C(α, n){sup 16}O and {sup 22}Ne(α, n){sup 25}Mg as neutron sources for the s-process. More recently, observations of lithium abundances in the oldest stars, or of nuclear gamma-ray lines from space, have required new laboratory experiments. New evaluation of thermonuclear reaction rates now includes the associated rate uncertainties that are used in astrophysical models to i) estimate final uncertainties on nucleosynthesis yields and ii) identify those reactions that require further experimental investigation. Sometimes direct cross section measurements are possible, but more generally the use of indirect methods is compulsory in view of the very low cross sections. Non-thermal processes are often overlooked but are also important for nuclear astrophysics, e.g., in gamma-ray emission from solar flares or in the interaction of cosmic rays with matter, and also motivate laboratory experiments. Finally, we show that beyond the historical motivations of nuclear astrophysics, understanding i) the energy sources that drive stellar evolution and ii) the origin of the elements can also be used to give new insights into physics beyond the standard model. (orig.)

  9. Recent results in nuclear astrophysics

    International Nuclear Information System (INIS)

    Coc, Alain; Kiener, Juergen; Hammache, Fairouz

    2015-01-01

    In this review, we emphasize the interplay between astrophysical observations, modeling, and nuclear physics laboratory experiments. Several important nuclear cross sections for astrophysics have long been identified, e.g., 12 C(α, γ) 16 O for stellar evolution, or 13 C(α, n) 16 O and 22 Ne(α, n) 25 Mg as neutron sources for the s-process. More recently, observations of lithium abundances in the oldest stars, or of nuclear gamma-ray lines from space, have required new laboratory experiments. New evaluation of thermonuclear reaction rates now includes the associated rate uncertainties that are used in astrophysical models to i) estimate final uncertainties on nucleosynthesis yields and ii) identify those reactions that require further experimental investigation. Sometimes direct cross section measurements are possible, but more generally the use of indirect methods is compulsory in view of the very low cross sections. Non-thermal processes are often overlooked but are also important for nuclear astrophysics, e.g., in gamma-ray emission from solar flares or in the interaction of cosmic rays with matter, and also motivate laboratory experiments. Finally, we show that beyond the historical motivations of nuclear astrophysics, understanding i) the energy sources that drive stellar evolution and ii) the origin of the elements can also be used to give new insights into physics beyond the standard model. (orig.)

  10. Astrophysical S-factor for destructive reactions of lithium-7 in big bang nucleosynthesis

    Energy Technology Data Exchange (ETDEWEB)

    Komatsubara, Tetsuro; Kwon, YoungKwan; Moon, JunYoung; Kim, Yong-Kyun [Rare Isotope Science Project, Institute for Basic Science, Daejeon (Korea, Republic of); Moon, Chang-Bum [Hoseo University, Asan, Chungnam (Korea, Republic of); Ozawa, Akira; Sasa, Kimikazu; Onishi, Takahiro; Yuasa, Toshiaki; Okada, Shunsuke; Saito, Yuta [Division of Physics, University of Tsukuba, Tsukuba, Ibaraki (Japan); Hayakawa, Takehito; Shizuma, Toshiyuki [Japan Atomic Energy Agency, Shirakata Shirane, Tokai, Ibaraki (Japan); Kubono, Shigeru [RIKEN, Hirosawa, Wako, Saitama (Japan); Kusakabe, Motohiko [School of Liberal Arts and Science, Korea Aerospace University (Korea, Republic of); Kajino, Toshitaka [National Astronomical Observatory, Osawa, Mitaka, Tokyo (Japan)

    2014-05-02

    One of the most prominent success with the Big Bang models is the precise reproduction of mass abundance ratio for {sup 4}He. In spite of the success, abundances of lithium isotopes are still inconsistent between observations and their calculated results, which is known as lithium abundance problem. Since the calculations were based on the experimental reaction data together with theoretical estimations, more precise experimental measurements may improve the knowledge of the Big Bang nucleosynthesis. As one of the destruction process of lithium-7, we have performed measurements for the reaction cross sections of the {sup 7}L({sup 3}He,p){sup 9}Be reaction.

  11. Astrophysical neutron capture rates in s- and r-process nucleosynthesis

    International Nuclear Information System (INIS)

    Beer, H.; Mohr, P.; Oberhummer, H.; Rauscher, T.; Mutti, P.; Corvi, F.; Sedyshev, P.V.; Popov, Yu.P.

    1997-01-01

    The astrophysical neutron capture rates of light and heavy nuclei are measured and calculated. The measurements are realized using the activation technique at the 3.75 MV Karlsruhe Van de Graaff accelerator and by means of the time-of-flight method at the Geel electron linear accelerator (GELINA). The setup for the fast cyclic activation measurements made on 26 Mg and 48 Ca, as well as on Pt isotopes is described. The time-of-flight method is used for neutron capture measurements of the bottleneck isotopes 138 Ba and 208 Pb. The calculations are made using direct and compound nuclear capture models. The s-process nucleosynthesis path in the Os and Pt mass region is discussed in details. It is shown that for 19 '1 Os, 192 Ir and 193 Pt there is a competition between β-decay and neutron capture. The β-decay half-lives are dependent on temperature and electron density of the s-process environment. The abundance of s-only 192 Pt originates from the branching at 191 Os and 192 Ir. The isotopes 190 Pt and 198 Pt are not on the s-process path, therefore the seed abundance vanish during nucleosynthesis. Calculations are carried out using parametrized models in order to reproduce the s-process abundance in the mass region from Os up to Pt. The neutron density is adjusted to reproduce the solar abundance of the s-only isotope 9 2 Pt in the analysis of the present branching especially

  12. Astrophysical S-factor of the 32He(α,γ) 733 7Be reaction in the Big-Bang nucleosynthesis

    Science.gov (United States)

    Ghamary, Motahareh; Sadeghi, Hossein; Mohammadi, Saeed

    2018-05-01

    In the present work, we have studied the properties of the 23He(α , γ) 47Be reaction. The direct radiative capture nuclear reactions in the Big-Bang nucleosynthesis mainly, are done in the external areas of inter-nuclear interaction range and play an essential role in nuclear astrophysics. Among of these reactions, the 23He(α , γ) 47Be reaction with Q = 1.586 MeV is the main part of the Big-Bang nucleosynthesis chain reactions. This reaction can be used to understand the physical and chemical properties of the sun as well as can be justified the lake of the observed solar neutrino in the detector of the Earth. Since product neutrino fluxes are predicated in the center of the sun by the decay of 7Be and 8B, and almost are proportional to the astrophysical S-factor for the 23He(α , γ) 47Be reaction, S34. The 23He(α , γ) 47Be reaction is considered the key to solve the solar neutrino puzzle. Finally, we have astrophysical S-factor obtained for the ground S1,3/2-, first excited S1,1/2-and total S34 states by modern nucleon-nucleon two-body local potential models. We have also compared the obtained S-factor with experimental data and other theoretical works.

  13. Determination by transfer reaction of alpha widths in fluorine for astrophysical interest; Determination par reaction de transfert de largeurs alpha dans le fluor 19. Applications a l'astrophysique

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira Santos, F. de

    1995-04-15

    The nucleosynthesis of fluorine is not known. Several astrophysical models predict the alpha radiative capture onto N{sup 15} as the main fluorine production reaction. In the expression of the reaction rate, one parameter is missing: the alpha width of the resonance on the E = 4.377 MeV level in fluorine. A direct measurement is excluded due to the very low cross-section expected. We have determined this alpha width using a transfer reaction followed by analyses with FR-DWBA (Finite Range Distorted Wave Born Approximation) in a simple cluster alpha model. This experiment was carried out with a Li{sup 7} beam with E = 28 MeV onto a N{sup 15} gas target. The 16 first levels were studied. Spectroscopic factors were extracted for most of them. Alpha widths for unbound levels were determined. Many alpha width were compared with known values from direct reaction and the differences lie within the uncertainty range (factor 2). The alpha width for the E = 4.377 MeV level was determined ({gamma}{sub {alpha}} = 1.5*10{sup -15} MeV), its value is about 60 times weaker than the used value. The influence of our new rate was studied in AGB (Asymptotic Giant Branch) stars during thermal pulses. In this model the alteration is sensitive. (author)

  14. Determination by transfer reaction of alpha widths in fluorine for astrophysical interest; Determination par reaction de transfert de largeurs alpha dans le fluor 19. Applications a l'astrophysique

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira Santos, F de

    1995-04-15

    The nucleosynthesis of fluorine is not known. Several astrophysical models predict the alpha radiative capture onto N{sup 15} as the main fluorine production reaction. In the expression of the reaction rate, one parameter is missing: the alpha width of the resonance on the E = 4.377 MeV level in fluorine. A direct measurement is excluded due to the very low cross-section expected. We have determined this alpha width using a transfer reaction followed by analyses with FR-DWBA (Finite Range Distorted Wave Born Approximation) in a simple cluster alpha model. This experiment was carried out with a Li{sup 7} beam with E = 28 MeV onto a N{sup 15} gas target. The 16 first levels were studied. Spectroscopic factors were extracted for most of them. Alpha widths for unbound levels were determined. Many alpha width were compared with known values from direct reaction and the differences lie within the uncertainty range (factor 2). The alpha width for the E = 4.377 MeV level was determined ({gamma}{sub {alpha}} = 1.5*10{sup -15} MeV), its value is about 60 times weaker than the used value. The influence of our new rate was studied in AGB (Asymptotic Giant Branch) stars during thermal pulses. In this model the alteration is sensitive. (author)

  15. Study of the reaction of astrophysical interest 60Fe(n,γ)61Fe via (d,pγ) transfer reaction

    International Nuclear Information System (INIS)

    Giron, S.

    2011-12-01

    60 Fe is of special interest in nuclear astrophysics. Indeed the recent observations of 60 Fe characteristic gamma-ray lines by the RHESSI and INTEGRAL spacecrafts allowed to measure the total flux of 60 Fe over the Galaxy. Moreover the observation in presolar grains of an excess of the daughter-nuclei of 60 Fe, 60 Ni, gives constraints on the conditions of formation of the early solar system. However, the cross-sections of some reactions involved in 60 Fe nucleosynthesis and included to stellar models are still uncertain. The destruction reaction of 60 Fe, 60 Fe(n, γ) 61 Fe, is one of them. The total cross-section can be separate into two contributions: the direct one, involving states below the neutron separation threshold of 61 Fe, and the resonant one.We improved 61 Fe spectroscopy in order to evaluate the direct capture part of the 60 Fe(n, γ) 61 Fe reaction cross-section. 60 Fe(n, γ) 61 Fe was thus studied via d( 60 Fe, pγ) 61 Fe transfer reaction with the CATS/MUST2/EXOGAM setup at LISE-GANIL. DWBA analysis of experimental proton differential cross-sections allowed to extract orbital angular momentum and spectroscopic factors of different populated states identified below the neutron threshold. A comparison of experimental results for 61 Fe with experimental results for similar nuclei and with shell-model calculations was also performed. (author) [fr

  16. Visible light photon counters (VLPCs) for high rate tracking medical imaging and particle astrophysics

    International Nuclear Information System (INIS)

    Atac, M.

    1998-02-01

    This paper is on the operation principles of the Visible Light Photon Counters (VLPCs), application to high luminosity-high multiplicity tracking for High Energy Charged Particle Physics, and application to Medical Imaging and Particle Astrophysics. The VLPCs as Solid State Photomultipliers (SSPMS) with high quantum efficiency can detect down to single photons very efficiently with excellent time resolution and high avalanche gains

  17. Effect of excited states on thermonuclear reaction rates

    International Nuclear Information System (INIS)

    Sargood, D.G.

    1983-01-01

    Values of the ratio of the thermonuclear reaction rate of a reaction, with target nuclei in a thermal distribution of energy states, to the reaction rate with all target nuclei in their ground states are tabulated for neutron, proton and α-particle induced reactions on the naturally occurring nuclei from 20 Ne to 70 Zn, at temperatures of 1, 2, 3.5 and 5x10 9 K. The ratios are determined from reaction rates based on statistical model cross sections

  18. Global transmission coefficients in Hauser-Feshbach calculations for astrophysics

    Energy Technology Data Exchange (ETDEWEB)

    Rauscher, T [Inst. fuer Physik, Univ. Basel, Basel (Switzerland)

    1998-06-01

    The current status of optical potentials employed in the prediction of thermonuclear reaction rates for astrophysics in the Hauser-Feshbach formalism is discussed. Special emphasis is put on {alpha}+nucleus potentials. Further experimental efforts are motivated. (orig.)

  19. Representing Rate Equations for Enzyme-Catalyzed Reactions

    Science.gov (United States)

    Ault, Addison

    2011-01-01

    Rate equations for enzyme-catalyzed reactions are derived and presented in a way that makes it easier for the nonspecialist to see how the rate of an enzyme-catalyzed reaction depends upon kinetic constants and concentrations. This is done with distribution equations that show how the rate of the reaction depends upon the relative quantities of…

  20. Neutron Energy Spectra and Yields from the 7Li(p,n) Reaction for Nuclear Astrophysics

    Science.gov (United States)

    Tessler, M.; Friedman, M.; Schmidt, S.; Shor, A.; Berkovits, D.; Cohen, D.; Feinberg, G.; Fiebiger, S.; Krása, A.; Paul, M.; Plag, R.; Plompen, A.; Reifarth, R.

    2016-01-01

    Neutrons produced by the 7Li(p, n)7Be reaction close to threshold are widely used to measure the cross section of s-process nucleosynthesis reactions. While experiments have been performed so far with Van de Graaff accelerators, the use of RF accelerators with higher intensities is planned to enable investigations on radioactive isotopes. In parallel, high-power Li targets for the production of high-intensity neutrons at stellar energies are developed at Goethe University (Frankfurt, Germany) and SARAF (Soreq NRC, Israel). However, such setups pose severe challenges for the measurement of the proton beam intensity or the neutron fluence. In order to develop appropriate methods, we studied in detail the neutron energy distribution and intensity produced by the thick-target 7Li(p,n)7Be reaction and compared them to state-of- the-art simulation codes. Measurements were performed with the bunched and chopped proton beam at the Van de Graaff facility of the Institute for Reference Materials and Measurements (IRMM) using the time-of-flight (TOF) technique with thin (1/8") and thick (1") detectors. The importance of detailed simulations of the detector structure and geometry for the conversion of TOF to a neutron energy is stressed. The measured neutron spectra are consistent with those previously reported and agree well with Monte Carlo simulations that include experimentally determined 7Li(p,n) cross sections, two-body kinematics and proton energy loss in the Li-target.

  1. New astrophysical S factor for the 15N(p,γ)16O reaction via the asymptotic normalization coefficient (ANC) method

    International Nuclear Information System (INIS)

    Mukhamedzhanov, A. M.; Gagliardi, C. A.; Goldberg, V. Z.; Plunkett, A.; Trache, L.; Tribble, R. E.; Bem, P.; Burjan, V.; Hons, Z.; Kroha, V.; Mrazek, J.; Novak, J.; Piskor, S.; Simeckova, E.; Vesely, F.; Vincour, J.; La Cognata, M.; Pizzone, R. G.; Romano, S.; Spitaleri, C.

    2008-01-01

    The 15 N(p,γ) 16 O reaction provides a path from the CN cycle to the CNO bi-cycle and CNO tri-cycle. The measured astrophysical factor for this reaction is dominated by resonant capture through two strong J π =1 - resonances at E R =312 and 962 keV and direct capture to the ground state. Asymptotic normalization coefficients (ANCs) for the ground and seven excited states in 16 O were extracted from the comparison of experimental differential cross sections for the 15 N( 3 He,d) 16 O reaction with distorted-wave Born approximation calculations. Using these ANCs and proton and α resonance widths determined from an R-matrix fit to the data from the 15 N(p,α) 12 C reaction, we carried out an R-matrix calculation to obtain the astrophysical factor for the 15 N(p,γ) 16 O reaction. The results indicate that the direct capture contribution was previously overestimated. We find the astrophysical factor to be S(0)=36.0±6.0 keV b, which is about a factor of 2 lower than the presently accepted value. We conclude that for every 2200±300 cycles of the main CN cycle one CN catalyst is lost due to this reaction

  2. Direct projectile break up its relation to the astrophysically revelant fusion reactions

    International Nuclear Information System (INIS)

    Bertulani, C.A.; Hussein, M.S.

    1990-05-01

    The break-up into two pieces of weakly bound nuclei passing by the Coulomb field of a large Z nucleus can provide useful information on the inverse fusion reactions which are important for the elemental formation in the stars. However, the nuclear interaction complicates considerably the extraction of such information. A study is made of the contributions of the Coulomb and nuclear interaction to the process, showing when the Coulomb break-up prevails and how a reliable separation of multipolarities can be done. (author)

  3. Capture reactions at astrophysically relevant energies: extended gas target experiments and GEANT simulations

    CERN Document Server

    Kölle, V; Braitmayer, S E; Mohr, P J; Wilmes, S; Staudt, G; Hammer, J W; Jäger, M; Knee, H; Kunz, R; Mayer, A

    1999-01-01

    Several resonances of the capture reaction sup 2 sup 0 Ne(alpha, gamma) sup 2 sup 4 Mg were measured using an extended windowless gas target system. Detailed GEANT simulations were performed to derive the strength and the total width of the resonances from the measured yield curve. The crucial experimental parameters, which are mainly the density profile in the gas target and the efficiency of the gamma-ray detector, were analyzed by a comparison between the measured data and the corresponding simulation calculations. The excellent agreement between the experimental data and the simulations gives detailed insight into these parameters. (author)

  4. The 12C+α reaction rate from the elastic 16O breakup

    International Nuclear Information System (INIS)

    Kiener, J.; Kraus, L.; Lefebvre, A.; Mittig, W.; Motobayashi, T.; De Oliveira-Santos, F.; Stephan, C.; Thibaud, J.P.

    1997-01-01

    Evidence for direct elastic breakup of 16 O into the α- 12 C continuum with relative energies ranging from 900 to 1800 keV has been obtained in the scattering of 1527 MeV 16 O projectiles off 208 Pb. An interpretation of E2 breakup including nuclear and Coulomb contributions leads to reduced electromagnetic transition probabilities and astrophysical S E2 factors in reasonable agreement with direct measurements, showing that the method can be applied to extract the E2 part of the 12 C(α,γ) reaction rate. (orig.)

  5. Capture and photonuclear reaction rates involving charged-particles: Impacts of nuclear ingredients and future measurement on ELI-NP

    Directory of Open Access Journals (Sweden)

    Xu Y.

    2018-01-01

    Full Text Available The astrophysical p-process is an important way of nucleosynthesis to produce the stable and proton-rich nuclei beyond Fe which can not be reached by the s- and r-processes. In the present study, the impact of nuclear ingredients, especially the nuclear potential, level density and strength function, to the astrophysical re-action rates of (p,γ, (α,γ, (γ,p, and (γ,α reactions are systematically studied. The calculations are performed basad on the modern reaction code TALYS for about 3000 stable and proton-rich nuclei with 12≤Z≤110. In particular, both of the Wood-Saxon potential and the microscopic folding potential are taken into account. It is found that both the capture and photonuclear reaction rates are very sensitive to the nuclear potential, thus the better determination of nuclear potential would be important to reduce the uncertainties of reaction rates. Meanwhile, the Extreme Light Infrastructure-Nuclear Physics (ELI-NP facility is being developed, which will provide the great opportunity to experimentally study the photonuclear reactions in p-process. Simulations of the experimental setup for the measurements of the photonuclear reactions 96Ru(γ,p and 96Ru(γ,α are performed. It is shown that the experiments of photonuclear reactions in p-process based on ELI-NP are quite promising.

  6. Capture and photonuclear reaction rates involving charged-particles: Impacts of nuclear ingredients and future measurement on ELI-NP

    Science.gov (United States)

    Xu, Y.; Goriely, S.; Balabanski, D. L.; Chesnevskaya, S.; Guardo, G. L.; La Cognata, M.; Lan, H. Y.; Lattuada, D.; Luo, W.; Matei, C.

    2018-05-01

    The astrophysical p-process is an important way of nucleosynthesis to produce the stable and proton-rich nuclei beyond Fe which can not be reached by the s- and r-processes. In the present study, the impact of nuclear ingredients, especially the nuclear potential, level density and strength function, to the astrophysical re-action rates of (p,γ), (α,γ), (γ,p), and (γ,α) reactions are systematically studied. The calculations are performed basad on the modern reaction code TALYS for about 3000 stable and proton-rich nuclei with 12≤Z≤110. In particular, both of the Wood-Saxon potential and the microscopic folding potential are taken into account. It is found that both the capture and photonuclear reaction rates are very sensitive to the nuclear potential, thus the better determination of nuclear potential would be important to reduce the uncertainties of reaction rates. Meanwhile, the Extreme Light Infrastructure-Nuclear Physics (ELI-NP) facility is being developed, which will provide the great opportunity to experimentally study the photonuclear reactions in p-process. Simulations of the experimental setup for the measurements of the photonuclear reactions 96Ru(γ,p) and 96Ru(γ,α) are performed. It is shown that the experiments of photonuclear reactions in p-process based on ELI-NP are quite promising.

  7. 78Kr(α,γ) reaction of astrophysical interest in inverse kinematics and the electronic screening effect on the beta decay

    International Nuclear Information System (INIS)

    Ujic, P.

    2011-12-01

    The thesis is constituted of two different topics related to astrophysics. The titles of these topics are: 'Alpha capture reaction in inverse kinematics, measurement of 78 Kr(α,γ) 82 Sr reaction' and 'Measurement of the radioactive decay of 19 O and 19 Ne implanted in niobium'. The goal of the first part of the thesis was to establish an experimental technique for measuring radiative alpha capture reaction at low energies in inverse kinematics. The measurement of these reactions is very important in astrophysics since it will help to improve the reliability of alpha particle optical model potentials which are used for prediction of cross sections of nuclear reaction used in different astrophysical models of supernovae explosions. In this part we insisted on a technical feasibility of this type of experiment. In the second part of the thesis, we examined the influence of the environment on the beta decay probability, in particular the influence of the electronic screening of Coulomb barrier of nuclei induced by Cooper pairs in superconductors. The indication of an extremely weak effect was noticed. (author)

  8. DEPENDENCE OF X-RAY BURST MODELS ON NUCLEAR REACTION RATES

    Energy Technology Data Exchange (ETDEWEB)

    Cyburt, R. H.; Keek, L.; Schatz, H. [National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824 (United States); Amthor, A. M. [Department of Physics and Astronomy, Bucknell University, Lewisburg, PA 17837 (United States); Heger, A.; Meisel, Z.; Smith, K. [Joint Institute for Nuclear Astrophysics (JINA), Michigan State University, East Lansing, MI 48824 (United States); Johnson, E. [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States)

    2016-10-20

    X-ray bursts are thermonuclear flashes on the surface of accreting neutron stars, and reliable burst models are needed to interpret observations in terms of properties of the neutron star and the binary system. We investigate the dependence of X-ray burst models on uncertainties in (p, γ ), ( α , γ ), and ( α , p) nuclear reaction rates using fully self-consistent burst models that account for the feedbacks between changes in nuclear energy generation and changes in astrophysical conditions. A two-step approach first identified sensitive nuclear reaction rates in a single-zone model with ignition conditions chosen to match calculations with a state-of-the-art 1D multi-zone model based on the Kepler stellar evolution code. All relevant reaction rates on neutron-deficient isotopes up to mass 106 were individually varied by a factor of 100 up and down. Calculations of the 84 changes in reaction rate with the highest impact were then repeated in the 1D multi-zone model. We find a number of uncertain reaction rates that affect predictions of light curves and burst ashes significantly. The results provide insights into the nuclear processes that shape observables from X-ray bursts, and guidance for future nuclear physics work to reduce nuclear uncertainties in X-ray burst models.

  9. Electron capture rates in stars studied with heavy ion charge exchange reactions

    Science.gov (United States)

    Bertulani, C. A.

    2018-01-01

    Indirect methods using nucleus-nucleus reactions at high energies (here, high energies mean ~ 50 MeV/nucleon and higher) are now routinely used to extract information of interest for nuclear astrophysics. This is of extreme relevance as many of the nuclei involved in stellar evolution are short-lived. Therefore, indirect methods became the focus of recent studies carried out in major nuclear physics facilities. Among such methods, heavy ion charge exchange is thought to be a useful tool to infer Gamow-Teller matrix elements needed to describe electron capture rates in stars and also double beta-decay experiments. In this short review, I provide a theoretical guidance based on a simple reaction model for charge exchange reactions.

  10. Nuclear astrophysics with indirect methods

    International Nuclear Information System (INIS)

    Shubhchintak

    2016-01-01

    In the area of astrophysics, it is well known that several different type of nuclear reactions are involved in the production of elements and for energy generation in stars. The knowledge of rates and cross section of these reactions is necessary in order to understand the origin of elements in the universe. Particularly, interests are there in the processes like pp-chain, CNO cycle, r-process and s-process, which are responsible for the formation of majority of the nuclei via various reactions like (p, γ), (n, γ), (α, γ) etc

  11. Temperature dependence of muonium reaction rates in the gas phase

    International Nuclear Information System (INIS)

    Fleming, D.G.; Garner, D.M.; Mikula, R.J.; British Columbia Univ., Vancouver

    1981-01-01

    A study of the temperature dependence of reaction rates has long been an important tool in establishing reaction pathways in chemical reactions. This is particularly true for the reactions of muonium (in comparison with those of hydrogen) since a measurement of the activation energy for chemical reaction is sensitive to both the height and the position of the potential barrier in the reaction plane. For collision controlled reactions, on the other hand, the reaction rate is expected to exhibit a weak T 1 sup(/) 2 dependence characteristic of the mean collision velocity. These concepts are discussed and their effects illustrated in a comparison of the chemical and spin exchange reaction rates of muonium and hydrogen in the temperature range approx.300-approx.500 K. (orig.)

  12. Typewriting rate as a function of reaction time.

    Science.gov (United States)

    Hayes, V; Wilson, G D; Schafer, R L

    1977-12-01

    This study was designed to determine the relationship between reaction time and typewriting rate. Subjects were 24 typists ranging in age from 19 to 39 yr. Reaction times (.001 sec) to a light were recorded for each finger and to each alphabetic character and three punctuation marks. Analysis of variance yielded significant differences in reaction time among subjects and fingers. Correlation between typewriting rate and average reaction time to the alphabetic characters and three punctuation marks was --.75. Correlation between typewriting rate and the difference between the reaction time of the hands was --.42. Factors influencing typewriting rate may include reaction time of the fingers, difference between the reaction time of the hands, and reaction time to individual keys on the typewriter. Implications exist for instructional methodology and further research.

  13. Model independent spectroscopic information from an analysis of peripheral direct radiative capture reaction and its application for an extrapolation of an astrophysical S-factor to stellar energies

    International Nuclear Information System (INIS)

    Igamov, S.B.; Tursunmuratov, T.M.; Yarmukhamedov, R.

    2003-01-01

    In this work, within the framework of the cluster potential approach we develop a method which can be used an independent source of getting information on the value of the nuclear vertex constant (NVC) (or respective asymptotical normalization coefficient (ANC)) from the analysis of the direct radiative capture cross section σ(E)(or the astrophysical S-factor S(E)) at extremely low energies by a model independent way as possible. The main idea of the proposed method is that at stellar energies peripheral direct radiative capture reaction of astrophysical interest proceeds mainly through the tail of the overlap integral, which is completely determined by the binding energy and the respective ANC (or NVC). The main advantage of the proposed method is that it allows us to determine both the absolute value of NVC (or ANC) and the astrophysical S-factor S(E) at solar energies (0-50 keV) by means of the analysis of the same experimental astrophysical S-factor S exp (E) in a correct self consistent way using the same potential both for the bound state and for scattering state. The method has been applied for an investigation of the direct radiative capture t(α, γ) 7 Li and 3 He(α, γ) 7 Be reactions at extremely low energies. At first, this method was used for analysis of the S exp (E) to determine values of the modulus squared of the NVC's (or the respective ANC's). The values of NVC's are presented. Then, the obtained NVC's are used by us for extrapolation of the S(E) of the reactions considered to stellar energies (E=0-50 keV) for the 3 He(α, γ) 7 Be reaction and for the t(α, γ) 7 Li reaction. The obtained results are compared with those other authors

  14. Astrophysical limitations to the identification of dark matter: Indirect neutrino signals vis-a-vis direct detection recoil rates

    International Nuclear Information System (INIS)

    Serpico, Pasquale D.; Bertone, Gianfranco

    2010-01-01

    A convincing identification of dark matter (DM) particles can probably be achieved only through a combined analysis of different detections strategies, which provides an effective way of removing degeneracies in the parameter space of DM models. In practice, however, this program is made complicated by the fact that different strategies depend on different physical quantities, or on the same quantities but in a different way, making the treatment of systematic errors rather tricky. We discuss here the uncertainties on the recoil rate in direct-detection experiments and on the muon rate induced by neutrinos from dark matter annihilations in the Sun, and we show that, contrarily to the local DM density or overall cross section scale, irreducible astrophysical uncertainties affect the two rates in a different fashion, therefore limiting our ability to reconstruct the parameters of the dark matter particles. By varying within their respective errors astrophysical parameters such as the escape velocity and the velocity dispersion of dark matter particles, we show that the uncertainty on the relative strength of the neutrino and direct-detection signal is as large as a factor of 2 for typical values of the parameters, but can be even larger in some circumstances.

  15. Cross sections and reaction rates of d+{sup 8}Li reactions involved in Big Bang nucleosynthesis

    Energy Technology Data Exchange (ETDEWEB)

    Balbes, M.J. [Ohio State Univ., Columbus, OH (United States). Dept. of Physics; Farrell, M.M. [Ohio State Univ., Columbus, OH (United States). Dept. of Physics; Boyd, R.N. [Ohio State Univ., Columbus, OH (United States). Dept. of Physics]|[Department of Astronomy, Ohio State University, Columbus, OH 43210 (United States); Gu, X. [Ohio State Univ., Columbus, OH (United States). Dept. of Physics; Hencheck, M. [Ohio State Univ., Columbus, OH (United States). Dept. of Physics; Kalen, J.D. [Ohio State Univ., Columbus, OH (United States). Dept. of Physics; Mitchell, C.A. [Ohio State Univ., Columbus, OH (United States). Dept. of Physics; Kolata, J.J. [Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States); Lamkin, K. [Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States); Smith, R. [Division of Nuclear Medicine, Department of Radiology, Hospital of the University of Pennsylvania, Philadelphia, PA 19104 (United States); Tighe, R. [Lawrence Berkeley Laboratory, Berkeley, CA 94720 (United States); Ashktorab, K. [Department of Physics, University of Michigan, Ann Arbor, MI 48109 (United States); Becchetti, F.D. [Department of Physics, University of Michigan, Ann Arbor, MI 48109 (United States); Brown, J. [Department of Physics, University of Michigan, Ann Arbor, MI 48109 (United States); Roberts, D. [Department of Physics, University of Michigan, Ann Arbor, MI 48109 (United States); Wang, T.F. [Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States); Humphrey, D. [Department of Physics, University of Western Kentucky, Bowling Green, KY 42101 (United States); Vourvopoulos, G. [Department of Physics, University of Western Kentucky, Bowling Green, KY 42101 (United States); Islam, M.S. [Department of Physics, Ball State University, Muncie, IN 47306 (United States)

    1995-02-20

    We have measured angular distributions of the {sup 2}H({sup 8}Li, {sup 7}Li){sup 3}H and {sup 2}H({sup 8}Li, {sup 9}Be)n reactions at E{sub c.m.}=1.5 to 2.8 MeV using an {sup 8}Li-radioactive-beam technique. Astrophysical S-factors and reaction rates were calculated from the measured cross sections. Although the {sup 2}H({sup 8}Li, {sup 9}Be)n cross section is small, it can contribute to {sup 9}Be synthesis. The {sup 2}H({sup 8}Li, {sup 7}Li){sup 3}H reaction has a sufficiently large cross section to destroy {sup 8}Li, which may decrease the synthesis of heavier elements. No products from the {sup 2}H({sup 8}Li, {sup 9}Li)p reaction were detected. We also present the results of calculations using the inhomogeneous model of primordial nucleosynthesis in several regions of parameter space. ((orig.))

  16. Thermonuclear reaction rates in a deuterium-tritium plasma

    International Nuclear Information System (INIS)

    Beckman, L.

    1978-12-01

    In a deuterium-tritium plasma six thermonuclear reactions take place between the deuterons, tritons and the 3 He-particles formed in about half of the d-d-reactions. The rate constants for these six reactions have been calculated from the latest evaluations of the reaction cross sections which were available. In some cases, notably the reactions t+t, t+ 3 He and 3 He+ 3 He, the number of published cross section measurements is small, and the uncertainty in the calculated rate constants consequently large. Analytical expressions for the rate constants as functions of the plasma temperature have been set up. (author)

  17. Rates for some reactions involving 42Ca and 44Ca

    International Nuclear Information System (INIS)

    Cheng, C.W.; King, J.D.

    1980-01-01

    Ground-state reaction rates have been deduced from recent cross section measurements for the 42 CA(α, n) 45 Ti, 42 Ca(p, γ) 43 Sc, and 44 Ca(p, n) 44 Sc reactions. Comparison of these rates with those calculated from a statistical model of nuclear reactions. (Woosley et al) shows good agreement for the first two, but the 44 Ca(p, n) rate is more than a factor of 2 less than the theoretical prediction. Stellar reaction rates have been derived from the ground-state rates by multiplying the ground-state rates by the ratio of stellar to ground-state rates given by the statistical model. Both ground-state and stellar rates have been represented by analytic functions of the temperature. The role of these reactions in the approach to quasi-equilibrium during explosive silicon burning is discussed

  18. Calculation of astrophysical S-factor in reaction ^{13}C(p,γ )^{14}N for first resonance levels

    Science.gov (United States)

    Moghadasi, A.; Sadeghi, H.; Pourimani, R.

    2018-01-01

    The ^{13}C(p,γ )^{14}N reaction is one of the important reactions in the CNO cycle, which is a key process in nucleosynthesis. We first calculated wave functions for the bound state of ^{14}N with Faddeev's method. In this method, the considered reaction components are ^{12}C+n+p. Then, by using direct capture cross section and Breit-Wigner formulae, the non-resonant and resonant cross sections were calculated, respectively. In the next step, we calculated the total S-factor and compared it with experimental data, which showed good agreement between them. Next, we extrapolated the S-factor for the transition to the ground state at zero energy and obtained S(0)=5.8 ± 0.7 (keV b) and then calculate reaction rate. These ones are in agreement with previous reported results.

  19. Effect of nuclear reaction rates on primordial abundances

    International Nuclear Information System (INIS)

    Mishra, Abhishek; Basu, D.N.

    2011-01-01

    The theoretical predictions of the primordial abundances of elements in the big-bang nucleosynthesis (BBN) are dominated by uncertainties in the input nuclear reaction rates. The effect of modifying these reaction rates on light element abundance yields in BBN by replacing the thirty-five reaction rates out of the existing eighty-eight has been investigated. Also the study have been taken of these yields as functions of evolution time or temperature. Here it has been found that using these new reaction rates results in only a little increase in helium mass fraction over that obtained previously in BBN calculations. This allows insights into the role of the nuclear reaction rates in the setting of the neutron-to-proton ratio during the BBN epoch. We observe that most of these nuclear reactions have minimal effect on the standard BBN abundance yields of 6 Li and 7 Li

  20. Evaluation of the implementation of the R-matrix formalism with reference to the astrophysically important {sup 18}F(p,α){sup 15}O reaction

    Energy Technology Data Exchange (ETDEWEB)

    Mountford, D.J., E-mail: d.j.mountford86@gmail.com [SUPA, School of Physics and Astronomy, University of Edinburgh, EH9 3JZ (United Kingdom); Boer, R.J. de [Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Descouvemont, P. [Physique Nucléaire Théorique et Physique Mathématique, C.P. 229, Université Libre de Bruxelles (ULB), B 1050 Brussels (Belgium); Murphy, A. St. J. [SUPA, School of Physics and Astronomy, University of Edinburgh, EH9 3JZ (United Kingdom); Uberseder, E.; Wiescher, M. [Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States)

    2014-12-11

    Background. The R-Matrix formalism is a crucial tool in the study of nuclear astrophysics reactions, and many codes have been written to implement the relevant mathematics. One such code makes use of Visual Basic macros. A further open-source code, AZURE, written in the FORTRAN programming language is available from the JINA collaboration and a C++ version, AZURE2, has recently become available. Purpose The detailed mathematics and extensive programming required to implement broadly applicable R-Matrix codes make comparisons between different codes highly desirable in order to check for errors. This paper presents a comparison of the three codes based around data and recent results of the astrophysically important {sup 18}F(p,α){sup 15}O reaction. Methods Using the same analysis techniques as in the work of Mountford et al. parameters are extracted from the two JINA codes, and the resulting cross-sections are compared. This includes both refitting data with each code and making low-energy extrapolations. Results All extracted parameters are shown to be broadly consistent between the three codes and the resulting calculations are in good agreement barring a known low-energy problem in the original AZURE code. Conclusion The three codes are shown to be broadly consistent with each other and equally valid in the study of astrophysical reactions, although one must be careful when considering low lying, narrow resonances which can be problematic when integrating.

  1. Rate coefficients for hydrogen abstraction reaction of pinonaldehyde

    Indian Academy of Sciences (India)

    The H abstraction reaction from the –CHO group was found to be the most dominant reaction channelamong all the possible reaction pathways and its corresponding rate coefficient at 300 K is kEckart's unsymmetrical= 3.86 ×10-10 cm3 molecule-1 s-1. Whereas the channel with immediate lower activation energy is the ...

  2. Chemical changes in groundwater and their reaction rates

    International Nuclear Information System (INIS)

    Talma, A.S.

    1981-01-01

    The evolution of the major ion concentrations of groundwater (Na, K, Ca, Mg, HCO 3 , SO 4 , Cl and NO 3 ) can be described as the consequence of a number of competing chemical reactions. With the aid of the naturally occuring radioactive and stable isotopes some of these reactions can be separated, identified and followed in space and time. In some field studies, especialy of artesian water, the rates of reactions can be estimated. A number of processes observed in South African sandstones aquifers are discussed and the variable reaction rates demonstrated. Reactions that can be identified include carbonate solution, chemical weathering, salt leaching, cation exchange and redox processes

  3. Thermonuclear 19F(p, {{\\boldsymbol{\\alpha }}}_{0})16O reaction rate

    Science.gov (United States)

    He, Jian-Jun; Lombardo, Ivano; Dell'Aquila, Daniele; Xu, Yi; Zhang, Li-Yong; Liu, Wei-Ping

    2018-01-01

    The thermonuclear 19F(p, {{{α }}}0)16O reaction rate in the temperature region 0.007-10 GK has been derived by re-evaluating the available experimental data, together with the low-energy theoretical R-matrix extrapolations. Our new rate deviates by up to about 30% compared to the previous results, although all rates are consistent within the uncertainties. At very low temperature (e.g. 0.01 GK) our reaction rate is about 20% lower than the most recently published rate, because of a difference in the low energy extrapolated S-factor and a more accurate estimate of the reduced mass used in the calculation of the reaction rate. At temperatures above ˜1 GK, our rate is lower, for instance, by about 20% around 1.75 GK, because we have re-evaluated the previous data (Isoya et al., Nucl. Phys. 7, 116 (1958)) in a meticulous way. The present interpretation is supported by the direct experimental data. The uncertainties of the present evaluated rate are estimated to be about 20% in the temperature region below 0.2 GK, and are mainly caused by the lack of low-energy experimental data and the large uncertainties in the existing data. Asymptotic giant branch (AGB) stars evolve at temperatures below 0.2 GK, where the 19F(p, {{α }})16O reaction may play a very important role. However, the current accuracy of the reaction rate is insufficient to help to describe, in a careful way, the fluorine over-abundances observed in AGB stars. Precise cross section (or S factor) data in the low energy region are therefore needed for astrophysical nucleosynthesis studies. Supported by National Natural Science Foundation of China (11490562, 11490560, 11675229) and National Key Research and Development Program of China (2016YFA0400503)

  4. Enzymatic spectrophotometric reaction rate determination of aspartame

    Directory of Open Access Journals (Sweden)

    Trifković Kata T.

    2015-01-01

    Full Text Available Aspartame is an artificial sweetener of low caloric value (approximately 200 times sweeter than sucrose. Aspartame is currently permitted for use in food and beverage production in more than 90 countries. The application of aspartame in food products requires development of rapid, inexpensive and accurate method for its determination. The new assay for determination of aspartame was based on set of reactions that are catalyzed by three different enzymes: α-chymotrypsin, alcohol oxidase and horseradish peroxidase. Optimization of the proposed method was carried out for: (i α-chymotrypsin activity; (ii time allowed for α-chymotrypsin action, (iii temperature. Evaluation of the developed method was done by determining aspartame content in “diet” drinks, as well as in artificial sweetener pills. [Projekat Ministarstva nauke Republike Srbije, br. III46010

  5. A review of reaction rates in high temperature air

    Science.gov (United States)

    Park, Chul

    1989-01-01

    The existing experimental data on the rate coefficients for the chemical reactions in nonequilibrium high temperature air are reviewed and collated, and a selected set of such values is recommended for use in hypersonic flow calculations. For the reactions of neutral species, the recommended values are chosen from the experimental data that existed mostly prior to 1970, and are slightly different from those used previously. For the reactions involving ions, the recommended rate coefficients are newly chosen from the experimental data obtained more recently. The reacting environment is assumed to lack thermal equilibrium, and the rate coefficients are expressed as a function of the controlling temperature, incorporating the recent multitemperature reaction concept.

  6. New rate coefficients of CS in collision with para- and ortho-H2 and astrophysical implications

    Science.gov (United States)

    Denis-Alpizar, Otoniel; Stoecklin, Thierry; Guilloteau, Stéphane; Dutrey, Anne

    2018-05-01

    Astronomers use the CS molecule as a gas mass tracer in dense regions of the interstellar medium, either to measure the gas density through multi-line observations or the level of turbulence. This necessarily requires the knowledge of the rates coefficients with the most common colliders in the interstellar medium, He and H2. In the present work, the close coupling collisional rates are computed for the first thirty rotational states of CS in collision with para- and ortho-H2 using a recent rigid rotor potential energy surface. Some radiative transfer calculations, using typical astrophysical conditions, are also performed to test this new set of data and to compare with the existing ones.

  7. Nuclear astrophysics and the Trojan Horse Method

    Energy Technology Data Exchange (ETDEWEB)

    Spitaleri, C. [University of Catania, Dipartimento di Fisica e Astronomia, Catania (Italy); Laboratori Nazionali del Sud - INFN, Catania (Italy); La Cognata, M.; Pizzone, R.G. [Laboratori Nazionali del Sud - INFN, Catania (Italy); Lamia, L. [University of Catania, Dipartimento di Fisica e Astronomia, Catania (Italy); Mukhamedzhanov, A.M. [Texas A and M University, Cyclotron Institute, College Station, TX (United States)

    2016-04-15

    In this review, we discuss the new recent results of the Trojan Horse Method that is used to determine reaction rates for nuclear processes in several astrophysical scenarios. The theory behind this technique is shortly presented. This is followed by an overview of some new experiments that have been carried out using this indirect approach. (orig.)

  8. Raman Spectral Determination of Chemical Reaction Rate Characteristics

    Science.gov (United States)

    Balakhnina, I. A.; Brandt, N. N.; Mankova, A. A.; Chikishev, A. Yu.; Shpachenko, I. G.

    2017-09-01

    The feasibility of using Raman spectroscopy to determine chemical reaction rates and activation energies has been demonstrated for the saponification of ethyl acetate. The temperature dependence of the reaction rate was found in the range from 15 to 45°C.

  9. Temperature effects on lithium-nitrogen reaction rates

    International Nuclear Information System (INIS)

    Ijams, W.J.; Kazimi, M.S.

    1985-08-01

    A series of experiments have been run with the aim of measuring the reaction rate of lithium and nitrogen over a wide spectrum of lithium pool temperatures. In these experiments, pure nitrogen was blown at a controlled flow rate over a preheated lithium pool. The pool had a surface area of approximately 4 cm 2 and a total volume of approximately 6 cm 3 . The system pressure varied from 0 to 4 psig. The reaction rate was very small - approximately 0.002 to 0.003 g Li min cm 2 for lithium temperatures below 500 0 C. Above 500 0 C the reaction rate began to increase sharply, and reached a maximum of approximately 0.80 g Li min cm 2 above 700 0 C. It dropped off beyond 1000 0 C and seemed to approach zero at 1150 0 C. The maximum reaction rate observed in these forced convection experiments was higher by 60% than those previously observed in experiments where the nitrogen flowed to the reaction site by means of natural convection. During a reaction, a hard nitride layer built up on the surface of the lithium pool - its effect on the reaction rate was observed. The effect of the nitrogen flow rate on the reaction rate was also observed

  10. Estimating the Backup Reaction Wheel Orientation Using Reaction Wheel Spin Rates Flight Telemetry from a Spacecraft

    Science.gov (United States)

    Rizvi, Farheen

    2013-01-01

    A report describes a model that estimates the orientation of the backup reaction wheel using the reaction wheel spin rates telemetry from a spacecraft. Attitude control via the reaction wheel assembly (RWA) onboard a spacecraft uses three reaction wheels (one wheel per axis) and a backup to accommodate any wheel degradation throughout the course of the mission. The spacecraft dynamics prediction depends upon the correct knowledge of the reaction wheel orientations. Thus, it is vital to determine the actual orientation of the reaction wheels such that the correct spacecraft dynamics can be predicted. The conservation of angular momentum is used to estimate the orientation of the backup reaction wheel from the prime and backup reaction wheel spin rates data. The method is applied in estimating the orientation of the backup wheel onboard the Cassini spacecraft. The flight telemetry from the March 2011 prime and backup RWA swap activity on Cassini is used to obtain the best estimate for the backup reaction wheel orientation.

  11. Non-equilibrium reaction rates in chemical kinetic equations

    Science.gov (United States)

    Gorbachev, Yuriy

    2018-05-01

    Within the recently proposed asymptotic method for solving the Boltzmann equation for chemically reacting gas mixture, the chemical kinetic equations has been derived. Corresponding one-temperature non-equilibrium reaction rates are expressed in terms of specific heat capacities of the species participate in the chemical reactions, bracket integrals connected with the internal energy transfer in inelastic non-reactive collisions and energy transfer coefficients. Reactions of dissociation/recombination of homonuclear and heteronuclear diatomic molecules are considered. It is shown that all reaction rates are the complex functions of the species densities, similarly to the unimolecular reaction rates. For determining the rate coefficients it is recommended to tabulate corresponding bracket integrals, additionally to the equilibrium rate constants. Correlation of the obtained results with the irreversible thermodynamics is established.

  12. Nuclear reaction rates and primordial 6Li

    International Nuclear Information System (INIS)

    Nollett, K.M.; Schramm, D.N.; Lemoine, M.; Schramm, D.N.; Lemoine, M.; Schramm, D.N.

    1997-01-01

    We examine the possibility that big-bang nucleosynthesis (BBN) may produce nontrivial amounts of 6 Li. If a primordial component of this isotope could be observed, it would provide a new fundamental test of big-bang cosmology, as well as new constraints on the baryon density of the universe. At present, however, theoretical predictions of the primordial 6 Li abundance are extremely uncertain due to difficulties in both theoretical estimates and experimental determinations of the 2 H(α,γ) 6 Li radiative capture reaction cross section. We also argue that present observational capabilities do not yet allow the detection of primeval 6 Li in very metal-poor stars of the galactic halo. However, if the critical cross section is very high in its plausible range and the baryon density is relatively low, then improvements in 6 Li detection capabilities may allow the establishment of 6 Li as another product of BBN. It is also noted that a primordial 6 Li detection could help resolve current concerns about the extragalactic D/H determination. copyright 1997 The American Physical Society

  13. Charged-particle thermonuclear reaction rates: II. Tables and graphs of reaction rates and probability density functions

    International Nuclear Information System (INIS)

    Iliadis, C.; Longland, R.; Champagne, A.E.; Coc, A.; Fitzgerald, R.

    2010-01-01

    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.

  14. High-precision (p,t) reactions to determine reaction rates of explosive stellar processes

    NARCIS (Netherlands)

    Matić, Andrija

    2007-01-01

    The aim of my study was to investigate the nuclear structure of 22Mg and 26Si. These two nuclei play a significant role in stellar reaction processes at high temperatures. On base of the obtained nuclear structure we calculated the stellar reaction rates for the following reactions: 18Ne(α,p)21Na,

  15. Re-examining the 26Mg(α ,α')26Mg reaction: Probing astrophysically important states in 26Mg

    Science.gov (United States)

    Adsley, P.; Brümmer, J. W.; Li, K. C. W.; Marín-Lámbarri, D. J.; Kheswa, N. Y.; Donaldson, L. M.; Neveling, R.; Papka, P.; Pellegri, L.; Pesudo, V.; Pool, L. C.; Smit, F. D.; van Zyl, J. J.

    2017-11-01

    Background: The 22Ne(α ,n )25Mg reaction is one of the neutron sources for the s process in massive stars. The properties of levels in 26Mg above the α -particle threshold control the strengths of the 22Ne(α ,n )25Mg and 22Ne(α ,γ )26Mg reactions. The strengths of these reactions as functions of temperature are one of the major uncertainties in the s process. Purpose: Information on the existence, spin, and parity of levels in 26Mg can assist in constraining the strengths of the 22Ne(α ,γ )26Mg and 22Ne(α ,n )25Mg reactions, and therefore in constraining s -process abundances. Methods: Inelastically scattered α particles from a 26Mg target were momentum-analyzed in the K600 magnetic spectrometer at iThemba LABS, South Africa. The differential cross sections of states were deduced from the focal-plane trajectory of the scattered α particles. Based on the differential cross sections, spin and parity assignments to states are made. Results: A newly assigned 0+ state was observed in addition to a number of other states, some of which can be associated with states observed in other experiments. Some of the deduced Jπ values of the states observed in the present study show discrepancies with those assigned in a similar experiment performed at RCNP Osaka. The reassignments and additions of the various states can strongly affect the reaction rate at low temperatures. Conclusion: The number, location, and assignment of levels in 26Mg that may contribute to the 22Ne+α reactions are not clear. Future experimental investigations of 26Mg must have an extremely good energy resolution to separate the contributions from different levels. Coincidence experiments of 26Mg provide a possible route for future investigations.

  16. The search for a main cause of uncertainty of the calculated astrophysical S factor for the direct radiative capture d(α, γ)6Li reaction at stellar energies

    International Nuclear Information System (INIS)

    Blokhintsev, L.D.; Igamov, S.B.; Nishonov, M.M.; Yarmukhamedov, R.

    2004-01-01

    Full text: It is well known that the d( α,γ ) 6 Li reaction is one of the sources of the 6 Li production in the Big Bang nucleosynthesis. At the present time rather large uncertainties exist in the prediction of the rate of this reaction, which are mainly due to the absence both of the reliable experimental cross section (or the astrophysical S factor, S(E)) and of the theoretical calculations at extremely low energies E (E ≤ 600 keV) (see [1] and references therein). The aim of our work is to find out the principal cause of the existing large spread of the calculated values of S(E) at extremely low energies obtained by different authors, including the results of the present work. The basic idea of our consideration is that the d( α, γ) 6 Li reaction at such energies is predominantly peripheral [2]-[4]. Therefore the values of S(E) at extremely low energies are mainly determined by the nuclear vertex constant (NVC) (or by the asymptotic normalization constant (ANC)) for the virtual decay 6 Li→α+ d. Taking this circumstance into account, we calculated the NVC for the virtual decay 6 Li→α + d in the framework of three- body ( np) Faddeev equations in the momentum space. The Malfliet-Tjon and Graz potentials for NN interaction and the Sack-Biedenharn-Breit and Yamaguchi type potentials for αN interaction were used. The results of our calculations show that the obtained values of the NVC (or the ANC) are sensitive to the form of NN and αN potentials. This result is also corroborated by the values of the NVC calculated within the microscopic model using the Minnesota and Volkov potentials for NN- interaction [5]. The values of the NVC obtained in the present work were used to determine the values of the astrophysical S factor for the direct radiative capture d( α,γ ) 6 Li reaction at extremely low energies. It is shown that the values of the NVC corresponding to the different forms of NN and αN potentials lead to the different values of the

  17. APUAMA: a software tool for reaction rate calculations.

    Science.gov (United States)

    Euclides, Henrique O; P Barreto, Patricia R

    2017-06-01

    APUAMA is a free software designed to determine the reaction rate and thermodynamic properties of chemical species of a reagent system. With data from electronic structure calculations, the APUAMA determine the rate constant with tunneling correction, such as Wigner, Eckart and small curvature, and also, include the rovibrational level of diatomic molecules. The results are presented in the form of Arrhenius-Kooij form, for the reaction rate, and the thermodynamic properties are written down in the polynomial form. The word APUAMA means "fast" in Tupi-Guarani Brazilian language, then the code calculates the reaction rate on a simple and intuitive graphic interface, the form fast and practical. As program output, there are several ASCII files with tabulated information for rate constant, rovibrational levels, energy barriers and enthalpy of reaction, Arrhenius-Kooij coefficient, and also, the option to the User save all graphics in BMP format.

  18. Indirect techniques in nuclear astrophysics

    International Nuclear Information System (INIS)

    Mukhamedzhanov, A.M.; Tribble, R.E.; Blokhintsev, L.D.; Cherubini, S.; Spitaleri, C.; Kroha, V.; Nunes, F.M.

    2005-01-01

    It is very difficult or often impossible to measure in the lab conditions nuclear cross sections at astrophysically relevant energies. That is why different indirect techniques are used to extract astrophysical information. In this talk different experimental possibilities to get astrophysical information using radioactive and stable beams will be addressed. 1. The asymptotic normalization coefficient (ANC) method. 2. Radiative neutron captures are determined by the spectroscopic factors (SP). A new experimental technique to determine the neutron SPs will be addressed. 3. 'Trojan Horse' is another unique indirect method, which allows one to extract the astrophysical factors for direct and resonant nuclear reactions at astrophysically relevant energies. (author)

  19. Rate constant for reaction of atomic hydrogen with germane

    Science.gov (United States)

    Nava, David F.; Payne, Walter A.; Marston, George; Stief, Louis J.

    1990-01-01

    Due to the interest in the chemistry of germane in the atmospheres of Jupiter and Saturn, and because previously reported kinetic reaction rate studies at 298 K gave results differing by a factor of 200, laboratory measurements were performed to determine the reaction rate constant for H + GeH4. Results of the study at 298 K, obtained via the direct technique of flash photolysis-resonance fluorescence, yield the reaction rate constant, k = (4.08 + or - 0.22) x 10(exp -12) cu cm/s.

  20. Astrophysical 3He(α ,γ )7Be and 3H(α ,γ )7Li direct capture reactions in a potential-model approach

    Science.gov (United States)

    Tursunov, E. M.; Turakulov, S. A.; Kadyrov, A. S.

    2018-03-01

    The astrophysical 3He(α ,γ )7Be and 3H(α ,γ )7Li direct capture processes are studied in the framework of the two-body model with potentials of a simple Gaussian form, which describe correctly the phase shifts in the s , p , d , and f waves, as well as the binding energy and the asymptotic normalization constant of the ground p3 /2 and the first excited p1 /2 bound states. It is shown that the E 1 transition from the initial s wave to the final p waves is strongly dominant in both capture reactions. On this basis the s -wave potential parameters are adjusted to reproduce the new data of the LUNA Collaboration around 100 keV and the newest data at the Gamov peak estimated with the help of the observed neutrino fluxes from the sun, S34(23-5+6keV ) =0.548 ±0.054 keV b for the astrophysical S factor of the capture process 3He(α ,γ )7Be . The resulting model describes well the astrophysical S factor in the low-energy big-bang nucleosynthesis region of 180-400 keV; however, it has a tendency to underestimate the data above 0.5 MeV. The energy dependence of the S factor is mostly consistent with the data and the results of the no-core shell model with continuum, but substantially different from the fermionic molecular dynamics model predictions. Two-body potentials, adjusted for the properties of the 7Be nucleus, 3He+α elastic scattering data, and the astrophysical S factor of the 3He(α ,γ )7Be direct capture reaction, are able to reproduce the properties of the 7Li nucleus, the binding energies of the ground 3 /2- and first excited 1 /2- states, and phase shifts of the 3H+α elastic scattering in partial waves. Most importantly, these potential models can successfully describe both absolute value and energy dependence of the existing experimental data for the mirror astrophysical 3H(α ,γ )7Li capture reaction without any additional adjustment of the parameters.

  1. Nuclear Data on Unstable Nuclei for Astrophysics

    International Nuclear Information System (INIS)

    Smith, Michael Scott; Meyer, Richard A; Lingerfelt, Eric; Scott, J.P.; Hix, William Raphael; Ma, Zhanwen; Bardayan, Daniel W.; Blackmon, Jeff C.; Guidry, Mike W.; KOZUB, RAYMOND L.; Chae, Kyung YuK.

    2004-01-01

    Recent measurements with radioactive beams at ORNL's Holifield Radioactive Ion Beam Facility (HRIBF) have prompted the evaluation of a number of reactions involving unstable nuclei needed for stellar explosion studies. We discuss these evaluations, as well as the development of a new computational infrastructure to enable the rapid incorporation of the latest nuclear physics results in astrophysics models. This infrastructure includes programs that simplify the generation of reaction rates, manage rate databases, and visualize reaction rates, all hosted at a new website http://www.nucastrodata.org

  2. The Investors- Reaction to Investment Rating Change Announcements

    OpenAIRE

    Chih-Hsiang Chang; Liang-Chien Lee; Shu-Ling Wu

    2012-01-01

    This study investigates the investors- behavioral reaction to the investment rating change announcements from the views of behavioral finance. The empirical results indicate that self-interest does affect the intention of securities firms to release investment ratings for individual stocks. In addition, behavioral pitfalls are also found in the response of retail investors to investment rating change announcements.

  3. Modular rate laws for enzymatic reactions: thermodynamics, elasticities and implementation.

    Science.gov (United States)

    Liebermeister, Wolfram; Uhlendorf, Jannis; Klipp, Edda

    2010-06-15

    Standard rate laws are a key requisite for systematically turning metabolic networks into kinetic models. They should provide simple, general and biochemically plausible formulae for reaction velocities and reaction elasticities. At the same time, they need to respect thermodynamic relations between the kinetic constants and the metabolic fluxes and concentrations. We present a family of reversible rate laws for reactions with arbitrary stoichiometries and various types of regulation, including mass-action, Michaelis-Menten and uni-uni reversible Hill kinetics as special cases. With a thermodynamically safe parameterization of these rate laws, parameter sets obtained by model fitting, sampling or optimization are guaranteed to lead to consistent chemical equilibrium states. A reformulation using saturation values yields simple formulae for rates and elasticities, which can be easily adjusted to the given stationary flux distributions. Furthermore, this formulation highlights the role of chemical potential differences as thermodynamic driving forces. We compare the modular rate laws to the thermodynamic-kinetic modelling formalism and discuss a simplified rate law in which the reaction rate directly depends on the reaction affinity. For automatic handling of modular rate laws, we propose a standard syntax and semantic annotations for the Systems Biology Markup Language. An online tool for inserting the rate laws into SBML models is freely available at www.semanticsbml.org. Supplementary data are available at Bioinformatics online.

  4. Optimized reaction mechanism rate rules for ignition of normal alkanes

    KAUST Repository

    Cai, Liming; Pitsch, Heinz; Mohamed, Samah; Raman, Venkat; Bugler, John; Curran, Henry; Sarathy, Mani

    2016-01-01

    fidelity reacting flow simulations capable of improving combustor design and operation. The development of such models for many new fuel components and/or surrogate molecules is greatly facilitated by the application of reaction classes and rate rules

  5. NACRE II: an update of the NACRE compilation of charged-particle-induced thermonuclear reaction rates for nuclei with mass number A<16

    International Nuclear Information System (INIS)

    Xu, Y.; Takahashi, K.; Goriely, S.; Arnould, M.; Ohta, M.; Utsunomiya, H.

    2013-01-01

    An update of the NACRE compilation [3] is presented. This new compilation, referred to as NACRE II, reports thermonuclear reaction rates for 34 charged-particle induced, two-body exoergic reactions on nuclides with mass number A 6 ≲T⩽10 10 K range. Along with the ‘adopted’ rates, their low and high limits are provided. The new rates are available in electronic form as part of the Brussels Library (BRUSLIB) of nuclear data. The NACRE II rates also supersede the previous NACRE rates in the Nuclear Network Generator (NETGEN) for astrophysics. [ (http://www.astro.ulb.ac.be/databases.html)

  6. Study of astrophysically important resonant states in 30 S using the 32S(p,t30 S reaction

    Directory of Open Access Journals (Sweden)

    Wrede C.

    2010-03-01

    Full Text Available A small fraction (< 1% of presolar SiC grains is suggested to have been formed in the ejecta of classical novae. The 29P(p,γ30S reaction plays an important role in understanding the Si isotopic abundances in such grains, which in turn provide us with information on the nature of the probable white dwarf progenitor’s core, as well as the peak temperatures achieved during nova outbursts, and thus the nova nucleosynthetic path. The 29P(p,γ30S reaction rate at nova temperatures is determined by two low-lying 3+ and 2+ resonances above the proton threshold at 4399 keV in 30S. Despite several experimental studies in the past, however, only one of these two states has only been observed very recently. We have studied the 30S nuclear structure via the 32S(p,t 30S reaction at 5 laboratory angles between 9° to 62°. We have observed 14 states, eleven of which are above the proton threshold, including two levels at 4692.7 ± 4.5 keV and 4813.8 ± 3.4 keV that are candidates for the 3+ and the previously “issing” 2+ state, respectively.

  7. Modified two-body potential approach to the peripheral direct capture astrophysical a+A->B+γ reaction and asymptotic normalization coefficients

    International Nuclear Information System (INIS)

    Igamov, S.B.; Yarmukhamedov, R.

    2007-01-01

    A modified two-body potential approach is proposed for determination of both the asymptotic normalization coefficient (ANC) (or the respective nuclear vertex constant (NVC)) for the A+a->B (for the virtual decay B->A+a) from an analysis of the experimental S-factor for the peripheral direct capture a+A->B+γ reaction and the astrophysical S-factor, S(E), at low experimentally inaccessible energy regions. The approach proposed involves two additional conditions which verify the peripheral character of the considered reaction and expresses S(E) in terms of the ANC. The connection between NVC (ANC) and the effective range parameters for Aa-scattering is derived. To test this approach we reanalyse the precise experimental astrophysical S-factors for t+α->Li7+γ reaction at energies E= Li7(g.s.), α+t->Li7(0.478 MeV) and of S(E) at E=<50 keV. These ANC values have been used for getting information about the ''indirect'' measured values of the effective range parameters and the p-wave phase shift for αt-scattering in the energy range of 100-bar E-bar 180 keV

  8. Accurate and approximate thermal rate constants for polyatomic chemical reactions

    International Nuclear Information System (INIS)

    Nyman, Gunnar

    2007-01-01

    In favourable cases it is possible to calculate thermal rate constants for polyatomic reactions to high accuracy from first principles. Here, we discuss the use of flux correlation functions combined with the multi-configurational time-dependent Hartree (MCTDH) approach to efficiently calculate cumulative reaction probabilities and thermal rate constants for polyatomic chemical reactions. Three isotopic variants of the H 2 + CH 3 → CH 4 + H reaction are used to illustrate the theory. There is good agreement with experimental results although the experimental rates generally are larger than the calculated ones, which are believed to be at least as accurate as the experimental rates. Approximations allowing evaluation of the thermal rate constant above 400 K are treated. It is also noted that for the treated reactions, transition state theory (TST) gives accurate rate constants above 500 K. TST theory also gives accurate results for kinetic isotope effects in cases where the mass of the transfered atom is unchanged. Due to neglect of tunnelling, TST however fails below 400 K if the mass of the transferred atom changes between the isotopic reactions

  9. Astrophysical s-factor measurements for 120Te(p,γ)121I and 120Te(p,n)120I reactions

    International Nuclear Information System (INIS)

    Gueray, R. T.; Oezkan, N.; Yalcin, C.; Goerres, J.; DeBoer, R.; Palumbo, A.; Tan, W. P.; Wiescher, M.; Fueloep, Zs.; Somorjai, E.; Lee, H. Y.

    2009-01-01

    Astrophysical S-factors for the 1 20Te(p,γ) 1 21I and 1 20Te(p,n) 1 20I reactions have been measured in the effective center-of-mass energies between 2.47 MeV and 7.93 MeV. Experimental data have been compared with the Hauser-Fesbach statistical model calculations obtained with the model codes NON-SMOKER and TALYS. The discrepancies between the experimental results and calculations can mainly be attributed to the optical model potentials used in the codes.

  10. Non-resonant triple alpha reaction rate at low temperature

    Energy Technology Data Exchange (ETDEWEB)

    Itoh, T.; Tamii, A.; Aoi, N.; Fujita, H.; Hashimoto, T.; Miki, K.; Ogata, K. [Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047 (Japan); Carter, J.; Donaldson, L.; Sideras-Haddad, E. [Schools of Physics, University of Witwatersrand, Johannesburg 2050 (South Africa); Furuno, T.; Kawabata, T. [Departments of Physics, Kyoto University, Sakyo, Kyoto, 606-8502 (Japan); Kamimura, M. [RIKEN Nishina Center, Wako, Saitama, 351-0198 (Japan); Nemulodi, F.; Neveling, R.; Smit, F. D.; Swarts, C. [iThemba Laboratory for Accelerator Based Sciences Somerset, West, 7129 (South Africa)

    2014-05-02

    Our experimental goal is to study the non-resonant triple alpha reaction rate at low temperture (T < 10{sup 8} K). The {sup 13}C(p,d) reaction at 66 MeV has been used to probe the alpha-unbound continuum state in {sup 12}C just below the 2{sup nd} 0{sup +} state at 7.65 MeV. The transition strength to the continuum state is predicted to be sensitive to the non-resonant triple alpha reaction rate. The experiment has been performed at iThemba LABS. We report the present status of the experiment.

  11. Nuclear astrophysics with radioactive beams: a TRIUMF perspective

    International Nuclear Information System (INIS)

    Shotter, A.C.

    2003-01-01

    Explosive nuclear burning in stellar environments involves reactions with a wide range of isotopes. For isotopes that are unstable, information on relevant reaction rates can only generally be obtained at radioactive beam facilities. The ISAC facility at TRIUMF is purpose built to provide a wide range of radioactive beams for nuclear astrophysics purposes as well as a range of other science

  12. Analysis of reaction schemes using maximum rates of constituent steps

    Science.gov (United States)

    Motagamwala, Ali Hussain; Dumesic, James A.

    2016-01-01

    We show that the steady-state kinetics of a chemical reaction can be analyzed analytically in terms of proposed reaction schemes composed of series of steps with stoichiometric numbers equal to unity by calculating the maximum rates of the constituent steps, rmax,i, assuming that all of the remaining steps are quasi-equilibrated. Analytical expressions can be derived in terms of rmax,i to calculate degrees of rate control for each step to determine the extent to which each step controls the rate of the overall stoichiometric reaction. The values of rmax,i can be used to predict the rate of the overall stoichiometric reaction, making it possible to estimate the observed reaction kinetics. This approach can be used for catalytic reactions to identify transition states and adsorbed species that are important in controlling catalyst performance, such that detailed calculations using electronic structure calculations (e.g., density functional theory) can be carried out for these species, whereas more approximate methods (e.g., scaling relations) are used for the remaining species. This approach to assess the feasibility of proposed reaction schemes is exact for reaction schemes where the stoichiometric coefficients of the constituent steps are equal to unity and the most abundant adsorbed species are in quasi-equilibrium with the gas phase and can be used in an approximate manner to probe the performance of more general reaction schemes, followed by more detailed analyses using full microkinetic models to determine the surface coverages by adsorbed species and the degrees of rate control of the elementary steps. PMID:27162366

  13. Nuclear physics and astrophysics

    International Nuclear Information System (INIS)

    Schramm, D.N.; Olinto, A.V.

    1992-09-01

    We have investigated a variety of research topics on the interface of nuclear physics and astrophysics during the past year. We have continued our study of dihyperon states in dense matter and have started to make a connection between their properties in the core of neutron stars with the ongoing experimental searches at Brookhaven National Laboratory. We started to build a scenario for the origin of gamma-ray bursts using the conversion of neutron stars to strange stars close to an active galactic nucleous. We have been reconsidering the constraints due to neutron star cooling rates on the equation of state for high density matter in the light, of recent findings which show that the faster direct Urca cooling process is possible for a range of nuclear compositions. We have developed a model for the formation of primordial magnetic fields due to the dynamics of the quark-hadron phase transition. Encouraged by the most recent observational developments, we have investigated the possible origin of the boron and beryllium abundances. We have greatly improved the calculations of the primordial abundances of these elements I>y augmenting the reaction networks and by updating the most recent experimental nuclear reaction rates. Our calculations have shown that the primordial abundances are much higher than previously thought but that the observed abundances cannot be explained by primordial sources alone. We have also studied the origin of the boron and beryllium abundances due to cosmic ray spallation. Finally, we have continued to address the solar neutrino problem by investigating the impact of astrophysical uncertainties on the MSW solution for a full three-family treatment of MSW mixing

  14. Nuclear physics and astrophysics

    Energy Technology Data Exchange (ETDEWEB)

    Schramm, D.N.; Olinto, A.V.

    1992-09-01

    We have investigated a variety of research topics on the interface of nuclear physics and astrophysics during the past year. We have continued our study of dihyperon states in dense matter and have started to make a connection between their properties in the core of neutron stars with the ongoing experimental searches at Brookhaven National Laboratory. We started to build a scenario for the origin of gamma-ray bursts using the conversion of neutron stars to strange stars close to an active galactic nucleous. We have been reconsidering the constraints due to neutron star cooling rates on the equation of state for high density matter in the light, of recent findings which show that the faster direct Urca cooling process is possible for a range of nuclear compositions. We have developed a model for the formation of primordial magnetic fields due to the dynamics of the quark-hadron phase transition. Encouraged by the most recent observational developments, we have investigated the possible origin of the boron and beryllium abundances. We have greatly improved the calculations of the primordial abundances of these elements I>y augmenting the reaction networks and by updating the most recent experimental nuclear reaction rates. Our calculations have shown that the primordial abundances are much higher than previously thought but that the observed abundances cannot be explained by primordial sources alone. We have also studied the origin of the boron and beryllium abundances due to cosmic ray spallation. Finally, we have continued to address the solar neutrino problem by investigating the impact of astrophysical uncertainties on the MSW solution for a full three-family treatment of MSW mixing.

  15. 2-16 Thermonuclear Reaction Rates in rp Process of sd

    Institute of Scientific and Technical Information of China (English)

    Lam; Yihua[1; Nadezda; A.; Smirnova[2; W.A.; Richter[3

    2014-01-01

    Recently, we have constructed a new set of isospin non-conserving (INC) shell-model Hamiltonians as a combinationof isospin conserving (IC) Hamiltonian, Coulomb interaction and effective isospin-symmetry breaking forcesof nuclear origin[1]. The advantage is that Coulomb effects are taken into account with great care, thus the new ap-Fig. 1 (color online) The comparison of resonant rates of23Al(p;)24Si calculated by IC and INC Hamiltonians. TheINC Hamiltonians of OB+USD, OB+USDA, OB+USDBwere constructed in Ref. [5]; whereas (cd-USD), (cd-USDA),(cd-USDB) are INC Hamiltonians in Ref. [1]. USD, USDA,USDB are IC Hamiltonians in Ref. [6].proach allows one to describe more accurately and topredict unknown nuclear level schemes and decay modes.Since the approximate isospin-symmetry becomes broken,a realistic amount of isospin-mixing in nuclearstates is thus introduced. Among numerous applicationsto the structure of proton-rich nuclei, we usedthe new Hamiltonian to calculate resonant reaction andnon-resonant reaction (direct capture) rates of radiativeproton-capture reactions important for astrophysical rpprocess.

  16. Direct and inverse reactions of LiH+ with He(1S) from quantum calculations: mechanisms and rates.

    Science.gov (United States)

    Tacconi, M; Bovino, S; Gianturco, F A

    2012-01-14

    The gas-phase reaction of LiH(+) (X(2)Σ) with He((1)S) atoms, yielding Li(+)He with a small endothermicity for the rotovibrational ground state of the reagents, is analysed using the quantum reactive approach that employs the Negative Imaginary Potential (NIP) scheme discussed earlier in the literature. The dependence of low-T rates on the initial vibrational state of LiH(+) is analysed and the role of low-energy Feshbach resonances is also discussed. The inverse destruction reaction of LiHe(+), a markedly exothermic process, is also investigated and the rates are computed in the same range of temperatures. The possible roles of these reactions in early universe astrophysical networks, in He droplets environments or in cold traps are briefly discussed.

  17. Extension of a Kinetic-Theory Approach for Computing Chemical-Reaction Rates to Reactions with Charged Particles

    Science.gov (United States)

    Liechty, Derek S.; Lewis, Mark J.

    2010-01-01

    Recently introduced molecular-level chemistry models that predict equilibrium and nonequilibrium reaction rates using only kinetic theory and fundamental molecular properties (i.e., no macroscopic reaction rate information) are extended to include reactions involving charged particles and electronic energy levels. The proposed extensions include ionization reactions, exothermic associative ionization reactions, endothermic and exothermic charge exchange reactions, and other exchange reactions involving ionized species. The extensions are shown to agree favorably with the measured Arrhenius rates for near-equilibrium conditions.

  18. Reaction rate constant for uranium in water and water vapor

    Energy Technology Data Exchange (ETDEWEB)

    TRIMBLE, D.J.

    1998-11-09

    The literature on uranium oxidation in water and oxygen free water vapor was reviewed. Arrhenius rate equations were developed from the review data. These data and equations will be used as a baseline from which to compare reaction rates measured for K Basin fuel.

  19. BIG-10 fission product generation and reaction rates

    International Nuclear Information System (INIS)

    Rogers, J.W.

    1976-01-01

    Fission product generation rates for high quality fission foils and reaction rates of nonfission foils have been measured by gamma ray activation analyses. These foils were irradiated in the BIG-10 facility and the activities were measured by NaI counting techniques

  20. Introduction to Nuclear Astrophysics

    International Nuclear Information System (INIS)

    Iliadis, Christian

    2010-01-01

    In the first lecture of this volume, we will present the basic fundamental ideas regarding nuclear processes occurring in stars. We start from stellar observations, will then elaborate on some important quantum-mechanical phenomena governing nuclear reactions, continue with how nuclear reactions proceed in a hot stellar plasma and, finally, we will provide an overview of stellar burning stages. At the end, the current knowledge regarding the origin of the elements is briefly summarized. This lecture is directed towards the student of nuclear astrophysics. Our intention is to present seemingly unrelated phenomena of nuclear physics and astrophysics in a coherent framework.

  1. Collective plasma corrections to thermonuclear reactions rates in dense plasmas

    International Nuclear Information System (INIS)

    Tsytovich, V.N.

    2002-01-01

    General kinetic equations for nuclear reaction in dense plasmas are obtained. They take into account the first order collective plasma effects. Together with previously known corrections proportional to Z i Z j , the product of the charges Z i and Z j of two interacting nuclei, it is shown that there exist corrections proportional to the squares Z i 2 and Z j 2 of the charges. It is shown that the Salpeter's [1] correction due to the plasma screening of the interaction potential is at least r/d smaller (r is the nuclei size and d is Debye screening length) than previously thought and is zero in the approximation when the terms of the order r/d are neglected. But the correlation effects in the first approximation in the parameter 1/N d (where N d is the number of particle in the Debye sphere) give corrections which often coincide with the first order Salpeter's corrections (found by expansion in another small parameter, the ratio of thermal energy to Gamov's energy). The correlation corrections are ∝ Z i Z j , have a different physical meaning than the corrections [1], can have a different sign and are present for reactions where the Salpeter's corrections are zero. Previously in astrophysical applications it was widely used the interpolation formulas between weak and strong Salpeter's screening corrections. Since the correlation correction take place the previously known Salpeter's corrections and the strong correlation corrections is difficult to describe analytically, the interpolation formulas between the weak and strong correlations cannot be yet found. A new type of corrections are found here which are proportional to the square of the charges. They are due to collective change in electrostatic self-energy of the plasma system during the nuclear reactions. The latter corrections are found by taking into account the changes of plasma particle fluctuations by the nuclear reactions. Numerical evaluation of the plasma corrections for the nuclear reactions of the

  2. Relativistic Astrophysics

    International Nuclear Information System (INIS)

    Font, J. A.

    2015-01-01

    The relativistic astrophysics is the field of astrophysics employing the theory of relativity Einstein as physical-mathematical model is to study the universe. This discipline analyzes astronomical contexts in which the laws of classical mechanics of Newton's law of gravitation are not valid. (Author)

  3. Essential astrophysics

    CERN Document Server

    Lang, Kenneth R

    2013-01-01

    Essential Astrophysics is a book to learn or teach from, as well as a fundamental reference volume for anyone interested in astronomy and astrophysics. It presents astrophysics from basic principles without requiring any previous study of astronomy or astrophysics. It serves as a comprehensive introductory text, which takes the student through the field of astrophysics in lecture-sized chapters of basic physical principles applied to the cosmos. This one-semester overview will be enjoyed by undergraduate students with an interest in the physical sciences, such as astronomy, chemistry, engineering or physics, as well as by any curious student interested in learning about our celestial science. The mathematics required for understanding the text is on the level of simple algebra, for that is all that is needed to describe the fundamental principles. The text is of sufficient breadth and depth to prepare the interested student for more advanced specialized courses in the future. Astronomical examples are provide...

  4. Thermonuclear astrophysics

    International Nuclear Information System (INIS)

    Clayton, D.D.; Woosley, S.E.

    1974-01-01

    We discuss the types of thermonuclear reactions that are of importance to stellar evolution and nucleosynthesis, with particular attention to the explosive ejection of shells of He, C, O, and Si. We present tables of the reactions important in the various burning phases, including the reason for their importance and an estimate of the value of a carefully measured rate. This format is chosen for dual purpose: (1) to clarify the nuclear needs by evaluating the importance of specific reactions within the astronomical settings and (2) by assigning a value scale for cross-section measurements

  5. Effects of Surfactants on the Rate of Chemical Reactions

    Directory of Open Access Journals (Sweden)

    B. Samiey

    2014-01-01

    Full Text Available Surfactants are self-assembled compounds that depend on their structure and electric charge can interact as monomer or micelle with other compounds (substrates. These interactions which may catalyze or inhibit the reaction rates are studied with pseudophase, cooperativity, and stoichiometric (classical models. In this review, we discuss applying these models to study surfactant-substrate interactions and their effects on Diels-Alder, redox, photochemical, decomposition, enzymatic, isomerization, ligand exchange, radical, and nucleophilic reactions.

  6. Benchmark calculations of thermal reaction rates. I - Quantal scattering theory

    Science.gov (United States)

    Chatfield, David C.; Truhlar, Donald G.; Schwenke, David W.

    1991-01-01

    The thermal rate coefficient for the prototype reaction H + H2 yields H2 + H with zero total angular momentum is calculated by summing, averaging, and numerically integrating state-to-state reaction probabilities calculated by time-independent quantum-mechanical scattering theory. The results are very carefully converged with respect to all numerical parameters in order to provide high-precision benchmark results for confirming the accuracy of new methods and testing their efficiency.

  7. Cross-section and reaction rates for some reactions involved in explosive nucleosynthesis

    International Nuclear Information System (INIS)

    Cheng, C.W.

    1979-03-01

    Total proton-induced and alpha-induced reaction cross sections have been determined for the 24 Mg(α,n), 25 Mg(p,n), 26 Mg(p,n), 27 Al(p,n), 28 Si(α,n), 42 Ca(p,γ), 42 Ca(α,n) and 44 Ca(p,n) reactions from energies near threshold (except the exothermic (p,γ) reaction) to about 3 to 4 MeV above threshold. The product nuclei are all positron emitters with half-lives ranging from about 3 sec to about 4 hours. From the measured cross sections reaction rates have been calculated in the temperature range 1 9 9 =1, at which the discrepancy is large. Included also are analytic forms for (p,n), (α,n), and (p,γ) reactions which can be used to describe the reaction rate within the temperature range 1 9 <=6 and which agree with the experimental rates at the discrete temperatures where the reaction rates have been calculated

  8. RPMDrate: Bimolecular chemical reaction rates from ring polymer molecular dynamics

    KAUST Repository

    Suleimanov, Yu.V.

    2013-03-01

    We present RPMDrate, a computer program for the calculation of gas phase bimolecular reaction rate coefficients using the ring polymer molecular dynamics (RPMD) method. The RPMD rate coefficient is calculated using the Bennett-Chandler method as a product of a static (centroid density quantum transition state theory (QTST) rate) and a dynamic (ring polymer transmission coefficient) factor. The computational procedure is general and can be used to treat bimolecular polyatomic reactions of any complexity in their full dimensionality. The program has been tested for the H+H2, H+CH 4, OH+CH4 and H+C2H6 reactions. © 2012 Elsevier B.V. All rights reserved.

  9. The reaction rates of electrons with native and irradiated ribonuclease

    International Nuclear Information System (INIS)

    Schuessler, H.; Ebert, M.; Davies, J.V.

    1977-01-01

    The rate of reaction of hydrated electrons with proteins depends, amongst other things, on the conformational structure of the protein, and irradiation itself causes conformational changes in proteins. A study has been made of variations in the reaction rates of hydrated electrons with RNase pre-irradiated by the Linac or by a 60 Co γ-source. The reaction rate constants varied with the pre-irradiation dose, the concentration of phosphate buffer, the enzyme concentration and also the presence of 10 -2 M ethanol. These variations serve to emphasize the importance of the tertiary structure of biological molecules in irradiation processes and have significant implications in the mathematical analysis of the inactivation of enzymes in steady-state irradiation processes. (U.K.)

  10. RPMDrate: Bimolecular chemical reaction rates from ring polymer molecular dynamics

    KAUST Repository

    Suleimanov, Yu.V.; Allen, J.W.; Green, W.H.

    2013-01-01

    We present RPMDrate, a computer program for the calculation of gas phase bimolecular reaction rate coefficients using the ring polymer molecular dynamics (RPMD) method. The RPMD rate coefficient is calculated using the Bennett-Chandler method as a product of a static (centroid density quantum transition state theory (QTST) rate) and a dynamic (ring polymer transmission coefficient) factor. The computational procedure is general and can be used to treat bimolecular polyatomic reactions of any complexity in their full dimensionality. The program has been tested for the H+H2, H+CH 4, OH+CH4 and H+C2H6 reactions. © 2012 Elsevier B.V. All rights reserved.

  11. Back reaction and the local cosmological expansion rate

    CERN Document Server

    Geshnizjani, G

    2002-01-01

    We calculate the back reaction of cosmological perturbations on a general relativistic variable which measures the local expansion rate of the Universe. Specifically, we consider a cosmological model in which matter is described by a single field. We analyze back reaction both in a matter-dominated Universe and in a phase of scalar field-driven chaotic inflation. In both cases, we find that the leading infrared terms contributing to the back reaction vanish when the local expansion rate is measured at a fixed value of the matter field which is used as a clock, whereas they do not appear to vanish if the expansion rate is evaluated at a fixed value of the background time. We discuss possible implications for more realistic models with a more complicated matter sector.

  12. Effects of ion and electron screening on thermonuclear reaction rates

    International Nuclear Information System (INIS)

    Brady, L.R. Jr.

    1977-01-01

    The effects of screening by ions and electrons on thermonuclear reaction rates in stellar plasmas are considered. The enhancement of the reaction rate ranges from negligible to extremely large (on the order of 10 26 or greater). In order to calculate these effects, the potential about a given reacting nucleus is determined. First, Boltzmann-Vlasov and Poisson-Boltzmann equations are solved to yield a Yukawa potential. A suitable approximation to this potential is integrated in the action integral to give the barrier penetration. The screened reaction rate is then found by the saddle-point method. In developing a general formalism to calculate the screened reaction rate and the screening factor, effects due to the finite size of the nucleus are considered and found to be negligible. An expression for the screening factor for resonant reaction rates is also derived. A different and relatively simple approach, based on work of Stewart and Pyatt (1966), is used to find the barrier penetration from the action integral in two approximations: a modified Coulomb potential and a constant-shift potential. Screening factors are calculated for carbon burning at T 6 = 100 and T 6 = 400 for a wide range of densities and also for several examples in late stellar evolution. These screening factors are, for the most part, greater than those given by most others by a few percent at low density to 4 or more orders of magnitude at T 6 = 100 and rho = 10 10 g/cm 3 . Near the edge of the crystalline lattice region, however, they are significantly lower than those of some others. The increase in reaction rates for carbon burning indicates that carbon ignition may occur at lower densities than previously thought and may affect the density at which a supernova shock may occur

  13. Charge state distribution of 16O from the 4He(12C,16O)γ reaction of astrophysical interest studied both experimentally and theoretically

    International Nuclear Information System (INIS)

    Liu, Shengjin; Sakurai, Makoto; Sagara, Kenshi; Teranishi, Takashi; Fujita, Kunihiro; Yamaguchi, Hiroyuki; Matsuda, Sayaka; Mitsuzumi, Tatsuki; Iwazaki, Makoto; Rosary, Mariya T.; Kato, Daiji; Tolstikhina, I.Yu.

    2014-01-01

    In astrophysics, 4 He( 12 C, 16 O)γ reaction places an important role. At Kyushu University Tandem accelerator Laboratory (KUTL), the measurement of 4 He( 12 C, 16 O)γ cross section is in progress in the energy range of astrophysical nuclear reaction. Since the charge state of product 16 O ions after passing through the gas target is spread and only one charge state can be measured at terminal detector, it is necessary to know the charge state distribution of 16 O ions passing through the He gas target precisely. Here, we report the charge state distribution of the 16 O recoils both experimentally and theoretically. Experimentally, we measured the equilibrium charge state distribution of 16 O ions in the windowless helium gas target with the beam energy of primary 16 O ions at 7.2, 4.5, and 3.45 MeV at KUTL. The measured results showed a Gaussian distribution for the charge state fraction. Theoretically, we proposed a framework for the charge state distribution study. Charge state distribution was computed by solving a set of differential equations including a series of charge exchange cross sections. For the ionization cross section, plane-wave Born approximation was applied and modified by taking target atomic screening as a function of momentum transfer into account. For the capture cross section, continuum distorted wave approximation was applied and the influence of the gas target density was taken into account in the process of electron capture. Using above charge exchange cross sections, the charge state evolution was simulated. According to the equilibrium distribution, we compared the theoretical calculation to the experimental data. After taking into account the density effects in the charge exchange process, the theoretical charge state distributions shows a good agreement with the experimental data. Both experimental and theoretical results are useful to understand the charge fraction of recoil oxygen created via 4 He( 12 C, 16 O)γ reaction

  14. Liquid Film Diffusion on Reaction Rate in Submerged Biofilters

    DEFF Research Database (Denmark)

    Christiansen, Pia; Hollesen, Line; Harremoës, Poul

    1995-01-01

    Experiments were carried out in order to investigate the influence of liquid film diffusion on reaction rate in a submerged biofilter with denitrification and in order to compare with a theoretical study of the mass transfer coefficient. The experiments were carried out with varied flow, identified...... by the empty bed velocity of inflow and recirculation, respectively 1.3, 2.8, 5.6 and 10.9 m/h. The filter material consisted of 3 mm biostyren spheres. The results indicate that the influence of liquid film diffusion on reaction rate can be ignored....

  15. The Influence of Particle Charge on Heterogeneous Reaction Rate Coefficients

    Science.gov (United States)

    Aikin, A. C.; Pesnell, W. D.

    2000-01-01

    The effects of particle charge on heterogeneous reaction rates are presented. Many atmospheric particles, whether liquid or solid are charged. This surface charge causes a redistribution of charge within a liquid particle and as a consequence a perturbation in the gaseous uptake coefficient. The amount of perturbation is proportional to the external potential and the square of the ratio of debye length in the liquid to the particle radius. Previous modeling has shown how surface charge affects the uptake coefficient of charged aerosols. This effect is now included in the heterogeneous reaction rate of an aerosol ensemble. Extension of this analysis to ice particles will be discussed and examples presented.

  16. Astrophysical Flows

    Science.gov (United States)

    Pringle, James E.; King, Andrew

    2003-07-01

    Almost all conventional matter in the Universe is fluid, and fluid dynamics plays a crucial role in astrophysics. This new graduate textbook provides a basic understanding of the fluid dynamical processes relevant to astrophysics. The mathematics used to describe these processes is simplified to bring out the underlying physics. The authors cover many topics, including wave propagation, shocks, spherical flows, stellar oscillations, the instabilities caused by effects such as magnetic fields, thermal driving, gravity, shear flows, and the basic concepts of compressible fluid dynamics and magnetohydrodynamics. The authors are Directors of the UK Astrophysical Fluids Facility (UKAFF) at the University of Leicester, and editors of the Cambridge Astrophysics Series. This book has been developed from a course in astrophysical fluid dynamics taught at the University of Cambridge. It is suitable for graduate students in astrophysics, physics and applied mathematics, and requires only a basic familiarity with fluid dynamics.• Provides coverage of the fundamental fluid dynamical processes an astrophysical theorist needs to know • Introduces new mathematical theory and techniques in a straightforward manner • Includes end-of-chapter problems to illustrate the course and introduce additional ideas

  17. Applications of the Trojan Horse method in nuclear astrophysics

    Energy Technology Data Exchange (ETDEWEB)

    Spitaleri, Claudio, E-mail: spitaleri@lns.infn.it [Dipartimento di Fisica e Astronomia, Università di Catania, Catania, Italy and Laboratori Nazionali del Sud-INFN, Catania (Italy)

    2015-02-24

    The study of the energy production in stars and related nucleosyntesis processes requires increasingly precise knowledge of the nuclear reaction cross section and reaction rates at interaction energy. In order to overcome the experimental difficulties, arising from small cross-sections involved in charge particle induced reactions at astrophysical energies, and from the presence of electron screening, it was necessary to introduce indirect methods. Trough these methods it is possible to measure cross sections at very small energies and retrieve information on electron screening effect when ultra-low energy direct measurements are available. The Trojan Horse Method (THM) represents the indirect technique to determine the bare nucleus astrophysical S-factor for reactions between charged particles at astrophysical energies. The basic theory of the THM is discussed in the case of non-resonant.

  18. Semiclassical Calculation of Reaction Rate Constants for Homolytical Dissociations

    Science.gov (United States)

    Cardelino, Beatriz H.

    2002-01-01

    There is growing interest in extending organometallic chemical vapor deposition (OMCVD) to III-V materials that exhibit large thermal decomposition at their optimum growth temperature, such as indium nitride. The group III nitrides are candidate materials for light-emitting diodes and semiconductor lasers operating into the blue and ultraviolet regions. To overcome decomposition of the deposited compound, the reaction must be conducted at high pressures, which causes problems of uniformity. Microgravity may provide the venue for maintaining conditions of laminar flow under high pressure. Since the selection of optimized parameters becomes crucial when performing experiments in microgravity, efforts are presently geared to the development of computational OMCVD models that will couple the reactor fluid dynamics with its chemical kinetics. In the present study, we developed a method to calculate reaction rate constants for the homolytic dissociation of III-V compounds for modeling OMCVD. The method is validated by comparing calculations with experimental reaction rate constants.

  19. X particle effect for 6Li reaction rates calculations

    International Nuclear Information System (INIS)

    Kocak, G.; Balantekin, A. B.

    2009-01-01

    The inferred primordial 6 L i-7 L i abundances are different from standard big bang nucleosynthesis results, 6 L i is 1000 times larger and 7 L i is 3 times smaller than the big bang prediction. In big bang nucleosynthesis, negatively charged massive X particles a possible solution to explain this primordial Li abundances problem [1]. In this study, we consider only X particle effect for nuclear reactions to obtain S-factor and reaction rates for Li. All S-factors calculated within the Optical Model framework for d(α,γ)6 L i system. We showed that the enhancement effect of massive negatively charged X particle for 6 L i system reaction rate.(author)

  20. Rates of ionic reactions with charged nanoparticles in aqueous media

    NARCIS (Netherlands)

    Duval, J.F.L.; Leeuwen, van H.P.

    2012-01-01

    A theory is developed to evaluate the electrostatic correction for the rate of reaction between a small ion and a charged ligand nanoparticle. The particle is assumed to generally consist of an impermeable core and a shell permeable to water and ions. A derivation is proposed for the ion diffusion

  1. Calculation of multigroup reaction rates for the Ghana Research ...

    African Journals Online (AJOL)

    The discrete ordinate spatial model, which pro-vides solution to the differential form of the transport equation by the Carlson-SN (N=4) approach was adopted to solve the Ludwig-Boltzmann multigroup neutron transport equation for this analysis. The results show that for any fissile resonance absorber, the reaction rates ...

  2. Neutron detector for fusion reaction-rate measurements

    International Nuclear Information System (INIS)

    Lerche, R.A.; Phillion, D.W.; Tietbohl, G.L.

    1993-01-01

    We have developed a fast, sensitive neutron detector for recording the fusion reaction-rate history of inertial-confinement fusion (ICF) experiments. The detector is based on the fast rise-time of a commercial plastic scintillator (BC-422) and has a response 7 neutrons

  3. The astrophysical r-process and its dependence on properties of nuclei far from stability: Beta strength functions and neutron capture rates

    International Nuclear Information System (INIS)

    Klapdor, H.V.; Metzinger, J.; Oda, T.; Thielemann, F.K.; Hillebrandt, W.

    1981-01-01

    The question of the astrophysical site of the rapid neutron capture (r-) process which is believed to be responsible for the production of the heavy elements in the universe has been a problem in astrophysics for more than two decades. The solution of this problem is not only dependent on the development of realistic astrophysical supernova models, i.e. correct treatment of the hydrodynamics of gravitational collapse and supernova explosion and the equation of state of hot and dense matter, but is shown in this paper to be very sensitive also to 'standard' nuclear physics properties of nuclei far from stability such as beta decay properties and neutron capture rates. For both of the latter, strongly oversimplifying assumptions, not applying the development in nuclear physics during the last decade, have been made in almost all r-process calculations performed up to now. A critical discussion of the state of the art of such calculations seems therefore to be indicated. In this paper procedures are described which allow one to obtain: 1) β-decay properties (decay rates, β-delayed neutron emissions and fission rates); 2) neutron capture rates for neutron-rich nuclei considerably improved over what has been used up to now. The beta strength functions are calculated for approx. equal to6000 nuclei between beta stability line and neutron drip line. By hydrodynamical supernova explosion calculations using realistic stellar models it is shown that as a consequence of the improved β-rates explosive He burning is a convincing alternative site to the 'classical' r-process whose existence still is questionable. The new β-rates will be important also for the investigation of further astrophysical sites producing heavy elements such as the r(n)-processes in explosive C or Ne burning. (orig.)

  4. Estimates of the astrophysical S-factors for proton radiative capture by 10B and 24Mg nuclei using the ANCs from proton transfer reactions

    International Nuclear Information System (INIS)

    Artemov, S.V.; Igamov, S.B.; Karakhodzhaev, A.A.; Nie, G.K.; Yarmukhamedov, R.; Zaparov, E.A.; Burtebaev, N.; Rehm, K.E.

    2010-01-01

    The contribution of the direct radiative capture of protons by 10 B and 24 Mg nuclei at low energies to the astrophysical S-factors in the reactions 10 B(p,γ) 11 C and 24 Mg(p,γ) 25 Al have been calculated within the R-matrix formalism by using empirical proton asymptotical normalization coefficients (ANC). The ANCs for bound proton configurations { 10 B+p} and { 24 Mg+p} were obtained from the analysis of the reactions ( 3 He, d). The ANCs were also estimated from the values of the neutron ANCs in the mirror nucleus 25 Mg following the suggestion that the neutron and the proton in the mirror states have equivalent nuclear potentials. It has been found that the S-factor for the reaction 10 B(p,γ) 11 C extrapolated to zero energy contributes ~100 keV b to the radiative capture to the ground state of 11 C. For the reaction 24 Mg(p,γ) 25 Al the value S(0) gives 58 keV b with a direct capture contribution of 41 keV b. (author)

  5. Nuclear astrophysics

    International Nuclear Information System (INIS)

    Haxton, W.C.

    1992-01-01

    The problem of core-collapse supernovae is used to illustrate the many connections between nuclear astrophysics and the problems nuclear physicists study in terrestrial laboratories. Efforts to better understand the collapse and mantle ejection are also motivated by a variety of interdisciplinary issues in nuclear, particle, and astrophysics, including galactic chemical evolution, neutrino masses and mixing, and stellar cooling by the emission of new particles. The current status of theory and observations is summarized

  6. Relativistic astrophysics

    CERN Document Server

    Demianski, Marek

    2013-01-01

    Relativistic Astrophysics brings together important astronomical discoveries and the significant achievements, as well as the difficulties in the field of relativistic astrophysics. This book is divided into 10 chapters that tackle some aspects of the field, including the gravitational field, stellar equilibrium, black holes, and cosmology. The opening chapters introduce the theories to delineate gravitational field and the elements of relativistic thermodynamics and hydrodynamics. The succeeding chapters deal with the gravitational fields in matter; stellar equilibrium and general relativity

  7. Estimation of the rate of volcanism on Venus from reaction rate measurements

    Science.gov (United States)

    Fegley, Bruce, Jr.; Prinn, Ronald G.

    1989-01-01

    Laboratory rate data for the reaction between SO2 and calcite to form anhydrite are presented. If this reaction rate represents the SO2 reaction rate on Venus, then all SO2 in the Venusian atmosphere will disappear in 1.9 Myr unless volcanism replenishes the lost SO2. The required volcanism rate, which depends on the sulfur content of the erupted material, is in the range 0.4-11 cu km of magma erupted per year. The Venus surface composition at the Venera 13, 14, and Vega 2 landing sites implies a volcanism rate of about 1 cu km/yr. This geochemically estimated rate can be used to determine if either (or neither) of two discordant geophysically estimated rates is correct. It also suggests that Venus may be less volcanically active than the earth.

  8. Determination of rate constants for the oxygen reduction reaction

    Energy Technology Data Exchange (ETDEWEB)

    Racz, A.; Walter, T.; Stimming, U. [Munich Technical Univ., Garching (Germany). Dept. of Physics

    2008-07-01

    The oxygen reduction reaction (ORR) in fuel cells is a complex and fundamental electrochemical reaction. However, greater insight is needed into this multi-electron reaction in order to develop efficient and innovative catalysts. The rotating ring disc electrode (RRDE) is a useful tool for studying reaction intermediates of the ORR and to better understand the reaction pathway. Carbon materials such as carbon nanofilaments-platelets (CNF-PL) have high electrical conductivity and may be considered for fuel cells. In particular Pt and RuSe{sub x}, deposited on CNF-PL materials could act as efficient catalysts in fuel cells. This study used the RRDE to evaluate the oxygen reduction kinetics of these catalysts in oxygen-saturated, diluted sulphuric acid at room temperature. Kinetic data and hydrogen peroxide formation were determined by depositing a thin-film of the catalyst on the Au disc. The values for the constants k1, k2 and k3 were obtained using diagnostic criteria and expressions to calculate the rate constants of the cathodic oxygen reduction reaction for RuSe on new carbon supports. A potential dependency of the constants k1 and k2 for RuSe{sub x}/CNF-PL was observed. The transition of the Tafel slopes for this catalyst was obtained. 4 refs., 1 fig.

  9. Recent developments in semiclassical mechanics: eigenvalues and reaction rate constants

    International Nuclear Information System (INIS)

    Miller, W.H.

    1976-04-01

    A semiclassical treatment of eigenvalues for a multidimensional non-separable potential function and of the rate constant for a chemical reaction with an activation barrier is presented. Both phenomena are seen to be described by essentially the same semiclassical formalism, which is based on a construction of the total Hamiltonian in terms of the complete set of ''good'' action variables (or adiabatic invariants) associated with the minimum in the potential energy surface for the eigenvalue case, or the saddle point in the potential energy surface for the case of chemical reaction

  10. Rate constant for reaction of hydroxyl radicals with bicarbonate ions

    International Nuclear Information System (INIS)

    Buxton, G.V.; Elliot, A.J.

    1986-01-01

    The rate constant for reaction of hydroxyl radicals with the bicarbonate ion has been determined to be 8.5 x 10 6 dm 3 mol -1 s -1 . This value was calculated from: the measured rate of formation of the CO 3 - radical in pulsed electron irradiation of bicarbonate solutions over the pH range 7.0 to 9.4; the pK for the equilibrium HCO 3 - = CO 3 2- + H + ; and the rate constant for hydroxyl radicals reacting with the carbonate ion. (author)

  11. Astrophysical S factor for the 7Li(d,n0)8Be and 7Li(d,n1)8Be reactions

    International Nuclear Information System (INIS)

    Sabourov, A.; Ahmed, M.W.; Blackston, M.A.; Crowell, A.S.; Howell, C.R.; Perdue, B.A.; Sabourov, K.; Tonchev, A.; Weller, H.R.; Prior, R.M.; Spraker, M.C.

    2006-01-01

    The absolute astrophysical S factor and cross section for the 7 Li(d,n 0 ) 8 Be and 7 Li(d,n 1 ) 8 Be reactions have been determined using deuteron beams with energies between 45 and 80 keV. The slope of the S factor is consistent with zero in the n 0 case but is slightly negative in the n 1 case. The S factor for the sum of both neutron groups at c.m. energies below 70 keV is S(E)=5400(±1500)-37(±21)E keV b, where E is the c.m. energy in keV

  12. Development of a Monte Carlo code for the data analysis of the {sup 18}F(p,α){sup 15}O reaction at astrophysical energies

    Energy Technology Data Exchange (ETDEWEB)

    Caruso, A.; Cherubini, S.; Spitaleri, C.; La Cognata, M.; Lamia, L.; Rapisarda, G.; Romano, S.; Sergi, ML. [Dipartimento di Fisica e Astronomia, Catania, Italy and INFN-Laboratori Nazionali del Sud, Catania (Italy); Crucillà, V. [INFN-Laboratori Nazionali del Sud, Catania (Italy); Gulino, M. [Universitá di Enna KORE, Enna, Italy and INFN-Laboratori Nazionali del Sud, Catania (Italy); Kubono, S. [Riken, Wako, Tokyo, Japan and Center for Nuclear Study, The University of Tokyo (Japan); Yamaguchi, H.; Hayakawa, S.; Wakabayashi, Y. [Center for Nuclear Study, The University of Tokyo (Japan); Iwasa, N. [Department of Physics, Tohoku University, Sendai (Japan); Kato, S. [Department of Physics, Yamagata University, Yamagata (Japan); Komatsubara, T. [Rare Isotope Science Project, Institute for Basic Science, Yuseong-daero, Yuseong-gu, Daejeon 305-811 (Korea, Republic of); Teranishi, T. [Department of Physics, Kyushu University, Fukuoka (Japan); Coc, A. [Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, Orsay (France); Hammache, F. [Institut de Physique Nucléaire, IN2P3, Orsay (France); and others

    2015-02-24

    Novae are astrophysical events (violent explosion) occurring in close binary systems consisting of a white dwarf and a main-sequence star or a star in a more advanced stage of evolution. They are called 'narrow systems' because the two components interact with each other: there is a process of mass exchange with resulting in the transfer of matter from the companion star to the white dwarf, leading to the formation of this last of the so-called accretion disk, rich mainly of hydrogen. Over time, more and more material accumulates until the pressure and the temperature reached are sufficient to trigger nuclear fusion reactions, rapidly converting a large part of the hydrogen into heavier elements. The products of 'hot hydrogen burning' are then placed in the interstellar medium as a result of violent explosions. Studies on the element abundances observed in these events can provide important information about the stages of evolution stellar. During the outbursts of novae some radioactive isotopes are synthesized: in particular, the decay of short-lived nuclei such as {sup 13}N and {sup 18}F with subsequent emission of gamma radiation energy below 511 keV. The gamma rays from products electron-positron annihilation of positrons emitted in the decay of {sup 18}F are the most abundant and the first observable as soon as the atmosphere of the nova starts to become transparent to gamma radiation. Hence the importance of the study of nuclear reactions that lead both to the formation and to the destruction of {sup 18}F. Among these, the {sup 18}F(p,α){sup 15}O reaction is one of the main channels of destruction. This reaction was then studied at energies of astrophysical interest. The experiment done at Riken, Japan, has as its objective the study of the {sup 18}F(p,α){sup 15}O reaction, using a beam of {sup 18}F produced at CRIB, to derive important information about the phenomenon of novae. In this paper we present the experimental technique and the

  13. Nuclear physics and astrophysics

    International Nuclear Information System (INIS)

    Schramm, D.N.; Olinto, A.V.

    1993-06-01

    The authors report on recent progress of research at the interface of nuclear physics and astrophysics. During the past year, the authors continued to work on Big Bang and stellar nucleosynthesis, the solar neutrino problem, the equation of state for dense matter, the quark-hadron phase transition, and the origin of gamma-ray bursts; and began studying the consequences of nuclear reaction rates in the presence of strong magnetic fields. They have shown that the primordial production of B and Be cannot explain recent detections of these elements in halo stars and have looked at spallation as the likely source of these elements. By looking at nucleosynthesis with inhomogeneous initial conditions, they concluded that the Universe must have been very smooth before nucleosynthesis. They have also constrained neutrino oscillations and primordial magnetic fields by Big Bang nucleosynthesis. On the solar neutrino problem, they have analyzed the implications of the SAGE and GALLEX experiments. They also showed that the presence of dibaryons in neutron stars depends weakly on uncertainties of nuclear equations of state. They have started to investigate the consequences of strong magnetic fields on nuclear reactions and implications for neutron star cooling and supernova nucleosynthesis

  14. Non extensive corrections to stellar nuclear reactions rate

    Energy Technology Data Exchange (ETDEWEB)

    Assuncao, M. [Universidade Federal de Sao Paulo (DCET/UNIFESP), Diadema, SP (Brazil). Dept. de Ciencias Exatas e da Terra; Silveira, F.E.M. [Universidade Federal do ABC, Santo Andre, SP (Brazil). Centro de Ciencias Naturais e Humanas; Lima, J.A.S. [Universidade de Sao Paulo (IAG/USP), SP (Brazil). Inst. de Astronomia, Geofisica e Ciencias Atmosfericas

    2010-07-01

    Full text: Stellar nucleosynthesis is widely accepted as the basic mechanism for creation of chemical elements in the Universe. In particular, nuclear reactions occurring in the Sun are recognized as responsible for its energy generation. The problem of to determine the energy generation mechanism in stars was firstly attacked by Gamow in the framework of his quantum mechanical theory of potential barrier penetration. According to that approach, the reactions rate is calculated by averaging the penetration factor over the velocity distribution of the plasma particles. A randomization of that distribution is expected as a consequence of the reactions. However, diffusion processes in the macroscopic environment should balance the resulting particles number depletion. Therefore, matter, energy, and momentum might steadily flow. In other words, a quasi-stationary equilibrium state must be attained. In this work, the potential barrier penetration approach to stellar nuclear reactions rate has been rediscussed with basis on Tsallis nonextensive statistics. The investigation has been restricted to non-resonant reactions, for which the S-factor can be regarded as a constant. It has been found that, within the extended formulation, the nonextensive q-parameter is constrained to a maximum value. Accordingly, the q-energy has been shown to exhibit a minimum. The q-Gamow peak has been derived and, in connection with the usual Gaussian approximation, the corresponding half q-width has been also estimated. Plots of the q-energy, q-Gamow peak and half q-width for some reactions with stellar physics interest have been produced. (author)

  15. Cross sections and thermonuclear reaction rates of proton-induced reactions on 37Cl

    International Nuclear Information System (INIS)

    Weber, R.O.; Tingwell, C.I.W.; Mitchell, L.W.; Sevior, M.E.; Sargood, D.G.

    1984-01-01

    The yields of γ-rays from the reactions of 37 Cl(p,γ) 38 Ar and 37 Cl(p,αγ) 34 S have been measured as a of bombarding energy over the ranges 0.65 - 2.15 MeV and 1.25 -2.15 MeV respectively, and the yield of neutrons from 37 Cl(p,n) 37 Ar from threshold to 2.50 MeV. The results are compared with global statistical-model calculations and thermonuclear reaction rates are calculated for the temperature range 5 x 10 8 - 10 10 K. The significance of these thermonuclear reaction rates for stellar nucleosynthesis calculations is discussed

  16. A model for reaction rates in turbulent reacting flows

    Science.gov (United States)

    Chinitz, W.; Evans, J. S.

    1984-01-01

    To account for the turbulent temperature and species-concentration fluctuations, a model is presented on the effects of chemical reaction rates in computer analyses of turbulent reacting flows. The model results in two parameters which multiply the terms in the reaction-rate equations. For these two parameters, graphs are presented as functions of the mean values and intensity of the turbulent fluctuations of the temperature and species concentrations. These graphs will facilitate incorporation of the model into existing computer programs which describe turbulent reacting flows. When the model was used in a two-dimensional parabolic-flow computer code to predict the behavior of an experimental, supersonic hydrogen jet burning in air, some improvement in agreement with the experimental data was obtained in the far field in the region near the jet centerline. Recommendations are included for further improvement of the model and for additional comparisons with experimental data.

  17. Estimation of the Polymerization Rate of Liquid Propylene Using Adiabatic Reaction Calorimetry and Reaction Dilatometry

    NARCIS (Netherlands)

    Al-haj Ali, Mohammad; Betlem, Ben; Roffel, Brian; Weickert, Günter

    2007-01-01

    The use of pressure-drop and constant-pressure dilatometry for obtaining rate data for liquid propylene polymerization in filled batch reactors was examined. The first method uses reaction temperature and pressure as well as the compressibility of the reactor contents to calculate the polymerization

  18. Kinetic aspects of the embedded clusters: Reaction - Rate Theory

    International Nuclear Information System (INIS)

    Despa, F.; Apostol, M.

    1995-07-01

    The main stages of the cluster growth process are reviewed using Reaction - Rate Theory. The precipitation stage is shown as a relaxation of the solute towards a cluster state characterized by a higher stability. The kinetic of the late stage of phase separation, the coarsening process, is analyzed by an off-centre diffusion mechanism. The theoretical results are compared to the experimental ones. (author). 37 refs, 6 figs

  19. Astrophysical Concepts

    CERN Document Server

    Harwit, Martin

    2006-01-01

    This classic text, aimed at senior undergraduates and beginning graduate students in physics and astronomy, presents a wide range of astrophysical concepts in sufficient depth to give the reader a quantitative understanding of the subject. Emphasizing physical concepts, the book outlines cosmic events but does not portray them in detail: it provides a series of astrophysical sketches. For this fourth edition, nearly every part of the text has been reconsidered and rewritten, new sections have been added to cover recent developments, and others have been extensively revised and brought up to date. The book begins with an outline of the scope of modern astrophysics and enumerates some of the outstanding problems faced in the field today. The basic physics needed to tackle these questions are developed in the next few chapters using specific astronomical processes as examples. The second half of the book enlarges on these topics and shows how we can obtain quantitative insight into the structure and evolution of...

  20. Nuclear astrophysics

    International Nuclear Information System (INIS)

    Arnould, M.; Takahashi, K.

    1999-01-01

    Nuclear astrophysics is that branch of astrophysics which helps understanding of the Universe, or at least some of its many faces, through the knowledge of the microcosm of the atomic nucleus. It attempts to find as many nuclear physics imprints as possible in the macrocosm, and to decipher what those messages are telling us about the varied constituent objects in the Universe at present and in the past. In the last decades much advance has been made in nuclear astrophysics thanks to the sometimes spectacular progress made in the modelling of the structure and evolution of the stars, in the quality and diversity of the astronomical observations, as well as in the experimental and theoretical understanding of the atomic nucleus and of its spontaneous or induced transformations. Developments in other subfields of physics and chemistry have also contributed to that advance. Notwithstanding the accomplishment, many long-standing problems remain to be solved, and the theoretical understanding of a large variety of observational facts needs to be put on safer grounds. In addition, new questions are continuously emerging, and new facts endangering old ideas. This review shows that astrophysics has been, and still is, highly demanding to nuclear physics in both its experimental and theoretical components. On top of the fact that large varieties of nuclei have to be dealt with, these nuclei are immersed in highly unusual environments which may have a significant impact on their static properties, the diversity of their transmutation modes, and on the probabilities of these modes. In order to have a chance of solving some of the problems nuclear astrophysics is facing, the astrophysicists and nuclear physicists are obviously bound to put their competence in common, and have sometimes to benefit from the help of other fields of physics, like particle physics, plasma physics or solid-state physics. Given the highly varied and complex aspects, we pick here some specific nuclear

  1. Plasma astrophysics

    CERN Document Server

    Kaplan, S A; ter Haar, D

    2013-01-01

    Plasma Astrophysics is a translation from the Russian language; the topics discussed are based on lectures given by V.N. Tsytovich at several universities. The book describes the physics of the various phenomena and their mathematical formulation connected with plasma astrophysics. This book also explains the theory of the interaction of fast particles plasma, their radiation activities, as well as the plasma behavior when exposed to a very strong magnetic field. The text describes the nature of collective plasma processes and of plasma turbulence. One author explains the method of elementary

  2. Neutrino astrophysics

    International Nuclear Information System (INIS)

    Roulet, E.

    2001-01-01

    A general overview of neutrino physics and astrophysics is given, starting with a historical account of the development of our understanding of neutrinos and how they helped to unravel the structure of the Standard Model. We discuss why it is so important to establish if neutrinos are massive and introduce the main scenarios to provide them a mass. The present bounds and the positive indications in favor of non-zero neutrino masses are discussed, including the recent results on atmospheric and solar neutrinos. The major role that neutrinos play in astrophysics and cosmology is illustrated. (author)

  3. Resonance Strength Measurement at Astrophysical Energies: The 17O(p,α14N Reaction Studied via THM

    Directory of Open Access Journals (Sweden)

    Sergi M.L.

    2016-01-01

    Full Text Available In recent years, the Trojan Horse Method (THM has been used to investigate the low-energy cross sections of proton-induced reactions on 17O nuclei, overcoming extrapolation procedures and enhancement effects due to electron screening. We will report on the indirect study of the 17O(p,α14N reaction via the Trojan Horse Method by applying the approach developed for extracting the resonance strength of narrow resonance in the ultralow energy region. The mean value of the strengths obtained in the two measurements was calculated and compared with the direct data available in literature.

  4. The TDF System for Thermonuclear Plasma Reaction Rates, Mean Energies and Two-Body Final State Particle Spectra

    International Nuclear Information System (INIS)

    Warshaw, S I

    2001-01-01

    The rate of thermonuclear reactions in hot plasmas as a function of local plasma temperature determines the way in which thermonuclear ignition and burning proceeds in the plasma. The conventional model approach to calculating these rates is to assume that the reacting nuclei in the plasma are in Maxwellian equilibrium at some well-defined plasma temperature, over which the statistical average of the reaction rate quantity σv is calculated, where σ is the cross-section for the reaction to proceed at the relative velocity v between the reacting particles. This approach is well-understood and is the basis for much nuclear fusion and astrophysical nuclear reaction rate data. The Thermonuclear Data File (TDF) system developed at the Lawrence Livermore National Laboratory (Warshaw 1991), which is the topic of this report, contains data on the Maxwellian-averaged thermonuclear reaction rates for various light nuclear reactions and the correspondingly Maxwellian-averaged energy spectra of the particles in the final state of those reactions as well. This spectral information closely models the output particle and energy distributions in a burning plasma, and therefore leads to more accurate computational treatments of thermonuclear burn, output particle energy deposition and diagnostics, in various contexts. In this report we review and derive the theoretical basis for calculating Maxwellian-averaged thermonuclear reaction rates, mean particle energies, and output particle spectral energy distributions for these reactions in the TDF system. The treatment of the kinematics is non-relativistic. The current version of the TDF system provides exit particle energy spectrum distributions for two-body final state reactions only. In a future report we will discuss and describe how output particle energy spectra for three- and four-body final states can be developed for the TDF system. We also include in this report a description of the algorithmic implementation of the TDF

  5. The B-10((p)over-right-arrow, gamma)C-11 reaction at astrophysically relevant energies

    NARCIS (Netherlands)

    Tonchev, AP; Nelson, SO; Sabourov, K; Crowley, BT; Joshi, K; Weller, HR; Kelley, JH; Prior, RM; Spraker, M; Kalantar-Nayestanaki, N

    2003-01-01

    The B-10(, gamma)C-11 reaction was studied by detecting the gamma-rays produced when 100, 130-, and 160-keV polarized protons were stopped in a thick B-10 target. Polarized and unpolarized incident beams were used to measure the cross section and vector analyzing power as a function of angle and

  6. Neutron-capture reactions by stable and unstable neutron-rich nuclei and their relevance for nucleosynthesis in hot and explosive astrophysical scenarios

    International Nuclear Information System (INIS)

    Hofinger, R.

    1997-10-01

    This thesis deals on the one hand with neutron-capture reactions by carbon-, nitrogen-, oxygen- and sulfur-isotopes, and on the other hand with the two-step processes 4 He(2n, γ) 6 He and 9 Li(2n, γ) 11 Li. Some of the involved carbon-, nitrogen- and oxygen-isotopes possess neutron-halos characterized by the unexpected large radial extension of the nuclear matter density distribution. Special attention is paid to the halo properties in the calculation of the direct neutron capture cross section. For the determination of the nuclear structure, models are used, when no experimental information is available. The results for the reaction rates are compared to previously used rates. The rates obtained in this work are partly orders of magnitude higher than the previously used reaction rates. The reaction rates for the two-step processes are on the one hand calculated assuming a two-step process, on the other hand from genuine three-body models for the process of photodisintegration of the nuclei 6 He and 11 Li. It turns out that the calculations assuming a trio-step process underestimate the reaction rates by orders of magnitude. The influence of the reaction rate for the reaction 4 He(2n, γ) 6 He and the formation of 12 C is examined in a nuclear reaction network under conditions which are typical for the α- process in supernovae of type II. It turns out that under these conditions the influence of the reaction 4 He(2n, γ) 6 He is negligible on the formation of 12 C. (author)

  7. Relativistic astrophysics

    CERN Document Server

    Price, R H

    1993-01-01

    Work reported in the workshop on relativistic astrophysics spanned a wide varicy of topics. Two specific areas seemed of particular interest. Much attention was focussed on gravitational wave sources, especially on the waveforms they produce, and progress was reported in theoretical and observational aspects of accretion disks.

  8. Astrophysics today

    International Nuclear Information System (INIS)

    Cameron, A.G.W.

    1984-01-01

    Examining recent history, current trends, and future possibilities, the author reports the frontiers of research on the solar system, stars, galactic physics, and cosmological physics. The book discusses the great discoveries in astronomy and astrophysics and examines the circumstances in which they occurred. It discusses the physics of white dwarfs, the inflationary universe, the extinction of dinosaurs, black hole, cosmological models, and much more

  9. Optimized reaction mechanism rate rules for ignition of normal alkanes

    KAUST Repository

    Cai, Liming

    2016-08-11

    The increasing demand for cleaner combustion and reduced greenhouse gas emissions motivates research on the combustion of hydrocarbon fuels and their surrogates. Accurate detailed chemical kinetic models are an important prerequisite for high fidelity reacting flow simulations capable of improving combustor design and operation. The development of such models for many new fuel components and/or surrogate molecules is greatly facilitated by the application of reaction classes and rate rules. Accurate and versatile rate rules are desirable to improve the predictive accuracy of kinetic models. A major contribution in the literature is the recent work by Bugler et al. (2015), which has significantly improved rate rules and thermochemical parameters used in kinetic modeling of alkanes. In the present study, it is demonstrated that rate rules can be used and consistently optimized for a set of normal alkanes including n-heptane, n-octane, n-nonane, n-decane, and n-undecane, thereby improving the predictive accuracy for all the considered fuels. A Bayesian framework is applied in the calibration of the rate rules. The optimized rate rules are subsequently applied to generate a mechanism for n-dodecane, which was not part of the training set for the optimized rate rules. The developed mechanism shows accurate predictions compared with published well-validated mechanisms for a wide range of conditions.

  10. Reaction of H2 with O2 in Excited Electronic States: Reaction Pathways and Rate Constants.

    Science.gov (United States)

    Pelevkin, Alexey V; Loukhovitski, Boris I; Sharipov, Alexander S

    2017-12-21

    Comprehensive quantum chemical analysis with the use of the multireference state-averaged complete active space self-consistent field approach was carried out to study the reactions of H 2 with O 2 in a 1 Δ g , b 1 Σ g + , c 1 Σ u - , and A' 3 Δ u electronically excited states. The energetically favorable reaction pathways and possible intersystem crossings have been revealed. The energy barriers were refined employing the extended multiconfiguration quasi-degenerate second-order perturbation theory. It has been shown that the interaction of O 2 (a 1 Δ g ) and O 2 (A' 3 Δ u ) with H 2 occurs through the H-abstraction process with relatively low activation barriers that resulted in the formation of the HO 2 molecule in A″ and A' electronic states, respectively. Meanwhile, molecular oxygen in singlet sigma states (b 1 Σ g + and c 1 Σ u - ) was proved to be nonreactive with respect to the molecular hydrogen. Appropriate rate constants for revealed reaction and quenching channels have been estimated using variational transition-state theory including corrections for the tunneling effect, possible nonadiabatic transitions, and anharmonicity of vibrations for transition states and reactants. It was demonstrated that the calculated reaction rate constant for the H 2 + O 2 (a 1 Δ g ) process is in reasonable agreement with known experimental data. The Arrhenius approximations for these processes have been proposed for the temperature range T = 300-3000 K.

  11. Primordial lithium: New reaction rates, new abundances, new constraints

    International Nuclear Information System (INIS)

    Kawano, L.; Schramm, D.; Steigman, G.

    1986-12-01

    Newly measured nuclear reaction rates for 3 H(α,γ) 7 Li (higher than previous values) and 7 Li(p,α) 4 He (lower than previous values) are shown to increase the 7 Li yield from big bang nucleosynthesis for lower baryon to photon ratio (eta ≤ 4 x 10 -10 ); the yield for higher eta is not affected. New, independent determinations of Li abundances in extreme Pop II stars are in excellent agreement with the earlier work of the Spites and give continued confidence in the use of 7 Li in big bang baryon density determinations. The new 7 Li constraints imply a lower limit on eta of 2 x 10 -10 and an upper limit of 5 x 10 -10 . This lower limit to eta is concordant with that obtained from considerations of D + 3 He. The upper limit is consistent with, but even more restrictive than, the D bound. With the new rates, any observed primordial Li/H ratio below 10 -10 would be inexplicable by the standard big bang nucleosynthesis. A review is made of the strengths and possible weaknesses of utilizing conclusions drawn from big bang lithium considerations. An appendix discusses the null effect of a factor of 32 increase in the experimental rate for the D(d,γ) 4 He reaction. 28 refs., 1 fig

  12. Reaction rate constant for radiative association of CF{sup +}

    Energy Technology Data Exchange (ETDEWEB)

    Öström, Jonatan, E-mail: jonatan.ostrom@gmail.com; Gustafsson, Magnus, E-mail: magnus.gustafsson@ltu.se [Applied Physics, Division of Materials Science, Department of Engineering Science and Mathematics, Luleå University of Technology, 97187 Luleå (Sweden); Bezrukov, Dmitry S. [Department of Chemistry, M. V. Lomonosov Moscow State University, Moscow, 119991 (Russian Federation); Nyman, Gunnar [Department of Chemistry and Molecular Biology, University of Gothenburg, 41296 Gothenburg (Sweden)

    2016-01-28

    Reaction rate constants and cross sections are computed for the radiative association of carbon cations (C{sup +}) and fluorine atoms (F) in their ground states. We consider reactions through the electronic transition 1{sup 1}Π → X{sup 1}Σ{sup +} and rovibrational transitions on the X{sup 1}Σ{sup +} and a{sup 3}Π potentials. Semiclassical and classical methods are used for the direct contribution and Breit–Wigner theory for the resonance contribution. Quantum mechanical perturbation theory is used for comparison. A modified formulation of the classical method applicable to permanent dipoles of unequally charged reactants is implemented. The total rate constant is fitted to the Arrhenius–Kooij formula in five temperature intervals with a relative difference of <3%. The fit parameters will be added to the online database KIDA. For a temperature of 10–250 K, the rate constant is about 10{sup −21} cm{sup 3} s{sup −1}, rising toward 10{sup −16} cm{sup 3} s{sup −1} for a temperature of 30 000 K.

  13. Metal-silicon reaction rates - The effects of capping

    Science.gov (United States)

    Weizer, Victor G.; Fatemi, Navid S.

    1989-01-01

    Evidence is presented showing that the presence of the commonly used anti-reflection coating material Ta2O5 on the free surface of contact metallization can either suppress or enhance, depending on the system, the interaction that takes place at elevated temperatures between the metallization and the underlying Si. The cap layer is shown to suppress both the generation and annihilation of vacancies at the free surface of the metal which are necessary to support metal-Si interactons. Evidence is also presented indicating that the mechanical condition of the free metal surface has a significant effect on the metal-silicon reaction rate.

  14. Recent astrophysical applications of the Trojan Horse Method to nuclear astrophysics

    International Nuclear Information System (INIS)

    Spitaleri, C.; Cherubini, S.; Crucilla, V.; Gulino, M.; La Cognata, M.; Lamia, L.; Pizzone, R. G.; Puglia, S. M. R.; Rapisarda, G. G.; Romano, S.; Sergi, M. L.; Tumino, A.; Fu, C.; Tribble, R.; Banu, A.; Al-Abdullah, T.; Goldberg, V.; Mukhamedzhanov, A.; Tabacaru, G.; Trache, L.

    2008-01-01

    The Trojan Horse Method (THM) is an unique indirect technique allowing to measure astrophysical rearrangement reactions down to astrophysical relevant energies. The basic principle and a review of the recent applications of the Trojan Horse Method are presented. The applications aiming to the extraction of the bare astrophysical S b (E) for some two-body processes are discussed

  15. First measurement of the 34S(p ,γ )35Cl reaction rate through indirect methods for presolar nova grains

    Science.gov (United States)

    Gillespie, S. A.; Parikh, A.; Barton, C. J.; Faestermann, T.; José, J.; Hertenberger, R.; Wirth, H.-F.; de Séréville, N.; Riley, J. E.; Williams, M.

    2017-08-01

    Sulphur isotopic ratio measurements may help to establish the astrophysical sites in which certain presolar grains were formed. Nova model predictions of the 34S/32S ratio are, however, unreliable due to the lack of an experimental 34S(p ,γ )35Cl reaction rate. To this end, we have measured the 34S(3He,d )35Cl reaction at 20 MeV using a high resolution quadrupole-dipole-dipole-dipole magnetic spectrograph. Twenty-two levels over 6.2 MeV rate has been determined using a Monte Carlo method. Hydrodynamic nova model calculations have been performed using this new reaction rate. These models show that remaining uncertainties in the 34S(p ,γ ) rate affect nucleosynthesis predictions by less than a factor of 1.4, and predict a 34S/32S isotopic ratio of 0.014-0.017. Since recent type II supernova models predict 34S/32S=0.026 -0.053 , the 34S/32S isotopic ratio may be used, in conjunction with other isotopic signatures, to distinguish presolar grains from oxygen-neon nova and type II supernova origin. Our results address a key nuclear physics uncertainty on which recent considerations discounting the nova origin of several grains depend.

  16. THE INFLUENCE OF UNCERTAINTIES IN THE 15O(α, γ)19Ne REACTION RATE ON MODELS OF TYPE I X-RAY BURSTS

    International Nuclear Information System (INIS)

    Davids, Barry; Cyburt, Richard H.; Jose, Jordi; Mythili, Subramanian

    2011-01-01

    We present a Monte Carlo calculation of the astrophysical rate of the 15 O(α, γ) 19 Ne reaction based on an evaluation of published experimental data. By considering the likelihood distributions of individual resonance parameters derived from measurements, estimates of upper and lower limits on the reaction rate at the 99.73% confidence level are derived in addition to the recommended, median value. These three reaction rates are used as input for three separate calculations of Type I X-ray bursts (XRBs) using spherically symmetric, hydrodynamic simulations of an accreting neutron star. In this way the influence of the 15 O(α, γ) 19 Ne reaction rate on the peak luminosity, recurrence time, and associated nucleosynthesis in models of Type I XRBs is studied. Contrary to previous findings, no substantial effect on any of these quantities is observed in a sequence of four bursts when varying the reaction rate between its lower and upper limits. Rather, the differences in these quantities are comparable to the burst-to-burst variations with a fixed reaction rate, indicating that uncertainties in the 15 O(α, γ) 19 Ne reaction rate do not strongly affect the predictions of this Type I XRB model.

  17. Ozonation of norfloxacin and levofloxacin in water: Specific reaction rate constants and defluorination reaction.

    Science.gov (United States)

    Ling, Wencui; Ben, Weiwei; Xu, Ke; Zhang, Yu; Yang, Min; Qiang, Zhimin

    2018-03-01

    The degradation kinetics and mechanism of two typical fluoroquinolones (FQs), norfloxacin (NF) and levofloxacin (LOF), by ozone in water were investigated. Semi-continuous mode and competition kinetics mode experiments were conducted to determine the reaction rate constants of target FQs with ozone and OH, separately. Results indicate that both NF and LOF were highly reactive toward ozone, and the reactivity was strongly impacted by the solution pH. The specific reaction rate constants of the diprotonated, monoprotonated and deprotonated species were determined to be 7.20 × 10 2 , 8.59 × 10 3 , 4.54 × 10 5  M -1  s -1 respectively for NF and 1.30 × 10 3 , 1.40 × 10 4 , 1.33 × 10 6  M -1  s -1 respectively for LOF. The reaction rate constants of target FQs toward OH were measured to be (4.81-7.41) × 10 9  M -1  s -1 in the pH range of 6.3-8.3. Furthermore, NF was selected as a model compound to clarify the degradation pathways, with a particular focus on the defluorination reaction. The significant release of F - ions and the formation of three F-free organic byproducts indicated that defluorination was a prevalent pathway in ozonation of FQs, while six F-containing organic byproducts indicated that ozone also attacked the piperazinyl and quinolone moieties. Escherichia coli growth inhibition tests revealed that ozonation could effectively eliminate the antibacterial activity of target FQ solutions, and the residual antibacterial activity had a negative linear correlation with the released F - concentration. Copyright © 2017 Elsevier Ltd. All rights reserved.

  18. Phenomenon of quantum low temperature limit of chemical reaction rates

    International Nuclear Information System (INIS)

    Gol'danskij, V.I.

    1975-01-01

    The influence of quantum-mechanical effects on one of the fundamental laws of chemical kinetics - the Arrhenius law - is considered. Criteria characterising the limits of the low-temperature region where the extent of quantum-mechanical tunnelling transitions exceeds exponentially the transitions over the barrier are quoted. Studies of the low-temperature tunnelling of electrons and hydrogen atoms are briefly mentioned and the history of research on low-temperature radiation-induced solid-phase polymerisation, the development of which led to the discovery of the phenomenon of the low-temperature quantum-mechanical limit for the rates of chemical reactions in relation to the formaldehyde polymerisation reaction, is briefly considered. The results of experiments using low-inertia calorimeters, whereby it is possible to determine directly the average time (tau 0 ) required to add one new link to the polymer chain of formaldehyde during its polymerisation by radiation and during postpolymerisation and to establish that below 80K the increase of tau 0 slows down and that at T approximately equal to 10-4K the time tau 0 reaches a plateau (tau 0 approximately equals 0.01s), are described. Possible explanations of the observed low-temperature limit for the rate of a chemical reaction are critically examined and a semiquantitative explanation is given for this phenomenon, which may be particularly common in combined electronic-confirmational transitions in complex biological molecules and may play a definite role in chemical and biological evolution (cold prehistory of life)

  19. Phenomenon of quantum low temperature limit of chemical reaction rates

    Energy Technology Data Exchange (ETDEWEB)

    Gol' danskii, V I [AN SSSR, Moscow. Inst. Khimicheskoj Fiziki

    1975-12-01

    The influence of quantum-mechanical effects on one of the fundamental laws of chemical kinetics - the Arrhenius Law - is considered. Criteria characterising the limits of the low-temperature region where the extent of quantum-mechanical tunnelling transitions exceeds exponentially the transitions over the barrier are quoted. Studies of the low-temperature tunnelling of electrons and hydrogen atoms are briefly mentioned and the history of research on low-temperature radiation-induced solid-phase polymerization, the development of which led to the discovery of the phenomenon of the low-temperature quantum-mechanical limit for the rates of chemical reactions in relation to the formaldehyde polymerization reaction, is briefly considered. The results of experiments using low-inertia calorimeters, whereby it is possible to determine directly the average time (tau/sub 0/) required to add one new link to the polymer chain of formaldehyde during its polymerization by radiation and during postpolymerization and to establish that below 80K the increase of tau/sub 0/ slows down and that at T approximately equal to 10-4K the time tau/sub 0/ reaches a plateau (tau/sub 0/ approximately equals 0.01s), are described. Possible explanations of the observed low-temperature limit for the rate of a chemical reaction are critically examined and a semiquantitative explanation is given for this phenomenon, which may be particularly common in combined electronic-confirmational transitions in complex biological molecules and may play a definite role in chemical and biological evolution (cold prehistory of life).

  20. Observational astrophysics

    CERN Document Server

    Léna, Pierre; Lebrun, François; Mignard, François; Pelat, Didier

    2012-01-01

    This is the updated, widely revised, restructured and expanded third edition of Léna et al.'s successful work Observational Astrophysics. It presents a synthesis on tools and methods of observational astrophysics of the early 21st century. Written specifically for astrophysicists and graduate students, this textbook focuses on fundamental and sometimes practical limitations on the ultimate performance that an astronomical system may reach, rather than presenting particular systems in detail. In little more than a decade there has been extraordinary progress in imaging and detection technologies, in the fields of adaptive optics, optical interferometry, in the sub-millimetre waveband, observation of neutrinos, discovery of exoplanets, to name but a few examples. The work deals with ground-based and space-based astronomy and their respective fields. And it also presents the ambitious concepts behind space missions aimed for the next decades. Avoiding particulars, it covers the whole of the electromagnetic spec...

  1. astrophysical significance

    Directory of Open Access Journals (Sweden)

    Dartois E.

    2014-02-01

    Full Text Available Clathrate hydrates, ice inclusion compounds, are of major importance for the Earth’s permafrost regions and may control the stability of gases in many astrophysical bodies such as the planets, comets and possibly interstellar grains. Their physical behavior may provide a trapping mechanism to modify the absolute and relative composition of icy bodies that could be the source of late-time injection of gaseous species in planetary atmospheres or hot cores. In this study, we provide and discuss laboratory-recorded infrared signatures of clathrate hydrates in the near to mid-infrared and the implications for space-based astrophysical tele-detection in order to constrain their possible presence.

  2. Observational astrophysics

    CERN Document Server

    Smith, Robert C

    1995-01-01

    Combining a critical account of observational methods (telescopes and instrumentation) with a lucid description of the Universe, including stars, galaxies and cosmology, Smith provides a comprehensive introduction to the whole of modern astrophysics beyond the solar system. The first half describes the techniques used by astronomers to observe the Universe: optical telescopes and instruments are discussed in detail, but observations at all wavelengths are covered, from radio to gamma-rays. After a short interlude describing the appearance of the sky at all wavelengths, the role of positional astronomy is highlighted. In the second half, a clear description is given of the contents of the Universe, including accounts of stellar evolution and cosmological models. Fully illustrated throughout, with exercises given in each chapter, this textbook provides a thorough introduction to astrophysics for all physics undergraduates, and a valuable background for physics graduates turning to research in astronomy.

  3. Charged-particle thermonuclear reaction rates: IV. Comparison to previous work

    International Nuclear Information System (INIS)

    Iliadis, C.; Longland, R.; Champagne, A.E.; Coc, A.

    2010-01-01

    We compare our Monte Carlo reaction rates (see Paper II of this issue) to previous results that were obtained by using the classical method of computing thermonuclear reaction rates. For each reaction, the comparison is presented using two types of graphs: the first shows the change in reaction rate uncertainties, while the second displays our new results normalized to the previously recommended reaction rate. We find that the rates have changed significantly for almost all reactions considered here. The changes are caused by (i) our new Monte Carlo method of computing reaction rates (see Paper I of this issue), and (ii) newly available nuclear physics information (see Paper III of this issue).

  4. Nuclear astrophysics with radioactive beams

    International Nuclear Information System (INIS)

    Bertulani, C.A.; Gade, A.

    2010-01-01

    The quest to comprehend how nuclear processes influence astrophysical phenomena is driving experimental and theoretical research programs worldwide. One of the main goals in nuclear astrophysics is to understand how energy is generated in stars, how elements are synthesized in stellar events and what the nature of neutron stars is. New experimental capabilities, the availability of radioactive beams and increased computational power paired with new astronomical observations have advanced the present knowledge. This review summarizes the progress in the field of nuclear astrophysics with a focus on the role of indirect methods and reactions involving beams of rare isotopes.

  5. Stellar astrophysics

    International Nuclear Information System (INIS)

    1987-01-01

    A number of studies in the field of steller astrophysics were undertaken by the South African Astronomical Observatory in 1986. These studies included; evolutionary effects on the surface abundances of an early-type supergiant; hydrogen deficient stars; t tauri stars; rotational modulation and flares on RS CVn and BY Dra stars; carbon and heavy element stars, and slow variability and circumstellar shells of red variable stars. 4 figs

  6. Relationship among reaction rate, release rate and efficiency of nanomachine-based targeted drug delivery.

    Science.gov (United States)

    Zhao, Qingying; Li, Min; Luo, Jun

    2017-12-04

    In nanomachine applications towards targeted drug delivery, drug molecules released by nanomachines propagate and chemically react with tumor cells in aqueous environment. If the nanomachines release drug molecules faster than the tumor cells react, it will result in loss and waste of drug molecules. It is a potential issue associated with the relationship among reaction rate, release rate and efficiency. This paper aims to investigate the relationship among reaction rate, release rate and efficiency based on two drug reception models. We expect to pave a way for designing a control method of drug release. We adopted two analytical methods that one is drug reception process based on collision with tumors and another is based on Michaelis Menten enzymatic kinetics. To evaluate the analytical formulations, we used the well-known simulation framework N3Sim to establish simulations. The analytical results of the relationship among reaction rate, release rate and efficiency is obtained, which match well with the numerical simulation results in a 3-D environment. Based upon two drug reception models, the results of this paper would be beneficial for designing a control method of nanomahine-based drug release.

  7. Improved predictions of nuclear data: A continued challenge in astrophysics

    International Nuclear Information System (INIS)

    Goriely, S.

    2001-01-01

    Although important effort has been devoted in the last decades to measure reaction cross sections and decay half-lives of interest in astrophysics, most of the nuclear astrophysics applications still require the use of theoretical predictions to estimate experimentally unknown rates. The nuclear ingredients to the reaction or weak interaction models should preferentially be estimated from microscopic or semi-microscopic global predictions based on sound and reliable nuclear models which, in turn, can compete with more phenomenological highly-parametrized models in the reproduction of experimental data. The latest developments made in deriving the nuclear inputs of relevance in astrophysics applications are reviewed. It mainly concerns nuclear structure properties (atomic masses, deformations, radii, etc...), nuclear level densities, nucleon and α-optical potentials, γ-ray and Gamow-Teller strength functions

  8. Effect of alpha states in the 16O+12C scattering and in the 12C +α → 16O capture reaction of astrophysical interest

    International Nuclear Information System (INIS)

    Morais, M.C.; Lichtenthaele, R.; Arazi, A.; Hojman, D.; Cardona, M.A.; Fimiani, L.; Carnelli, P.F.; Marti, G.V.; Pacheco, A.J.; Martinez Heimann, D.; Negri, A.E.; Capurro, O.A.; Niello, Fernandez; Montero, P.

    2011-01-01

    Full text: The 16 O+ 12 C elastic scattering was investigated considering the effect of exchange of an alpha particle between projectile and target leading to the same nuclei of the entrance channel (elastic transfer). Angular distributions were analyzed in an energy range from 8.55 MeV to 56.57 MeV in the center of mass frame. The Coulomb barrier is around 11MeV for this system. Measurements of angular distributions of elastic and inelastic transfer reactions to states of the 16 O in the 16 O+ 12 C system were performed at the TANDAR Laboratory in Buenos Aires, using an 16 O beam of E lab = 46; 26 MeV. The transfer angular distributions were analyzed by DWBA using the computer code FRESCO. Those measurements provided the spectroscopic factors of 12 C + α → 16 O for the ground state and for J π = 2 + and J π = 1 - 16 O excited states, both just below the α-threshold at 7.16 MeV. The Asymptotic Normalization Coefficient (ANC) for the J π = 2 + state was obtained (1.05 ±0,13(10 5 fm -1/2 )) and used to calculate the reduced width of this state, with this value a R-matrix calculation was performed to determine the astrophysical S-factor in energies around the Gamow peak, S(E2)=37keVb. (author)

  9. First measurement of 30S+α resonant elastic scattering for the 30S(α ,p ) reaction rate

    Science.gov (United States)

    Kahl, D.; Yamaguchi, H.; Kubono, S.; Chen, A. A.; Parikh, A.; Binh, D. N.; Chen, J.; Cherubini, S.; Duy, N. N.; Hashimoto, T.; Hayakawa, S.; Iwasa, N.; Jung, H. S.; Kato, S.; Kwon, Y. K.; Nishimura, S.; Ota, S.; Setoodehnia, K.; Teranishi, T.; Tokieda, H.; Yamada, T.; Yun, C. C.; Zhang, L. Y.

    2018-01-01

    Background: Type I x-ray bursts are the most frequently observed thermonuclear explosions in the galaxy, resulting from thermonuclear runaway on the surface of an accreting neutron star. The 30S(α ,p ) reaction plays a critical role in burst models, yet insufficient experimental information is available to calculate a reliable, precise rate for this reaction. Purpose: Our measurement was conducted to search for states in 34Ar and determine their quantum properties. In particular, natural-parity states with large α -decay partial widths should dominate the stellar reaction rate. Method: We performed the first measurement of 30S+α resonant elastic scattering up to a center-of-mass energy of 5.5 MeV using a radioactive ion beam. The experiment utilized a thick gaseous active target system and silicon detector array in inverse kinematics. Results: We obtained an excitation function for 30S(α ,α ) near 150∘ in the center-of-mass frame. The experimental data were analyzed with R -matrix calculations, and we observed three new resonant patterns between 11.1 and 12.1 MeV, extracting their properties of resonance energy, widths, spin, and parity. Conclusions: We calculated the resonant thermonuclear reaction rate of 30S(α ,p ) based on all available experimental data of 34Ar and found an upper limit about one order of magnitude larger than a rate determined using a statistical model. The astrophysical impact of these two rates has been investigated through one-zone postprocessing type I x-ray burst calculations. We find that our new upper limit for the 30S(α ,p )33Cl rate significantly affects the predicted nuclear energy generation rate during the burst.

  10. An introduction to nuclear astrophysics

    International Nuclear Information System (INIS)

    Norman, E.B.

    1987-09-01

    The role of nuclear reactions in astrophysics is described. Stellar energy generation and heavy element nucleosynthesis is explained in terms of specific sequences of charged-particle and neutron induced reactions. The evolution and final states of stars are examined. 20 refs. 11 figs., 2 tabs

  11. Laboratory Astrophysics Prize: Laboratory Astrophysics with Nuclei

    Science.gov (United States)

    Wiescher, Michael

    2018-06-01

    Nuclear astrophysics is concerned with nuclear reaction and decay processes from the Big Bang to the present star generation controlling the chemical evolution of our universe. Such nuclear reactions maintain stellar life, determine stellar evolution, and finally drive stellar explosion in the circle of stellar life. Laboratory nuclear astrophysics seeks to simulate and understand the underlying processes using a broad portfolio of nuclear instrumentation, from reactor to accelerator from stable to radioactive beams to map the broad spectrum of nucleosynthesis processes. This talk focuses on only two aspects of the broad field, the need of deep underground accelerator facilities in cosmic ray free environments in order to understand the nucleosynthesis in stars, and the need for high intensity radioactive beam facilities to recreate the conditions found in stellar explosions. Both concepts represent the two main frontiers of the field, which are being pursued in the US with the CASPAR accelerator at the Sanford Underground Research Facility in South Dakota and the FRIB facility at Michigan State University.

  12. Quantum chemical protocols for modeling reactions and spectra in astrophysical ice analogs: the challenging case of the C⁺ + H₂O reaction in icy grain mantles.

    Science.gov (United States)

    Woon, David E

    2015-11-21

    Icy grain mantles that accrete on refractory dust particles in the very cold interstellar medium or beyond the snow line in protoplanetary disks serve as minute incubators for heterogeneous chemistry. Ice mantle chemistry can differ significantly from the gas phase chemistry that occurs in these environments and is often richer. Modeling ices and their chemistry is a challenging task for quantum theoretical methods, but theory promises insight into these systems that is difficult to attain with experiments. Density functional theory (DFT) is predominately employed for modeling reactions in icy grain mantles due to its favorable scalability, but DFT has limitations that risk undercutting its reliability for this task. In this work, basic protocols are proposed for identifying the degree to which DFT methods are able to reproduce experimental or higher level theoretical results for the fundamental interactions upon which ice mantle chemistry depends, including both reactive interactions and non-reactive scaffolding interactions. The exemplar of this study is the reaction of C(+) with H2O, where substantial methodological differences are found in the prediction of gas phase relative energetics for stationary points (about 10 kcal mol(-1) for the C-O bond energy of the H2OC(+) intermediate), which in turn casts doubt about employing it to treat the C(+) + H2O reaction on an ice surface. However, careful explorations demonstrate that B3LYP with small correlation consistent basis sets performs in a sufficiently reliable manner to justify using it to identify plausible chemical pathways, where the dominant products were found to be neutral HOC and the CO(-) anion plus one and two H3O(+) cations, respectively. Predicted vibrational and electronic spectra are presented that would serve to verify or disconfirm the pathways; the latter were computed with time-dependent DFT. Conclusions are compared with those of a recent similar study by McBride and coworkers (J. Phys. Chem

  13. Enhancement of nuclear reaction rates in asymmetric binary ionic mixtures

    Energy Technology Data Exchange (ETDEWEB)

    Clerouin, J.; Arnault, P.; Desbiens, N. [CEA, DAM, DIF, Arpajon (France); White, A.; Ticknor, C.; Kress, J.D.; Collins, L.A. [Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM (United States)

    2017-11-15

    Using orbital-free molecular dynamics simulations we study the structure and dynamics of increasingly asymmetric mixtures such as hydrogen-carbon, hydrogen-aluminium, hydrogen-copper, and hydrogen-silver. We show that, whereas the heavy component structure is close to an effective one-component plasma (OCP), the light component appears more structured than the corresponding OCP. This effect is related to the crossover towards a Lorentz-type diffusion triggered by strongly coupled, highly charged heavy ions, and witnessed by the change of temperature scaling laws of diffusion. This over-correlation translates into an enhancement of nuclear reaction rates much higher than its classical OCP counterpart. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  14. Transcriptional dynamics with time-dependent reaction rates

    Science.gov (United States)

    Nandi, Shubhendu; Ghosh, Anandamohan

    2015-02-01

    Transcription is the first step in the process of gene regulation that controls cell response to varying environmental conditions. Transcription is a stochastic process, involving synthesis and degradation of mRNAs, that can be modeled as a birth-death process. We consider a generic stochastic model, where the fluctuating environment is encoded in the time-dependent reaction rates. We obtain an exact analytical expression for the mRNA probability distribution and are able to analyze the response for arbitrary time-dependent protocols. Our analytical results and stochastic simulations confirm that the transcriptional machinery primarily act as a low-pass filter. We also show that depending on the system parameters, the mRNA levels in a cell population can show synchronous/asynchronous fluctuations and can deviate from Poisson statistics.

  15. Transcriptional dynamics with time-dependent reaction rates

    International Nuclear Information System (INIS)

    Nandi, Shubhendu; Ghosh, Anandamohan

    2015-01-01

    Transcription is the first step in the process of gene regulation that controls cell response to varying environmental conditions. Transcription is a stochastic process, involving synthesis and degradation of mRNAs, that can be modeled as a birth–death process. We consider a generic stochastic model, where the fluctuating environment is encoded in the time-dependent reaction rates. We obtain an exact analytical expression for the mRNA probability distribution and are able to analyze the response for arbitrary time-dependent protocols. Our analytical results and stochastic simulations confirm that the transcriptional machinery primarily act as a low-pass filter. We also show that depending on the system parameters, the mRNA levels in a cell population can show synchronous/asynchronous fluctuations and can deviate from Poisson statistics. (paper)

  16. The effects of vacuum polarization on thermonuclear reaction rates

    Science.gov (United States)

    Gould, Robert J.

    1990-01-01

    Added to the pure Coulomb potential, the contribution from vacuum polarization increases the barrier, reducing the wave function (u) for reacting nuclei within the range of nuclear forces. The cross section and reaction rate are then reduced accordingly by a factor proportional to u squared. The effect is treated by evaluating the vacuum polarization potential as a small correction to the Coulomb term, then computing u in a WKB formulation. The calculation is done analytically employing the small r power-series expansion for the Uehling potential to express the final result in terms of convenient parameters. At a temperature of 1.4 x 10 to the 7th K the (negative) correction is 1.3 percent for the fundamental fusion process p + p yields d + e(+) + nu.

  17. Astrophysical cosmology

    Science.gov (United States)

    Bardeen, J. M.

    The last several years have seen a tremendous ferment of activity in astrophysical cosmology. Much of the theoretical impetus has come from particle physics theories of the early universe and candidates for dark matter, but what promise to be even more significant are improved direct observations of high z galaxies and intergalactic matter, deeper and more comprehensive redshift surveys, and the increasing power of computer simulations of the dynamical evolution of large scale structure. Upper limits on the anisotropy of the microwave background radiation are gradually getting tighter and constraining more severely theoretical scenarios for the evolution of the universe.

  18. Astrophysical cosmology

    International Nuclear Information System (INIS)

    Bardeen, J.M.

    1986-01-01

    The last several years have seen a tremendous ferment of activity in astrophysical cosmology. Much of the theoretical impetus has come from particle physics theories of the early universe and candidates for dark matter, but what promise to be even more significant are improved direct observations of high z galaxies and intergalactic matter, deeper and more comprehensive redshift surveys, and the increasing power of computer simulations of the dynamical evolution of large scale structure. Upper limits on the anisotropy of the microwave background radiation are gradually getting tighter and constraining more severely theoretical scenarios for the evolution of the universe. 47 refs

  19. Manual Choice Reaction Times in the Rate-Domain

    Directory of Open Access Journals (Sweden)

    Chris eHarris

    2014-06-01

    Full Text Available Over the last 150 years, human manual reaction times (RTs have been recorded countless times. Yet, our understanding of them remains remarkably poor. RTs are highly variable with positively skewed frequency distributions, often modelled as an inverse Gaussian distribution reflecting a stochastic rise to threshold (diffusion process. However, latency distribution of saccades are very close to the reciprocal Normal, suggesting that ‘rate’ (reciprocal RT may be the more fundamental variable. We explored whether this phenomenon extends to choice manual RTs. We recorded two-alternative choice RTs from 24 subjects, each with 4 blocks of 200 trials with two task difficulties (easy vs. difficult discrimination and two instruction sets (urgent vs. accurate. We found that rate distributions were, indeed, very close to Normal, shifting to lower rates with increasing difficulty and accuracy, and for some blocks subjects they appeared to become left-truncated, but still close to Normal. Using autoregressive techniques, we found temporal sequential dependencies for lags of at least 3. We identified a transient and steady-state component in each block. Because rates were Normal, we were able to estimate autoregressive weights using the Box-Jenkins technique, and convert to a moving average model using z-transforms to show explicit dependence on stimulus input. We also found a spatial sequential dependence for the previous 3 lags depending on whether the laterality of previous trials was repeated or alternated. This was partially dissociated from temporal dependency as it only occurred in the easy tasks. We conclude that 2-alternative choice manual RT distributions are close to reciprocal Normal and not the inverse Gaussian. This is not consistent with stochastic rise to threshold models, and we propose a simple optimality model in which reward is maximized to yield to an optimal rate, and hence an optimal time to respond. We discuss how it might be

  20. Few-body models for nuclear astrophysics

    Energy Technology Data Exchange (ETDEWEB)

    Descouvemont, P., E-mail: pdesc@ulb.ac.be [Physique Nucléaire Théorique et Physique Mathématique, C.P. 229, Université Libre de Bruxelles (ULB), B 1050 Brussels (Belgium); Baye, D., E-mail: dbaye@ulb.ac.be [Physique Nucléaire Théorique et Physique Mathématique, C.P. 229, Université Libre de Bruxelles (ULB), B 1050 Brussels (Belgium); Physique Quantique, C.P. 165/82, Université Libre de Bruxelles (ULB), B 1050 Brussels (Belgium); Suzuki, Y., E-mail: suzuki@nt.sc.niigata-u.ac.jp [Department of Physics, Niigata University, Niigata 950-2181 (Japan); RIKEN Nishina Center, Wako 351-0198 (Japan); Aoyama, S., E-mail: aoyama@cc.niigata-u.ac.jp [Center for Academic Information Service, Niigata University, Niigata 950-2181 (Japan); Arai, K., E-mail: arai@nagaoka-ct.ac.jp [Division of General Education, Nagaoka National College of Technology, 888 Nishikatakai, Nagaoka, Niigata 940-8532 (Japan)

    2014-04-15

    We present applications of microscopic models to nuclear reactions of astrophysical interest, and we essentially focus on few-body systems. The calculation of radiative-capture and transfer cross sections is outlined, and we discuss the corresponding reaction rates. Microscopic theories are briefly presented, and we emphasize on the matrix elements of four-body systems. The microscopic extension of the R-matrix theory to nuclear reactions is described. Applications to the {sup 2}H(d, γ){sup 4}He, {sup 2}H(d, p){sup 3}H and {sup 2}H(d, n){sup 3}He reactions are presented. We show the importance of the tensor force to reproduce the low-energy behaviour of the cross sections.

  1. Reaction-rate formula in out of equilibrium quantum field theory

    OpenAIRE

    Niegawa, A.; Okano, K.; Ozaki, H.

    1999-01-01

    A complete derivation, from first principles, of the reaction-rate formula for a generic reaction taking place in an out of equilibrium quantum-field system is given. It is shown that the formula involves no finite-volume correction. Each term of the reaction-rate formula represents a set of physical processes that contribute to the reaction under consideration.

  2. THE FLUORINE DESTRUCTION IN STARS: FIRST EXPERIMENTAL STUDY OF THE (19)F(p, alpha(0))(16)O REACTION AT ASTROPHYSICAL ENERGIES

    Czech Academy of Sciences Publication Activity Database

    La Cognata, M.; Mukhamedzhanov, A. M.; Spitaleri, C.; Indelicato, I.; Aliotta, M.; Burjan, Václav; Cherubini, S.; Coc, A.; Gulino, M.; Hons, Zdeněk; Kiss, G.G.; Kroha, Václav; Lamia, L.; Mrázek, Jaromír; Palmerini, S.; Piskoř, Štěpán; Pizzone, R. G.; Puglia, S. M. R.; Rapisarda, G. G.; Romano, S.; Sergi, M. L.; Tumino, A.

    2011-01-01

    Roč. 739, č. 2 (2011), L54 ISSN 2041-8205 R&D Projects: GA MŠk LC07050; GA ČR GAP203/10/0310 Institutional research plan: CEZ:AV0Z10480505 Keywords : ASYMPTOTIC GIANT BRANCH * CORONAE-BOREALIS STARS * NUCLEAR ASTROPHYSICS * COULOMB BARRIER * CROSS-SECTION * LOW-MASS * NUCLEOSYNTHESIS * CARBON Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 5.526, year: 2011

  3. On the mechanism of effective chemical reactions with turbulent mixing of reactants and finite rate of molecular reactions

    Energy Technology Data Exchange (ETDEWEB)

    Vorotilin, V. P., E-mail: VPVorotilin@yandex.ru [Russian Academy of Sciences, Institute of Applied Mechanics (Russian Federation)

    2017-01-15

    A generalization of the theory of chemical transformation processes under turbulent mixing of reactants and arbitrary values of the rate of molecular reactions is presented that was previously developed for the variant of an instantaneous reaction [13]. The use of the features of instantaneous reactions when considering the general case, namely, the introduction of the concept of effective reaction for the reactant volumes and writing a closing conservation equation for these volumes, became possible due to the partition of the whole amount of reactants into “active” and “passive” classes; the reactants of the first class are not mixed and react by the mechanism of instantaneous reactions, while the reactants of the second class approach each other only through molecular diffusion, and therefore their contribution to the reaction process can be neglected. The physical mechanism of reaction for the limit regime of an ideal mixing reactor (IMR) is revealed and described. Although formally the reaction rate in this regime depends on the concentration of passive fractions of the reactants, according to the theory presented, the true (hidden) mechanism of the reaction is associated only with the reaction of the active fractions of the reactants with vanishingly small concentration in the volume of the reactor. It is shown that the rate constant of fast chemical reactions can be evaluated when the mixing intensity of reactants is much less than that needed to reach the mixing conditions in an IMR.

  4. Proton-proton reaction rates at extreme energies

    International Nuclear Information System (INIS)

    Nagano, Motohiko

    1993-01-01

    Results on proton-antiproton reaction rates (total cross-section) at collision energies of 1.8 TeV from experiments at Fermilab have suggested a lower rate of increase with energy compared to the extrapolation based on results previously obtained at CERN's proton-antiproton collider (CERN Courier, October 1991). Now an independent estimate of the values for the proton-proton total cross-section for collision energies from 5 to 30 TeV has been provided by the analysis of cosmic ray shower data collected over ten years at the Akeno Observatory operated by the Institute for Cosmic Ray Research of University of Tokyo. These results are based on the inelastic cross-section for collisions of cosmic ray protons with air nuclei at energies in the range10 16-18 eV. A new extensive air shower experiment was started at Akeno, 150 km west of Tokyo, in 1979 with a large array of detectors, both on the ground and under a 1-metre concrete absorber. This measured the total numbers of electrons and muons of energies above 1GeV for individual showers with much better accuracy than before. Data collection was almost continuous for ten years without any change in the triggering criteria for showers above10 16 eV. The mean free path for proton-air nuclei collisions has been determined from the zenith angle of the observed frequency of air showers which have the same effective path length for development in the atmosphere and the same primary energy

  5. On the ambiguity of the reaction rate constants in multivariate curve resolution for reversible first-order reaction systems.

    Science.gov (United States)

    Schröder, Henning; Sawall, Mathias; Kubis, Christoph; Selent, Detlef; Hess, Dieter; Franke, Robert; Börner, Armin; Neymeyr, Klaus

    2016-07-13

    If for a chemical reaction with a known reaction mechanism the concentration profiles are accessible only for certain species, e.g. only for the main product, then often the reaction rate constants cannot uniquely be determined from the concentration data. This is a well-known fact which includes the so-called slow-fast ambiguity. This work combines the question of unique or non-unique reaction rate constants with factor analytic methods of chemometrics. The idea is to reduce the rotational ambiguity of pure component factorizations by considering only those concentration factors which are possible solutions of the kinetic equations for a properly adapted set of reaction rate constants. The resulting set of reaction rate constants corresponds to those solutions of the rate equations which appear as feasible factors in a pure component factorization. The new analysis of the ambiguity of reaction rate constants extends recent research activities on the Area of Feasible Solutions (AFS). The consistency with a given chemical reaction scheme is shown to be a valuable tool in order to reduce the AFS. The new methods are applied to model and experimental data. Copyright © 2016 Elsevier B.V. All rights reserved.

  6. Reactions of sulfur atoms. XV. Absolute rate parameters for the S(3P210) + alkyne reactions

    International Nuclear Information System (INIS)

    van Roodselaar, A.; Safarik, I.; Strausz, O.P.; Gunning, H.E.

    1978-01-01

    Using flash photolysis with vacuum uv kinetic absorption spectroscopy, absolute rate constants and Arrhenius parameters have been measured for the addition of ground state S( 3 P 2 , 1 , 0 ) atoms to alkynes. The decay of sulfur atoms in COS, alkyne, and CO 2 -diluent mixtures is first order in sulfur atom concentration and the first-order decay rate constants are proportional to the alkyne concentration. The following rate constants were determined at room temperature: k(C 2 H 2 ) = k(C 2 D 2 ) + (2.3 +- 0.4) x 10 8 ; k(CHCCH 3 ) = (4.8 +- 0.2) x 10 9 ; k(CHCC 2 H 5 ) = (3.3 +- 0.2) x 10 9 ; k(CH 3 CCCH 3 ) = 1.6 +- 0.2) x 10 10 ; k(CH 3 CCC 2 C 5 ) = 1.8 +- 0.3) x 10 10 ; and k(CF 3 CCCF 3 ) = (2.1 +- 0.4) x 10 8 L mol -1 s -1 . The Arrhenius parameters determined are k(C 2 H 2 ) = (3.4 +- 1.9) x 10 10 exp[(-3000 +- 400)/RT] L mol -1 s -1 and k(CHCCH 3 ) = (2.0 +- 1.2) x 10 10 exp[(-900 +- 200)/RT] L mol -1 s -1 where error limits represent standard deviations. The rate parameters are compared to those obtained for the addition of other electrophilic reagents to alkynes and the results discussed in terms of structural and kinetic factors. Theoretical treatment of the secondary H/D isotope effect in the acetylene reaction satisfactorily reproduces the experimental value. 5 tables, 4 figures, 59 references

  7. From cutting-edge pointwise cross-section to groupwise reaction rate: A primer

    Science.gov (United States)

    Sublet, Jean-Christophe; Fleming, Michael; Gilbert, Mark R.

    2017-09-01

    The nuclear research and development community has a history of using both integral and differential experiments to support accurate lattice-reactor, nuclear reactor criticality and shielding simulations, as well as verification and validation efforts of cross sections and emitted particle spectra. An important aspect to this type of analysis is the proper consideration of the contribution of the neutron spectrum in its entirety, with correct propagation of uncertainties and standard deviations derived from Monte Carlo simulations, to the local and total uncertainty in the simulated reactions rates (RRs), which usually only apply to one application at a time. This paper identifies deficiencies in the traditional treatment, and discusses correct handling of the RR uncertainty quantification and propagation, including details of the cross section components in the RR uncertainty estimates, which are verified for relevant applications. The methodology that rigorously captures the spectral shift and cross section contributions to the uncertainty in the RR are discussed with quantified examples that demonstrate the importance of the proper treatment of the spectrum profile and cross section contributions to the uncertainty in the RR and subsequent response functions. The recently developed inventory code FISPACT-II, when connected to the processed nuclear data libraries TENDL-2015, ENDF/B-VII.1, JENDL-4.0u or JEFF-3.2, forms an enhanced multi-physics platform providing a wide variety of advanced simulation methods for modelling activation, transmutation, burnup protocols and simulating radiation damage sources terms. The system has extended cutting-edge nuclear data forms, uncertainty quantification and propagation methods, which have been the subject of recent integral and differential, fission, fusion and accelerators validation efforts. The simulation system is used to accurately and predictively probe, understand and underpin a modern and sustainable understanding

  8. Some nuclear data needs in astrophysics

    International Nuclear Information System (INIS)

    Mathews, G.J.; Bauer, R.W.; Bloom, S.D.; Haight, R.C.; Howard, W.M.; Takahashi, K.; Ward, R.A.

    1985-05-01

    In this paper we discuss a number of astrophysical environments and how improved nuclear data could facilitate a better understanding of them. One area of interest includes proton and alpha-particle reactions with unstable nuclei which are necessary for understanding the nucleosynthesis and energy generation in hot hydrogen-burning environments. Efforts underway at LLNL and elsewhere to develop the technology for the measurement of these reaction rates are discussed. Heavy-element nucleosynthesis in the late stages of red-giant stars and supernovae requires a complete network of neutron capture rates and beta-decay rates for nuclei near and far from stability. Experimental and theoretical efforts at LLNL to supply the input data and to model the nucleosynthetic environments will be outlined. Suggestions are made as to which nuclear data are most critical for the various scenarios. 42 refs., 11 figs., 1 tab

  9. Experimental measurements of the 15O(alpha,gamma)19Ne reaction rate and the stability of thermonuclear burning on accreting neutron stars

    International Nuclear Information System (INIS)

    Fisker, J; Tan, W; Goerres, J; Wiescher, M; Cooper, R

    2007-01-01

    Neutron stars in close binary star systems often accrete matter from their companion stars. Thermonuclear ignition of the accreted material in the atmosphere of the neutron star leads to a thermonuclear explosion which is observed as an X-ray burst occurring periodically between hours and days depending on the accretion rate. The ignition conditions are characterized by a sensitive interplay between the accretion rate of the fuel supply and its depletion rate by nuclear burning in the hot CNO cycle and the rp-process. For accretion rates close to stable burning the burst ignition therefore depends critically on the hot CNO breakout reaction 15 O(α, γ) 19 Ne that regulates the flow between the hot CNO cycle and the rapid proton capture process. Until recently, the 15 O(α, γ) 19 Ne reaction rate was not known experimentally and the theoretical estimates carried significant uncertainties. In this paper we perform a parameter study of the uncertainty of this reaction rate and determine the astrophysical consequences of the first measurement of this reaction rate. Our results corroborate earlier predictions and show that theoretically burning remains unstable up to accretion rates near the Eddington limit, in contrast to astronomical observations

  10. The effect of composition of mixture on rate of radiation initiation of chain reactions

    International Nuclear Information System (INIS)

    Poluehktov, V.A.; Begishev, I.R.; Podkhalyuzin, A.T.; Babkina, Eh.I.; Morozov, V.A.; Shapovalov, V.V.

    1977-01-01

    The effect of the composition of starting components on the rate of a number of chain liquid-phase reactions initiated by γ-quanta of Co 60 has been investigated at constant temperature and dosage rate. In regard to 1,1-difluoroethane chlorination, cyclohexene phosphorylation and adamantane alkylation with hexafluoropropylene reactions, abnormal effect of the reagent compositions on reaction rates has been discovered. The possible radical - starting molecule complexing reaction and molecular complexing from the starting components have been considered

  11. The astrophysical r-process and its dependence on properties of nuclei far from stability beta strength functions and neutron capture rates

    CERN Document Server

    Klapdor-Kleingrothaus, H V; Metzinger, J; Oda, T; Thielemann, F K

    1981-01-01

    It is shown that the astrophysical r-process and the question of its site are very sensitive to 'standard' nuclear physics parameters like the beta decay properties and neutron capture rates. Since for these quantities in almost all r-process calculations up to now, and also in all estimates of the production rates of chronometric pairs, only very rough assumptions have been made, it is attempted to present procedures which put the calculation of these quantities for nuclei far from stability on a reliable physical basis. This is done by a microscopic description of the beta strength function and by using a statistical model based on a 'next to first principles' optical potential including effects of deformation for the neutron capture rates. The beta -decay rates for approximately 6000 nuclei between the beta -stability line and the neutron drip line are calculated. The heavy element synthesis by explosive He burning then is calculated using these beta -rates and using realistic star models treating the supe...

  12. Asymptotic normalization coefficients and astrophysical factors

    International Nuclear Information System (INIS)

    Mukhamedzhanov, A.M.; Azhari, A.; Clark, H.L.; Gagliardi, C.A.; Lui, Y.-W.; Sattarov, A.; Trache, L.; Tribble, R.E.; Burjan, V.; Kroha, V.; Carstoiu, F.

    2000-01-01

    The S factor for the direct capture reaction 7 Be(p,γ) 8 B can be found at astrophysical energies from the asymptotic normalization coefficients (ANC's) which provide the normalization of the tails of the overlap functions for 8 B → 7 Be + p. Peripheral transfer reactions offer a technique to determine these ANC's. Using this technique, the 10 B( 7 Be, 8 B) 9 Be and 14 N( 7 Be, 8 B) 13 C reactions have been used to measure the asymptotic normalization coefficient for 7 Be(p, γ) 8 B. These results provide an indirect determination of S 17 (0). Analysis of the existing 9 Be(p, γ) 10 B experimental data within the framework of the R-matrix method demonstrates that experimentally measured ANC's can provide a reasonable determination of direct radiative capture rates. (author)

  13. Triple-differential cross section of the 208Pb(6Li, αd)208 Pb Coulomb breakup and astrophysical S-factor of the d(α,γ)6 Li reaction at extremely low energies

    International Nuclear Information System (INIS)

    Igamov, S.B.; Yarmukhamedov, R.

    1999-10-01

    A method of calculation of the triple-differential cross section of the 208 Pb( 6 Li, αd) 208 Pb Coulomb breakup at astrophysically relevant energies E of the relative motion of the breakup fragments, taking into account the three-body (α - d - 208 Pb) Coulomb effects and the contributions from the E1- and E2- multipoles, including their interference, has been proposed. The new results for the astrophysical S-factor of the direct radiative capture d(α, γ) 6 Li reaction at E ≤ 250 keV have been obtained. It is shown that the experimental triple-differential cross section of the 208 Pb( 6 Li, αd) 208 Pb Coulomb breakup can also be used to give information about the value of the modulus squared of the nuclear vertex constant for the virtual 6 Li → α + d. (author)

  14. Computational and experimental studies on stabilities, reactions and reaction rates of cations and ion-dipole complexes

    NARCIS (Netherlands)

    Ervasti, H.K.

    2008-01-01

    In this thesis, ion stability, ion-molecule reactions and reaction rates are studied using mass spectrometry and molecular modelling. In Chapter 2 the effect of functional group substitution on neutral and ionised ketene are studied. Electron-donating substituents show a stabilising positive

  15. Pop-It Beads to Introduce Catalysis of Reaction Rate and Substrate Depletion Effects

    Science.gov (United States)

    Gehret, Austin U.

    2017-01-01

    A kinesthetic classroom activity was designed to help students understand enzyme activity and catalysis of reaction rate. Students served the role of enzymes by manipulating Pop-It Beads as the catalytic event. This activity illuminates the relationship between reaction rate and reaction progress by allowing students to experience first-hand the…

  16. Constrained least squares methods for estimating reaction rate constants from spectroscopic data

    NARCIS (Netherlands)

    Bijlsma, S.; Boelens, H.F.M.; Hoefsloot, H.C.J.; Smilde, A.K.

    2002-01-01

    Model errors, experimental errors and instrumental noise influence the accuracy of reaction rate constant estimates obtained from spectral data recorded in time during a chemical reaction. In order to improve the accuracy, which can be divided into the precision and bias of reaction rate constant

  17. Estimating reaction rate constants: comparison between traditional curve fitting and curve resolution

    NARCIS (Netherlands)

    Bijlsma, S.; Boelens, H. F. M.; Hoefsloot, H. C. J.; Smilde, A. K.

    2000-01-01

    A traditional curve fitting (TCF) algorithm is compared with a classical curve resolution (CCR) approach for estimating reaction rate constants from spectral data obtained in time of a chemical reaction. In the TCF algorithm, reaction rate constants an estimated from the absorbance versus time data

  18. Students' Ideas about Reaction Rate and Its Relationship with Concentration or Pressure

    Science.gov (United States)

    Cakmakci, Gultekin; Leach, John; Donnelly, James

    2006-01-01

    This cross-sectional study identifies key conceptual difficulties experienced by upper secondary school and pre-service chemistry teachers (N = 191) in the area of reaction rates. Students' ideas about reaction rates were elicited through a series of written tasks and individual interviews. In this paper, students' ideas related to reaction rate…

  19. Alpha-capture reaction rates for 22 Ne (α , n) via sub-Coulomb alpha-transfer and its effect on final abundances of s-process isotopes

    Science.gov (United States)

    Jayatissa, Heshani; Rogachev, Grigory; Koshchiy, Yevgeny; Goldberg, Vladilen; Hooker, Joshua; Hunt, Curtis; Magana, Cordero; Roeder, Brian; Saastamoinen, Antti; Spiridon, Alexandria; Upadhyayula, Sriteja; Trippella, Oscar

    2017-09-01

    The 22 Ne (α , n) reaction is a very important neutron source reaction for the slow neutron capture process (s-process) in asymptotic giant branch stars. These direct measurements are very difficult to carry out at the energy regimes of interest for astrophysics (Gamow energies) due to the extremely small reaction cross section. The large uncertainties introduced when extrapolating direct measurements at high energies down to the Gamow energies can be overcome by measuring the Asymptotic Normalization Coefficients (ANC) of the relevant states using α-transfer reactions at sub-Coulomb energies to reduce the optical model dependence. The study of the 22Ne(6Li,d) and 22Ne(7Li,t) reaction was carried out at the Cyclotron Institute at Texas A&M University. The α-ANC measurements for the near α-threshold resonances of 26Mg provide constraints for the 22Ne(α,n) reaction rate. The effect of this reaction rate on the final abundances of the s-process isotopes will be discussed.

  20. Experimental Investigation of the ^{19}Ne(p,γ)^{20}Na Reaction Rate and Implications for Breakout from the Hot CNO Cycle.

    Science.gov (United States)

    Belarge, J; Kuvin, S A; Baby, L T; Baker, J; Wiedenhöver, I; Höflich, P; Volya, A; Blackmon, J C; Deibel, C M; Gardiner, H E; Lai, J; Linhardt, L E; Macon, K T; Need, E; Rasco, B C; Quails, N; Colbert, K; Gay, D L; Keeley, N

    2016-10-28

    The ^{19}Ne(p,γ)^{20}Na reaction is the second step of a reaction chain which breaks out from the hot CNO cycle, following the ^{15}O(α,γ)^{19}Ne reaction at the onset of x-ray burst events. We investigate the spectrum of the lowest proton-unbound states in ^{20}Na in an effort to resolve contradictions in spin-parity assignments and extract reliable information about the thermal reaction rate. The proton-transfer reaction ^{19}Ne(d,n)^{20}Na is measured with a beam of the radioactive isotope ^{19}Ne at an energy around the Coulomb barrier and in inverse kinematics. We observe three proton resonances with the ^{19}Ne ground state, at 0.44, 0.66, and 0.82 MeV c.m. energies, which are assigned 3^{+}, 1^{+}, and (0^{+}), respectively. In addition, we identify two resonances with the first excited state in ^{19}Ne, one at 0.20 MeV and one, tentatively, at 0.54 MeV. These observations allow us for the first time to experimentally quantify the astrophysical reaction rate on an excited nuclear state. Our experiment shows an efficient path for thermal proton capture in ^{19}Ne(p,γ)^{20}Na, which proceeds through ground state and excited-state capture in almost equal parts and eliminates the possibility for this reaction to create a bottleneck in the breakout from the hot CNO cycle.

  1. "Depletion": A Game with Natural Rules for Teaching Reaction Rate Theory.

    Science.gov (United States)

    Olbris, Donald J.; Herzfeld, Judith

    2002-01-01

    Depletion is a game that reinforces central concepts of reaction rate theory through simulation. Presents the game with a set of follow-up questions suitable for either a quiz or discussion. Also describes student reaction to the game. (MM)

  2. Reaction rate oscillations during catalytic CO oxidation: A brief overview

    Science.gov (United States)

    Tsotsis, T. T.; Sane, R. C.

    1987-01-01

    It is not the intent here to present a comprehensive review of the dynamic behavior of the catalytic oxidation of CO. This reaction is one of the most widely studied in the field of catalysis. A review paper by Engel and Ertl has examined the basic kinetic and mechanistic aspects, and a comprehensive paper by Razon and Schmitz was recently devoted to its dynamic behavior. Those interested in further study of the subject should consult these reviews and a number of general review papers on catalytic reaction dynamics. The goal is to present a brief overview of certain interesting aspects of the dynamic behavior of this reaction and to discuss a few questions and issues, which are still the subject of study and debate.

  3. On the use temperature parameterized rate coefficients in the estimation of non-equilibrium reaction rates

    Science.gov (United States)

    Shizgal, Bernie D.; Chikhaoui, Aziz

    2006-06-01

    The present paper considers a detailed analysis of the nonequilibrium effects for a model reactive system with the Chapman-Eskog (CE) solution of the Boltzmann equation as well as an explicit time dependent solution. The elastic cross sections employed are a hard sphere cross section and the Maxwell molecule cross section. Reactive cross sections which model reactions with and without activation energy are used. A detailed comparison is carried out with these solutions of the Boltzmann equation and the approximation introduced by Cukrowski and coworkers [J. Chem. Phys. 97 (1992) 9086; Chem. Phys. 89 (1992) 159; Physica A 188 (1992) 344; Chem. Phys. Lett. A 297 (1998) 402; Physica A 275 (2000) 134; Chem. Phys. Lett. 341 (2001) 585; Acta Phys. Polonica B 334 (2003) 3607.] based on the temperature of the reactive particles. We show that the Cukrowski approximation has limited applicability for the large class of reactive systems studied in this paper. The explicit time dependent solutions of the Boltzmann equation demonstrate that the CE approach is valid only for very slow reactions for which the corrections to the equilibrium rate coefficient are very small.

  4. Simple Analytic Collisional Rates for non-LTE Vibrational Populations in Astrophysical Environments: the Cases of Circumstellar SiO Masers and Shocked H2

    Science.gov (United States)

    Bieniek, Ronald

    2008-05-01

    Rates for collisionally induced transitions between molecular vibrational levels are important in modeling a variety of non-LTE processes in astrophysical environments. Two examples are SiO masering in circumstellar envelopes in certain late-type stars [1] and the vibrational populations of molecular hydrogen in shocked interstellar medium [cf 2]. A simple exponential-potential model of molecular collisions leads to a two-parameter analytic expression for state-to-state and thermally averaged rates for collisionally induced vibrational-translational (VT) transitions in diatomic molecules [3,4]. The thermally averaged rates predicted by this formula have been shown to be in excellent numerical agreement with absolute experimental and quantum mechanical rates over large temperature ranges and initial vibrational excitation levels in a variety of species, e.g., OH, O2, N2 [3] and even for the rate of H2(v=1)+H2, which changes by five orders of magnitude in the temperature range 50-2000 K [4]. Analogous analytic rates will be reported for vibrational transitions in SiO due to collisions with H2 and compared to the numerical fit of quantum-mechanical rates calculated by Bieniek and Green [5]. [1] Palov, A.P., Gray, M.D., Field, D., & Balint-Kurti, G.G. 2006, ApJ, 639, 204. [2] Flower, D. 2007, Molecular Collisions in the Interstellar Medium (Cambridge: Cambridge Univ. Press) [3] Bieniek, R.J. & Lipson, S.J. 1996, Chem. Phys. Lett. 263, 276. [4] Bieniek, R.J. 2006, Proc. NASA LAW (Lab. Astrophys. Workshop) 2006, 299; http://www.physics.unlv.edu/labastro/nasalaw2006proceedings.pdf. [5] Bieniek, R.J., & Green, S. 1983, ApJ, 265, L29 and 1983, ApJ, 270, L101.

  5. Constant rate thermal analysis of a dehydrogenation reaction

    Czech Academy of Sciences Publication Activity Database

    Perejon, A.; Perez-Maqueda, L. A.; Sanchez-Jimenez, P.E.; Criado, J. M.; Murafa, Nataliya; Šubrt, Jan

    2016-01-01

    Roč. 6, č. 84 (2016), s. 81454-81460 ISSN 2046-2069 Institutional support: RVO:61388980 Keywords : solid-state reaction s * hydrogen storage properties * milled magnesium hydride Subject RIV: CA - Inorganic Chemistry Impact factor: 3.108, year: 2016

  6. Quick and Easy Rate Equations for Multistep Reactions

    Science.gov (United States)

    Savage, Phillip E.

    2008-01-01

    Students rarely see closed-form analytical rate equations derived from underlying chemical mechanisms that contain more than a few steps unless restrictive simplifying assumptions (e.g., existence of a rate-determining step) are made. Yet, work published decades ago allows closed-form analytical rate equations to be written quickly and easily for…

  7. Physical-chemical processes of astrophysical interest: nitrogen chemistry

    International Nuclear Information System (INIS)

    Loison, Jean-Christophe; Hickson, Kevin; Hily-Blant, Pierre; Faure, Alexandre; Vuitton, Veronique; Bacmann, A.; Maret, Sebastien; Legal, Romane; Rist, Claire; Roncero, Octavio; Larregaray, Pascal; Hochlaf, Majdi; Senent, M. L.; Capron, Michael; Biennier, Ludovic; Carles, Sophie; Bourgalais, Jeremy; Le Picard, Sebastien; Cordier, Daniel; Guillemin, Jean-Claude; Trolez, Yann; Bertin, M.; Poderoso, H.A.M.; Michaut, X.; Jeseck, P.; Philippe, L.; Fillion, J.H.; Fayolle, E.C.; Linnartz, H.; Romanzin, C.; Oeberg, K.I.; Roueff, Evelyne; Pagani, Laurent; Padovani, Marco; Wakelam, Veronique; Honvault, Beatrice; Zvereva-Loete, Natalia; Ouk, Chanda-Malis; Scribano, Yohann; Hartmann, J.M.; Pineau des Forets, Guillaume; Hernandez, Mario; Lique, Francois; Kalugina, Yulia N.; Stoecklin, T.; Hochlaf, M.; Crespos, C.; Larregaray, P.; Martin-Gondre, L.; Petuya, R.; Quintas Sanchez, E.L.; Zanchet, Alexandre; Rodriguez-Lazcano, Yamilet; Mate, Belen

    2013-06-01

    This document contains the programme and abstracts of contributions to a workshop on nitrogen chemistry within an astrophysical perspective. These contributions have been presented in sessions: Introduction (opening lecture, experimental approaches to molecular astrophysics, theoretical approaches to astrophysics, observations in molecular astrophysics), Physical-chemical theory of the gas phase (time-dependent approach in elementary activity, statistic approach in elementary activity in the case of the N+H_2 reaction, potential energy surfaces for inelastic and reactive collisions, collision rate for N_2H"+, ortho/para selection rules in the chemistry of nitrogen hydrides, cyanides/iso-cyanides excitation in the ISM, CN excitation, radiative association with N_2H as new interstellar anion, ro-vibratory excitation of HCN) Laboratory astrophysics (measurement of reaction products in the CRESUSOL project, reactivity of the CN- anion, N_2 photo-desorption in ices, CRESU study of nitrogen chemistry, chemistry of nitrogen complex molecules), Observations and chemistry of astrophysical media (the problem of interstellar nitrogen fractioning, abundance of N_2 in proto-stellar cores, HNC in Titan atmosphere and nitrogen-related mechanisms in hot Jupiters, HCN and HNC in dark clouds or how theoretical modelling helps in interpreting observations, nitrogen chemistry in cold clouds, deuteration of nitrogen hydrides, nitrogen in interstellar ices, biochemical molecules on Titan, coupling between excitation and chemistry, radiative transfer of nitrogen hydrides, ortho/para chemistry of nitrogen hydrides), Physical-chemical theory of gas-grain interactions (nitrogen reactivity on surfaces, IR spectra of ices of NH_3 and NH_3/N_2 mixtures)

  8. Measurement of sub threshold resonance contributions to fusion reactions: the case of the 13C(α, n16O astrophysical neutron source

    Directory of Open Access Journals (Sweden)

    La Cognata M.

    2015-01-01

    of the 6.356 MeV level was deduced. For the first time, the Trojan Horse Method and the asymptotic normalization coefficient were used in synergy. Our indirect approach lead to (C̃17O(1/2+α13C2 = 7.7−1.5+1.6 fm−1, slightly larger than the values in the literature, determining a 13C(α, n16O reaction rate slightly larger than the one in the literature at temperatures lower than 108 K, with enhanced accuracy.

  9. Reactions and reaction rates in the regional aquifer beneath the Pajarito Plateau, north-central New Mexico, USA

    Science.gov (United States)

    Hereford, Anne G.; Keating, Elizabeth H.; Guthrie, George D.; Zhu, Chen

    2007-05-01

    Reactions and reaction rates within aquifers are fundamental components of critical hydrological processes. However, reactions simulated in laboratory experiments typically demonstrate rates that are much faster than those observed in the field. Therefore, it is necessary to conduct more reaction rate analyses in natural settings. This study of geochemical reactions in the regional aquifer in the Pajarito Plateau near Los Alamos, New Mexico combines modeling with petrographic assessment to further knowledge and understanding of complex natural hydrologic systems. Groundwater geochemistry shows marked evolution along assumed flow paths. The flow path chosen for this study was evaluated using inverse mass balance modeling to calculate the mass transfer. X-ray diffraction and field emission gun scanning electron microscopy were used to identify possible reactants and products. Considering the mineralogy of the aquifer and saturation indices for the regional water refined initial interpretations. Calculations yielded dissolution rates for plagioclase on the order of 10-15 mol s-1 m-2 and for K-feldspar on the order of 10-17 mol s-1 m-2, orders of magnitude slower than laboratory rates. While these rates agree with other aquifer studies, they must be considered in the light of the uncertainty associated with geometric surface area estimates, 14C ages, and aquifer properties.

  10. for the inference of Furan combustion reaction rate

    KAUST Repository

    Long, Quan

    2016-01-06

    We carry out the design of experiments for the identification of the reaction parameters in Furan combustion. The lacks of information on the true value of the control parameters, specifically, the initial temperature and the initial TBHP concentration, are considered in the design procedure by errors-invariables models. We use two types of observables. The first is a scaler observable, i.e., half decay time of the [TBHP]. The second is the time history of the concentration.

  11. Multiscale Investigation on Biofilm Distribution and Its Impact on Macroscopic Biogeochemical Reaction Rates: BIOFILM DISTRIBUTION AND RATE SCALING

    Energy Technology Data Exchange (ETDEWEB)

    Yan, Zhifeng [Institute of Surface-Earth System Science, Tianjin University, Tianjin China; Pacific Northwest National Laboratory, Richland WA USA; Liu, Chongxuan [Pacific Northwest National Laboratory, Richland WA USA; School of Environmental Science and Engineering, Southern University of Science and Technology, Shenzhen China; Liu, Yuanyuan [Pacific Northwest National Laboratory, Richland WA USA; School of Earth Science and Engineering, Nanjing University, Nanjing China; Bailey, Vanessa L. [Pacific Northwest National Laboratory, Richland WA USA

    2017-11-01

    Biofilms are critical locations for biogeochemical reactions in the subsurface environment. The occurrence and distribution of biofilms at microscale as well as their impacts on macroscopic biogeochemical reaction rates are still poorly understood. This paper investigated the formation and distributions of biofilms in heterogeneous sediments using multiscale models, and evaluated the effects of biofilm heterogeneity on local and macroscopic biogeochemical reaction rates. Sediment pore structures derived from X-ray computed tomography were used to simulate the microscale flow dynamics and biofilm distribution in the sediment column. The response of biofilm formation and distribution to the variations in hydraulic and chemical properties was first examined. One representative biofilm distribution was then utilized to evaluate its effects on macroscopic reaction rates using nitrate reduction as an example. The results revealed that microorganisms primarily grew on the surfaces of grains and aggregates near preferential flow paths where both electron donor and acceptor were readily accessible, leading to the heterogeneous distribution of biofilms in the sediments. The heterogeneous biofilm distribution decreased the macroscopic rate of biogeochemical reactions as compared with those in homogeneous cases. Operationally considering the heterogeneous biofilm distribution in macroscopic reactive transport models such as using dual porosity domain concept can significantly improve the prediction of biogeochemical reaction rates. Overall, this study provided important insights into the biofilm formation and distribution in soils and sediments as well as their impacts on the macroscopic manifestation of reaction rates.

  12. Metabolic control analysis of biochemical pathways based on a thermokinetic description of reaction rates

    DEFF Research Database (Denmark)

    Nielsen, Jens Bredal

    1997-01-01

    Metabolic control analysis is a powerful technique for the evaluation of flux control within biochemical pathways. Its foundation is the elasticity coefficients and the flux control coefficients (FCCs). On the basis of a thermokinetic description of reaction rates it is here shown...... that the elasticity coefficients can be calculated directly from the pool levels of metabolites at steady state. The only requirement is that one thermodynamic parameter be known, namely the reaction affinity at the intercept of the tangent in the inflection point of the curve of reaction rate against reaction...... of the thermokinetic description of reaction rates to include the influence of effecters. Here the reaction rate is written as a linear function of the logarithm of the metabolite concentrations. With this type of rate function it is shown that the approach of Delgado and Liao [Biochem. J. (1992) 282, 919-927] can...

  13. Charged-particle thermonuclear reaction rates: I. Monte Carlo method and statistical distributions

    International Nuclear Information System (INIS)

    Longland, R.; Iliadis, C.; Champagne, A.E.; Newton, J.R.; Ugalde, C.; Coc, A.; Fitzgerald, R.

    2010-01-01

    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.

  14. Upper atmosphere research: Reaction rate and optical measurements

    Science.gov (United States)

    Stief, L. J.; Allen, J. E., Jr.; Nava, D. F.; Payne, W. A., Jr.

    1990-01-01

    The objective is to provide photochemical, kinetic, and spectroscopic information necessary for photochemical models of the Earth's upper atmosphere and to examine reactions or reactants not presently in the models to either confirm the correctness of their exclusion or provide evidence to justify future inclusion in the models. New initiatives are being taken in technique development (many of them laser based) and in the application of established techniques to address gaps in the photochemical/kinetic data base, as well as to provide increasingly reliable information.

  15. Interlaboratory reaction rate program. 12th progress report, November 1976-October 1979

    International Nuclear Information System (INIS)

    Lippincott, E.P.; McElroy, W.N.; Preston, C.C.

    1980-09-01

    The Interlaboratory Reaction Rate UILRR) program is establishing the capability to accurately measure neutron-induced reactions and reaction rates for reactor fuels and materials development programs. The goal for the principal fission reactions, 235 U, 238 U and 239 Pu, is an accuracy to within +- 5% at the 95% confidence level. Accurate measurement of other fission and nonfission reactions is also required, but to a lesser accuracy, between +- 5% and 10% at the 95% confidence level. A secondary program objective is improvement in knowledge of the nuclear parameters involved in the standarization of fuels and materials dosimetry measurements of neutron flux, spectra, fluence and burnup

  16. From cutting-edge pointwise cross-section to groupwise reaction rate: A primer

    Directory of Open Access Journals (Sweden)

    Sublet Jean-Christophe

    2017-01-01

    Full Text Available The nuclear research and development community has a history of using both integral and differential experiments to support accurate lattice-reactor, nuclear reactor criticality and shielding simulations, as well as verification and validation efforts of cross sections and emitted particle spectra. An important aspect to this type of analysis is the proper consideration of the contribution of the neutron spectrum in its entirety, with correct propagation of uncertainties and standard deviations derived from Monte Carlo simulations, to the local and total uncertainty in the simulated reactions rates (RRs, which usually only apply to one application at a time. This paper identifies deficiencies in the traditional treatment, and discusses correct handling of the RR uncertainty quantification and propagation, including details of the cross section components in the RR uncertainty estimates, which are verified for relevant applications. The methodology that rigorously captures the spectral shift and cross section contributions to the uncertainty in the RR are discussed with quantified examples that demonstrate the importance of the proper treatment of the spectrum profile and cross section contributions to the uncertainty in the RR and subsequent response functions. The recently developed inventory code FISPACT-II, when connected to the processed nuclear data libraries TENDL-2015, ENDF/B-VII.1, JENDL-4.0u or JEFF-3.2, forms an enhanced multi-physics platform providing a wide variety of advanced simulation methods for modelling activation, transmutation, burnup protocols and simulating radiation damage sources terms. The system has extended cutting-edge nuclear data forms, uncertainty quantification and propagation methods, which have been the subject of recent integral and differential, fission, fusion and accelerators validation efforts. The simulation system is used to accurately and predictively probe, understand and underpin a modern and

  17. A New ECR Ion Source for Nuclear Astrophysics Studies

    Science.gov (United States)

    Cesaratto, John M.

    2008-10-01

    The Laboratory for Experimental Nuclear Astrophysics (LENA) is a low energy facility designed to study nuclear reactions of astrophysical interest at energies which are important for nucleosysthesis. In general, these reactions have extremely small cross sections, requiring intense beams and efficient detection systems. Recently, a new, high intensity electron-cyclotron-resonance (ECR) ion source has been constructed (based on a design by Wills et al.[1]), which represents a substantial improvement in the capabilities of LENA. Beam is extracted from an ECR plasma excited at 2.45 GHz and confined by an array of permanent magnets. It has produced H^+ beams in excess of 1 mA on target over the energy range 100 - 200 keV, which greatly increases our ability to measure small cross sections. Initial measurements will focus on the ^23Na(p,γ)^24Mg reaction, which is of interest in a variety of astrophysical scenarios. The present uncertainty in the rate of this reaction is the result of an unobserved resonance expected at Elab =144 keV, which should be detectable using beams from the new ECR source. In collaboration with Arthur E. Champagne and Thomas B. Clegg, University of North Carolina, Chapel Hill and TUNL. [3pt] [1] J. S. C. Wills et al., Rev. Sci. Instrum. 69, 65 (1999).

  18. A systematic and detailed investigation of radiative rates for forbidden transitions of astrophysical interest in doubly ionized iron peak elements

    Science.gov (United States)

    Quinet, Pascal; Fivet, Vanessa; Bautista, Manuel

    2015-08-01

    The knowledge of accurate and reliable atomic data for lowly ionized iron peak elements, from scandium to copper, is of paramount importance for the analysis of the high resolution spectra currently available. The third spectra of several iron group elements have been observed in different galactic sources like Herbig-Haro objects in the Orion Nebula [1] and stars like Eta Carinae [2]. However, forbidden transitions between low-lying metastable levels of doubly ionized species have been little investigated so far and radiative rates for those lines remain sparse or inexistent.In the present contribution, we report on the recent study we have performed concerning the determination of magnetic dipole (M1) and electric quadrupole (E2) transition probabilities in those ions. For the calculations, we have extensively used the pseudo-relativistic Hartree-Fock (HFR) code of Cowan [3] and the central Thomas-Fermi-Dirac potential approximation implemented in AUTOSTRUCTURE [4]. This multi-platform approach allowed us to check the consistency and to assess the accuracy of the results obtained.[1] Mesa-Delgado A. et al., MNRAS 395, 855 (2009)[2] Johansson S. et al., A&A 361, 977 (2000)[3] Cowan R.D., The Theory of Atomic Structure and Spectra, Univ. California Press, Berkeley (1981)[4] Badnell N.R., J. Phys. B: At. Mol. Opt. Phys. 30, 1 (1997)

  19. Nuclear astrophysics

    International Nuclear Information System (INIS)

    Penionzhkevich, Yu. E.

    2010-01-01

    The International Year of Astronomy 2009 (IYA2009) was declared by the 62nd General Assembly of the United Nations and was also endorsed by UNESCO. Investigations in the realms of particle and nuclear physicsmake a large contribution in the development of our ideas of the properties of the Universe. The present article discusses some problems of the evolution of the Universe, nucleosyntheses, and cosmochronology from the point of view of nuclear and particle physics. Processes occurring in the Universe are compared with the mechanisms of the production and decay of nuclei, as well as with the mechanisms of their interaction at high energies. Examples that demonstrate the potential of nuclearphysics methods for studying cosmic objects and the properties of the Universe are given. The results that come from investigations into nuclear reactions induced by beams of radioactive nuclei and which make it possible to take a fresh look at the nucleosynthesis scenario in the range at light nuclei are presented.

  20. Evaluation of Chemical Kinetic for Mathematics Model Reduction of Cadmium Reaction Rate, Constant and Reaction Orde in to Electrochemical Process

    International Nuclear Information System (INIS)

    Prayitno

    2007-01-01

    The experiment was reduction of cadmium rate with electrochemical influenced by time process, concentration, current strength and type of electrode plate. The aim of the experiment was to know the influence, mathematic model reduction of cadmium the reaction rate, reaction rate constant and reaction orde influenced by time process, concentration, current strength and type of electrode plate. Result of research indicate the time processing if using plate of copper electrode is during 30 minutes and using plate of aluminium electrode is during 20 minutes. Condition of strong current that used in process of electrochemical is only 0.8 ampere and concentration effective is 5.23 mg/l. The most effective type Al of electrode plate for reduction from waste and the efficiency of reduction is 98 %. (author)

  1. Rate Constants for the Reactions of Hydroxyl Radical with Several Alkanes, Cycloalkanes, and Dimethyl Ether

    Science.gov (United States)

    DeMore, W.; Bayes, K.

    1998-01-01

    Relative rate experiements were used to measure rate constants and temperature denpendencies of the reactions of OH with propane, n-butane, n-pentane, n-hexane, cyclopropane, cyclobutane, cyclopentane, and dimethyl ether.

  2. Indirect techniques in nuclear astrophysics. Asymptotic normalization coefficient and trojan horse

    International Nuclear Information System (INIS)

    Mukhamedzhanov, A.M.; Gagliardi, C.A.; Pirlepesov, F.; Trache, L.; Tribble, R.E.; Blokhintsev, L.D.; Brown, B.A.; Nunes, F.M.; Burjan, V.; Kroha, V.; Cherubini, S.; Pizzone, R.G.; Romano, S.; Spitaleri, C.; Tumino, A.; Irgaziev, B.F.; Tang, X.D.

    2006-01-01

    Owing to the presence of the Coulomb barrier at astrophysically relevant kinetic energies it is very difficult, or sometimes impossible, to measure astrophysical reaction rates in the laboratory. That is why different indirect techniques are being used along with direct measurements. Here we address two important indirect techniques, the asymptotic normalization coefficient (ANC) and the Trojan Horse (TH) methods. We discuss the application of the ANC technique for calculation of the astrophysical processes in the presence of subthreshold bound states, in particular, two different mechanisms are discussed: direct capture to the subthreshold state and capture to the low-lying bound states through the subthreshold state, which plays the role of the subthreshold resonance. The ANC technique can also be used to determine the interference sign of the resonant and nonresonant (direct) terms of the reaction amplitude. The TH method is unique indirect technique allowing one to measure astrophysical rearrangement reactions down to astrophysically relevant energies. We explain why there is no Coulomb barrier in the sub-process amplitudes extracted from the TH reaction. The expressions for the TH amplitude for direct and resonant cases are presented. (orig.)

  3. Systematic variation of threshold reaction rates in EBR-II

    International Nuclear Information System (INIS)

    Lippincott, E.P.; Combs, B.L.; Davis, A.I.

    1976-01-01

    Characterization of neutron flux, fluence, and spectra in fast reactor irradiation environments is presently being carried out at HEDL utilizing the multiple foil technique. These fluences and spectra are then used to correlate damage effects data to produce damage functions or equations to predict materials effects under future irradiation conditions. The neutron flux and spectrum, then, act as a transfer function to relate present observations to future effects in the same or different environments and thus consistent fluence evaluations are of utmost importance. As part of a continuing program to establish the data base to meet consistency requirements, a systematic correlation of data from a recent dosimetry test in EBR-II is being made. The paper presents preliminary results of some of these correlations involving threshold reactions

  4. Co-solvent effects on reaction rate and reaction equilibrium of an enzymatic peptide hydrolysis.

    Science.gov (United States)

    Wangler, A; Canales, R; Held, C; Luong, T Q; Winter, R; Zaitsau, D H; Verevkin, S P; Sadowski, G

    2018-04-25

    This work presents an approach that expresses the Michaelis constant KaM and the equilibrium constant Kth of an enzymatic peptide hydrolysis based on thermodynamic activities instead of concentrations. This provides KaM and Kth values that are independent of any co-solvent. To this end, the hydrolysis reaction of N-succinyl-l-phenylalanine-p-nitroanilide catalysed by the enzyme α-chymotrypsin was studied in pure buffer and in the presence of the co-solvents dimethyl sulfoxide, trimethylamine-N-oxide, urea, and two salts. A strong influence of the co-solvents on the measured Michaelis constant (KM) and equilibrium constant (Kx) was observed, which was found to be caused by molecular interactions expressed as activity coefficients. Substrate and product activity coefficients were used to calculate the activity-based values KaM and Kth for the co-solvent free reaction. Based on these constants, the co-solvent effect on KM and Kx was predicted in almost quantitative agreement with the experimental data. The approach presented here does not only reveal the importance of understanding the thermodynamic non-ideality of reactions taking place in biological solutions and in many technological applications, it also provides a framework for interpreting and quantifying the multifaceted co-solvent effects on enzyme-catalysed reactions that are known and have been observed experimentally for a long time.

  5. Reaction rate constants of HO2 + O3 in the temperature range 233-400 K

    Science.gov (United States)

    Wang, Xiuyan; Suto, Masako; Lee, L. C.

    1988-01-01

    The reaction rate constants of HO2 + O3 were measured in the temperature range 233-400 K using a discharge flow system with photofragment emission detection. In the range 233-253 K, the constants are approximately a constant value, and then increase with increasing temperature. This result suggests that the reaction may have two different channels. An expression representing the reaction rate constants is presented.

  6. Accurate quantum calculations of the reaction rates for H/D+ CH4

    NARCIS (Netherlands)

    Harrevelt, R. van; Nyman, G.; Manthe, U.

    2007-01-01

    In previous work [T. Wu, H. J. Werner, and U. Manthe, Science 306, 2227 (2004)], accurate quantum reaction rate calculations of the rate constant for the H+CH4 -> CH3+H-2 reaction have been presented. Both the electronic structure calculations and the nuclear dynamics calculations are converged with

  7. Rate of reaction of dimethylmercury with oxygen atoms in the gas phase

    DEFF Research Database (Denmark)

    Egsgaard, Helge

    1986-01-01

    The rate constant for the reaction of atomic oxygen (O(3P)) with dimethylmercury has been measured at room temperature at a pressure of about 1 Torr using a fast flow system with electron paramagnetic resonance and mass spectrometric detection. Some reaction products were identified. The rate...

  8. Putting Reaction Rates and Collision Theory in the Hands of Your Students.

    Science.gov (United States)

    Evenson, Andy

    2002-01-01

    Describes a simulation that can be used to give concrete analogies of collision theory and the factors that affect reaction rates including temperature, concentration, catalyst, and molecular orientation. The simulation works best if done as an introduction to the concepts to help prevent misconceptions about reaction rates and collision theory.…

  9. Applications of the absolute reaction rate theory to biological responses in electric and magnetic fields

    International Nuclear Information System (INIS)

    Brannen, J.P.; Wayland, J.R.

    1976-01-01

    This paper develops a theoretical foundation for the study of biological responses of electric and magnetic fields. The basis of the development is the absolute reaction rate theory and the effects of fields on reaction rates. A simple application to the response of Bacillus subtilis var niger in a microwave field is made. Potential areas of application are discussed

  10. Compilation and R-matrix analysis of Big Bang nuclear reaction rates

    International Nuclear Information System (INIS)

    Descouvemont, Pierre; Adahchour, Abderrahim; Angulo, Carmen; Coc, Alain; Vangioni-Flam, Elisabeth

    2004-01-01

    We use the R-matrix theory to fit low-energy data on nuclear reactions involved in Big Bang nucleosynthesis. Special attention is paid to the rate uncertainties which are evaluated on statistical grounds. We provide S factors and reaction rates in tabular and graphical formats

  11. Enhancement of D-T reaction rate due to D-T contact

    International Nuclear Information System (INIS)

    Hitoki, Shigehisa; Ogasawara, Masatada; Aono, Osamu.

    1979-09-01

    The reaction rate that is appropriate for magnetized nonuniform plasma is numerically calculated to investigate the enhancement of the D-T reaction rate. Spatial separation of the guiding center distributions of D and T enhances the reaction rate. Cases of several guiding center configurations are investigated. The largest enhancement is obtained, when both guiding center distributions are delta-functions which are separated by a length that corresponds to the Gamow peak energy. As compared with the case of no separation of D and T, the maximum enhancing factors obtained are 2.3 for total reaction rate and 1.6 for local reaction rate. Cases of the guiding center distributions with finite widths are also investigated. (author)

  12. Contribution of 194.1 keV Resonance to 17O(p, alpha) 14N Reaction Rate using R Matrix Code

    International Nuclear Information System (INIS)

    Chafa, A.; Messili, F.Z.; Barhoumi, S.

    2009-01-01

    Knowledge of the 17 O(p, alpha ) 14 N reaction rates is required for evaluating elemental abundances in a number of hydrogen - burning stellar sites. This reaction is specifically very important for nucleosynthesis of the rare oxygen isotope 17 O. Classical novae are thought to be a major source of 17 O in the Galaxy and produce the short-live radioisotope 18 F whose + decay is followed by a gamma ray emission which could be observed with satellites such as the Integral observatory. As the 17 O(p, alpha) 14 N and 17 O(p, alpha ) 18 F reactions govern the destruction of 17 O and the formation of 1 '8F, their rates are decisive in determining the final abundances of these isotopes. Stellar temperatures of primary importance for nucleosynthesis are typically in the ranges T = 0.01-0.1 GK for red giant, AGB, and massive stars, and T 0.01-0.4 GK for classical nova explosions In recent work, we observed, for the first time, a resonance a 183.3 keV corresponding to level in 18 F at Ex 5789.8 ± 0.3 keV. A new astrophysical parameters of this resonance are found. In this work we study this reaction using numerical code based on R matrix method including the new values of level energy and parameters of 183.3 keV resonance in order to show his contribution to 17 O(p, alpha) 14 N reaction rates. We also use old parameters values of this resonance given in Keiser work for comparison. We show that this resonance predominate the reaction rates in all range of stellar temperature for classical nova explosions. This is in good agreement with our work with experimental method. We also study cross section and differential cross section 17 O(p, alpha ) 14 N reaction with R matrix method

  13. Diffusion-controlled reaction. V. Effect of concentration-dependent diffusion coefficient on reaction rate in graft polymerization

    International Nuclear Information System (INIS)

    Imre, K.; Odian, G.

    1979-01-01

    The effect of diffusion on radiation-initiated graft polymerization has been studied with emphasis on the single- and two-penetrant cases. When the physical properties of the penetrants are similar, the two-penetrant problems can be reduced to the single-penetrant problem by redefining the characteristic parameters of the system. The diffusion-free graft polymerization rate is assumed to be proportional to the upsilon power of the monomer concentration respectively, and, in which the proportionality constant a = k/sub p/R/sub i//sup w//k/sub t//sup z/, where k/sub p/ and k/sub t/ are the propagation and termination rate constants, respectively, and R/sub i/ is the initiation rate. The values of upsilon, w, and z depend on the particular reaction system. The results of earlier work were generalized by allowing a non-Fickian diffusion rate which predicts an essentially exponential dependence on the monomer concentration of the diffusion coefficient, D = D 0 [exp(deltaC/M)], where M is the saturation concentration. A reaction system is characterized by the three dimensionless parameters, upsilon, delta, and A = (L/2)[aM/sup (upsilon--1)//D 0 ]/sup 1/2/, where L is the polymer film thickness. Graft polymerization tends to become diffusion controlled as A increases. Larger values of delta and ν cause a reaction system to behave closer to the diffusion-free regime. Transition from diffusion-free to diffusion-controlled reaction involves changes in the dependence of the reaction rate on film thickness, initiation rate, and monomer concentration. Although the diffusion-free rate is w order in initiation rate, upsilon order in monomer, and independent of film thickness, the diffusion-controlled rate is w/2 order in initiator rate and inverse first-order in film thickness. Dependence of the diffusion-controlled rate on monomer is dependent in a complex manner on the diffusional characteristics of the reaction system. 11 figures, 4 tables

  14. Reaction rate of the 13C(α,n)16O neutron source using the ANC of the -3 keV resonance measured with the THM

    International Nuclear Information System (INIS)

    La Cognata, M; Spitaleri, C; Trippella, O; Kiss, G G; Guardo, G L; Puglia, S M R; Romano, S; Spartà, R; Rogachev, G V; Avila, M; Koshchiy, E; Kuchera, A; Santiago, D; Mukhamedzhanov, A M; Lamia, L

    2016-01-01

    The s-process is responsible of the synthesis of most of the nuclei in the mass range 90 ≤ A ≤ 208. It consists in a series of neutron capture reactions on seed nuclei followed by β-decays, since the neutron accretion rate is slower than the β-decay rate. Such small neutron flux is supplied by the 13 C(α,n) 16 O reaction. It is active inside the helium-burning shell of asymptotic giant branch stars, at temperatures < 10 8 K, corresponding to an energy interval of 140–230 keV. In this region, the astrophysical S (E)-factor is dominated by the −3 keV sub-threshold resonance due to the 6.356 MeV level in 17 O. In this work, we have applied the Trojan Horse Method (THM) to the 13 C( 6 Li,n 16 O)d quasi-free reaction to extract the 6.356 MeV level resonance parameters, in particular the asymptotic normalization coefficient . A preliminary analysis of a partial data set has lead to , slightly larger than the values in the literature. However, the deduced 13 C(α, n) 16 O reaction rate is in agreement with most results in the literature at ∼ 10 8 K, with enhanced accuracy thanks to our innovative approach merging together ANC and THM. (paper)

  15. Effect of Substrate Character on Heterogeneous Ozone Reaction Rate with Individual PAHs and Their Reaction Mixtures

    Science.gov (United States)

    Holmen, B. A.; Stevens, T.

    2009-12-01

    Vehicle exhaust contains many unregulated chemical compounds that are harmful to human health and the natural environment, including polycyclic aromatic hydrocarbons (PAH), a class of organic compounds derived from fuel combustion that can be carcinogenic and mutagenic. PAHs have been quantified in vehicle-derived ultrafine particles (Dpsolid, reacting the samples with gas-phase ozone, and determining both PAH loss over time and products formed, using thermal-desorption gas chromatography / mass spectrometry (TD-GC/MS). The individual PAHs anthracene, phenanthrene, and fluorene, adsorbed to a QFF were also separately reacted with 0.4 ppm ozone. A volatilization control and the collection of volatilized PAHs using a Tenax-packed thermal desorption vial completed the mass balance and aided determination parent-product relationships. Heterogeneous reaction products analyzed directly without derivatization indicate the formation of 9,10-anthracenedione, 9H-fluoren-9-one, and (1,1’-biphenyl)-2,2’-dicarboxaldehyde from the reaction of ozone with the PAH mix on a QFF, but only 9,10-anthracenedione was detected for the diesel PM reaction. The implications of these results for aging of diesel particulate in urban environments will be discussed.

  16. Simulation of biochemical reactions with time-dependent rates by the rejection-based algorithm

    Energy Technology Data Exchange (ETDEWEB)

    Thanh, Vo Hong, E-mail: vo@cosbi.eu [The Microsoft Research - University of Trento Centre for Computational and Systems Biology, Piazza Manifattura 1, Rovereto 38068 (Italy); Priami, Corrado, E-mail: priami@cosbi.eu [The Microsoft Research - University of Trento Centre for Computational and Systems Biology, Piazza Manifattura 1, Rovereto 38068 (Italy); Department of Mathematics, University of Trento, Trento (Italy)

    2015-08-07

    We address the problem of simulating biochemical reaction networks with time-dependent rates and propose a new algorithm based on our rejection-based stochastic simulation algorithm (RSSA) [Thanh et al., J. Chem. Phys. 141(13), 134116 (2014)]. The computation for selecting next reaction firings by our time-dependent RSSA (tRSSA) is computationally efficient. Furthermore, the generated trajectory is exact by exploiting the rejection-based mechanism. We benchmark tRSSA on different biological systems with varying forms of reaction rates to demonstrate its applicability and efficiency. We reveal that for nontrivial cases, the selection of reaction firings in existing algorithms introduces approximations because the integration of reaction rates is very computationally demanding and simplifying assumptions are introduced. The selection of the next reaction firing by our approach is easier while preserving the exactness.

  17. Research in nuclear astrophysics

    International Nuclear Information System (INIS)

    Lattimer, J.M.; Yahil, A.

    1989-01-01

    The interaction between nuclear theory and some outstanding problems in astrophysics is examined. We are actively researching both the astrophysics of gravitational collapse, neutron star birth, and the emission of neutrinos from supernovae, on the one hand, and the nuclear physics of the equation of state of hot, dense matter on the other hand. There is close coupling between nuclear theory and the supernova phenomenon; in fact, nuclear matter properties, especially at supernuclear densities, might be best delineated by astrophysical considerations. Our research has also focused on the neutrinos emitted from supernovae, since they are the only available observables of the internal supernova mechanism. The recent observations of neutrinos from SN 1987A proved to be in remarkable agreement with models we pioneered in the one and one half years prior to its explosion in February 1987. We have also developed a novel hydrodynamical code in which shocks are treated via Riemann resolution rather than with artificial viscosity. We propose to modify it to use implicit differencing and to include multi-group neutrino diffusion and General Relativity. In parallel, we are extending calculations of the birth of a neutron star to include convection and mass accretion, by incorporating a hydrodynamic envelope onto a hydrostatic core. In view of the possible recent discovery of a pulsar in SN1987A, we are including the effects of rotation. We are undertaking a detailed comparison of current equations of state, focusing on disagreements regarding the nuclear incompressibly, symmetry energy and specific heat. Especially important is the symmetry energy, which below nuclear density controls free proton fractions and weak interaction rates and above this density critically influences the neutron star maximum mass and binding energy. 60 refs

  18. Rate constants for some electrophilic reactions of benzyl, benzhydryl, and trityl cations in solution

    International Nuclear Information System (INIS)

    Ujdak, R.J.; Jones, R.L.; Dorfman, L.M.

    1976-01-01

    Absolute rate constants have been determined by the pulse radiolysis technique for several electrophilic reactions of the benzyl, the benzhydryl, and the trityl cation in 1,2-dichloroethane solution. The rate constants for the reactions of these carbonium ions with chloride ion, with bromide ion, and with iodide ion are all very nearly the same, namely 6 x 10 10 M -1 s -1 at 24 0 C. The values very likely represent the diffusion controlled limit for the ion combination reactions. The rate constants for the reactions with triethylamine, tri-n-propylamine, and tri-n-butylamine range from 2.0 x 10 9 to 7 x 10 6 M -1 s -1 at 24 0 C. With increasing phenyl substitution, the decreasing trend in the magnitude of the rate constant is consistent with the combined electronic and steric effects. With increasing size of the amine, the decrease in the value of the rate constant seems to indicate that the steric effect predominates. The values of the rate constants for reactions of benzyl and benzhydryl cation with methanol, ethanol, and 2-propanol indicate the following. The rate constant is higher for reaction with the alcohol dimer in solution than with alcohol monomer. The rate constants for reaction with alcohol monomer have values of 1 x 10 8 M -1 s -1 or lower

  19. Reaction rate and composition dependence of the stability of thermonuclear burning on accreting neutron stars

    International Nuclear Information System (INIS)

    Keek, L.; Cyburt, R. H.; Heger, A.

    2014-01-01

    The stability of thermonuclear burning of hydrogen and helium accreted onto neutron stars is strongly dependent on the mass accretion rate. The burning behavior is observed to change from Type I X-ray bursts to stable burning, with oscillatory burning occurring at the transition. Simulations predict the transition at a 10 times higher mass accretion rate than observed. Using numerical models we investigate how the transition depends on the hydrogen, helium, and CNO mass fractions of the accreted material, as well as on the nuclear reaction rates of 3α and the hot-CNO breakout reactions 15 O(α, γ) 19 Ne and 18 Ne(α, p) 21 Na. For a lower hydrogen content the transition is at higher accretion rates. Furthermore, most experimentally allowed reaction rate variations change the transition accretion rate by at most 10%. A factor 10 decrease of the 15 O(α, γ) 19 Ne rate, however, produces an increase of the transition accretion rate of 35%. None of our models reproduce the transition at the observed rate, and depending on the true 15 O(α, γ) 19 Ne reaction rate, the actual discrepancy may be substantially larger. We find that the width of the interval of accretion rates with marginally stable burning depends strongly on both composition and reaction rates. Furthermore, close to the stability transition, our models predict that X-ray bursts have extended tails where freshly accreted fuel prolongs nuclear burning.

  20. Absolute calibration of the Rh-103(n,n')Rh-103m reaction rate

    International Nuclear Information System (INIS)

    Taylor, W.H.; Murphy, M.F.; March, M.R.

    1979-05-01

    The uncertainties in determining the absolute values of the Rh-103(n, n') Rh-103m reaction rate (which is widely used as a neutron damage flux monitor) have been reduced to approximately +-5%. This has been achieved with the use of a calibrated source of Pd-103-Rh-103m activity supplied by the IAEA. Agreement to within 3% between measured and calculated values of the reaction rate (normalised to the U-238 fission rate) has been achieved. (author)

  1. Estimation of the prevalence and rate of acute transfusion reactions occurring in Windhoek, Namibia

    Science.gov (United States)

    Meza, Benjamin P.L.; Lohrke, Britta; Wilkinson, Robert; Pitman, John P.; Shiraishi, Ray W.; Bock, Naomi; Lowrance, David W.; Kuehnert, Matthew J.; Mataranyika, Mary; Basavaraju, Sridhar V.

    2014-01-01

    Background Acute transfusion reactions are probably common in sub-Saharan Africa, but transfusion reaction surveillance systems have not been widely established. In 2008, the Blood Transfusion Service of Namibia implemented a national acute transfusion reaction surveillance system, but substantial under-reporting was suspected. We estimated the actual prevalence and rate of acute transfusion reactions occurring in Windhoek, Namibia. Methods The percentage of transfusion events resulting in a reported acute transfusion reaction was calculated. Actual percentage and rates of acute transfusion reactions per 1,000 transfused units were estimated by reviewing patients’ records from six hospitals, which transfuse >99% of all blood in Windhoek. Patients’ records for 1,162 transfusion events occurring between 1st January – 31st December 2011 were randomly selected. Clinical and demographic information were abstracted and Centers for Disease Control and Prevention National Healthcare Safety Network criteria were applied to categorize acute transfusion reactions1. Results From January 1 – December 31, 2011, there were 3,697 transfusion events (involving 10,338 blood units) in the selected hospitals. Eight (0.2%) acute transfusion reactions were reported to the surveillance system. Of the 1,162 transfusion events selected, medical records for 785 transfusion events were analysed, and 28 acute transfusion reactions were detected, of which only one had also been reported to the surveillance system. An estimated 3.4% (95% confidence interval [CI]: 2.3–4.4) of transfusion events in Windhoek resulted in an acute transfusion reaction, with an estimated rate of 11.5 (95% CI: 7.6–14.5) acute transfusion reactions per 1,000 transfused units. Conclusion The estimated actual rate of acute transfusion reactions is higher than the rate reported to the national haemovigilance system. Improved surveillance and interventions to reduce transfusion-related morbidity and mortality

  2. Temperature-Dependent Rate Coefficients for the Reaction of CH2OO with Hydrogen Sulfide.

    Science.gov (United States)

    Smith, Mica C; Chao, Wen; Kumar, Manoj; Francisco, Joseph S; Takahashi, Kaito; Lin, Jim Jr-Min

    2017-02-09

    The reaction of the simplest Criegee intermediate CH 2 OO with hydrogen sulfide was measured with transient UV absorption spectroscopy in a temperature-controlled flow reactor, and bimolecular rate coefficients were obtained from 278 to 318 K and from 100 to 500 Torr. The average rate coefficient at 298 K and 100 Torr was (1.7 ± 0.2) × 10 -13 cm 3 s -1 . The reaction was found to be independent of pressure and exhibited a weak negative temperature dependence. Ab initio quantum chemistry calculations of the temperature-dependent reaction rate coefficient at the QCISD(T)/CBS level are in reasonable agreement with the experiment. The reaction of CH 2 OO with H 2 S is 2-3 orders of magnitude faster than the reaction with H 2 O monomer. Though rates of CH 2 OO scavenging by water vapor under atmospheric conditions are primarily controlled by the reaction with water dimer, the H 2 S loss pathway will be dominated by the reaction with monomer. The agreement between experiment and theory for the CH 2 OO + H 2 S reaction lends credence to theoretical descriptions of other Criegee intermediate reactions that cannot easily be probed experimentally.

  3. Recent Efforts in Data Compilations for Nuclear Astrophysics

    International Nuclear Information System (INIS)

    Dillmann, Iris

    2008-01-01

    Some recent efforts in compiling data for astrophysical purposes are introduced, which were discussed during a JINA-CARINA Collaboration meeting on 'Nuclear Physics Data Compilation for Nucleosynthesis Modeling' held at the ECT* in Trento/Italy from May 29th-June 3rd, 2007. The main goal of this collaboration is to develop an updated and unified nuclear reaction database for modeling a wide variety of stellar nucleosynthesis scenarios. Presently a large number of different reaction libraries (REACLIB) are used by the astrophysics community. The 'JINA Reaclib Database' on http://www.nscl.msu.edu/~nero/db/ aims to merge and fit the latest experimental stellar cross sections and reaction rate data of various compilations, e.g. NACRE and its extension for Big Bang nucleosynthesis, Caughlan and Fowler, Iliadis et al., and KADoNiS.The KADoNiS (Karlsruhe Astrophysical Database of Nucleosynthesis in Stars, http://nuclear-astrophysics.fzk.de/kadonis) project is an online database for neutron capture cross sections relevant to the s process. The present version v0.2 is already included in a REACLIB file from Basel university (http://download.nucastro.org/astro/reaclib). The present status of experimental stellar (n,γ) cross sections in KADoNiS is shown. It contains recommended cross sections for 355 isotopes between 1 H and 210 Bi, over 80% of them deduced from experimental data.A ''high priority list'' for measurements and evaluations for light charged-particle reactions set up by the JINA-CARINA collaboration is presented. The central web access point to submit and evaluate new data is provided by the Oak Ridge group via the http://www.nucastrodata.org homepage. 'Workflow tools' aim to make the evaluation process transparent and allow users to follow the progress

  4. Recent Efforts in Data Compilations for Nuclear Astrophysics

    Science.gov (United States)

    Dillmann, Iris

    2008-05-01

    Some recent efforts in compiling data for astrophysical purposes are introduced, which were discussed during a JINA-CARINA Collaboration meeting on ``Nuclear Physics Data Compilation for Nucleosynthesis Modeling'' held at the ECT* in Trento/Italy from May 29th-June 3rd, 2007. The main goal of this collaboration is to develop an updated and unified nuclear reaction database for modeling a wide variety of stellar nucleosynthesis scenarios. Presently a large number of different reaction libraries (REACLIB) are used by the astrophysics community. The ``JINA Reaclib Database'' on http://www.nscl.msu.edu/~nero/db/ aims to merge and fit the latest experimental stellar cross sections and reaction rate data of various compilations, e.g. NACRE and its extension for Big Bang nucleosynthesis, Caughlan and Fowler, Iliadis et al., and KADoNiS. The KADoNiS (Karlsruhe Astrophysical Database of Nucleosynthesis in Stars, http://nuclear-astrophysics.fzk.de/kadonis) project is an online database for neutron capture cross sections relevant to the s process. The present version v0.2 is already included in a REACLIB file from Basel university (http://download.nucastro.org/astro/reaclib). The present status of experimental stellar (n,γ) cross sections in KADoNiS is shown. It contains recommended cross sections for 355 isotopes between 1H and 210Bi, over 80% of them deduced from experimental data. A ``high priority list'' for measurements and evaluations for light charged-particle reactions set up by the JINA-CARINA collaboration is presented. The central web access point to submit and evaluate new data is provided by the Oak Ridge group via the http://www.nucastrodata.org homepage. ``Workflow tools'' aim to make the evaluation process transparent and allow users to follow the progress.

  5. Trojan Horse Method: recent applications in nuclear astrophysics

    International Nuclear Information System (INIS)

    Spitaleri, C.; Cherubini, S.; La Cognata, M.; Lamia, L.; Mukhamedzhanov, A.; Pizzone, R.G.; Romano, S.; Sergi, M.L.; Tumino, A.

    2010-01-01

    The Trojan Horse Method (THM) is a powerful indirect technique to extract the bare nucleus cross section (or equivalently the bare nucleus astrophysical factor) for astrophysically relevant reactions. The theory has been discussed in many works in relation to the different types of reactions studied. Here we present the methodology to select the quasi free mechanism in order to extract this important parameter.

  6. Trojan Horse Method: recent applications in nuclear astrophysics

    Energy Technology Data Exchange (ETDEWEB)

    Spitaleri, C.; Cherubini, S.; La Cognata, M.; Lamia, L. [Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali del Sud, Catania (Italy); Dipartimento di Metodologie Chimiche e Fisiche per l' Ingegneria, Universita di Catania (Italy); Mukhamedzhanov, A. [Cyclotron Institute, Texas A and M University, College Station, Texas (United States); Pizzone, R.G.; Romano, S.; Sergi, M.L. [Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali del Sud, Catania (Italy); Dipartimento di Metodologie Chimiche e Fisiche per l' Ingegneria, Universita di Catania (Italy); Tumino, A. [Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali del Sud, Catania (Italy); Universita degli Studi di Enna ' Kore' , Enna (Italy)

    2010-03-01

    The Trojan Horse Method (THM) is a powerful indirect technique to extract the bare nucleus cross section (or equivalently the bare nucleus astrophysical factor) for astrophysically relevant reactions. The theory has been discussed in many works in relation to the different types of reactions studied. Here we present the methodology to select the quasi free mechanism in order to extract this important parameter.

  7. A mesoscopic reaction rate model for shock initiation of multi-component PBX explosives.

    Science.gov (United States)

    Liu, Y R; Duan, Z P; Zhang, Z Y; Ou, Z C; Huang, F L

    2016-11-05

    The primary goal of this research is to develop a three-term mesoscopic reaction rate model that consists of a hot-spot ignition, a low-pressure slow burning and a high-pressure fast reaction terms for shock initiation of multi-component Plastic Bonded Explosives (PBX). Thereinto, based on the DZK hot-spot model for a single-component PBX explosive, the hot-spot ignition term as well as its reaction rate is obtained through a "mixing rule" of the explosive components; new expressions for both the low-pressure slow burning term and the high-pressure fast reaction term are also obtained by establishing the relationships between the reaction rate of the multi-component PBX explosive and that of its explosive components, based on the low-pressure slow burning term and the high-pressure fast reaction term of a mesoscopic reaction rate model. Furthermore, for verification, the new reaction rate model is incorporated into the DYNA2D code to simulate numerically the shock initiation process of the PBXC03 and the PBXC10 multi-component PBX explosives, and the numerical results of the pressure histories at different Lagrange locations in explosive are found to be in good agreements with previous experimental data. Copyright © 2016 Elsevier B.V. All rights reserved.

  8. A comprehensive model to determine the effects of temperature and species fluctuations on reaction rates in turbulent reaction flows

    Science.gov (United States)

    Magnotti, F.; Diskin, G.; Matulaitis, J.; Chinitz, W.

    1984-01-01

    The use of silane (SiH4) as an effective ignitor and flame stabilizing pilot fuel is well documented. A reliable chemical kinetic mechanism for prediction of its behavior at the conditions encountered in the combustor of a SCRAMJET engine was calculated. The effects of hydrogen addition on hydrocarbon ignition and flame stabilization as a means for reduction of lengthy ignition delays and reaction times were studied. The ranges of applicability of chemical kinetic models of hydrogen-air combustors were also investigated. The CHARNAL computer code was applied to the turbulent reaction rate modeling.

  9. Measurements of rates of some reactions related to radiolytic effect on aqueous iodide solution

    International Nuclear Information System (INIS)

    Shiraishi, H.; Okuda, H.; Ishigure, K.

    1986-01-01

    A number of reactions takes place concurrently when aqueous iodide solution is subjected to radiation field. In order to help analyze this complicated radiation effect measurements of rate constants were undertaken for several important reactions. One of these concerns reduction of hypoiodous acid by hydrogen peroxide. For this reaction catalytic effect was found to be significant, and old rate data was revised. Measurements on reactions involving radicals were carried out by use of pulse radiolysis technique, which also include reexamination of results by previous workers. The reactions studied are (1) oxidation of iodide ion by hydroxyl radical (2) recombination reactions of atomic iodine and diiodide ion and (3) reduction of atomic and molecular iodine either by superoxide ion or by hydroperoxyl radical

  10. Quantum theory of enhanced unimolecular reaction rates below the ergodicity threshold

    International Nuclear Information System (INIS)

    Leitner, David M.; Wolynes, Peter G.

    2006-01-01

    A variety of unimolecular reactions exhibit measured rates that exceed Rice-Ramsperger-Kassel-Marcus (RRKM) predictions. We show using the local random matrix theory (LRMT) of vibrational energy flow how the quantum localization of the vibrational states of a molecule, by violating the ergodicity assumption, can give rise to such an enhancement of the apparent reaction rate. We present an illustrative calculation using LRMT for a model 12-vibrational mode organic molecule to show that below the ergodicity threshold the reaction rate may exceed many times the RRKM prediction due to quantum localization of vibrational states

  11. The time dependence of rate constants of esub(aq)sup(-) reactions

    International Nuclear Information System (INIS)

    Burcl, R.; Byakov, V.M.; Grafutin, V.I.

    1982-01-01

    Published data about the time dependence of rate constants k(esub(aq)sup(-)+Ac) of esub(aq)sup(-) reactions with the acceptor Ac are analyzed, using the results of rate constant k(Ps+Ac) measurements for positronium reactions. It is shown that neither esub(aq)sup(-) nor Ps reaction rate constants depend on time in the observable range. Experimentally found concentration dependence of k(esub(aq)sup(-)+Ac) is due to other factors, connected with the existence of electric charge of esub(aq)sup(-), e.g. ionic strength, tunnelling effect etc. (author)

  12. Comparing transfusion reaction rates for various plasma types: a systematic review and meta-analysis/regression.

    Science.gov (United States)

    Saadah, Nicholas H; van Hout, Fabienne M A; Schipperus, Martin R; le Cessie, Saskia; Middelburg, Rutger A; Wiersum-Osselton, Johanna C; van der Bom, Johanna G

    2017-09-01

    We estimated rates for common plasma-associated transfusion reactions and compared reported rates for various plasma types. We performed a systematic review and meta-analysis of peer-reviewed articles that reported plasma transfusion reaction rates. Random-effects pooled rates were calculated and compared between plasma types. Meta-regression was used to compare various plasma types with regard to their reported plasma transfusion reaction rates. Forty-eight studies reported transfusion reaction rates for fresh-frozen plasma (FFP; mixed-sex and male-only), amotosalen INTERCEPT FFP, methylene blue-treated FFP, and solvent/detergent-treated pooled plasma. Random-effects pooled average rates for FFP were: allergic reactions, 92/10 5 units transfused (95% confidence interval [CI], 46-184/10 5 units transfused); febrile nonhemolytic transfusion reactions (FNHTRs), 12/10 5 units transfused (95% CI, 7-22/10 5 units transfused); transfusion-associated circulatory overload (TACO), 6/10 5 units transfused (95% CI, 1-30/10 5 units transfused); transfusion-related acute lung injury (TRALI), 1.8/10 5 units transfused (95% CI, 1.2-2.7/10 5 units transfused); and anaphylactic reactions, 0.8/10 5 units transfused (95% CI, 0-45.7/10 5 units transfused). Risk differences between plasma types were not significant for allergic reactions, TACO, or anaphylactic reactions. Methylene blue-treated FFP led to fewer FNHTRs than FFP (risk difference = -15.3 FNHTRs/10 5 units transfused; 95% CI, -24.7 to -7.1 reactions/10 5 units transfused); and male-only FFP led to fewer cases of TRALI than mixed-sex FFP (risk difference = -0.74 TRALI/10 5 units transfused; 95% CI, -2.42 to -0.42 injuries/10 5 units transfused). Meta-regression demonstrates that the rate of FNHTRs is lower for methylene blue-treated compared with FFP, and the rate of TRALI is lower for male-only than for mixed-sex FFP; whereas no significant differences are observed between plasma types for allergic reactions, TACO

  13. Hydrogen isotope exchange reaction rates in tritium, hydrogen and deuterium mixed gases

    International Nuclear Information System (INIS)

    Uda, Tatsuhiko

    1992-01-01

    Hydrogen isotope exchange reaction rates in H 2 +T 2 , D 2 +T 2 and H 2 +D 2 +T 2 mixed gases, as induced by tritium decay and beta radiation, were experimentally measured by laser Raman spectrometry. Initially a glass cell was filled with T 2 gas to a pressure of 30-40 kPa, and an equivalent partial pressure of H 2 and/or D 2 was added. The first-order hydrogen isotope exchange reaction rates were 5.54x10 -2 h -1 for H 2 +T 2 mixed gas and 4.76x10 -2 h -1 for D 2 +T 2 . The actual HT producing rate was nearly equivalent to the rate of DT, but the reverse reaction rate of HT was faster than that of DT. The exchange reaction rates between H, D and T showed the isotope effect, HD>HT>DT. The hydrogen isotope exchange reaction rates observed were about twenty times larger than ion formation rates by beta radiation. This result suggests that a free radical chain reaction in hydrogen isotopes is occurring. (orig.)

  14. Excitation of compound states in the subsystems as indirect tool in nuclear astrophysics

    Directory of Open Access Journals (Sweden)

    Tribble R.E.

    2010-03-01

    Full Text Available Astrophysical reactions proceeding through compound states represent one of the crucial part of nuclear astrophysics. However, due to the presence of the Coulomb barrier, it is often very difficult or even impossible to obtain the astrophysical S (E factor from measurements in the laboratory at astrophysically relevant energies. The Trojan Horse method (THM provides a unique tool to obtain the information about resonant astrophysical reactions at astrophysically relevant energies. Here the theory and application of the THM for the resonant reactions is addressed.

  15. Multiscale Investigation on Biofilm Distribution and Its Impact on Macroscopic Biogeochemical Reaction Rates

    Science.gov (United States)

    Yan, Zhifeng; Liu, Chongxuan; Liu, Yuanyuan; Bailey, Vanessa L.

    2017-11-01

    Biofilms are critical locations for biogeochemical reactions in the subsurface environment. The occurrence and distribution of biofilms at microscale as well as their impacts on macroscopic biogeochemical reaction rates are still poorly understood. This paper investigated the formation and distributions of biofilms in heterogeneous sediments using multiscale models and evaluated the effects of biofilm heterogeneity on local and macroscopic biogeochemical reaction rates. Sediment pore structures derived from X-ray computed tomography were used to simulate the microscale flow dynamics and biofilm distribution in the sediment column. The response of biofilm formation and distribution to the variations in hydraulic and chemical properties was first examined. One representative biofilm distribution was then utilized to evaluate its effects on macroscopic reaction rates using nitrate reduction as an example. The results revealed that microorganisms primarily grew on the surfaces of grains and aggregates near preferential flow paths where both electron donor and acceptor were readily accessible, leading to the heterogeneous distribution of biofilms in the sediments. The heterogeneous biofilm distribution decreased the macroscopic rate of biogeochemical reactions as compared with those in homogeneous cases. Operationally considering the heterogeneous biofilm distribution in macroscopic reactive transport models such as using dual porosity domain concept can significantly improve the prediction of biogeochemical reaction rates. Overall, this study provided important insights into the biofilm formation and distribution in soils and sediments as well as their impacts on the macroscopic manifestation of reaction rates.

  16. Capture cross-section and rate of the 14 C (n, γ) 15 C reaction from ...

    Indian Academy of Sciences (India)

    We calculate the Coulomb dissociation of 15C on a Pb target at 68 MeV/u incident beam energy within the fully quantum mechanical distorted wave Born approximation formalism of breakup reactions. The capture cross-section and the subsequent rate of the 14C(, )15C reaction are calculated from the ...

  17. Analyzing Reaction Rates with the Distortion/Interaction-Activation Strain Model

    NARCIS (Netherlands)

    Bickelhaupt, F. Matthias; Houk, Kendall N.

    2017-01-01

    The activation strain or distortion/interaction model is a tool to analyze activation barriers that determine reaction rates. For bimolecular reactions, the activation energies are the sum of the energies to distort the reactants into geometries they have in transition states plus the interaction

  18. Selected specific rates of reactions of transients from water in aqueous solution. II. Hydrogen atom

    International Nuclear Information System (INIS)

    Anbar, M.; Farhataziz; Ross, A.B.

    1975-05-01

    Rates of reactions of hydrogen atoms (from radiolysis of water and other sources) with organic and inorganic molecules, ions, and transients in aqueous solution were tabulated. Directly measured rates obtained by kinetic spectroscopy or conductimetric methods, and relative rates determined by competition kinetics are included. (U.S.)

  19. Matching of experimental and statistical-model thermonuclear reaction rates at high temperatures

    International Nuclear Information System (INIS)

    Newton, J. R.; Longland, R.; Iliadis, C.

    2008-01-01

    We address the problem of extrapolating experimental thermonuclear reaction rates toward high stellar temperatures (T>1 GK) by using statistical model (Hauser-Feshbach) results. Reliable reaction rates at such temperatures are required for studies of advanced stellar burning stages, supernovae, and x-ray bursts. Generally accepted methods are based on the concept of a Gamow peak. We follow recent ideas that emphasized the fundamental shortcomings of the Gamow peak concept for narrow resonances at high stellar temperatures. Our new method defines the effective thermonuclear energy range (ETER) by using the 8th, 50th, and 92nd percentiles of the cumulative distribution of fractional resonant reaction rate contributions. This definition is unambiguous and has a straightforward probability interpretation. The ETER is used to define a temperature at which Hauser-Feshbach rates can be matched to experimental rates. This matching temperature is usually much higher compared to previous estimates that employed the Gamow peak concept. We suggest that an increased matching temperature provides more reliable extrapolated reaction rates since Hauser-Feshbach results are more trustwhorthy the higher the temperature. Our ideas are applied to 21 (p,γ), (p,α), and (α,γ) reactions on A=20-40 target nuclei. For many of the cases studied here, our extrapolated reaction rates at high temperatures differ significantly from those obtained using the Gamow peak concept

  20. Rate coefficients from quantum and quasi-classical cumulative reaction probabilities for the S(1D) + H2 reaction

    Science.gov (United States)

    Jambrina, P. G.; Lara, Manuel; Menéndez, M.; Launay, J.-M.; Aoiz, F. J.

    2012-10-01

    Cumulative reaction probabilities (CRPs) at various total angular momenta have been calculated for the barrierless reaction S(1D) + H2 → SH + H at total energies up to 1.2 eV using three different theoretical approaches: time-independent quantum mechanics (QM), quasiclassical trajectories (QCT), and statistical quasiclassical trajectories (SQCT). The calculations have been carried out on the widely used potential energy surface (PES) by Ho et al. [J. Chem. Phys. 116, 4124 (2002), 10.1063/1.1431280] as well as on the recent PES developed by Song et al. [J. Phys. Chem. A 113, 9213 (2009), 10.1021/jp903790h]. The results show that the differences between these two PES are relatively minor and mostly related to the different topologies of the well. In addition, the agreement between the three theoretical methodologies is good, even for the highest total angular momenta and energies. In particular, the good accordance between the CRPs obtained with dynamical methods (QM and QCT) and the statistical model (SQCT) indicates that the reaction can be considered statistical in the whole range of energies in contrast with the findings for other prototypical barrierless reactions. In addition, total CRPs and rate coefficients in the range of 20-1000 K have been calculated using the QCT and SQCT methods and have been found somewhat smaller than the experimental total removal rates of S(1D).

  1. Nonequilibrium Contribution to the Rate of Reaction. III. Isothermal Multicomponent Systems

    Science.gov (United States)

    Shizgal, B.; Karplus, M.

    1970-10-01

    The nonequilibrium contribution to the reaction rate of an isothermal multicomponent system is obtained by solution of the appropriate Chapman-Enskog equation; the system is composed of reactive species in contact with a heat bath of inert atoms M.

  2. Compilation of neutron flux density spectra and reaction rates in different neutron fields. V.3

    International Nuclear Information System (INIS)

    Ertek, C.

    1980-04-01

    Upon the recommendation of the International Working Group of Reactor Radiation Measurements (IWGRRM) a compilation of documents containing neutron flux density spectra and the reaction rates obtained by activiation and fission foils in different neutron fields is presented

  3. Reaction mechanisms and rate constants of waste degradation in landfill bioreactor systems with enzymatic-enhancement.

    Science.gov (United States)

    Jayasinghe, P A; Hettiaratchi, J P A; Mehrotra, A K; Kumar, S

    2014-06-01

    Augmenting leachate before recirculation with peroxidase enzymes is a novel method to increase the available carbon, and therefore the food supply to microorganisms at the declining phase of the anaerobic landfill bioreactor operation. In order to optimize the enzyme-catalyzed leachate recirculation process, it is necessary to identify the reaction mechanisms and determine rate constants. This paper presents a kinetic model developed to ascertain the reaction mechanisms and determine the rate constants for enzyme catalyzed anaerobic waste degradation. The maximum rate of reaction (Vmax) for MnP enzyme-catalyzed reactors was 0.076 g(TOC)/g(DS).day. The catalytic turnover number (k(cat)) of the MnP enzyme-catalyzed was 506.7 per day while the rate constant (k) of the un-catalyzed reaction was 0.012 per day. Copyright © 2014 Elsevier Ltd. All rights reserved.

  4. Neutron Scattering in Hydrogenous Moderators, Studied by Time Dependent Reaction Rate Method

    Energy Technology Data Exchange (ETDEWEB)

    Larsson, L G; Moeller, E; Purohit, S N

    1966-03-15

    The moderation and absorption of a neutron burst in water, poisoned with the non-1/v absorbers cadmium and gadolinium, has been followed on the time scale by multigroup calculations, using scattering kernels for the proton gas and the Nelkin model. The time dependent reaction rate curves for each absorber display clear differences for the two models, and the separation between the curves does not depend much on the absorber concentration. An experimental method for the measurement of infinite medium reaction rate curves in a limited geometry has been investigated. This method makes the measurement of the time dependent reaction rate generally useful for thermalization studies in a small geometry of a liquid hydrogenous moderator, provided that the experiment is coupled to programs for the calculation of scattering kernels and time dependent neutron spectra. Good agreement has been found between the reaction rate curve, measured with cadmium in water, and a calculated curve, where the Haywood kernel has been used.

  5. Method and apparatus for obtaining enhanced production rate of thermal chemical reactions

    Science.gov (United States)

    Tonkovich, Anna Lee Y [Pasco, WA; Wang, Yong [Richland, WA; Wegeng, Robert S [Richland, WA; Gao, Yufei [Kennewick, WA

    2003-04-01

    The present invention is a method and apparatus (vessel) for providing a heat transfer rate from a reaction chamber through a wall to a heat transfer chamber substantially matching a local heat transfer rate of a catalytic thermal chemical reaction. The key to the invention is a thermal distance defined on a cross sectional plane through the vessel inclusive of a heat transfer chamber, reaction chamber and a wall between the chambers. The cross sectional plane is perpendicular to a bulk flow direction of the reactant stream, and the thermal distance is a distance between a coolest position and a hottest position on the cross sectional plane. The thermal distance is of a length wherein the heat transfer rate from the reaction chamber to the heat transfer chamber substantially matches the local heat transfer rate.

  6. On the existence of and mechanism for microwave-specific reaction rate enhancement.

    Science.gov (United States)

    Dudley, Gregory B; Richert, Ranko; Stiegman, A E

    2015-04-01

    The use of microwave radiation to drive chemical reactions has become ubiquitous in almost all fields of chemistry. In all of these areas it is principally due to rapid and convenient heating resulting in significantly higher rates of reaction, with other advantages including enhanced product selectivity and control of materials properties. Although microwave heating continues to grow as an enabling technology, fundamental research into the nature of microwave heating has not grown at the same rate. In the case of chemical reactions run in homogeneous solution, particularly synthetic organic reactions, there is considerable controversy over the origins of rate enhancement, with a fundamental question being whether there exist microwave-specific effects, distinct from what can be attained under conventional convective heating, that can accelerate a reaction rate. In this Perspective, we discuss unique aspects of microwave heating of molecules in solution and discuss the origin and nature of microwave-specific effects arising from the process of "selective heating" of reactants in solution. Integral to this discussion is work from the field of dielectric relaxation spectroscopy, which provides a model for selective heating by Debye relaxation processes. The Perspective also includes a critical discussion of hypotheses of non-thermal effects (alternatively classified here as resonant processes) and an outline of specific reaction parameters for chemical systems in which microwave-specific Debye relaxation processes can result in observable reaction rate enhancement.

  7. Coloring Rate of Phenolphthalein by Reaction with Alkaline Solution Observed by Liquid-Droplet Collision.

    Science.gov (United States)

    Takano, Yuuka; Kikkawa, Shigenori; Suzuki, Tomoko; Kohno, Jun-ya

    2015-06-11

    Many important chemical reactions are induced by mixing two solutions. This paper presents a new way to measure rates of rapid chemical reactions induced by mixing two reactant solutions using a liquid-droplet collision. The coloring reaction of phenolphthalein (H2PP) by a reaction with NaOH is investigated kinetically. Liquid droplets of H2PP/ethanol and NaOH/H2O solutions are made to collide, which induces a reaction that transforms H2PP into a deprotonated form (PP(2-)). The concentration of PP(2-) is evaluated from the RGB values of pixels in the colored droplet images, and is measured as a function of the elapsed time from the collision. The obtained rate constant is (2.2 ± 0.7) × 10(3) M(-1) s(-1), which is the rate constant for the rate-determining step of the coloring reaction of H2PP. This method was shown to be applicable to determine rate constants of rapid chemical reactions between two solutions.

  8. Nuclear-reaction rates in the thermonuclear runaway phase of accreting neutron stars

    International Nuclear Information System (INIS)

    Wiescher, M.; Barnard, V.; Goerres, J.; Fisker, J.L.; Martinez-Pinedo, G.; Langanke, K.; Rembges, F.; Thielemann, F.K.; Schatz, H.

    2002-01-01

    The rp-process has been suggested as the dominant nucleosynthesis process in explosive hydrogen burning at high temperature and density conditions. The process is characterized by a sequence of fast proton capture reactions and subsequent β-decays. The reaction path of the rp-process runs along the drip line up to Z∼50. Most of the charged-particle reaction rates for the reaction path are presently based on statistical Hauser-Feshbach calculations. While these rates are supposed to be reliable within a factor of two for conditions of high density in the compound nuclei, discrepancies may occur for nuclei near closed shells or near the proton drip line where the Q-values of proton capture processes are typically very small. It has been argued that the thermonuclear runaway is less sensitive to the reaction rates because of the rapid time-scale of the event. However, since these processes may operate at the same time-scale as fast mixing and convection processes, a change in reaction rates indeed may have a significant impact. In this paper we present two examples, the break-out from the hot CNO cycles, and the thermonuclear runaway in X-ray bursts itself, where changes in reaction rates have a direct impact on time-scale, energy generation and nucleosynthesis predictions for the explosive event. (orig.)

  9. Nuclear Astrophysics at DANCE

    International Nuclear Information System (INIS)

    Reifarth, R.; Bredeweg, T.A.; Esch, E.-I.; Haight, R.C.; Kronenberg, A.; O'Donnell, J.M.; Rundberg, R.S.; Schwantes, J.M.; Ullmann, J.L.; Vieira, D.J.; Wouters, J.M.; Alpizar-Vicente, A.; Hatarik, R.; Greife, U.

    2005-01-01

    One of the most interesting nuclear physics challenges is obtaining a detailed understanding of the nucleosynthesis processes of the elements. Knowledge about the stellar sites, and how they are governed by stellar evolution and cosmology are crucial in understanding the overall picture. Information on reaction rates for neutron- and charged-particle-induced reactions have a direct impact on existing stellar models. Except for the stable isotopes, very few neutron-induced reactions in the energy range of interest have been measured to date. DANCE measurements on stable and unstable isotopes will provide many of the missing key reactions that are needed to understand the nucleosynthesis of the heavy elements

  10. The correlation schemes in calculations of the rate constants of some radiation chemical reactions

    International Nuclear Information System (INIS)

    Zagorets, P.A.; Shostenko, A.G.; Kim, V.

    1983-01-01

    The various correlation relationships of the evaluation of the rate constants of radiation chemical reactions of addition, abstraction and isomerization were considered. It was shown that neglection of the influence of solvent can result in errors in calculations of rate constants equalling two orders in magnitude. Several examples of isokinetic relationship are given. The methods of calculation of transmission coefficient of reaction addition have been discussed. (author)

  11. Shell and explosive hydrogen burning. Nuclear reaction rates for hydrogen burning in RGB, AGB and Novae

    Energy Technology Data Exchange (ETDEWEB)

    Boeltzig, A. [Gran Sasso Science Institute, L' Aquila (Italy); Bruno, C.G.; Davinson, T. [University of Edinburgh, SUPA, School of Physics and Astronomy, Edinburgh (United Kingdom); Cavanna, F.; Ferraro, F. [Dipartimento di Fisica, Universita di Genova (Italy); INFN, Genova (Italy); Cristallo, S. [Osservatorio Astronomico di Collurania, INAF, Teramo (Italy); INFN, Napoli (Italy); Depalo, R. [Dipartimento di Fisica e Astronomia, Universita di Padova, Padova (Italy); INFN, Padova (Italy); DeBoer, R.J.; Wiescher, M. [University of Notre Dame, Institute for Structure and Nuclear Astrophysics, Joint Institute for Nuclear Astrophysics, Notre Dame, Indiana (United States); Di Leva, A.; Imbriani, G. [Dipartimento di Fisica, Universita di Napoli Federico II, Napoli (Italy); INFN, Napoli (Italy); Marigo, P. [Dipartimento di Fisica e Astronomia, Universita di Padova, Padova (Italy); Terrasi, F. [Dipartimento di Matematica e Fisica Seconda Universita di Napoli, Caserta (Italy); INFN, Napoli (Italy)

    2016-04-15

    The nucleosynthesis of light elements, from helium up to silicon, mainly occurs in Red Giant and Asymptotic Giant Branch stars and Novae. The relative abundances of the synthesized nuclides critically depend on the rates of the nuclear processes involved, often through non-trivial reaction chains, combined with complex mixing mechanisms. In this paper, we summarize the contributions made by LUNA experiments in furthering our understanding of nuclear reaction rates necessary for modeling nucleosynthesis in AGB stars and Novae explosions. (orig.)

  12. Communication: Rate coefficients from quasiclassical trajectory calculations from the reverse reaction: The Mu + H2 reaction re-visited

    Science.gov (United States)

    Homayoon, Zahra; Jambrina, Pablo G.; Aoiz, F. Javier; Bowman, Joel M.

    2012-07-01

    In a previous paper [P. G. Jambrina et al., J. Chem. Phys. 135, 034310 (2011), 10.1063/1.3611400] various calculations of the rate coefficient for the Mu + H2 → MuH + H reaction were presented and compared to experiment. The widely used standard quasiclassical trajectory (QCT) method was shown to overestimate the rate coefficients by several orders of magnitude over the temperature range 200-1000 K. This was attributed to a major failure of that method to describe the correct threshold for the reaction owing to the large difference in zero-point energies (ZPE) of the reactant H2 and product MuH (˜0.32 eV). In this Communication we show that by performing standard QCT calculations for the reverse reaction and then applying detailed balance, the resulting rate coefficient is in very good agreement with the other computational results that respect the ZPE, (as well as with the experiment) but which are more demanding computationally.

  13. Evaporation rates and surface profiles on heterogeneous surfaces with mass transfer and surface reaction

    Energy Technology Data Exchange (ETDEWEB)

    Flytzani-Stephanopoulos, M; Schmidt, L D

    1979-01-01

    Simple models incorporating surface reaction and diffusion of volatile products through a boundary layer are developed to calculate effective rates of evaporation and local surface profiles on surfaces having active and inactive regions. The coupling between surface heterogeneities with respect to a particular reaction and external mass transfer may provide a mechanism for the surface rearrangement and metal loss encountered in several catalytic systems of practical interest. Calculated transport rates for the volatilization of platinum in oxidizing environments and the rearrangement of this metal during the ammonia oxidation reaction agree well with published experimental data.

  14. Reevaluation of the O+(2P) reaction rate coefficients derived from atmosphere explorer C observations

    International Nuclear Information System (INIS)

    Chang, T.; Torr, D.G.; Richards, P.G.; Solomon, S.C.

    1993-01-01

    O + ( 2 P) is an important species for studies of the ionosphere and thermosphere: its emission at 7320 angstrom can be used as a diagnostic of the thermospheric atomic oxygen density. Unfortunately, there are no laboratory measurements of the O and N 2 reaction rates which are needed to determine the major sinks of O + ( 2 P). The reaction rates that are generally used were determined from aeronomic data by Rusch et al. but there is evidence that several important inputs that they used should be changed. The authors have recalculated the O and N 2 reaction rates for O + ( 2 P) using recent improvements in the solar EUV flux, cross sections, and photoelectron fluxes. For the standard solar EUV flux, the new N 2 reaction rate of 3.4 ± 1.5 x 10 -10 cm 3 s -1 is close to the value obtained by Rusch et al., but the new O reaction rate of 4.0 ± 1.9 x 10 -10 cm 3 s -1 is about 8 times larger. These new reaction rates are derived using neutral densities, electron density, and solar EUV fluxes measured by Atmosphere Explorer C in 1974 during solar minimum. The new theoretical emission rates are in good agreement with the data for the two orbits studied by Rusch et al. and they are in reasonable agreement with data from five additional orbits that are used in this study. The authors have also examined the effect of uncertainties in the solar EUV flux on the derived reaction rates and found that 15% uncertainties in the solar flux could cause additional uncertainties of up to a factor of 1.5 in the O quenching rate. 19 refs., 4 figs., 8 tabs

  15. Astrophysical Hydrodynamics An Introduction

    CERN Document Server

    Shore, Steven N

    2007-01-01

    This latest edition of the proven and comprehensive treatment on the topic -- from the bestselling author of ""Tapestry of Modern Astrophysics"" -- has been updated and revised to reflect the newest research results. Suitable for AS0000 and AS0200 courses, as well as advanced astrophysics and astronomy lectures, this is an indispensable theoretical backup for studies on celestial body formation and astrophysics. Includes exercises with solutions.

  16. Gravity, particles and astrophysics

    International Nuclear Information System (INIS)

    Wesson, P.S.

    1980-01-01

    The author deals with the relationship between gravitation and elementary particle physics, and the implications of these subjects for astrophysics. The text is split up into two parts. The first part represents a relatively non-technical overview of the subject, while the second part represents a technical examination of the most important aspects of non-Einsteinian gravitational theory and its relation to astrophysics. Relevant references from the fields of gravitation, elementary particle theory and astrophysics are included. (Auth.)

  17. The rate coefficients of unimolecular reactions in the systems with power-law distributions

    Science.gov (United States)

    Yin, Cangtao; Guo, Ran; Du, Jiulin

    2014-08-01

    The rate coefficient formulae of unimolecular reactions are generalized to the systems with the power-law distributions based on nonextensive statistics, and the power-law rate coefficients are derived in the high and low pressure limits, respectively. The numerical analyses are made of the rate coefficients as functions of the ν-parameter, the threshold energy, the temperature and the number of degrees of freedom. We show that the new rate coefficients depend strongly on the ν-parameter different from one (thus from a Boltzmann-Gibbs distribution). Two unimolecular reactions, CH3CO→CH3+CO and CH3NC→CH3CN, are taken as application examples to calculate their power-law rate coefficients, which obtained with the ν-parameters slightly different from one can be exactly in agreement with all the experimental studies on these two reactions in the given temperature ranges.

  18. Helium generation reaction rates for 6Li and 10B in benchmark facilities

    International Nuclear Information System (INIS)

    Farrar, Harry IV; Oliver, B.M.; Lippincott, E.P.

    1980-01-01

    The helium generation rates for 10 B and 6 Li have been measured in two benchmark reactor facilities having neutron spectra similar to those found in a breeder reactor. The irradiations took place in the Coupled Fast Reactivity Measurements Facility (CFRMF) and in the 10% enriched 235 U critical assembly, BIG-10. The helium reaction rates were obtained by precise high-sensitivity gas mass spectrometric analyses of the helium content of numerous small samples. Comparison of these reaction rates with other reaction rates measured in the same facilities, and with rates calculated from published cross sections and from best estimates of the neutron spectral shapes, indicate significant discrepancies in the calculated values. Additional irradiations in other benchmark facilities have been undertaken to better determine the energy ranges where the discrepancies lie

  19. Particle Physics & Astrophysics (PPA)

    Data.gov (United States)

    Federal Laboratory Consortium — Scientists at SLAC's Particle Physics and Astrophysics develop and utilize unique instruments from underground to outer space to explore the ultimate laws of nature...

  20. Standard Test Method for Measuring Fast-Neutron Reaction Rates by Radioactivation of Niobium

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    2008-01-01

    1.1 This test method describes procedures for measuring reaction rates by the activation reaction 93Nb(n,n′)93mNb. 1.2 This activation reaction is useful for monitoring neutrons with energies above approximately 0.5 MeV and for irradiation times up to about 30 years. 1.3 With suitable techniques, fast-neutron reaction rates for neutrons with energy distribution similar to fission neutrons can be determined in fast-neutron fluences above about 1016cm−2. In the presence of high thermal-neutron fluence rates (>1012cm−2·s−1), the transmutation of 93mNb due to neutron capture should be investigated. In the presence of high-energy neutron spectra such as are associated with fusion and spallation sources, the transmutation of 93mNb by reactions such as (n,2n) may occur and should be investigated. 1.4 Procedures for other fast-neutron monitors are referenced in Practice E 261. 1.5 Fast-neutron fluence rates can be determined from the reaction rates provided that the appropriate cross section information ...

  1. Reaction rate and energy-loss rate for photopair production by relativistic nuclei

    Science.gov (United States)

    Chodorowski, Michal J.; Zdziarski, Andrzej A.; Sikora, Marek

    1992-01-01

    The process of e(+/-) pair production by relativistic nuclei on ambient photons is considered. The process is important for cosmic-ray nuclei in interstellar and intergalactic space as well as in galactic and extragalactic compact objects. The rate of this process is given by an integral of the cross section over the photon angular and energy distribution. In the case of isotropic photons, the angular integration is performed to provide an expression for the rate at given photon energy in the nucleus rest frame. The total rate then becomes a single integral of that rate over the photon energy distribution. Formulas are also given for the fractional energy loss of a relativistic nucleus colliding with a photon of a given energy in the rest frame. The nucleus energy-loss rate is integrated over the photon angular distribution in the case of isotropic photons, and simple fits are provided.

  2. Measurement of astrophysical S-factors and electron screening potentials for d(d,n){sup 3}He reaction in ZrD{sub 2}, TiD{sub 2} and TaD{sub 0.5} targets in the ultralow energy region using plasma accelerator

    Energy Technology Data Exchange (ETDEWEB)

    Bystritsky, V.M., E-mail: bystvm@jinr.ru [Joint Institute for Nuclear Research, Dubna, Moscow Region (Russian Federation); Bystritskii, Vit.M. [Department of Physics and Astronomy, University of California, Irvine (United States); Dudkin, G.N. [National Scientific Research Tomsk Polytechnical University, Tomsk (Russian Federation); Filipowicz, M. [Faculty of Energy and Fuels, AGH, University of Science and Technology, Cracow (Poland); Gazi, S.; Huran, J. [Institute of Electrical Engineering, SAS, Bratislava (Slovakia); Kobzev, A.P. [Joint Institute for Nuclear Research, Dubna, Moscow Region (Russian Federation); Mesyats, G.A. [Lebedev Physical Institute of the Russian Academy of Sciences, Moscow (Russian Federation); Nechaev, B.A.; Padalko, V.N. [National Scientific Research Tomsk Polytechnical University, Tomsk (Russian Federation); Parzhitskii, S.S. [Joint Institute for Nuclear Research, Dubna, Moscow Region (Russian Federation); Pen' kov, F.M. [Institute of Nuclear Physics, NNC, Almaty (Kazakhstan); Philippov, A.V. [Joint Institute for Nuclear Research, Dubna, Moscow Region (Russian Federation); Kaminskii, V.L. [National Scientific Research Tomsk Polytechnical University, Tomsk (Russian Federation); Tuleushev, Yu.Zh. [Institute of Nuclear Physics, NNC, Almaty (Kazakhstan); Wozniak, J. [Faculty of Physics and Applied Computer Sciences, AGH, University of Science and Technology, Cracow (Poland)

    2012-09-01

    The present paper is devoted to the study of the electron screening effect influence on the rate of d(d,n){sup 3}He reaction in the ultralow deuteron collision energy range in the deuterated metals (ZrD{sub 2}, TiD{sub 2} and TaD{sub 0.5}). The ZrD{sub 2}, TiD{sub 2} and TaD0.5 targets were fabricated via magnetron sputtering of titanium, zirconium and tantalum in gas (deuterium) environment. The experiments have been carried out using the high-current pulsed Hall plasma accelerator (NSR TPU, Russia). The detection of neutrons with energy of 2.5 MeV from the dd reaction was done with plastic scintillation spectrometers. As a result of the experiments, the energy dependences of the astrophysical S-factor for the dd reaction in the deuteron collision energy range of 2-7 keV and the values of the electron screening potential U{sub e} of the interacting deuterons have been measured for the above targets: U{sub e}(ZrD{sub 2})=(205{+-}35) eV; U{sub e}(TiD{sub 2})=(125{+-}34) eV; U{sub e}(TaD{sub 0.5})=(313{+-}58) eV. Our results are compared with the other published experimental and calculated data.

  3. Measurement of astrophysical S-factors and electron screening potentials for d(d,n)3He reaction in ZrD2, TiD2 and TaD0.5 targets in the ultralow energy region using plasma accelerator

    International Nuclear Information System (INIS)

    Bystritsky, V.M.; Bystritskii, Vit.M.; Dudkin, G.N.; Filipowicz, M.; Gazi, S.; Huran, J.; Kobzev, A.P.; Mesyats, G.A.; Nechaev, B.A.; Padalko, V.N.; Parzhitskii, S.S.; Pen'kov, F.M.; Philippov, A.V.; Kaminskii, V.L.; Tuleushev, Yu.Zh.; Wozniak, J.

    2012-01-01

    The present paper is devoted to the study of the electron screening effect influence on the rate of d(d,n) 3 He reaction in the ultralow deuteron collision energy range in the deuterated metals (ZrD 2 , TiD 2 and TaD 0.5 ). The ZrD 2 , TiD 2 and TaD0.5 targets were fabricated via magnetron sputtering of titanium, zirconium and tantalum in gas (deuterium) environment. The experiments have been carried out using the high-current pulsed Hall plasma accelerator (NSR TPU, Russia). The detection of neutrons with energy of 2.5 MeV from the dd reaction was done with plastic scintillation spectrometers. As a result of the experiments, the energy dependences of the astrophysical S-factor for the dd reaction in the deuteron collision energy range of 2-7 keV and the values of the electron screening potential U e of the interacting deuterons have been measured for the above targets: U e (ZrD 2 )=(205±35) eV; U e (TiD 2 )=(125±34) eV; U e (TaD 0.5 )=(313±58) eV. Our results are compared with the other published experimental and calculated data.

  4. Advances in instrumentation for nuclear astrophysics

    Directory of Open Access Journals (Sweden)

    S. D. Pain

    2014-04-01

    Full Text Available The study of the nuclear physics properties which govern energy generation and nucleosynthesis in the astrophysical phenomena we observe in the universe is crucial to understanding how these objects behave and how the chemical history of the universe evolved to its present state. The low cross sections and short nuclear lifetimes involved in many of these reactions make their experimental determination challenging, requiring developments in beams and instrumentation. A selection of developments in nuclear astrophysics instrumentation is discussed, using as examples projects involving the nuclear astrophysics group at Oak Ridge National Laboratory. These developments will be key to the instrumentation necessary to fully exploit nuclear astrophysics opportunities at the Facility for Rare Isotope Beams which is currently under construction.

  5. Reevaluation of the O(+)(2P) reaction rate coefficients derived from Atmosphere Explorer C observations

    Science.gov (United States)

    Chang, T.; Torr, D. G.; Richards, P. G.; Solomon, S. C.

    1993-01-01

    O(+)(2P) is an important species for studies of the ionosphere and thermosphere: its emission at 7320 A can be used as a diagnostic of the thermospheric atomic oxygen density. Unfortunately, there are no laboratory measurements of the O and N2 reaction rates which are needed to determine the major sinks of (O+)(2p). We have recalculated the O and N2 reaction rates for O(+) (2P) using recent improvements in the solar EUV flux, cross sections, and photoelectron fluxes. For the standard solar EUV flux, the new N2 reaction rate of 3.4 +/- 1.5 x 10 exp -10 cu cm/s is close to the value obtained by Rusch et al. (1977), but the new O reaction rate of 4.0 +/- 1.9 x 10 exp -10 cu cm/sec is about 8 times larger. These new reaction rates are derived using neutral densities, electron density, and solar EUV fluxes measured by Atmosphere Explorer C in 1974 during solar minimum. The new theoretical emission rates are in good agreement with the data for the two orbits studied by Rusch et al.

  6. Determination of the enzyme reaction rate in a differential fixed-bed reactor: a case study

    Directory of Open Access Journals (Sweden)

    Baruque Filho E.A.

    2001-01-01

    Full Text Available The reaction rate of starch hydrolysis catalyzed by a glucoamylase covalently bound to chitin particles was measured in a Differential Fixed-Bed Reactor (DFBR. Under selected test conditions the initial reaction rate may represent biocatalyst activity. Some aspects which influence measurement of the initial reaction rate of an immobilized enzyme were studied: the amount of desorbed enzyme and its hydrolytic activity, the extent of pore blockage of the biocatalyst caused by substrate solution impurities and the internal and external diffusional mass transfer effects. The results showed that the enzyme glucoamylase was firmly bound to the support, as indicated by the very low amount of desorbed protein found in the recirculating liquid. Although this protein was very active, its contribution to the overall reaction rate was negligible. It was observed that the biocatalyst pores were susceptible to being blocked by the impurities of the starch solution. This latter effect was accumulative, increasing with the number of sequential experiments carried out. When the substrate solution was filtered before use, very reliable determinations of immobilized enzyme reaction rates could be performed in the DFBR. External and internal diffusional resistences usually play a significant role in fixed-bed reactors. However, for the experimental system studied, internal mass transfer effects were not significant, and it was possible to select an operational condition (recirculation flow rate value that minimized the external diffusional limitations.

  7. [Incidence rate of adverse reaction/event by Qingkailing injection: a Meta-analysis of single rate].

    Science.gov (United States)

    Ai, Chun-ling; Xie, Yan-ming; Li, Ming-quan; Wang, Lian-xin; Liao, Xing

    2015-12-01

    To systematically review the incidence rate of adverse drug reaction/event by Qingkailing injection. Such databases as the PubMed, EMbase, the Cochrane library, CNKI, VIP WanFang data and CBM were searched by computer from foundation to July 30, 2015. Two reviewers independently screened literature according to the inclusion and exclusion criteria, extracted data and cross check data. Then, Meta-analysis was performed by using the R 3.2.0 software, subgroup sensitivity analysis was performed based on age, mode of medicine, observation time and research quality. Sixty-three studies involving 9,793 patients with Qingkailing injection were included, 367 cases of adverse reactions/events were reported in total. The incidence rate of adverse reaction in skin and mucosa group was 2% [95% CI (0.02; 0.03)]; the digestive system adverse reaction was 6% [95% CI(0.05; 0.07); the injection site adverse reaction was 4% [95% CI (0.02; 0.07)]. In the digestive system as the main types of adverse reactions/events, incidence of children and adults were 4.6% [0.021 1; 0.097 7] and 6.9% [0.053 5; 0.089 8], respectively. Adverse reactions to skin and mucous membrane damage as the main performance/event type, the observation time > 7 days and ≤ 7 days incidence of 3% [0.012 9; 0.068 3] and 1.9% [0.007 8; 0.046 1], respectively. Subgroup analysis showed that different types of adverse reactions, combination in the incidence of adverse reactions/events were higher than that of single drug, the difference was statistically significant (P reactions occur, and clinical rational drug use, such as combination, age and other fators, and the influence factors vary in different populations. Therefore, clinical doctors for children and the elderly use special care was required for a clear and open spirit injection, the implementation of individualized medication.

  8. Rate constant and reaction coordinate of Trp-cage folding in explicit water

    NARCIS (Netherlands)

    Juraszek, J.; Bolhuis, P.G.

    2008-01-01

    We report rate constant calculations and a reaction coordinate analysis of the rate-limiting folding and unfolding process of the Trp-cage mini-protein in explicit solvent using transition interface sampling. Previous transition path sampling simulations revealed that in this (un)folding process the

  9. Rate constants for the reaction of OH radicals with 1-chloroalkanes at 295 K

    DEFF Research Database (Denmark)

    Markert, F.; Nielsen, O.J.

    1992-01-01

    The rate constants for the reaction of OH radicals with a series of 1-chloroalkanes were measured at 295 K and at a total pressure of 1 atm. The rate constants were obtained by using the absolute technique of pulse radiolysis combined with kinetic UV-spectroscopy. The results are discussed in terms...

  10. Reaction paths and rate constants of the reaction of hydroxyl radicals with environmental species under tropospheric conditions

    International Nuclear Information System (INIS)

    Leonard, C.; Wahner, A.; Zetzsch, C.

    1987-01-01

    The uv-laser absorption technique in a multipath cell (with excimer-laser photolysis for radical production) is used to investigate the rate constants of the reaction of OH with carbon monoxide. The pressure dependence and the influence of collision partners (measurements in pure oxygen up to one atmosphere) of this important atmospheric chemical reaction are determined. In the kinetic measurements detection limits of 10 7 OH cm -3 are reached with millisecond time resolution. Furthermore the application of the cw-Laser for stationary OH measurements (for example in smog chambers or the free troposphere) is described. The possibilities and limits of different detection methods are discussed with respect to of noise spectra. Modifications of the apparatus with a frequency modulation technique are presented, with an extrapolated detection limit of 10 5 OH cm -3 . (orig.) With 43 refs., 16 figs [de

  11. A variable reaction rate model for chlorine decay in drinking water due to the reaction with dissolved organic matter.

    Science.gov (United States)

    Hua, Pei; Vasyukova, Ekaterina; Uhl, Wolfgang

    2015-05-15

    A second order kinetic model for simulating chlorine decay in bulk water due to the reaction with dissolved organic matter (DOM) was developed. It takes into account the decreasing reactivity of dissolved organic matter using a variable reaction rate coefficient (VRRC) which decreases with an increasing conversion. The concentration of reducing species is surrogated by the maximum chlorine demand. Temperature dependency, respectively, is described by the Arrhenius-relationship. The accuracy and adequacy of the proposed model to describe chlorine decay in bulk water were evaluated and shown for very different waters and different conditions such as water mixing or rechlorination by applying statistical tests. It is thus very well suited for application in water quality modeling for distribution systems. Copyright © 2015 Elsevier Ltd. All rights reserved.

  12. Absolute calibration of the Rh-103 (n, n') Rh-103m reaction rate

    Energy Technology Data Exchange (ETDEWEB)

    Taylor, W.H.; Murphy, M.F.; March, M.R. [Reactor Physics Division, Atomic Energy Establishment, Winfrith, Dorchester, Dorset (United Kingdom)

    1979-05-15

    The uncertainties in determining the absolute values of the Rh-103 (n, n') Rh-103m reaction rate (which is widely used as a neutron damage flux monitor) have been reduced to {approx}{+-}5%. This has been achieved with the use of a calibrated source of Pd-103-Rh-103m activity supplied by the I.A.E.A. Agreement to within 3% between measured and calculated values of the reaction rate (normalised to the U-238 fission rate) has been achieved. (author)

  13. Absolute calibration of the Rh-103 (n, n') Rh-103m reaction rate

    International Nuclear Information System (INIS)

    Taylor, W.H.; Murphy, M.F.; March, M.R.

    1979-05-01

    The uncertainties in determining the absolute values of the Rh-103 (n, n') Rh-103m reaction rate (which is widely used as a neutron damage flux monitor) have been reduced to ∼±5%. This has been achieved with the use of a calibrated source of Pd-103-Rh-103m activity supplied by the I.A.E.A. Agreement to within 3% between measured and calculated values of the reaction rate (normalised to the U-238 fission rate) has been achieved. (author)

  14. Rate Constant Change of Photo Reaction of Bacteriorhodopsin Observed in Trimeric Molecular System.

    Science.gov (United States)

    Tsujiuchi, Yutaka; Masumoto, Hiroshi; Goto, Takashi

    2016-04-01

    To elucidate the time evolution of photo reaction of bacteriorhodopsin in glycerol mixed purple membrane at around 196 K under irradiation by red light, a kinetic model was constructed. The change of absorption with irradiation at times of 560 nm and 412 nm was analyzed for the purpose of determining reaction rates of photo reaction of bacteriorhodopsin and its product M intermediate. In this study it is shown that reaction rates of conversion from bacteriorhodopsin to the M intermediate can be explained by a set of linear differential equations. This model analysis concludes that bacteriorhodopsin in which constitutes a trimer unit with other two bacteriorhodopsin molecules changes into M intermediates in the 1.73 of reaction rate, in the initial step, and according to the number of M intermediate in a trimer unit, from three to one, the reaction rate of bacteriorhodopsin into M intermediates smaller as 1.73, 0.80, 0.19 which caused by influence of inter-molecular interaction between bacteriorhodopsin.

  15. Rate Coefficient Measurements of the Reaction CH3 + O2 = CH3O + O

    Science.gov (United States)

    Hwang, S. M.; Ryu, Si-Ok; DeWitt, K. J.; Rabinowitz, M. J.

    1999-01-01

    Rate coefficients for the reaction CH3 + O2 = CH3O + O were measured behind reflected shock waves in a series of lean CH4-O2-Ar mixtures using hydroxyl and methyl radical diagnostics. The rate coefficients are well represented by an Arrhenius expression given as k = (1.60(sup +0.67, sub -0.47 ) x 10(exp 13) e(-15813 +/- 587 K/T)/cubic cm.mol.s. This expression, which is valid in the temperature range 1575-1822 K, supports the downward trend in the rate coefficients that has been reported in recent determinations. All measurements to date, including the present study, have been to some extent affected by secondary reactions. The complications due to secondary reactions, choice of thermochemical data, and shock-boundary layer interactions that affect the determination of the rate coefficients are examined.

  16. Rate Coefficient Measurements of the Reaction CH3+O2+CH3O+O

    Science.gov (United States)

    Hwang, S. M.; Ryu, Si-Ok; DeWitt, K. J.; Rabinowitz, M. J.

    1999-01-01

    Rate coefficients for the reaction CH3 + O2 = CH3O + O were measured behind reflected shock waves in a series of lean CH4-O2-Ar mixtures using hydroxyl and methyl radical diagnostics. The rate coefficients are well represented by an Arrhenius expression given as k = (1.60(sup +0.67, -0.47)) X 10(exp 13) exp(- 15813 +/- 587 K/T)cc/mol s. This expression, which is valid in the temperature range 1575-1822 K, supports the downward trend in the rate coefficients that has been reported in recent determinations. All measurements to date, including the present study, have been to some extent affected by secondary reactions. The complications due to secondary reactions, choice of thermochemical data, and shock-boundary layer interactions that affect the determination of the rate coefficients are examined.

  17. A numerical evaluation of prediction accuracy of CO2 absorber model for various reaction rate coefficients

    Directory of Open Access Journals (Sweden)

    Shim S.M.

    2012-01-01

    Full Text Available The performance of the CO2 absorber column using mono-ethanolamine (MEA solution as chemical solvent are predicted by a One-Dimensional (1-D rate based model in the present study. 1-D Mass and heat balance equations of vapor and liquid phase are coupled with interfacial mass transfer model and vapor-liquid equilibrium model. The two-film theory is used to estimate the mass transfer between the vapor and liquid film. Chemical reactions in MEA-CO2-H2O system are considered to predict the equilibrium pressure of CO2 in the MEA solution. The mathematical and reaction kinetics models used in this work are calculated by using in-house code. The numerical results are validated in the comparison of simulation results with experimental and simulation data given in the literature. The performance of CO2 absorber column is evaluated by the 1-D rate based model using various reaction rate coefficients suggested by various researchers. When the rate of liquid to gas mass flow rate is about 8.3, 6.6, 4.5 and 3.1, the error of CO2 loading and the CO2 removal efficiency using the reaction rate coefficients of Aboudheir et al. is within about 4.9 % and 5.2 %, respectively. Therefore, the reaction rate coefficient suggested by Aboudheir et al. among the various reaction rate coefficients used in this study is appropriate to predict the performance of CO2 absorber column using MEA solution. [Acknowledgement. This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF, funded by the Ministry of Education, Science and Technology (2011-0017220].

  18. Astrophysical Institute, Potsdam

    Science.gov (United States)

    Murdin, P.

    2000-11-01

    Built upon a tradition of almost 300 years, the Astrophysical Institute Potsdam (AIP) is in an historical sense the successor of one of the oldest astronomical observatories in Germany. It is the first institute in the world which incorporated the term `astrophysical' in its name, and is connected with distinguished scientists such as Karl Schwarzschild and Albert Einstein. The AIP constitutes on...

  19. Black hole astrophysics

    International Nuclear Information System (INIS)

    Blandford, R.D.; Thorne, K.S.

    1979-01-01

    Following an introductory section, the subject is discussed under the headings: on the character of research in black hole astrophysics; isolated holes produced by collapse of normal stars; black holes in binary systems; black holes in globular clusters; black holes in quasars and active galactic nuclei; primordial black holes; concluding remarks on the present state of research in black hole astrophysics. (U.K.)

  20. Plasma in astrophysics

    International Nuclear Information System (INIS)

    Kulsrud, R.M.

    1982-10-01

    Two examples of plasma phenomena of importance to astrophysics are reviewed. These are examples where astrophysical understanding hinges on further progress in plasma physics understanding. The two examples are magnetic reconnection and the collisionless interaction between a population of energetic particles and a cooler gas or plasma, in particular the interaction between galactic cosmic rays and the interstellar medium

  1. Resonance strength measurement at astrophysical energies: The {sup 17}O(p,α){sup 14}N reaction studied via Trojan Horse Method

    Energy Technology Data Exchange (ETDEWEB)

    Sergi, M. L., E-mail: sergi@lns.infn.it; La Cognata, M.; Pizzone, R. G. [INFN, Laboratori Nazionali del Sud, Catania (Italy); Spitaleri, C. [INFN, Laboratori Nazionali del Sud, Catania (Italy); Dipartimento di Fisica e Astronomia, Università degli studi di Catania, Catania (Italy); Lamia, L.; Rapisarda, G. G. [Dipartimento di Fisica e Astronomia, Università degli studi di Catania, Catania (Italy); Mukhamedzhanov, A. [Cyclotron Institute, Texas A& M University, College Station, Texas 77843 (United States); Irgaziev, B. [GIK Institute of Engineering Sciences and Technology, Topi, Districti Swabi, Khyber Pakhtunkhwa (Pakistan); Tang, X. D.; Wiescher, M. [Department of Physics, Joint Institute for Nuclear Astrophysics, University of Notre Dame, Notre Dame 46556, Indiana (United States); Mrazek, J.; Kroha, V. [Nuclear Physics Institute of ASCR, Rez (Czech Republic)

    2015-10-15

    In recent years, the Trojan Horse Method (THM) has been used to investigate the low-energy cross sections of proton-induced reactions on {sup 17}O nuclei, overcoming extrapolation procedures and enhancement effects due to electron screening. We will report on the indirect study of the {sup 17}O(p,α){sup 14}N reaction via the THM by applying the approach developed for extracting the resonance strength of narrow resonance in the ultralow energy region. Two measurements will be described and the experimental THM cross sections will be shown for both experiments.

  2. The rate of the reaction between CN and C2H2 at interstellar temperatures

    Science.gov (United States)

    Woon, D. E.; Herbst, E.

    1997-01-01

    The rate coefficient for the important interstellar reaction between CN and C2H2 has been calculated as a function of temperature between 10 and 300 K. The potential surface for this reaction has been determined through ab initio quantum chemical techniques; the potential exhibits no barrier in the entrance channel but does show a small exit channel barrier, which lies below the energy of reactants. Phase-space calculations for the reaction dynamics, which take the exit channel barrier into account, show the same unusual temperature dependence as determined by experiment, in which the rate coefficient at first increases as the temperature is reduced below room temperature and then starts to decrease as the temperature drops below 50-100 K. The agreement between theory and experiment provides strong confirmation that the reaction occurs appreciably at cool interstellar temperatures.

  3. Effective reaction rates in diffusion-limited phosphorylation-dephosphorylation cycles

    Science.gov (United States)

    Szymańska, Paulina; Kochańczyk, Marek; Miekisz, Jacek; Lipniacki, Tomasz

    2015-02-01

    We investigate the kinetics of the ubiquitous phosphorylation-dephosphorylation cycle on biological membranes by means of kinetic Monte Carlo simulations on the triangular lattice. We establish the dependence of effective macroscopic reaction rate coefficients as well as the steady-state phosphorylated substrate fraction on the diffusion coefficient and concentrations of opposing enzymes: kinases and phosphatases. In the limits of zero and infinite diffusion, the numerical results agree with analytical predictions; these two limits give the lower and the upper bound for the macroscopic rate coefficients, respectively. In the zero-diffusion limit, which is important in the analysis of dense systems, phosphorylation and dephosphorylation reactions can convert only these substrates which remain in contact with opposing enzymes. In the most studied regime of nonzero but small diffusion, a contribution linearly proportional to the diffusion coefficient appears in the reaction rate. In this regime, the presence of opposing enzymes creates inhomogeneities in the (de)phosphorylated substrate distributions: The spatial correlation function shows that enzymes are surrounded by clouds of converted substrates. This effect becomes important at low enzyme concentrations, substantially lowering effective reaction rates. Effective reaction rates decrease with decreasing diffusion and this dependence is more pronounced for the less-abundant enzyme. Consequently, the steady-state fraction of phosphorylated substrates can increase or decrease with diffusion, depending on relative concentrations of both enzymes. Additionally, steady states are controlled by molecular crowders which, mostly by lowering the effective diffusion of reactants, favor the more abundant enzyme.

  4. Stellar reaction rate for 22Mg+p→23Al from the asymptotic normalization coefficient in the mirror nuclear system 22Ne+n→23Ne

    International Nuclear Information System (INIS)

    Al-Abdullah, T.; Carstoiu, F.; Chen, X.; Clark, H. L.; Fu, C.; Gagliardi, C. A.; Lui, Y.-W.; Mukhamedzhanov, A.; Tabacaru, G.; Tokimoto, Y.; Trache, L.; Tribble, R. E.

    2010-01-01

    The production of 22 Na in ONe novae can be influenced by the 22 Mg(p,γ) 23 Al reaction. To investigate this reaction rate at stellar energies, we have determined the asymptotic normalization coefficient (ANC) for 22 Mg+p→ 23 Al through measurements of the ANCs in the mirror nuclear system 22 Ne+n→ 23 Ne. The peripheral neutron-transfer reactions 13 C( 12 C, 13 C) 12 C and 13 C( 22 Ne, 23 Ne) 12 C were studied. The identical entrance and exit channels of the first reaction make it possible to extract independently the ground-state ANC in 13 C. Our experiment gives C p 1/2 2 ( 13 C)=2.24±0.11 fm -1 , which agrees with the value obtained from several previous measurements. The weighted average for all the obtained C p 1/2 2 is 2.31±0.08 fm -1 . This value is adopted to be used in obtaining the ANCs in 23 Ne. The differential cross sections for the reaction 13 C( 22 Ne, 23 Ne) 12 C leading to the J π =5/2 + and 1/2 + states in 23 Ne have been measured at 12 MeV/u. Optical model parameters for use in the DWBA calculations were obtained from measurements of the elastic scatterings 22 Ne+ 13 C and 22 Ne+ 12 C. The extracted ANC for the ground state in 23 Ne, C d 5/2 2 =0.86±0.08±0.12 fm -1 , is converted to its corresponding value in 23 Al using mirror symmetry to give C d 5/2 2 ( 23 Al)=(4.63±0.77)x10 3 fm -1 . The astrophysical S factor S(0) for the 22 Mg(p,γ) reaction was determined to be 0.96±0.11 keV b. The consequences for nuclear astrophysics are discussed.

  5. Generalization of the Activated Complex Theory of Reaction Rates. I. Quantum Mechanical Treatment

    Science.gov (United States)

    Marcus, R. A.

    1964-01-01

    In its usual form activated complex theory assumes a quasi-equilibrium between reactants and activated complex, a separable reaction coordinate, a Cartesian reaction coordinate, and an absence of interaction of rotation with internal motion in the complex. In the present paper a rate expression is derived without introducing the Cartesian assumption. The expression bears a formal resemblance to the usual one and reduces to it when the added assumptions of the latter are introduced.

  6. A review of the rates of reaction of unirradiated uranium in gaseous atmospheres

    International Nuclear Information System (INIS)

    Pearce, R.J.

    1989-10-01

    The review collates available quantitative rate data for the reaction of unirradiated uranium in dry and moist air, steam and carbon dioxide based atmospheres at temperatures ranging from room temperature to above the melting point of uranium. Reactions in nitrogen and carbon monoxide are also considered. The aim of the review is to provide a compilation of base data for the hazard analysis of fault conditions relating to Magnox fuel. (author)

  7. Exchange Rate and Interest Rate in the Monetary Policy Reaction Function

    Directory of Open Access Journals (Sweden)

    Krušković Borivoje D.

    2017-01-01

    Full Text Available In recent years there has been a particular interest in the relation between exchange rates and interest rates both in developed countries and emerging countries. This is understandable given the important role that these variables have in determining the movement of nominal and real economic variables, including the movement of domestic inflation, real output, exports and imports, foreign exchange reserves, etc. To realized the importance of the given instruments selected macroeconomic indicators, data analysis (monthly data relating to Serbia was made on the basis of the Transfer Function Model, a data analysis (annual data relating to emerging countries was done on the basis of the Stepvise Multiple Regression model. In the transfer function model we used the Maximum Likelihood method for assessing unknown coefficients. In the gradual multiple regression model we used the Least Square method for the evaluation of unknown coefficients. All indicator values were used in the original unmodified form, i.e. there was no need for a variety of transformations. Empirical analysis showed that the exchange rate is a more significant transmission mechanism than the interest rate both in emerging markets and Serbia.

  8. Rate constant computation on some elementary reactions of Hg during combustion

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Qing; Yang, Bo-wen; Bai, Jing-ru [Northeast Dianli Univ., Jilin (China). Inst. of Energy and Power Engineering

    2013-07-01

    The geometry optimizations of reactants, products and transition states were made by the quantum chemistry MP2 method at the SDD basis function level for Hg, and 6-311++G(3df, 3pd) for others. The properties of stable minimums were validated by vibration frequencies analysis. Furthermore, the microcosmic chemical reaction mechanisms of reactions were investigated by ab initio calculations of quantum chemistry. On the basis of the geometry optimization, reaction rate constants within 298-2,000 K are calculated neither from experimental data nor by estimated, but directly from Quantum Chemistry software-Khimera.

  9. A simple recipe for modeling reaction-rate in flows with turbulent-combustion

    Science.gov (United States)

    Girimaji, Sharath S.

    1991-01-01

    A computationally viable scheme to account for chemical reaction in turbulent flows is presented. The multivariate beta-pdf model for multiple scalar mixing forms the basis of this scheme. Using the model scalar joint pdf and a general form of the instantaneous reaction-rate, the unclosed chemical reaction terms are expressed as simple functions of scalar means and the turbulent scalar energy. The calculation procedure requires that the mean scalar equations and only one other transport equation - for the turbulent scalar energy - be solved.

  10. Standard Test Method for Measuring Fast-Neutron Reaction Rates by Radioactivation of Titanium

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    2008-01-01

    1.1 This test method covers procedures for measuring reaction rates by the activation reactions 46Ti(n,p) 46Sc + 47Ti(n, np)46Sc. Note 1—Since the cross section for the (n,np) reaction is relatively small for energies less than 12 MeV and is not easily distinguished from that of the (n,p) reaction, this test method will refer to the (n,p) reaction only. 1.2 The reaction is useful for measuring neutrons with energies above approximately 4.4 MeV and for irradiation times up to about 250 days (for longer irradiations, see Practice E 261). 1.3 With suitable techniques, fission-neutron fluence rates above 109 cm–2·s–1 can be determined. However, in the presence of a high thermal-neutron fluence rate, 46Sc depletion should be investigated. 1.4 Detailed procedures for other fast-neutron detectors are referenced in Practice E 261. 1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.6 This standard does not purport to address all...

  11. Thermonuclear reaction rate of 17O(p,γ)18F

    International Nuclear Information System (INIS)

    Fox, C.; Iliadis, C.; Champagne, A.E.; Fitzgerald, R.P.; Longland, R.; Newton, J.; Pollanen, J.; Runkle, R.

    2005-01-01

    The 17 O(p,γ) 18 F and 17 O(p,α) 14 N reactions have a profound influence on hydrogen-burning nucleosynthesis in a number of stellar sites, including red giants, asymptotic giant branch (AGB) stars, massive stars, and classical novae. Previously evaluated thermonuclear rates for both reactions carry large uncertainties. We investigated the proton-capture reaction on 17 O in the bombarding energy range of E p lab = 180-540 keV. We observed a previously undiscovered resonance at E R lab = 193.2 ± 0.9 keV. The resonance strength amounts to (ωγ) pγ (1.2±0.2)x10 -6 eV. With this value, the uncertainties of the 17 O(p,γ) 18 F reaction rates are reduced by orders of magnitude in the peak temperature range of classical novae (T=0.1-0.4 GK). We also report on a reevaluation of the 17 O(p,γ) 18 F reaction rates at lower temperatures that are pertinent to red giants, AGB stars, or massive stars. The present work establishes the 17 O(p,γ) 18 F reaction rates over a temperature range of T= 0.01-1.5 GK with statistical uncertainties of 10-50%. The new recommended reaction rates deviate from the previously accepted values by an order of magnitude around T≅0.2 GK and by factors of 2-3 at T < 0.1 GK

  12. Reaction rate constants of H-abstraction by OH from large ketones: measurements and site-specific rate rules.

    Science.gov (United States)

    Badra, Jihad; Elwardany, Ahmed E; Farooq, Aamir

    2014-06-28

    Reaction rate constants of the reaction of four large ketones with hydroxyl (OH) are investigated behind reflected shock waves using OH laser absorption. The studied ketones are isomers of hexanone and include 2-hexanone, 3-hexanone, 3-methyl-2-pentanone, and 4-methl-2-pentanone. Rate constants are measured under pseudo-first-order kinetics at temperatures ranging from 866 K to 1375 K and pressures near 1.5 atm. The reported high-temperature rate constant measurements are the first direct measurements for these ketones under combustion-relevant conditions. The effects of the position of the carbonyl group (C=O) and methyl (CH3) branching on the overall rate constant with OH are examined. Using previously published data, rate constant expressions covering, low-to-high temperatures, are developed for acetone, 2-butanone, 3-pentanone, and the hexanone isomers studied here. These Arrhenius expressions are used to devise rate rules for H-abstraction from various sites. Specifically, the current scheme is applied with good success to H-abstraction by OH from a series of n-ketones. Finally, general expressions for primary and secondary site-specific H-abstraction by OH from ketones are proposed as follows (the subscript numbers indicate the number of carbon atoms bonded to the next-nearest-neighbor carbon atom, the subscript CO indicates that the abstraction is from a site next to the carbonyl group (C=O), and the prime is used to differentiate different neighboring environments of a methylene group):

  13. Effect of crystallochemistry of starting materials on the rate of smectite to illite reaction

    International Nuclear Information System (INIS)

    Sato, Tsutomu; Isobe, Hiroshi; Ohnuki, Toshihiko; Murakami, Takashi

    1995-01-01

    A series of hydrothermal experiments was performed to determine the effect of layer charge of starting materials on the smectite to illite reaction rate that might be applied to nuclear-waste repository design. The experiments were conducted on K-saturated fractions of Wyoming smectite (SWy-1) and Tsukinuno smectite (SKu-F) in a closed system at temperatures of 95, 150, 200, 250, 300 C for run durations of up to 477 days with a 1:20 mass ratio of solid to deionized water. The mean layer charge and tetrahedral charge of SKu-F are larger than those of SWy-1. The proportion of smectite layers in illite/smectite interstratified minerals rapidly decreases, and then slowly decreases with increase in reaction time; a plot of ln (100/% smectite) vs. time produces two distinct straight lines in all experiments. These lines are suggestive of two first-order kinetic processes with different rates for this reaction; the first process has a greater rate than the second one. An Arrhenius plot of the reaction rates for each process produces a folding and straight lines for the first and second processes, respectively, suggesting that there are at least two parallel processes in the first process, and a dominant process is different between high- and low-temperature reactions. The activation energies of the first and second processes determined from the plots are the same for the two starting materials, meaning that the reaction mechanisms for the two starting materials are the same. However, the rate of the first process is different between the two starting materials, although that of the second process is similar. The difference in the rate of the first process results possibly from the difference in the amount of layer charge between the two starting smectites

  14. Simplified method of ''push-pull'' test data analysis for determining in situ reaction rate coefficients

    International Nuclear Information System (INIS)

    Haggerty, R.; Schroth, M.H.; Istok, J.D.

    1998-01-01

    The single-well, ''''push-pull'''' test method is useful for obtaining information on a wide variety of aquifer physical, chemical, and microbiological characteristics. A push-pull test consists of the pulse-type injection of a prepared test solution into a single monitoring well followed by the extraction of the test solution/ground water mixture from the same well. The test solution contains a conservative tracer and one or more reactants selected to investigate a particular process. During the extraction phase, the concentrations of tracer, reactants, and possible reaction products are measured to obtain breakthrough curves for all solutes. This paper presents a simplified method of data analysis that can be used to estimate a first-order reaction rate coefficient from these breakthrough curves. Rate coefficients are obtained by fitting a regression line to a plot of normalized concentrations versus elapsed time, requiring no knowledge of aquifer porosity, dispersivity, or hydraulic conductivity. A semi-analytical solution to the advective-dispersion equation is derived and used in a sensitivity analysis to evaluate the ability of the simplified method to estimate reaction rate coefficients in simulated push-pull tests in a homogeneous, confined aquifer with a fully-penetrating injection/extraction well and varying porosity, dispersivity, test duration, and reaction rate. A numerical flow and transport code (SUTRA) is used to evaluate the ability of the simplified method to estimate reaction rate coefficients in simulated push-pull tests in a heterogeneous, unconfined aquifer with a partially penetrating well. In all cases the simplified method provides accurate estimates of reaction rate coefficients; estimation errors ranged from 0.1 to 8.9% with most errors less than 5%

  15. Temperature dependence of electrocatalytic and photocatalytic oxygen evolution reaction rates using NiFe oxide

    KAUST Repository

    Nurlaela, Ela

    2016-01-25

    The present work compares oxygen evolution reaction (OER) in electrocatalysis and photocatalysis in aqueous solutions using nanostructured NiFeOx as catalysts. The impacts of pH and reaction temperature on the electrocatalytic and photocatalytic OER kinetics were investigated. For electrocatalysis, a NiFeOx catalyst was hydrothermally decorated on Ni foam. In 1 M KOH solution, the NiFeOx electrocatalyst achieved 10 mA cm-2 at an overpotential of 260 mV. The same catalyst was decorated on the surface of Ta3N5 photocatalyst powder. The reaction was conducted in the presence of 0.1 M Na2S2O8 as a strong electron scavenger, thus likely leading to the OER being kinetically relevant. When compared with the bare Ta3N5, NiFeOx/Ta3N5 demonstrated a 5-fold improvement in photocatalytic activity in the OER under visible light irradiation, achieving a quantum efficiency of 24 % at 480 nm. Under the conditions investigated, a strong correlation between the electrocatalytic and photocatalytic performances was identified: an improvement in electrocatalysis corresponded with an improvement in photocatalysis without altering the identity of the materials. The rate change at different pH was likely associated with electrocatalytic kinetics that accordingly influenced the photocatalytic rates. The sensitivity of the reaction rates with respective to the reaction temperature resulted in an apparent activation energy of 25 kJ mol-1 in electrocatalysis, whereas that in photocatalysis was 16 kJ mol-1. The origin of the difference in these activation energy values is likely attributed to the possible effects of temperature on the individual thermodynamic and kinetic parameters of the reaction process. The work described herein demonstrates a method of “transferring the knowledge of electrocatalysis to photocatalysis” as a strong tool to rationally and quantitatively understand the complex reaction schemes involved in photocatalytic reactions.

  16. Development of a high-density gas-jet target for nuclear astrophysics and reaction studies with rare isotope beams. Final Report

    Energy Technology Data Exchange (ETDEWEB)

    Uwe, Greife [Colorado School of Mines, Golden, CO (United States)

    2014-08-12

    The purpose of this project was to develop a high-density gas jet target that will enable a new program of transfer reaction studies with rare isotope beams and targets of hydrogen and helium that is not currently possible and will have an important impact on our understanding of stellar explosions and of the evolution of nuclear shell structure away from stability. This is the final closeout report for the project.

  17. Asymptotic normalization coefficients from proton transfer reactions and astrophysical S factors for the CNO 13C(p,gamma)14N radiative capture prosess

    Czech Academy of Sciences Publication Activity Database

    Mukhamedzhanov, A. M.; Azhari, A.; Burjan, Václav; Gagliardi, C. A.; Kroha, Václav; Sattarov, A.; Tang, X.; Trache, L.; Tribble, R. E.

    2003-01-01

    Roč. 725, č. 725 (2003), s. 279-294 ISSN 0375-9474 R&D Projects: GA ČR GA202/01/0709; GA MŠk ME 385 Institutional research plan: CEZ:AV0Z1048901 Keywords : radiative capture reaction * asymptotic normalization coefficient Subject RIV: BG - Nuclear, Atomic and Molecular Physics, Colliders Impact factor: 1.761, year: 2003

  18. Asymptotic normalization coefficients from proton transfer reactions and astrophysical S factors for the (CNOC)-C-13(p, gamma)N-14 radiative capture process

    Czech Academy of Sciences Publication Activity Database

    Mukhamedzhanov, A. M.; Azhari, A.; Burjan, Václav; Gagliardi, C. A.; Kroha, Václav; Sattarov, A.; Tang, X.; Trache, L.; Tribble, R. E.

    2003-01-01

    Roč. 725, č. 22 (2003), s. 279-294 ISSN 0375-9474 R&D Projects: GA ČR GA202/01/0709; GA MŠk ME 385 Institutional research plan: CEZ:AV0Z1048901 Keywords : radiative capture reaction * asymptotic normalization coefficient Subject RIV: BG - Nuclear, Atomic and Molecular Physics, Colliders Impact factor: 1.761, year: 2003

  19. Development of a high-density gas-jet target for nuclear astrophysics and reaction studies with rare isotope beams. Final Report

    International Nuclear Information System (INIS)

    Uwe, Greife

    2014-01-01

    The purpose of this project was to develop a high-density gas jet target that will enable a new program of transfer reaction studies with rare isotope beams and targets of hydrogen and helium that is not currently possible and will have an important impact on our understanding of stellar explosions and of the evolution of nuclear shell structure away from stability. This is the final closeout report for the project.

  20. Benchmark experiments at ASTRA facility on definition of space distribution of 235U fission reaction rate

    International Nuclear Information System (INIS)

    Bobrov, A. A.; Boyarinov, V. F.; Glushkov, A. E.; Glushkov, E. S.; Kompaniets, G. V.; Moroz, N. P.; Nevinitsa, V. A.; Nosov, V. I.; Smirnov, O. N.; Fomichenko, P. A.; Zimin, A. A.

    2012-01-01

    Results of critical experiments performed at five ASTRA facility configurations modeling the high-temperature helium-cooled graphite-moderated reactors are presented. Results of experiments on definition of space distribution of 235 U fission reaction rate performed at four from these five configurations are presented more detail. Analysis of available information showed that all experiments on criticality at these five configurations are acceptable for use them as critical benchmark experiments. All experiments on definition of space distribution of 235 U fission reaction rate are acceptable for use them as physical benchmark experiments. (authors)

  1. Reaction rate constant of HO2+O3 measured by detecting HO2 from photofragment fluorescence

    Science.gov (United States)

    Manzanares, E. R.; Suto, Masako; Lee, Long C.; Coffey, Dewitt, Jr.

    1986-01-01

    A room-temperature discharge-flow system investigation of the rate constant for the reaction 'HO2 + O3 yields OH + 2O2' has detected HO2 through the OH(A-X) fluorescence produced by photodissociative excitation of HO2 at 147 nm. A reaction rate constant of 1.9 + or - 0.3 x 10 to the -15th cu cm/molecule per sec is obtained from first-order decay of HO2 in excess O3; this agrees well with published data.

  2. Correlation analysis of the progesterone-induced sperm acrosome reaction rate and the fertilisation rate in vitro.

    Science.gov (United States)

    Jiang, T; Qin, Y; Ye, T; Wang, Y; Pan, J; Zhu, Y; Duan, L; Li, K; Teng, X

    2015-10-01

    In this study, we aimed to investigate whether progesterone-induced acrosome reaction (AR) rate could be an indicator for fertilisation rate in vitro. Twenty-six couples with unexplained infertility and undergoing in vitro fertilisation (IVF) treatment were involved. On the oocytes retrieval day after routine IVF, residual sperm samples were collected to receive progesterone induction (progesterone group) or not (control group). AR rate was calculated and fertilisation rate was recorded. The correlation between progesterone-induced AR and fertilisation rate and between sperm normal morphology and 3PN (tripronuclear) were analysed using the Spearman correlation analysis. The AR rate of progesterone group was statistically higher than that of the control group (15.6 ± 5.88% versus 9.66 ± 5.771%, P rate (r = -0.053, P > 0.01) or rate of high-quality embryo development (r = -0.055, P > 0.01). Normal sperm morphology also showed no significant correlation with the amount of 3PN zygotes (r = 0.029, P > 0.01), rate of 3PN zygotes production (r = 0.20, P > 0.01), rate of 3PN embryo development (r = -0.406, P > 0.01), fertilisation rate (r = -0.148, P > 0.01) or progesterone-induced AR rate (r = 0.214, P > 0.01). Progesterone can induce AR in vitro significantly; however, the progesterone-induced AR may not be used to indicate fertilisation rate. © 2014 Blackwell Verlag GmbH.

  3. Indirect study of {sup 11}B(p,alpha{sub 0}){sup 8}Be and {sup 10}B(p,alpha){sup 7}Be reactions at astrophysical energies by means of the Trojan Horse Method: recent results

    Energy Technology Data Exchange (ETDEWEB)

    Lamia, L.; Puglia, S.M.R.; Spitaleri, C.; Romano, S. [Laboratori Nazionali del Sud, Catania (Italy); Dipartimento di Metodologie Fisiche e Chimiche per l' Ingegneria, Universita di Catania, Catania (Italy); Del Santo, M. Gimenez; Carlin, N.; Munhoz, M. Gameiro [Departamento de Fisica Nuclear, Universitade de Sao Paulo, Sao Paulo (Brazil); Cherubini, S. [Laboratori Nazionali del Sud, Catania (Italy); Dipartimento di Metodologie Fisiche e Chimiche per l' Ingegneria, Universita di Catania, Catania (Italy); Kiss, G.G. [Laboratori Nazionali del Sud, Catania (Italy); Atomki, Debrecen (Hungary); Kroha, V. [Institute for Nuclear Physics, Prague (Czech Republic); Kubono, S. [CNS, University of Tokyo, Tokyo (Japan); La Cognata, M. [Laboratori Nazionali del Sud, Catania (Italy); Dipartimento di Metodologie Fisiche e Chimiche per l' Ingegneria, Universita di Catania, Catania (Italy); Centro Siciliano di Fisica Nucleare e Struttura della Materia, Catania (Italy); Li Chengbo [China Institute of Atomic Energy, Department of Physics, Beijing (China); Pizzone, R.G. [Laboratori Nazionali del Sud, Catania (Italy); Dipartimento di Metodologie Fisiche e Chimiche per l' Ingegneria, Universita di Catania, Catania (Italy); Wen Qungang [China Institute of Atomic Energy, Department of Physics, Beijing (China); Sergi, M.L. [Laboratori Nazionali del Sud, Catania (Italy); Dipartimento di Metodologie Fisiche e Chimiche per l' Ingegneria, Universita di Catania, Catania (Italy); Centro Siciliano di Fisica Nucleare e Struttura della Materia, Catania (Italy); Szanto de Toledo, A. [Departamento de Fisica Nuclear, Universitade de Sao Paulo, Sao Paulo (Brazil); Wakabayashi, Y. [CNS, University of Tokyo, Tokyo (Japan); Advanced Science Research Center - JAEA - Ibaraki (Japan); Yamaguchi, H. [CNS, University of Tokyo, Tokyo (Japan); Zhou Shuhua [China Institute of Atomic Energy, Department of Physics, Beijing (China)

    2010-03-01

    Nuclear (p,alpha) reactions destroying the so-called 'light-elements' lithium, beryllium and boron have been largely studied in the past mainly because their role in understanding some astrophysical phenomena, i.e. mixing-phenomena occurring in young F-G stars [A.M. Boesgaard et al., Astr. Phys. J, 991, 2005, 621]. Such mechanisms transport the surface material down to the region close to the nuclear destruction zone, where typical temperatures of the order of approx10{sup 6} K are reached. The corresponding Gamow energy E{sub 0}=1.22(Z{sub x}{sup 2}Z{sub X}{sup 2}T{sub 6}{sup 2}){sup 1/3} keV [C. Rolfs and W. Rodney, 'Cauldrons in the Cosmos', The Univ. of Chicago press, 1988] is about approx10 keV if one considers the 'boron-case' and replaces in the previous formula Z{sub x}=1, Z{sub X}=5 and T{sub 6}=5. Direct measurements of the two {sup 11}B(p,alpha{sub 0}){sup 8}Be and {sup 10}B(p,alpha){sup 7}Be reactions in correspondence of this energy region are difficult to perform mainly because the combined effects of Coulomb barrier penetrability and electron screening [H.J. Assenbaum, K. Langanke and C. Rolfs, Z. Phys., 327, 1987, 461]. The indirect method of the Trojan Horse (THM) [G. Baur et al., Phys. Lett. B, 178, 1986, 135; G. Calvi et al., Nucl. Phys. A, 621, 1997, 139; C. Spitaleri et al., Phys. Rev. C, 493, 1999, 206] allows one to extract the two-body reaction cross section of interest for astrophysics without the extrapolation-procedures. Due to the THM formalism, the extracted indirect data have to be normalized to the available direct ones at higher energies thus implying that the method is a complementary tool in solving some still open questions for both nuclear and astrophysical issues [S. Cherubini et al., Astr. Phys. J, 457, 1996, 855; C. Spitaleri et al., Phys. Rev. C, 63, 2001, 005801; C. Spitaleri et al., Phys. Rev. C, 63, 2004, 055806; A. Tumino et al., Phys. Rev. Lett., 98, 2007, 252502; M. La Cognata et al., Phys

  4. Astrophysics in a nutshell

    CERN Document Server

    Maoz, Dan

    2007-01-01

    A concise but thorough introduction to the observational data and theoretical concepts underlying modern astronomy, Astrophysics in a Nutshell is designed for advanced undergraduate science majors taking a one-semester course. This well-balanced and up-to-date textbook covers the essentials of modern astrophysics--from stars to cosmology--emphasizing the common, familiar physical principles that govern astronomical phenomena, and the interplay between theory and observation. In addition to traditional topics such as stellar remnants, galaxies, and the interstellar medium, Astrophysics in a N

  5. An invitation to astrophysics

    CERN Document Server

    Padmanabhan, Thanu

    2006-01-01

    This unique book provides a clear and lucid description of several aspects of astrophysics and cosmology in a language understandable to a physicist or beginner in astrophysics. It presents the key topics in all branches of astrophysics and cosmology in a simple and concise language. The emphasis is on currently active research areas and exciting new frontiers rather than on more pedantic topics. Many complicated results are introduced with simple, novel derivations which strengthen the conceptual understanding of the subject. The book also contains over one hundred exercises which will help s

  6. Electrochemical reaction rates in a dye sentisised solar cell - the iodide/tri-iodide redox system

    DEFF Research Database (Denmark)

    Bay, Lasse; West, Keld; Winter-Jensen, Bjørn

    2006-01-01

    The electrochemical reaction rate of the redox couple iodide / tri-iodide in acetonitrile is characterised by impedance spectroscopy. Different electrode materials relevant for the function of dye-sensitised solar cells (DSSC) are investigated. Preferably, the reaction with the iodide / tri......-iodide couple should be fast at the counter electrode, i.e. this electrode must have a high catalytic activity towards the redox couple, and the same reaction must be slow on the photo electrode. The catalytic activity is investigated for platinum, poly(3,4-ethylenedioxythiophene) (PEDOT), polypyrrole (PPy......), and polyaniline (PANI) - all deposited onto fluorine doped tin oxide (FTO) glass. Both Pt and PEDOT are found to have sufficiently high catalytic activities for practical use as counter electrode in DSSC. The reaction resistance on FTO and anatase confirmed the beneficial effect of a compact anatase layer on top...

  7. Nuclear energy and astrophysics applications of ENDF/B-VII.1 evaluated nuclear library

    International Nuclear Information System (INIS)

    Pritychenko, B.

    2012-01-01

    Recently released ENDF/B-VII.1 evaluated nuclear library contains the most up-to-date evaluated neutron cross section and covariance data. These data provide new opportunities for nuclear science and astrophysics application development. The improvements in neutron cross section evaluations and more extensive utilization of covariance files, by the Cross Section Evaluation Working Group (CSEWG) collaboration, allowed users to produce neutron thermal cross sections, Westcott factors, resonance integrals, Maxwellian-averaged cross sections and astrophysical reaction rates, and provide additional insights on the currently available neutron-induced reaction data. Nuclear reaction calculations using the ENDF/B-VII.1 library and current computer technologies will be discussed and new results will be presented

  8. Examining the reaction of monetary policy to exchange rate changes: A nonlinear ARDL approach

    Science.gov (United States)

    Manogaran, Lavaneesvari; Sek, Siok Kun

    2017-04-01

    Previous studies showed the exchange rate changes can have significant impacts on macroeconomic performance. Over fluctuation of exchange rate may lead to economic instability. Hence, monetary policy rule tends to react to exchange rate changes. Especially, in emerging economies where the policy-maker tends to limit the exchange rate movement through interventions. In this study, we seek to investigate how the monetary policy rule reacts to exchange rate changes. The nonlinear autoregressive distributed lag (NARDL) model is applied to capture the asymmetric effect of exchange rate changes on monetary policy reaction function (interest rate). We focus the study in ASEAN5 countries (Indonesia, Malaysia, Philippines, Thailand and Singapore). The results indicated the existence of asymmetric effect of exchange rates changes on the monetary reaction function for all ASEAN5 countries in the long-run. Where, in majority of the cases the monetary policy is reacting to the appreciation and depreciation of exchange rate by raising the policy rate. This affirms the intervention of policymakers with the `fear of floating' behavior.

  9. Nickel group cluster anion reactions with carbon monoxide: Rate coefficients and chemisorption efficiency

    Science.gov (United States)

    Hintz, Paul A.; Ervin, Kent M.

    1994-04-01

    Reactions of Ni-n(n=3-10), Pd-n(n=3-8), and Pt-n(n=3-7) with CO are studied in a flow tube reactor. Bimolecular rate coefficients are measured for the association reaction of CO adsorbing on the cluster surface. The rate coefficients range from about 10% of the collision rate for the trimer anions to near the collision rate for clusters larger than four atoms. The maximum number of CO molecules that bind to each cluster is determined. Whereas the saturation limits for nickel are typical for an 18 electron transition metal, the limits for platinum are lower, reflecting the electron deficient structures observed in condensed phase chemistry. The CO saturated palladium clusters represent the first examples of saturated binary palladium carbonyl compounds. Comparisons are made to similar studies on metal cation and neutral clusters and also to surface scattering studies of nickel group metals.

  10. Cross sections and rate coefficients for charge exchange reactions of protons with hydrocarbon molecules

    International Nuclear Information System (INIS)

    Janev, R.K.; Kato, T.; Wang, J.G.

    2001-05-01

    The available experimental and theoretical cross section data on charge exchange processes in collisions of protons with hydrocarbon molecules have been collected and critically assessed. Using well established scaling relationships for the charge exchange cross sections at low and high collision energies, as well as the known rate coefficients for these reactions in the thermal energy region, a complete cross section database is constructed for proton-C x H y charge exchange reactions from thermal energies up to several hundreds keV for all C x H y molecules with x=1, 2, 3 and 1 ≤ y ≤ 2x + 2. Rate coefficients for these charge exchange reactions have also been calculated in the temperature range from 0.1 eV to 20 keV. (author)

  11. Cross sections and rate coefficients for charge exchange reactions of protons with hydrocarbon molecules

    Energy Technology Data Exchange (ETDEWEB)

    Janev, R.K.; Kato, T. [National Inst. for Fusion Science, Toki, Gifu (Japan); Wang, J.G. [Department of Physics and Astronomy, University of Georgia, Athens (United States)

    2001-05-01

    The available experimental and theoretical cross section data on charge exchange processes in collisions of protons with hydrocarbon molecules have been collected and critically assessed. Using well established scaling relationships for the charge exchange cross sections at low and high collision energies, as well as the known rate coefficients for these reactions in the thermal energy region, a complete cross section database is constructed for proton-C{sub x}H{sub y} charge exchange reactions from thermal energies up to several hundreds keV for all C{sub x}H{sub y} molecules with x=1, 2, 3 and 1 {<=} y {<=} 2x + 2. Rate coefficients for these charge exchange reactions have also been calculated in the temperature range from 0.1 eV to 20 keV. (author)

  12. Standard Test Method for Measuring Fast-Neutron Reaction Rates by Radioactivation of Aluminum

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    2011-01-01

    1.1 This test method covers procedures measuring reaction rates by the activation reaction 27Al(n,α)24Na. 1.2 This activation reaction is useful for measuring neutrons with energies above approximately 6.5 MeV and for irradiation times up to about 2 days (for longer irradiations, see Practice E261). 1.3 With suitable techniques, fission-neutron fluence rates above 106 cm−2·s−1 can be determined. 1.4 Detailed procedures for other fast neutron detectors are referenced in Practice E261. 1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

  13. Relationship between reaction layer thickness and leach rate for nuclear waste glasses

    International Nuclear Information System (INIS)

    Chick, L.A.; Pederson, L.R.

    1984-02-01

    Three leaching tests, devised to distinguish among several proposed nuclear waste glass leaching mechanisms, were carried out for four different waste glasses. In the first test, the influence of a pre-formed reaction layer on elemental release was evaluated. In the second test, glass specimens were replaced with fresh samples halfway through the leaching experiment, to evaluate the influence of the concentration of glass components in leaching. Finally, regular replacement of the leachant at fixed time intervals essentially removed the variable changing solution concentration, and allowed an assessment of the influence of reaction layer thickness on the leaching rate. Results for all glasses tested indicated that the reaction layer presented little or no barrier to leaching, and that most of the retardation on leaching rates generally observed are attributable to saturation effects. 20 references, 6 figures, 1 table

  14. Numerical Analysis Of Hooke Jeeves-Runge Kutta To Determine Reaction Rate Equation In Pyrrole Polymerization

    International Nuclear Information System (INIS)

    Gunawan, Indra; Sulistyo, Harry; Rochmad

    2001-01-01

    The numerical analysis of Hooke Jeeves Methods combined with Runge Kutta Methods is used to determine the exact model of reaction rate equation of pyrrole polymerization. Chemical polymerization of pyrrole was conducted with FeCI 3 / pyrrole solution at concentration ratio of 1.62 mole / mole and 2.18 mole / mole with varrying temperature of 28, 40, 50, and 60 o C. FeCl 3 acts as an oxidation agent to form pyrrole cation that will polymerize. The numerical analysis was done to examine the exact model of reaction rate equation which is derived from reaction equation of initiation, propagation, and termination. From its numerical analysis, it is found that the pyrrole polymerization follows third order of pyrrole cation concentration

  15. Rate constant for the reaction of O(3P) with diacetylene from 210 to 423 K

    Science.gov (United States)

    Mitchell, M. B.; Nava, D. F.; Stief, L. J.

    1986-01-01

    The absolute rate constant for the reaction of O(3P) with diacetylene (C4H2) has been measured as a function of pressure and temperature by the flash-photolysis/resonance-fluorescence method. At 298 K and below, no pressure dependence of the rate constant was observed, but at 423 K a moderate (factor-of-2) increase was detected in the range 3 to 75 torr Ar.Results at or near the high-pressure limit are represented by an Arrhenius expression over the temperature range 210 to 423 K. The results are compared with previous determinations, all of which employed the discharge-flow/mass-spectrometry technique. The mechanism of the reaction is considered, including both primary and secondary processes. The heats of formation of the reactants, adducts, and products for the O(3P) + C4H2 reaction are discussed and contrasted with those for O(3P) + C2H2.

  16. Rate constant for the reaction of atomic oxygen with phosphine at 298 K

    Science.gov (United States)

    Stief, L. J.; Payne, W. A.; Nava, D. F.

    1987-01-01

    The rate constant for the reaction of atomic oxygen with phosphine has been measured at 298 K using flash photolysis combined with time-resolved detection of O(3P) via resonance fluorescence. Atomic oxygen was produced by flash photolysis of N2O or NO highly diluted in argon. The results were shown to be independent of (PH3), (O), total pressure and the source of O(3P). The mean value of all the experiments is k1 = (3.6 + or -0.8) x 10 to the -11th cu cm/s (1 sigma). Two previous measurements of k1 differed by more than an order of magnitude, and the results support the higher value obtained in a discharge flow-mass spectrometry study. A comparison with rate data for other atomic and free radical reactions with phosphine is presented, and the role of these reactions in the aeronomy or photochemistry of Jupiter and Saturn is briefly considered.

  17. SENSMG: First-Order Sensitivities of Neutron Reaction Rates, Reaction-Rate Ratios, Leakage, keff, and α Using PARTISN

    Energy Technology Data Exchange (ETDEWEB)

    Favorite, Jeffrey A. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2016-11-21

    SENSMG is a tool for computing first-order sensitivities of neutron reaction rates, reaction-rate ratios, leakage, keff, and α using the PARTISN multigroup discrete-ordinates code. SENSMG computes sensitivities to all of the transport cross sections and data (total, fission, nu, chi, and all scattering moments), two edit cross sections (absorption and capture), and the density for every isotope and energy group. It also computes sensitivities to the mass density for every material and derivatives with respect to all interface locations. The tool can be used for one-dimensional spherical (r) and two-dimensional cylindrical (r-z) geometries. The tool can be used for fixed-source and eigenvalue problems. The tool implements Generalized Perturbation Theory (GPT) as discussed by Williams and Stacey. Section II of this report describes the theory behind adjoint-based sensitivities, gives the equations that SENSMG solves, and defines the sensitivities that are output. Section III describes the user interface, including the input file and command line options. Section IV describes the output. Section V gives some notes about the coding that may be of interest. Section VI discusses verification, which is ongoing. Section VII lists needs and ideas for future work. Appendix A lists all of the input files whose results are presented in Sec. VI.

  18. Compilation of neutron flux density spectra and reaction rates in different neutron fields

    International Nuclear Information System (INIS)

    Ertek, C.

    1979-07-01

    Upon the recommendation of International Working Group of Reactor Radiation Measurements (IWGRRM), the compilation of neutron flux density spectra and the reaction rates obtained by activation and fission foils in different neutron fields is presented. The neutron fields considered are as follows: 1/E; iron block; LWR core and pressure vessel; LMFBR core and blanket; CTR first wall and blanket; fission spectrum

  19. Probing the Rate-Determining Step of the Claisen-Schmidt Condensation by Competition Reactions

    Science.gov (United States)

    Mak, Kendrew K. W.; Chan, Wing-Fat; Lung, Ka-Ying; Lam, Wai-Yee; Ng, Weng-Cheong; Lee, Siu-Fung

    2007-01-01

    Competition experiments are a useful tool for preliminary study of the linear free energy relationship of organic reactions. This article describes a physical organic experiment for upper-level undergraduates to identify the rate-determining step of the Claisen-Schmidt condensation of benzaldehyde and acetophenone by studying the linear free…

  20. Efficient Computation of Transition State Resonances and Reaction Rates from a Quantum Normal Form

    NARCIS (Netherlands)

    Schubert, Roman; Waalkens, Holger; Wiggins, Stephen

    2006-01-01

    A quantum version of a recent formulation of transition state theory in phase space is presented. The theory developed provides an algorithm to compute quantum reaction rates and the associated Gamov-Siegert resonances with very high accuracy. The algorithm is especially efficient for

  1. Measurement and analysis of reaction rate distributions of cores with spectrum shifter region

    International Nuclear Information System (INIS)

    Matsuura, Shigekazu; Shiroya, Seiji; Unesaki, Hironobu; Takeda, Toshikazu; Aizawa, Otohiko; Kanda, Keiji.

    1995-01-01

    A study for the neutronic characteristics of the spectrum-controlled neutron irradiation fields using various reflector materials was performed. Spectrum shifter regions were constructed in the upper reflector region of the solid moderated core (B-Core) of the Kyoto University Critical Assembly (KUCA). Beryllium, graphite and aluminum were selected as the loading materials for the spectrum shifter. Two tight-pitch lattice cores with different moderator-to-fuel volume ratio (V m /V f ) of 0.97 and 0.65 have been used. Axial reaction rate distributions of gold, nickel and indium wires were measured, and the spectrum index was defined as the Cd ratio of the gold wire and the ratio of gold reaction rate to nickel reaction rate. Using the conventional design calculation procedure, the experimental and calculated reaction rate and spectrum index show several disagreements. Detailed treatment of the neutron streaming effect, heterogeneous cell structure and depression factor are shown to be necessary for improving the agreement between experimental and calculated values. (author)

  2. Effect of Conceptual Change Approach on Students' Understanding of Reaction Rate Concepts

    Science.gov (United States)

    Kingir, Sevgi; Geban, Omer

    2012-01-01

    The purpose of the present study was to investigate the effect of conceptual change text oriented instruction compared to traditional instruction on 10th grade students' understanding of reaction rate concepts. 45 students from two classes of the same teacher in a public high school participated in this study. Students in the experimental group…

  3. The Effect of Conceptual Change Pedagogy on Students' Conceptions of Rate of Reaction

    Science.gov (United States)

    Calik, Muammer; Kolomuc, Ali; Karagolge, Zafer

    2010-01-01

    This paper reports on an investigation of the effect of conceptual change pedagogy on students' conceptions of "rate of reaction" concepts. The study used a pre-test/post-test non-equivalent comparison group design approach and the sample consisted of 72 Turkish grade-11 students (aged 16-18 years) selected from two intact classrooms.…

  4. Generalization of the Activated Complex Theory of Reaction Rates. II. Classical Mechanical Treatment

    Science.gov (United States)

    Marcus, R. A.

    1964-01-01

    In its usual classical form activated complex theory assumes a particular expression for the kinetic energy of the reacting system -- one associated with a rectilinear motion along the reaction coordinate. The derivation of the rate expression given in the present paper is based on the general kinetic energy expression.

  5. A modified Gaussian integration method for thermal reaction rate calculation in U- and Pu-isotopes

    International Nuclear Information System (INIS)

    Bosevski, T.; Fredin, B.

    1966-01-01

    An advanced multi-group cell calculations a lot of data information is very often necessary, and hence the data administration will be elaborate, and the spectrum calculation will be time consuming. We think it is possible to reduce the necessary data information by using an effective reaction rate integration method well suited for U- and Pu-absorptions (author)

  6. A method of inferring k-infinity from reaction rate measurements in thermal reactor systems

    International Nuclear Information System (INIS)

    Newmarch, D.A.

    1967-05-01

    A scheme is described for inferring a value of k-infinity from reaction rate measurements. The method is devised with the METHUSELAH group structure in mind and was developed for the analysis of S.G.H.W. reactor experiments; the underlying principles, however, are general. (author)

  7. High energy astrophysics

    International Nuclear Information System (INIS)

    Engel, A.R.

    1979-01-01

    High energy astrophysical research carried out at the Blackett Laboratory, Imperial College, London is reviewed. Work considered includes cosmic ray particle detection, x-ray astronomy, gamma-ray astronomy, gamma and x-ray bursts. (U.K.)

  8. 2004 ASTRONOMY & ASTROPHYSICS

    Indian Academy of Sciences (India)

    user

    This publication of the Academy on Astronomy and Astrophysics is unique in ... bring out position papers on societal issues where science plays a major ..... funding agencies, the Astronomical Society of ..... orbit very close to the parent star.

  9. Topics in Nuclear Astrophysics

    International Nuclear Information System (INIS)

    Chung, K.C.

    1982-01-01

    Some topics in nuclear astrophysics are discussed, e.g.: highly evolved stellar cores, stellar evolution (through the temperature analysis of stellar surface), nucleosynthesis and finally the solar neutrino problem. (L.C.) [pt

  10. Astrophysics Decoding the cosmos

    CERN Document Server

    Irwin, Judith A

    2007-01-01

    Astrophysics: Decoding the Cosmos is an accessible introduction to the key principles and theories underlying astrophysics. This text takes a close look at the radiation and particles that we receive from astronomical objects, providing a thorough understanding of what this tells us, drawing the information together using examples to illustrate the process of astrophysics. Chapters dedicated to objects showing complex processes are written in an accessible manner and pull relevant background information together to put the subject firmly into context. The intention of the author is that the book will be a 'tool chest' for undergraduate astronomers wanting to know the how of astrophysics. Students will gain a thorough grasp of the key principles, ensuring that this often-difficult subject becomes more accessible.

  11. Corrosion potential detection method, potential characteristic simulation method for reaction rate and plant monitoring system using the same

    International Nuclear Information System (INIS)

    Sakai, Masanori; Onaka, Noriyuki; Takahashi, Tatsuya; Yamanaka, Hiroshi.

    1995-01-01

    In a calculation controlling device for a plant monitoring system, concentrations of materials concerning reaction materials in a certain state of a reaction process, and an actually measured value for the potential of a material in this state are substituted into a reaction rate equation obtained in accordance with a reaction process model. With such procedures, a relation between the reaction rate (current value) and the potential of the material can be obtained. A potential at which the reaction rates of an anode reaction and a cathode reaction contained in a corrosion reaction are made equal is determined by a numerical value calculation, based on an electrochemical hybrid potential logic by using the reaction rate equation, the reaction rate information relative to the corrosion reaction of the material and the concentration of the material concerning the corrosion reaction is obtained by a numerical value calculation. Then, simulation for the corrosion potential is enabled based on the handling corresponding to the actual reaction. Further, even for a portion which can not be measured actually, the corrosion potential can be recognized by simulation. (N.H.)

  12. Ion-neutral gas reactions in a collision/reaction cell in inductively coupled plasma mass spectrometry: Correlation of ion signal decrease to kinetic rate constants

    Energy Technology Data Exchange (ETDEWEB)

    Gray, Patrick J. [Trace Element Research Laboratory, School of Earth Sciences, The Ohio State University, 125 S. Oval Mall, Columbus, OH 43210 (United States); Department of Chemistry, The Ohio State University, 120 18th Avenue, Columbus, OH 43210 (United States); Olesik, John W., E-mail: olesik.2@osu.edu [Trace Element Research Laboratory, School of Earth Sciences, The Ohio State University, 125 S. Oval Mall, Columbus, OH 43210 (United States)

    2015-03-01

    Reaction gas flow rate dependent Ar{sub 2}{sup +} and Ar{sup +} signals are correlated to fundamental kinetic rate coefficients. A simple calculation, assuming that gas exits the reaction cell due only to effusion, is described to estimate the gas pressure in the reaction cell. The value of the product of the kinetic rate constant and the ion residence time in the reaction cell can be determined from experimental measurement of the decrease in an ion signal as a function of reaction gas flow rate. New kinetic rate constants are determined for the reaction of CH{sub 3}F with Ar{sup +} and Ar{sub 2}{sup +}. - Highlights: • How to determine pressure and the product of the kinetic rate constant times the ion residence time in reaction cell • Relate measured ICP-DRC-MS signals versus gas flow rate to kinetic rate constants measured previously using SIFT-MS • Describe how to determine previously unmeasured kinetic rate constants using ICP-DRC-MS.

  13. Collisionless plasmas in astrophysics

    CERN Document Server

    Belmont, Gerard; Mottez, Fabrice; Pantellini, Filippo; Pelletier, Guy

    2013-01-01

    Collisionless Plasmas in Astrophysics examines the unique properties of media without collisions in plasma physics. Experts in this field, the authors present the first book to concentrate on collisionless conditions in plasmas, whether close or not to thermal equilibrium. Filling a void in scientific literature, Collisionless Plasmas in Astrophysics explains the possibilities of modeling such plasmas, using a fluid or a kinetic framework. It also addresses common misconceptions that even professionals may possess, on phenomena such as "collisionless (Landau) damping". Abundant illustrations

  14. Nonlinear dynamics and astrophysics

    International Nuclear Information System (INIS)

    Vallejo, J. C.; Sanjuan, M. A. F.

    2000-01-01

    Concepts and techniques from Nonlinear Dynamics, also known as Chaos Theory, have been applied successfully to several astrophysical fields such as orbital motion, time series analysis or galactic dynamics, providing answers to old questions but also opening a few new ones. Some of these topics are described in this review article, showing the basis of Nonlinear Dynamics, and how it is applied in Astrophysics. (Author)

  15. Rate Coefficients for the OH + (CHO)2 (Glyoxal) Reaction Between 240 and 400 K

    Science.gov (United States)

    Feierabend, K. J.; Talukdar, R. K.; Zhu, L.; Ravishankara, A. R.; Burkholder, J. B.

    2006-12-01

    Glyoxal (CHO)2, the simplest dialdehyde, is an end product formed in the atmospheric oxidation of biogenic hydrocarbons, for example, isoprene. As such, glyoxal plays a role in regional air quality and ozone production in certain locations. Glyoxal is lost in the atmosphere via UV photolysis and reaction with OH. However, the currently available rate coefficient data for the OH + glyoxal reaction is limited to a single room- temperature measurement made using the relative rate method. A determination of the rate coefficient temperature dependence is therefore needed for a more complete interpretation of the atmospheric processing of glyoxal. This study reports the rate coefficient for the OH + (CHO)2 reaction measured under pseudo- first-order conditions in OH ([(CHO)2] > 1000 [OH]0). OH radicals were produced using 248 nm pulsed laser photolysis of H2O2 or HNO3 and detected by pulsed laser induced fluorescence. The concentration of glyoxal in the reactor was determined using three independent techniques; gas flow rates as well as in situ UV and IR absorption. The total pressure in the reactor was varied from 40 to 300 Torr (He), and the rate coefficient was found to be independent of pressure over the temperature range studied. The rate coefficient exhibits a negative temperature dependence between 240 and 400 K consistent with the dependence previously observed for many other aldehydes. Our room-temperature rate coefficient is smaller than the relative rate value that is currently recommended for use in atmospheric model calculations. Our measured rate coefficients are discussed with respect to those for other aldehydes. The atmospheric implications of our work will also be discussed.

  16. Automated Prediction of Catalytic Mechanism and Rate Law Using Graph-Based Reaction Path Sampling.

    Science.gov (United States)

    Habershon, Scott

    2016-04-12

    In a recent article [ J. Chem. Phys. 2015 , 143 , 094106 ], we introduced a novel graph-based sampling scheme which can be used to generate chemical reaction paths in many-atom systems in an efficient and highly automated manner. The main goal of this work is to demonstrate how this approach, when combined with direct kinetic modeling, can be used to determine the mechanism and phenomenological rate law of a complex catalytic cycle, namely cobalt-catalyzed hydroformylation of ethene. Our graph-based sampling scheme generates 31 unique chemical products and 32 unique chemical reaction pathways; these sampled structures and reaction paths enable automated construction of a kinetic network model of the catalytic system when combined with density functional theory (DFT) calculations of free energies and resultant transition-state theory rate constants. Direct simulations of this kinetic network across a range of initial reactant concentrations enables determination of both the reaction mechanism and the associated rate law in an automated fashion, without the need for either presupposing a mechanism or making steady-state approximations in kinetic analysis. Most importantly, we find that the reaction mechanism which emerges from these simulations is exactly that originally proposed by Heck and Breslow; furthermore, the simulated rate law is also consistent with previous experimental and computational studies, exhibiting a complex dependence on carbon monoxide pressure. While the inherent errors of using DFT simulations to model chemical reactivity limit the quantitative accuracy of our calculated rates, this work confirms that our automated simulation strategy enables direct analysis of catalytic mechanisms from first principles.

  17. Mixing effects on apparent reaction rates and isotope fractionation during denitrification in a heterogeneous aquifer

    Science.gov (United States)

    Green, Christopher T.; Böhlke, John Karl; Bekins, Barbara A.; Phillips, Steven P.

    2010-01-01

    Gradients in contaminant concentrations and isotopic compositions commonly are used to derive reaction parameters for natural attenuation in aquifers. Differences between field‐scale (apparent) estimated reaction rates and isotopic fractionations and local‐scale (intrinsic) effects are poorly understood for complex natural systems. For a heterogeneous alluvial fan aquifer, numerical models and field observations were used to study the effects of physical heterogeneity on reaction parameter estimates. Field measurements included major ions, age tracers, stable isotopes, and dissolved gases. Parameters were estimated for the O2 reduction rate, denitrification rate, O2 threshold for denitrification, and stable N isotope fractionation during denitrification. For multiple geostatistical realizations of the aquifer, inverse modeling was used to establish reactive transport simulations that were consistent with field observations and served as a basis for numerical experiments to compare sample‐based estimates of “apparent” parameters with “true“ (intrinsic) values. For this aquifer, non‐Gaussian dispersion reduced the magnitudes of apparent reaction rates and isotope fractionations to a greater extent than Gaussian mixing alone. Apparent and true rate constants and fractionation parameters can differ by an order of magnitude or more, especially for samples subject to slow transport, long travel times, or rapid reactions. The effect of mixing on apparent N isotope fractionation potentially explains differences between previous laboratory and field estimates. Similarly, predicted effects on apparent O2threshold values for denitrification are consistent with previous reports of higher values in aquifers than in the laboratory. These results show that hydrogeological complexity substantially influences the interpretation and prediction of reactive transport.

  18. The Reaction Mechanism and Rate Constants in the Radiolysis of Fe2+-Cu2+ Solutions

    DEFF Research Database (Denmark)

    Bjergbakke, Erling; Sehested, Knud; Rasmussen, O. Lang

    1976-01-01

    Pulse radiolysis and gamma radiolysis have been used to study the reaction mechanism in the radiolysis of aqueous solutions of Fe2+ and Cu2+. A reaction scheme has been developed and confirmed by computation of the corresponding complete set of differential equations. The rate constants for some ...... 10^{8}$ and $1.3\\times 10^{8}\\ {\\rm mol}^{-1}\\ {\\rm sec}^{-1}$ in pH 2.1 H2 SO4 and HClO4, respectively.......Pulse radiolysis and gamma radiolysis have been used to study the reaction mechanism in the radiolysis of aqueous solutions of Fe2+ and Cu2+. A reaction scheme has been developed and confirmed by computation of the corresponding complete set of differential equations. The rate constants for some...... of the reactions have been determined at different pH's. $k_{{\\rm Cu}^{+}+{\\rm O}_{2}}=4.6\\times 10^{5}$ and $1.0\\times 10^{6}\\ {\\rm mol}^{-1}\\ {\\rm sec}^{-1}$, $k_{{\\rm Cu}^{+}+{\\rm Fe}^{3+}}=5.5\\times 10^{6}$ and $1.3\\times 10^{7}\\ {\\rm mol}^{-1}\\ {\\rm sec}^{-1}$, $k_{{\\rm Cu}({\\rm III)}+{\\rm Fe}^{2+}}=3.3\\times...

  19. Standard Test Method for Measuring Fast-Neutron Reaction Rates by Radioactivation of Copper

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    2011-01-01

    1.1 This test method covers procedures for measuring reaction rates by the activation reaction 63Cu(n,α)60Co. The cross section for 60Co produced in this reaction increases rapidly with neutrons having energies greater than about 5 MeV. 60Co decays with a half-life of 1925.27 days (±0.29 days)(1) and emits two gamma rays having energies of 1.1732278 and 1.332492 MeV (1). The isotopic content of natural copper is 69.17 % 63Cu and 30.83 % 65Cu (2). The neutron reaction, 63Cu(n,γ)64Cu, produces a radioactive product that emits gamma rays which might interfere with the counting of the 60Co gamma rays. 1.2 With suitable techniques, fission-neutron fluence rates above 109 cm−2·s−1 can be determined. The 63Cu(n,α)60Co reaction can be used to determine fast-neutron fluences for irradiation times up to about 15 years (for longer irradiations, see Practice E261). 1.3 Detailed procedures for other fast-neutron detectors are referenced in Practice E261. 1.4 This standard does not purport to address all of the...

  20. Estimating Reaction Rate Coefficients Within a Travel-Time Modeling Framework

    Energy Technology Data Exchange (ETDEWEB)

    Gong, R [Georgia Institute of Technology; Lu, C [Georgia Institute of Technology; Luo, Jian [Georgia Institute of Technology; Wu, Wei-min [Stanford University; Cheng, H. [Stanford University; Criddle, Craig [Stanford University; Kitanidis, Peter K. [Stanford University; Gu, Baohua [ORNL; Watson, David B [ORNL; Jardine, Philip M [ORNL; Brooks, Scott C [ORNL

    2011-03-01

    A generalized, efficient, and practical approach based on the travel-time modeling framework is developed to estimate in situ reaction rate coefficients for groundwater remediation in heterogeneous aquifers. The required information for this approach can be obtained by conducting tracer tests with injection of a mixture of conservative and reactive tracers and measurements of both breakthrough curves (BTCs). The conservative BTC is used to infer the travel-time distribution from the injection point to the observation point. For advection-dominant reactive transport with well-mixed reactive species and a constant travel-time distribution, the reactive BTC is obtained by integrating the solutions to advective-reactive transport over the entire travel-time distribution, and then is used in optimization to determine the in situ reaction rate coefficients. By directly working on the conservative and reactive BTCs, this approach avoids costly aquifer characterization and improves the estimation for transport in heterogeneous aquifers which may not be sufficiently described by traditional mechanistic transport models with constant transport parameters. Simplified schemes are proposed for reactive transport with zero-, first-, nth-order, and Michaelis-Menten reactions. The proposed approach is validated by a reactive transport case in a two-dimensional synthetic heterogeneous aquifer and a field-scale bioremediation experiment conducted at Oak Ridge, Tennessee. The field application indicates that ethanol degradation for U(VI)-bioremediation is better approximated by zero-order reaction kinetics than first-order reaction kinetics.

  1. Effects of Water Molecule on CO Oxidation by OH: Reaction Pathways, Kinetic Barriers, and Rate Constants.

    Science.gov (United States)

    Zhang, Linyao; Yang, Li; Zhao, Yijun; Zhang, Jiaxu; Feng, Dongdong; Sun, Shaozeng

    2017-07-06

    The water dilute oxy-fuel combustion is a clean combustion technology for near-zero emission power; and the presence of water molecule could have both kinetic and dynamic effects on combustion reactions. The reaction OH + CO → CO 2 + H, one of the most important elementary reactions, has been investigated by extensive electronic structure calculations. And the effects of a single water molecule on CO oxidation have been studied by considering the preformed OH(H 2 O) complex reacts with CO. The results show little change in the reaction pathways, but the additional water molecule actually increases the vibrationally adiabatic energy barriers (V a G ). Further thermal rate constant calculations in the temperature range of 200 to 2000 K demonstrate that the total low-pressure limit rate constant for the water assisted OH(H 2 O) + CO → CO 2 + H 2 O + H reaction is 1-2 orders lower than that of the water unassisted one, which is consistent with the change of V a G . Therefore, the hydrated radical OH(H 2 O) would actually slow down the oxidation of CO. Meanwhile, comparisons show that the M06-2X/aug-cc-pVDZ method gives a much better estimation in energy and thus is recommended to be employed for direct dynamics simulations.

  2. A randomised controlled trial of two infusion rates to decrease reactions to antivenom.

    Directory of Open Access Journals (Sweden)

    Geoffrey K Isbister

    Full Text Available BACKGROUND: Snake envenoming is a major clinical problem in Sri Lanka, with an estimated 40,000 bites annually. Antivenom is only available from India and there is a high rate of systemic hypersensitivity reactions. This study aimed to investigate whether the rate of infusion of antivenom reduced the frequency of severe systemic hypersensitivity reactions. METHODS AND FINDINGS: This was a randomized comparison trial of two infusion rates of antivenom for treatment of non-pregnant adult patients (>14 y with snake envenoming in Sri Lanka. Snake identification was by patient or hospital examination of dead snakes when available and confirmed by enzyme-immunoassay for Russell's viper envenoming. Patients were blindly allocated in a 11 randomisation schedule to receive antivenom either as a 20 minute infusion (rapid or a two hour infusion (slow. The primary outcome was the proportion with severe systemic hypersensitivity reactions (grade 3 by Brown grading system within 4 hours of commencement of antivenom. Secondary outcomes included the proportion with mild/moderate hypersensitivity reactions and repeat antivenom doses. Of 1004 patients with suspected snakebites, 247 patients received antivenom. 49 patients were excluded or not recruited leaving 104 patients allocated to the rapid antivenom infusion and 94 to the slow antivenom infusion. The median actual duration of antivenom infusion in the rapid group was 20 min (Interquartile range[IQR]:20-25 min versus 120 min (IQR:75-120 min in the slow group. There was no difference in severe systemic hypersensitivity reactions between those given rapid and slow infusions (32% vs. 35%; difference 3%; 95%CI:-10% to +17%;p = 0.65. The frequency of mild/moderate reactions was also similar. Similar numbers of patients in each arm received further doses of antivenom (30/104 vs. 23/94. CONCLUSIONS: A slower infusion rate would not reduce the rate of severe systemic hypersensitivity reactions from current high

  3. An analysis of ZEEP reaction rate measurements using the iterative five group scheme of METHUSELAH I

    Energy Technology Data Exchange (ETDEWEB)

    Allen, F R; Askew, J R [Technical Assessments and Services Division, Atomic Energy Establishment, Winfrith, Dorchester, Dorset (United Kingdom)

    1964-02-15

    The five group iterative scheme of METHUSELAH I has been used to provide estimates of reaction rates for comparison with measurements in a number of loop experiments in ZEEP. Theory and experiment show good agreement for individual fission rate distributions and for the Pu-239/U-235 reaction rate ratios. Estimates of Lu/Mn ratios are in reasonable agreement with measurements in the H{sub 2}O cores, but become progressively less satisfactory as the D{sub 2}O content of the coolant is increased. It is concluded that for assessment calculations, the introduction of an iterative five group scheme improves the representation of thermal spectra in pressure tube reactor lattices. (author)

  4. Addition and spin exchange rate constants by longitudinal field μSR: the Mu + NO reaction

    International Nuclear Information System (INIS)

    Senba, Masayoshi; Gonzalez, A.C.; Kempton, J.R.; Arseneau, D.J.; Pan, J.J.; Tempelmann, A.; Fleming, D.G.

    1991-01-01

    The addition reaction Mu + NO + M → MuNO + M and the spin exchange reaction Mu(↑) + NO(↓)→Mu(↓)+NO(↑) have been measured by longitudinal field μSR at room temperature in the presence of up to 58 atm of N 2 as inert collider. The pressure dependence of the longitudinal relaxation rate due to the addition reaction (λ c ) demonstrates that the system is still in the low pressure regime in this pressure range. The corresponding termolecular rate constant has been determined as k 0.Mu =(1.10±0.25)x10 -32 cm 6 molecules -2 s -1 , almost 4 times smaller than the corresponding H atom reaction k 0,H =3.90x10 -32 cm 6 molecules -2 s -1 . The average value of the spin exchange rate constants in the 2.5-58 atm pressure range, k SE = (3.16±0.06)x10 -10 cm 3 molecule -1 s -1 , is in good agreement with previous values obtained by transverse field μSR. (orig.)

  5. Aqueous Complexation Reactions Governing the Rate and Extent of Biogeochemical U(VI) Reduction

    International Nuclear Information System (INIS)

    Scott C. Brooks; Wenming Dong; Sue Carroll; James K. Fredrickson; Kenneth M. Kemner; Shelly D. Kelly

    2006-01-01

    The proposed research will elucidate the principal biogeochemical reactions that govern the concentration, chemical speciation, and reactivity of the redox-sensitive contaminant uranium. The results will provide an improved understanding and predictive capability of the mechanisms that govern the biogeochemical reduction of uranium in subsurface environments. In addition, the work plan is designed to: (1) Generate fundamental scientific understanding on the relationship between U(VI) chemical speciation and its susceptibility to biogeochemical reduction reactions. (2) Elucidate the controls on the rate and extent of contaminant reactivity. (3) Provide new insights into the aqueous and solid speciation of U(VI)/U(IV) under representative groundwater conditions

  6. Rates of chemical reaction and atmospheric heating during core debris expulsion from a pressurized vessel

    International Nuclear Information System (INIS)

    Powers, D.A.; Tarbell, W.W.; Brockman, J.E.; Pilch, M.

    1986-01-01

    Core debris may be expelled from a pressurized reactor vessel during a severe nuclear reactor accident. Experimental studies of core debris expulsion from pressurized vessels have established that the expelled material can be lofted into the atmosphere of the reactor containment as particulate 0.4 to 2 mm in diameter. These particles will vigorously react with steam and oxygen in the containment atmosphere. Data on such reactions during tests with 80 kg of expelled melt will be reported. A model of the reaction rates based on gas phase mass transport will be described and shown to account for atmospheric heating and aerosol generation observed in the tests

  7. Determination of the rate coefficient for the N2/+/ + O reaction in the ionosphere

    Science.gov (United States)

    Torr, D. G.; Torr, M. R.; Orsini, N.; Hanson, W. B.; Hoffman, J. H.; Walker, J. C. G.

    1977-01-01

    Using approximately 400 simultaneous measurements of ion and neutral densities and temperatures, and the spectrum of the solar flux measured by the Atmosphere Explorer C satellite, we have determined the rate constant k1 for the reaction between N2(+) and O in the ionosphere for ion temperatures between 600 and 700 K. We find that k1 = 1.1 x 10 to the minus 10th power cu cm per sec, with a standard deviation of + or - 15%. If we use the temperature dependence for this reaction determined in the laboratory then at 300 K we find excellent agreement with the recommended laboratory value.

  8. Nuclear astrophysics of the sun

    International Nuclear Information System (INIS)

    Kocharov, G.E.

    1980-01-01

    In the first chapter we will discuss the problem of nuclear reactions in the interior of the sun and consider the modern aspects of the neutrino astrophysics of the Sun. The second chapter is devoted to the high energy interactions in the solar atmosphere during the flares. Among a great number of events during the solar flares we shall consider mainly the nuclear reactions. Special attention will be paid to the genetic connection between the different components of solar electromagnetic and corpuscular radiation. The idea of the unity of processes in different parts of the Sun, from hot and dense interior up to the rare plasma of the solar corona will be the main line of the book. (orig./WL) 891 WL/orig.- 892 HIS

  9. Thermodynamic and molecular origin of interfacial rate enhancements and endo-selectivities of a Diels-Alder reaction.

    Science.gov (United States)

    Beniwal, Vijay; Kumar, Anil

    2017-02-08

    Organic reactions in general display large rate accelerations when performed under interfacial conditions, such as on water or at ionic liquid interfaces. However, a clear picture of the physicochemical factors responsible for this large rate enhancements is not available. To gain an understanding of the thermodynamic and molecular origin of these large rate enhancements, we performed a Diels-Alder reaction between cyclopentadiene and methyl acrylate at ionic liquid/n-hexane interfaces. This study describes, for the first time, a methodology for the calculation of the activation parameters of an interfacial reaction. It has been seen that the energy of activation for an interfacial reaction is much smaller than that of the corresponding homogeneous reaction, resulting into the large rate acceleration for the interfacial reaction. Furthermore, the study describes the effects of the alkyl chain length of ionic liquid cations, the extent of heterogeneity, and the polarity of ionic liquids on the rate constants and stereoselectivity of the reaction.

  10. Understanding and Improvement of an Experiment Measuring Chemical Reaction Rates by Monitoring Volume Change of a Gas: On the Reaction between HCl(aq) and Mg(s)

    International Nuclear Information System (INIS)

    Bang, Jeong Ah; Yoon, Hee Sook; Jeong, Dae Hong; Choi, Won Ho

    2006-01-01

    In this study we analyzed and improved an experiment measuring chemical reaction rates introduced in the high school science textbooks through an understanding of the phenomena observed in carrying out the experiment. For this purpose, the contents of textbooks related to the experiment were analyzed, and the problems observed in carrying out the experiment were addressed through experimental analysis. When the experiment was carried out by the method of aquatic transposition presented in textbooks, the observed volume change of H 2 gas was delayed and chemical reaction rate was increased in the early stage of reaction period. To resolve these problems, an improved method for measuring the reaction rates was suggested. In the improved experiment the reaction rate was measured to be constant on time, which was interpreted in terms of the concentration of H + and the surface area of magnesium

  11. Reaction of atomic bromine with acetylene and loss rate of atmospheric acetylene due to reaction with OH, Cl, O, and Br

    Science.gov (United States)

    Payne, W. A.; Nava, D. F.; Brunning, J.; Stief, L. J.

    1986-01-01

    The first-order, diffusion, and bimolecular rate constants for the reaction Br + C2H2 yields C2H3Br are evaluated. The rate constants are measured at 210, 248, 298, and 393 K and at pressures between 15-100 torr Ar using flash photolysis combined with time-resolved detection of atomic bromine via Br resonance radiation. It is observed that the reaction is not affected by pressure or temperature and the bimolecular constant = (4.0 + or - 0.8) x 10 to the -15th cu cm/sec with an error of two standard deviations. The C2H2 + Br reaction rates are compared with reactions of C2H2 with Cl, OH, NH2, and H. The loss rates for atmospheric C2H2 for reactions with OH, Cl, O, and Br are calculated as a function of altitude.

  12. A simple thermometric technique for reaction-rate determination of inorganic species, based on the iodide-catalysed cerium(IV)-arsenic(III) reaction.

    Science.gov (United States)

    Grases, F; Forteza, R; March, J G; Cerda, V

    1985-02-01

    A very simple reaction-rate thermometric technique is used for determination of iodide (5-20 ng ml ), based on its catalytic action on the cerium(IV)-arsenic(III) reaction, and for determination of mercury(II) (1.5-10 ng ml ) and silver(I) (2-10 ng ml ), based on their inhibitory effect on this reaction. The reaction is followed by measuring the rate of temperature increase. The method suffers from very few interferences and is applied to determination of iodide in biological and inorganic samples, and Hg(II) and Ag(I) in pharmaceutical products.

  13. Rate constants for the slow Mu + propane abstraction reaction at 300 K by diamagnetic RF resonance.

    Science.gov (United States)

    Fleming, Donald G; Cottrell, Stephen P; McKenzie, Iain; Ghandi, Khashayar

    2015-08-14

    The study of kinetic isotope effects for H-atom abstraction rates by incident H-atoms from the homologous series of lower mass alkanes (CH4, C2H6 and, here, C3H8) provides important tests of reaction rate theory on polyatomic systems. With a mass of only 0.114 amu, the most sensitive test is provided by the rates of the Mu atom. Abstraction of H by Mu can be highly endoergic, due to the large zero-point energy shift in the MuH bond formed, which also gives rise to high activation energies from similar zero-point energy corrections at the transition state. Rates are then far too slow near 300 K to be measured by conventional TF-μSR techniques that follow the disappearance of the spin-polarised Mu atom with time. Reported here is the first measurement of a slow Mu reaction rate in the gas phase by the technique of diamagnetic radio frequency (RF) resonance, where the amplitude of the MuH product formed in the Mu + C3H8 reaction is followed with time. The measured rate constant, kMu = (6.8 ± 0.5) × 10(-16) cm(3) s(-1) at 300 K, is surprisingly only about a factor of three slower than that expected for H + C3H8, indicating a dominant contribution from quantum tunneling in the Mu reaction, consistent with elementary transition state theory calculations of the kMu/kH kinetic isotope effect.

  14. Theoretical nuclear structure and astrophysics at FAIR

    International Nuclear Information System (INIS)

    Rodríguez, Tomás R

    2014-01-01

    Next generation of radioactive ion beam facilities like FAIR will open a bright future for nuclear structure and nuclear astrophysics research. In particular, very exotic nuclei (mainly neutron rich) isotopes will be produced and a lot of new exciting experimental data will help to test and improve the current nuclear models. In addition, these data (masses, reaction cross sections, beta decay half-lives, etc.) combined with the development of better theoretical approaches will be used as the nuclear physics input for astrophysical simulations. In this presentation I will review some of the state-of-the-art nuclear structure methods and their applications.

  15. Astrophysical relevance of γ transition energies

    International Nuclear Information System (INIS)

    Rauscher, Thomas

    2008-01-01

    The relevant γ energy range is explicitly identified where additional γ strength must be located to have an impact on astrophysically relevant reactions. It is shown that folding the energy dependences of the transmission coefficients and the level density leads to maximal contributions for γ energies of 2≤E γ ≤4 unless quantum selection rules allow isolated states to contribute. Under this condition, electric dipole transitions dominate. These findings allow us to more accurately judge the relevance of modifications of the γ strength for astrophysics

  16. Absolute rate constants for the reaction of hypochlorous acid with protein side chains and peptide bonds

    DEFF Research Database (Denmark)

    Pattison, D I; Davies, Michael Jonathan

    2001-01-01

    , absolute second-order rate constants for the reactions of HOCl with protein side chains, model compounds, and backbone amide (peptide) bonds have been determined at physiological pH values. The reactivity of HOCl with potential reactive sites in proteins is summarized by the series: Met (3.8 x 10(7) M(-1......Hypochlorous acid (HOCl) is a potent oxidant, which is produced in vivo by activated phagocytes. This compound is an important antibacterial agent, but excessive or misplaced production has been implicated in a number of human diseases, including atherosclerosis, arthritis, and some cancers....... Proteins are major targets for this oxidant, and such reaction results in side-chain modification, backbone fragmentation, and cross-linking. Despite a wealth of qualitative data for such reactions, little absolute kinetic data is available to rationalize the in vitro and in vivo data. In this study...

  17. Reaction Rate Distributions and Ratios in FR0 Assemblies 1, 2 and 3

    Energy Technology Data Exchange (ETDEWEB)

    Andersson, T L

    1966-06-15

    The spatial distribution of different reaction rates and reaction ratios in Assemblies 1, 2 and 3 of the fast reactor FR0 was measured by fission chamber scans and foil activation technique. Assemblies 1 and 2 had cores of undiluted fuel (uranium metal enriched to 20 % U{sup 235}) while the core of Assembly 3 was diluted with about 30 vol. % graphite. All the systems had a thick copper reflector, The experimental results were compared with calculated values obtained from DSN and TDC multigroup spectra and group cross-section sets for the reactions. Good agreement between experiment and calculations is generally obtained in the core region but in the reflector the neutron spectrum is calculated too hard.

  18. Rate coefficients for the reactions of ions with polar molecules at interstellar temperatures

    International Nuclear Information System (INIS)

    Adams, N.G.; Smith, D.; Clary, D.C.

    1985-01-01

    A theory has been developed recently which predicts that the rate coefficients, k, for the reactions of ions with polar molecules at low temperatures will be much greater than the canonical value of 10 -9 cm 3 s -1 . The new theory indicates that k is greatest for low-lying rotational sates and increases rapidly with decreasing temperature. We refer to recent laboratory measurements which validate the theory, present calculated values of k for the reactions of H + 3 ions with several polar molecules, and discuss their significance to interstellar chemistry. For the reactions of ions with molecules having large dipole moments, we recommend that k values as large as 10 -7 cm 3 s -1 should be used in ion-chemical models of low-temperature interstellar clouds

  19. Rate constant for the reaction SO + BrO yields SO2 + Br

    Science.gov (United States)

    Brunning, J.; Stief, L.

    1986-01-01

    The rate of the radical-radical reaction SO + BrO yields SO2 + Br has been determined at 298 K in a discharge flow system near 1 torr pressure with detection of SO and BrO via collision-free sampling mass spectrometry. The rate constant was determined using two different methods: measuring the decay of SO radicals in the presence of an excess of BrO and measuring the decay of BrO radicals in excess SO. The results from the two methods are in reasonable agreement and the simple mean of the two values gives the recommended rate constant at 298 K, k = (5.7 + or - 2.0) x 10 to the -11th cu cm/s. This represents the first determination of this rate constant and it is consistent with a previously derived lower limit based on SO2 formation. Comparison is made with other radical-radical reactions involving SO or BrO. The reaction SO + BrO yields SO2 + Br is of interest for models of the upper atmosphere of the earth and provides a potential coupling between atmospheric sulfur and bromine chemistry.

  20. Theoretical and Shock Tube Study of the Rate Constants for Hydrogen Abstraction Reactions of Ethyl Formate

    KAUST Repository

    Wu, Junjun; Khaled, Fathi; Ning, Hongbo; Ma, Liuhao; Farooq, Aamir; Ren, Wei

    2017-01-01

    We report a systematic chemical kinetics study of the H-atom abstractions from ethyl formate (EF) by H, O(3P), CH3, OH, and HO2 radicals. The geometry optimization and frequency calculation of all the species were conducted using the M06 method and the cc-pVTZ basis set. The one-dimensional hindered rotor treatment of the reactants and transition states and the intrinsic reaction coordinate analysis were also performed at the M06/cc-pVTZ level of theory. The relative electronic energies were calculated at the CCSD(T)/cc-pVXZ (where X = D, T) level of theory and further extrapolated to the complete basis set limit. Rate constants for the tittle reactions were calculated over the temperature range of 500‒2500 K by the transition state theory (TST) in conjunction with asymmetric Eckart tunneling effect. In addition, the rate constants of H-abstraction by hydroxyl radical were measured in shock tube experiments at 900‒1321 K and 1.4‒2.0 atm. Our theoretical rate constants of OH + EF → Products agree well with the experimental results within 15% over the experimental temperature range of 900‒1321 K. Branching ratios for the five types of H-abstraction reactions were also determined from their individual site-specific rate constants.

  1. Theoretical and Shock Tube Study of the Rate Constants for Hydrogen Abstraction Reactions of Ethyl Formate

    KAUST Repository

    Wu, Junjun

    2017-08-03

    We report a systematic chemical kinetics study of the H-atom abstractions from ethyl formate (EF) by H, O(3P), CH3, OH, and HO2 radicals. The geometry optimization and frequency calculation of all the species were conducted using the M06 method and the cc-pVTZ basis set. The one-dimensional hindered rotor treatment of the reactants and transition states and the intrinsic reaction coordinate analysis were also performed at the M06/cc-pVTZ level of theory. The relative electronic energies were calculated at the CCSD(T)/cc-pVXZ (where X = D, T) level of theory and further extrapolated to the complete basis set limit. Rate constants for the tittle reactions were calculated over the temperature range of 500‒2500 K by the transition state theory (TST) in conjunction with asymmetric Eckart tunneling effect. In addition, the rate constants of H-abstraction by hydroxyl radical were measured in shock tube experiments at 900‒1321 K and 1.4‒2.0 atm. Our theoretical rate constants of OH + EF → Products agree well with the experimental results within 15% over the experimental temperature range of 900‒1321 K. Branching ratios for the five types of H-abstraction reactions were also determined from their individual site-specific rate constants.

  2. Accurate label-free reaction kinetics determination using initial rate heat measurements

    Science.gov (United States)

    Ebrahimi, Kourosh Honarmand; Hagedoorn, Peter-Leon; Jacobs, Denise; Hagen, Wilfred R.

    2015-01-01

    Accurate label-free methods or assays to obtain the initial reaction rates have significant importance in fundamental studies of enzymes and in application-oriented high throughput screening of enzyme activity. Here we introduce a label-free approach for obtaining initial rates of enzyme activity from heat measurements, which we name initial rate calorimetry (IrCal). This approach is based on our new finding that the data recorded by isothermal titration calorimetry for the early stages of a reaction, which have been widely ignored, are correlated to the initial rates. Application of the IrCal approach to various enzymes led to accurate enzyme kinetics parameters as compared to spectroscopic methods and enabled enzyme kinetic studies with natural substrate, e.g. proteases with protein substrates. Because heat is a label-free property of almost all reactions, the IrCal approach holds promise in fundamental studies of various enzymes and in use of calorimetry for high throughput screening of enzyme activity. PMID:26574737

  3. Effects of the anion salt nature on the rate constants of the aqueous proton exchange reactions.

    Science.gov (United States)

    Paredes, Jose M; Garzon, Andres; Crovetto, Luis; Orte, Angel; Lopez, Sergio G; Alvarez-Pez, Jose M

    2012-04-28

    The proton-transfer ground-state rate constants of the xanthenic dye 9-[1-(2-methyl-4-methoxyphenyl)]-6-hydroxy-3H-xanthen-3-one (TG-II), recovered by Fluorescence Lifetime Correlation Spectroscopy (FLCS), have proven to be useful to quantitatively reflect specific cation effects in aqueous solutions (J. M. Paredes, L. Crovetto, A. Orte, J. M. Alvarez-Pez and E. M. Talavera, Phys. Chem. Chem. Phys., 2011, 13, 1685-1694). Since these phenomena are more sensitive to anions than to cations, in this paper we have accounted for the influence of salts with the sodium cation in common, and the anion classified according to the empirical Hofmeister series, on the proton transfer rate constants of TG-II. We demonstrate that the presence of ions accelerates the rate of the ground-state proton-exchange reaction in the same order than ions that affect ion solvation in water. The combination of FLCS with a fluorophore undergoing proton transfer reactions in the ground state, along with the desirable feature of a pseudo-dark state when the dye is protonated, allows one unique direct determination of kinetic rate constants of the proton exchange chemical reaction. This journal is © the Owner Societies 2012

  4. The chemistry of the carbothermal synthesis of β-SiC : reaction mechanism, reaction rate and grain growth

    NARCIS (Netherlands)

    van Dijen, F.K.; Metselaar, R.

    1991-01-01

    Evidence is given that in the present case the reaction mechanism of ß-SiC formation from silica and carbon is a direct solid-state reaction in which silica migrates over the silicon carbide surface to the carbon. A high value (440 kJ/mol) of activation energy is obtained for this reaction. This

  5. Effects of network dissolution changes on pore-to-core upscaled reaction rates for kaolinite and anorthite reactions under acidic conditions

    KAUST Repository

    Kim, Daesang

    2013-11-01

    We have extended reactive flow simulation in pore-network models to include geometric changes in the medium from dissolution effects. These effects include changes in pore volume and reactive surface area, as well as topological changes that open new connections. The computed changes were based upon a mineral map from an X-ray computed tomography image of a sandstone core. We studied the effect of these changes on upscaled (pore-scale to core-scale) reaction rates and compared against the predictions of a continuum model. Specifically, we modeled anorthite and kaolinite reactions under acidic flow conditions during which the anorthite reactions remain far from equilibrium (dissolution only), while the kaolinite reactions can be near-equilibrium. Under dissolution changes, core-scale reaction rates continuously and nonlinearly evolved in time. At higher injection rates, agreement with predictions of the continuum model degraded significantly. For the far-from-equilibrium reaction, our results indicate that the ability to correctly capture the heterogeneity in dissolution changes in the reactive mineral surface area is critical to accurately predict upscaled reaction rates. For the near-equilibrium reaction, the ability to correctly capture the heterogeneity in the saturation state remains critical. Inclusion of a Nernst-Planck term to ensure neutral ionic currents under differential diffusion resulted in at most a 9% correction in upscaled rates.

  6. Rate Constant and Temperature Dependence for the Reaction of Hydroxyl Radicals with 2-Flouropropane (FC-281ea) and Comparison with an Estimated Rate Constant

    Science.gov (United States)

    DeMore, W.; Wilson, E., Jr.

    1998-01-01

    Relative rate experiments were used to measure the rate constant and temperature dependence of the reaction of OH radicals with 2-fluoropropane (HFC-281ea), using ethane, propane, ethyl chloride as reference standards.

  7. Comparison of measured and calculated reaction rate distributions in an scwr-like test lattice

    Energy Technology Data Exchange (ETDEWEB)

    Raetz, Dominik, E-mail: dominik.raetz@psi.ch [Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland); Jordan, Kelly A., E-mail: kelly.jordan@psi.ch [Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland); Murphy, Michael F., E-mail: mike.murphy@psi.ch [Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland); Perret, Gregory, E-mail: gregory.perret@psi.ch [Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland); Chawla, Rakesh, E-mail: rakesh.chawla@psi.ch [Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland); Ecole Polytechnique Federale de Lausanne (EPFL), CH-1015 Lausanne, EPFL (Switzerland)

    2011-04-15

    High resolution gamma-ray spectroscopy measurements were performed on 61 rods of an SCWR-like fuel lattice, after irradiation in the central test zone of the PROTEUS zero-power research reactor at the Paul Scherrer Institute in Switzerland. The derived reaction rates are the capture rate in {sup 238}U (C{sub 8}) and the total fission rate (F{sub tot}), and also the reaction rate ratio C{sub 8}/F{sub tot}. Each of these has been mapped rod-wise on the lattice and compared to calculated results from whole-reactor Monte Carlo simulations with MCNPX. Ratios of calculated to experimental values (C/E's) have been assessed for the C{sub 8}, F{sub tot} and C{sub 8}/F{sub tot} distributions across the lattice. These C/E's show excellent agreement between the calculations and the measurements. For the {sup 238}U capture rate distribution, the 1{sigma} level in the comparisons corresponds to an uncertainty of {+-}0.8%, while for the total fission rate the corresponding value is {+-}0.4%. The uncertainty for C{sub 8}/F{sub tot}, assessed as a reaction rate ratio characterizing each individual rod position in the test lattice, is significantly higher at {+-}2.2%. To determine the reproducibility of these results, the measurements were performed twice, once in 2006 and again in 2009. The agreement between these two measurement sets is within the respective statistical uncertainties.

  8. Rate constants of chemical reactions from semiclassical transition state theory in full and one dimension

    Energy Technology Data Exchange (ETDEWEB)

    Greene, Samuel M., E-mail: samuel.greene@chem.ox.ac.uk; Shan, Xiao, E-mail: xiao.shan@chem.ox.ac.uk; Clary, David C., E-mail: david.clary@chem.ox.ac.u [Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ (United Kingdom)

    2016-06-28

    Semiclassical Transition State Theory (SCTST), a method for calculating rate constants of chemical reactions, offers gains in computational efficiency relative to more accurate quantum scattering methods. In full-dimensional (FD) SCTST, reaction probabilities are calculated from third and fourth potential derivatives along all vibrational degrees of freedom. However, the computational cost of FD SCTST scales unfavorably with system size, which prohibits its application to larger systems. In this study, the accuracy and efficiency of 1-D SCTST, in which only third and fourth derivatives along the reaction mode are used, are investigated in comparison to those of FD SCTST. Potential derivatives are obtained from numerical ab initio Hessian matrix calculations at the MP2/cc-pVTZ level of theory, and Richardson extrapolation is applied to improve the accuracy of these derivatives. Reaction barriers are calculated at the CCSD(T)/cc-pVTZ level. Results from FD SCTST agree with results from previous theoretical and experimental studies when Richardson extrapolation is applied. Results from our implementation of 1-D SCTST, which uses only 4 single-point MP2/cc-pVTZ energy calculations in addition to those for conventional TST, agree with FD results to within a factor of 5 at 250 K. This degree of agreement and the efficiency of the 1-D method suggest its potential as a means of approximating rate constants for systems too large for existing quantum scattering methods.

  9. A comparison of reaction rate calculations using Endf/B-VII with critical assembly measurements

    International Nuclear Information System (INIS)

    Wilkerson, C.; Mac Innes, M.; Barr, D.; Trellue, H.; MacFarlane, R.; Chadwick, M.

    2008-01-01

    We present critical assembly reaction rate data, and modeling of the same using the recently released Endf/B-VII library. While some of the experimental measurements were performed as long as 50 years ago, the results have not been widely used/available outside of Los Alamos. Over the years, a variety of target foils were fabricated and placed in differing neutron spectrum/fluence environments within critical assemblies. Neutron-induced reactions such as (n,γ), (n,2n), and (n,f) on these targets were measured, typically referenced to 235 U(n,f) or 239 Pu(n,f). Because the cross section for the latter reactions are now well known, these experiments provide a rich data set for testing evaluated cross sections. Due to the large variety of critical assemblies that were historically available at Los Alamos, it was possible to make measurements in spectral environments ranging from hard (Pu Jezebel, center of Pu Flattop) through intermediate (Big Ten) to degraded (reflector region of Flattop). This broad range of configurations allows us to test both the cross section magnitudes and their energy dependencies. We will present data, along with reaction rate predictions using primarily MCNP5 in conjunction with Endf/B-VII, for a number of target nuclei, including iridium, isotopes of uranium (e.g., 233, 235, 237, 238), neptunium (237), plutonium (239), and americium (241). (authors)

  10. Negativization rates of IgE radioimmunoassay and basophil activation test in immediate reactions to penicillins.

    Science.gov (United States)

    Fernández, T D; Torres, M J; Blanca-López, N; Rodríguez-Bada, J L; Gomez, E; Canto, G; Mayorga, C; Blanca, M

    2009-02-01

    Skin test sensitivity in patients with immediate allergy to penicillins tends to decrease over time, but no information is available concerning in vitro tests. We analysed the negativization rates of two in vitro methods that determine specific immunoglobulin E (IgE) antibodies, the basophil activation test using flow cytometry (BAT) and the radioallergosorbent test (RAST), in immediate allergic reactions to penicillins. Forty-one patients with immediate allergic reactions to amoxicillin were followed up over a 4-year period. BAT and RAST were performed at 6-month intervals. Patients were randomized into groups: Group I, skin tests carried out at regular intervals; Group II, skin tests made only at the beginning of the study. Differences were observed between RAST and BAT (P testing influenced the rate of negativization of the RAST assay, contributing to maintenance of in vitro sensitivity. Because of the loss of sensitivity over time, the determination of specific IgE antibodies to penicillins in patients with immediate allergic reactions must be done as soon as possible after the reaction.

  11. Survival behavior in the cyclic Lotka-Volterra model with a randomly switching reaction rate

    Science.gov (United States)

    West, Robert; Mobilia, Mauro; Rucklidge, Alastair M.

    2018-02-01

    We study the influence of a randomly switching reproduction-predation rate on the survival behavior of the nonspatial cyclic Lotka-Volterra model, also known as the zero-sum rock-paper-scissors game, used to metaphorically describe the cyclic competition between three species. In large and finite populations, demographic fluctuations (internal noise) drive two species to extinction in a finite time, while the species with the smallest reproduction-predation rate is the most likely to be the surviving one (law of the weakest). Here we model environmental (external) noise by assuming that the reproduction-predation rate of the strongest species (the fastest to reproduce and predate) in a given static environment randomly switches between two values corresponding to more and less favorable external conditions. We study the joint effect of environmental and demographic noise on the species survival probabilities and on the mean extinction time. In particular, we investigate whether the survival probabilities follow the law of the weakest and analyze their dependence on the external noise intensity and switching rate. Remarkably, when, on average, there is a finite number of switches prior to extinction, the survival probability of the predator of the species whose reaction rate switches typically varies nonmonotonically with the external noise intensity (with optimal survival about a critical noise strength). We also outline the relationship with the case where all reaction rates switch on markedly different time scales.

  12. Survival behavior in the cyclic Lotka-Volterra model with a randomly switching reaction rate.

    Science.gov (United States)

    West, Robert; Mobilia, Mauro; Rucklidge, Alastair M

    2018-02-01

    We study the influence of a randomly switching reproduction-predation rate on the survival behavior of the nonspatial cyclic Lotka-Volterra model, also known as the zero-sum rock-paper-scissors game, used to metaphorically describe the cyclic competition between three species. In large and finite populations, demographic fluctuations (internal noise) drive two species to extinction in a finite time, while the species with the smallest reproduction-predation rate is the most likely to be the surviving one (law of the weakest). Here we model environmental (external) noise by assuming that the reproduction-predation rate of the strongest species (the fastest to reproduce and predate) in a given static environment randomly switches between two values corresponding to more and less favorable external conditions. We study the joint effect of environmental and demographic noise on the species survival probabilities and on the mean extinction time. In particular, we investigate whether the survival probabilities follow the law of the weakest and analyze their dependence on the external noise intensity and switching rate. Remarkably, when, on average, there is a finite number of switches prior to extinction, the survival probability of the predator of the species whose reaction rate switches typically varies nonmonotonically with the external noise intensity (with optimal survival about a critical noise strength). We also outline the relationship with the case where all reaction rates switch on markedly different time scales.

  13. Up-Scaling Geochemical Reaction Rates for Carbon Dioxide (CO2) in Deep Saline Aquifers

    Energy Technology Data Exchange (ETDEWEB)

    Peters, Catherine A

    2013-02-28

    Geochemical reactions in deep subsurface environments are complicated by the consolidated nature and mineralogical complexity of sedimentary rocks. Understanding the kinetics of these reactions is critical to our ability to make long-term predictions about subsurface processes such as pH buffering, alteration in rock structure, permeability changes, and formation of secondary precipitates. In this project, we used a combination of experiments and numerical simulation to bridge the gap between our knowledge of these reactions at the lab scale and rates that are meaningful for modeling reactive transport at core scales. The focus is on acid-driven mineral dissolution, which is specifically relevant in the context of CO2-water-rock interactions in geological sequestration of carbon dioxide. The project led to major findings in three areas. First, we modeled reactive transport in pore-network systems to investigate scaling effects in geochemical reaction rates. We found significant scaling effects when CO2 concentrations are high and reaction rates are fast. These findings indicate that the increased acidity associated with geological sequestration can generate conditions for which proper scaling tools are yet to be developed. Second, we used mathematical modeling to investigate the extent to which SO2, if co-injected with CO2, would acidify formation brines. We found that there exist realistic conditions in which the impact on brine acidity will be limited due to diffusion rate-limited SO2 dissolution from the CO2 phase, and the subsequent pH shift may also be limited by the lack of availability of oxidants to produce sulfuric acid. Third, for three Viking sandstones (Alberta sedimentary basin, Canada), we employed backscattered electron microscopy and energy dispersive X-ray spectroscopy to statistically characterize mineral contact with pore space. We determined that for reactive minerals in sedimentary consolidated rocks, abundance alone is not a good predictor of

  14. Reaction rate distribution measurement and the core performance evaluation in the prototype FBR Monju

    Energy Technology Data Exchange (ETDEWEB)

    Usami, S.; Suzuoki, Z.; Deshimaru, T. [Monju Construction Office, Japan Nuclear Cycle Development Institute, Fukui-ken (Japan); Nakashima, F. [Tsuruga head Office, Japan Nuclear Cycle Development Institute, Fukui-ken (Japan)

    2001-07-01

    Monju is a prototype fast breeder reactor designed to have an output of 280 MW (714 MWt), fueled with mixed oxides of plutonium and uranium and cooled by liquid sodium. The principal data on plant design and performance are shown in Table 1. Monju attained initial criticality in April 1994 and the reactor physics tests were carried out from May through November 1994. The reaction rate distribution measurement by the foil activation method was one of these tests and was carried out in order to verify the core performance and to contribute to the development of the core design methods. On the basis of the reaction rate measurement data, the Monju initial core breeding ratio and the power distribution were evaluated. (author)

  15. Rate coefficients of exchange reactions accounting for vibrational excitation of reagents and products

    Science.gov (United States)

    Kustova, E. V.; Savelev, A. S.; Kunova, O. V.

    2018-05-01

    Theoretical models for the vibrational state-resolved Zeldovich reaction are assessed by comparison with the results of quasi-classical trajectory (QCT) calculations. An error in the model of Aliat is corrected; the model is generalized taking into account NO vibrational states. The proposed model is fairly simple and can be easily implemented to the software for non-equilibrium flow modeling. It provides a good agreement with the QCT rate coefficients in the whole range of temperatures and reagent/product vibrational states. The developed models are tested in simulations of vibrational and chemical relaxation of air mixture behind a shock wave. The importance of accounting for excitated NO vibrational states and accurate prediction of Zeldovich reactions rates is shown.

  16. Efficient kinetic Monte Carlo method for reaction-diffusion problems with spatially varying annihilation rates

    Science.gov (United States)

    Schwarz, Karsten; Rieger, Heiko

    2013-03-01

    We present an efficient Monte Carlo method to simulate reaction-diffusion processes with spatially varying particle annihilation or transformation rates as it occurs for instance in the context of motor-driven intracellular transport. Like Green's function reaction dynamics and first-passage time methods, our algorithm avoids small diffusive hops by propagating sufficiently distant particles in large hops to the boundaries of protective domains. Since for spatially varying annihilation or transformation rates the single particle diffusion propagator is not known analytically, we present an algorithm that generates efficiently either particle displacements or annihilations with the correct statistics, as we prove rigorously. The numerical efficiency of the algorithm is demonstrated with an illustrative example.

  17. Reaction rate distribution measurement and the core performance evaluation in the prototype FBR Monju

    International Nuclear Information System (INIS)

    Usami, S.; Suzuoki, Z.; Deshimaru, T.; Nakashima, F.

    2001-01-01

    Monju is a prototype fast breeder reactor designed to have an output of 280 MW (714 MWt), fueled with mixed oxides of plutonium and uranium and cooled by liquid sodium. The principal data on plant design and performance are shown in Table 1. Monju attained initial criticality in April 1994 and the reactor physics tests were carried out from May through November 1994. The reaction rate distribution measurement by the foil activation method was one of these tests and was carried out in order to verify the core performance and to contribute to the development of the core design methods. On the basis of the reaction rate measurement data, the Monju initial core breeding ratio and the power distribution were evaluated. (author)

  18. IMPACT OF A REVISED {sup 25}Mg(p, {gamma}){sup 26}Al REACTION RATE ON THE OPERATION OF THE Mg-Al CYCLE

    Energy Technology Data Exchange (ETDEWEB)

    Straniero, O.; Cristallo, S. [INAF-Osservatorio Astronomico di Collurania, Teramo (Italy); Imbriani, G.; DiLeva, A.; Limata, B. [INFN Sezione di Napoli, Napoli (Italy); Strieder, F. [Institut fuer Experimentalphysik, Ruhr-Universitaet Bochum, Bochum (Germany); Bemmerer, D. [Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400 (Germany); Broggini, C.; Caciolli, A. [Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Padova, via Marzolo 8, I-35131 Padova (Italy); Corvisiero, P.; Costantini, H.; Lemut, A. [Universita di Genova and INFN Sezione di Genova, Genova (Italy); Formicola, A.; Gustavino, C.; Junker, M. [INFN, Laboratori Nazionali del Gran Sasso (LNGS), Assergi (AQ) (Italy); Elekes, Z.; Fueloep, Zs.; Gyuerky, Gy. [Institute of Nuclear Research (ATOMKI), Debrecen (Hungary); Gervino, G. [Dipartimento di Fisica Universita di Torino and INFN Sezione di Torino, Torino (Italy); Guglielmetti, A., E-mail: straniero@oa-teramo.inaf.it [Universita degli Studi di Milano and INFN, Sezione di Milano (Italy); and others

    2013-02-15

    Proton captures on Mg isotopes play an important role in the Mg-Al cycle active in stellar H-burning regions. In particular, low-energy nuclear resonances in the {sup 25}Mg(p, {gamma}){sup 26}Al reaction affect the production of radioactive {sup 26}Al{sup gs} as well as the resulting Mg/Al abundance ratio. Reliable estimations of these quantities require precise measurements of the strengths of low-energy resonances. Based on a new experimental study performed at the Laboratory for Underground Nuclear Astrophysics, we provide revised rates of the {sup 25}Mg(p, {gamma}){sup 26}Al{sup gs} and the {sup 25}Mg(p, {gamma}){sup 26}Al {sup m} reactions with corresponding uncertainties. In the temperature range 50-150 MK, the new recommended rate of {sup 26}Al {sup m} production is up to five times higher than previously assumed. In addition, at T = 100 MK, the revised total reaction rate is a factor of two higher. Note that this is the range of temperature at which the Mg-Al cycle operates in a H-burning zone. The effects of this revision are discussed. Due to the significantly larger {sup 25}Mg(p, {gamma}){sup 26}Al {sup m} rate, the estimated production of {sup 26}Al{sup gs} in H-burning regions is less efficient than previously obtained. As a result, the new rates should imply a smaller contribution from Wolf-Rayet stars to the galactic {sup 26}Al budget. Similarly, we show that the asymptotic giant branch (AGB) extra-mixing scenario does not appear able to explain the most extreme values of {sup 26}Al/{sup 27}Al, i.e., >10{sup -2}, found in some O-rich presolar grains. Finally, the substantial increase of the total reaction rate makes the hypothesis of self-pollution by massive AGBs a more robust explanation for the Mg-Al anticorrelation observed in globular-cluster stars.

  19. Actinide complexation kinetics: rate and mechanism of dioxoneptunium (V) reaction with chlorophosphonazo III

    International Nuclear Information System (INIS)

    Fugate, G.; Feil-Jenkins, J.F.; Sullivan, J.C.; Nash, K.L.

    1996-12-01

    Rates of complex formation and dissociation in NpO 2 + - Chlorophosphonazo III (2,7-bis(4-chloro-2-phosphonobenzeneazo)-1,8- dihydroxynapthalene-3,6-disulfonic acid)(CLIII) were investigated by stopped-flow spectrophotometry. Also, limited studies were made of the rates of reaction of La 3+ , Eu 3+ , Dy 3+ , and Fe 3+ with CLIII. Rate determining step in each system is an intramolecular process, the NpO 2 + -CLIII reaction proceeding by a first order approach to equilibrium in the acid range from 0.1 to 1.0 M. Complex formation occurs independent of acidity, while both acid dependent and independent dissociation pathways are observed. Activation parameters for the complex formation reaction are ΔH=46.2±0.3 kJ/m and ΔS=7± J/mK (I=1.0 M); these for the acid dependent and independent dissociation pathways are ΔH=38.8±0.6 kJ/m, ΔS=-96±18 J/mK, ΔH=70.0± kJ/m, and ΔS=17±1 J/mK, respectively. An isokinetic relationship is observed between the activation parameters for CLIII complex formation with NpO 2 + , UO 2 2+ , Th 4+ , and Zr 4+ . Rates of CLIII complex formation reactions for Fe 3+ , Zr 4+ , NpO 2 + , UO 2 2+ , Th 4+ , La 3+ , Eu 3+ , and Dy 3+ correlate with cation radius rather than charge/radius ratio

  20. Reactivity and reaction rate studies on the fourth loading of ZENITH

    International Nuclear Information System (INIS)

    Cameron, I.R.; Freemantle, R.G.; Reed, D.L.; Wilson, D.J.

    1963-08-01

    The determination of the excess reactivity, control rod worths, prompt neutron lifetime, flux fine structure, and reaction rates of various nuclides for the fourth loading of the heated zero energy reactor ZENITH is described. The core contains 7.76 kg of U235, giving a carbon/U235 atom ratio of 7578, and forms the most dilute of the range studied. Comparisons of the experimental results with calculations using multigroup diffusion codes are presented. (author)