Thermonuclear Reaction Rates Research Articles

Measurement of the ( [formula omitted]) cross sections of 46Ti, 64Zn, 114Sn, and 116Sn at astrophysically relevant energies

The total cross sections for the Sn 116 ( p , γ ) Sb 117 , Sn 114 ( p , γ ) Sb 115 , Zn 64 ( p , γ ) Ga 65 , and Ti 46 ( p , γ ) V 47 reactions have been measured using an activation technique for protons with center-of-mass energies between about 1 and 4 MeV. Radiative proton captures on 116Sn and 64Zn are compared to previous measurements while extending the measured energy range of the cross sections. From these measurements, astrophysical S-factors have been deduced by integrating NON-SMOKER results which have been scaled to the deduced S-factors in the measured energy range. Comparisons are made to thermonuclear reaction rates from the MOST and NON-SMOKER statistical model calculations. The accuracies of these codes are discussed in light of possible structure differences of the nuclei in question.

Pathway parameter and thermonuclear functions

In the theory of thermonuclear reaction rates, analytical evaluation of thermonuclear functions for non-resonant reactions, including cases with cut-off and depletion of the tail of the Maxwell–Boltzmann distribution function were considered in a series of papers by Mathai and Haubold [A.M. Mathai, H.J. Haubold, Modern Problems in Nuclear and Neutrino Astrophysics, Akademie-Verlag, Berlin, 1988]. In the present paper we study more general classes of thermonuclear functions by introducing a pathway parameter α , so that when α → 1 the thermonuclear functions in the Maxwell–Boltzmannian case are recovered. We will also give interpretations for the pathway parameter α in the case of cut-off and in terms of moments. Non-extensive statistical mechanics, as developed by Tsallis [C. Tsallis, What should a statistical mechanics satisfy to reflect nature? Physica D 193 (2004) 3–34], provides the physical basis for the generalized thermonuclear functions considered in this paper.

First measurement of the 14N([formula omitted])15O cross section down to 70 keV

In stars with temperatures above 20×106 K, hydrogen burning is dominated by the CNO cycle. Its rate is determined by the slowest process, the 14N(p, γ)15O reaction. Deep underground in Italy's Gran Sasso laboratory, at the LUNA 400 kV accelerator, the cross section of this reaction has been measured at energies much lower than ever achieved before. Using a windowless gas target and a 4π BGO summing detector, direct cross section data has been obtained down to 70 keV, reaching a value of 0.24 picobarn. The Gamow peak has been covered by experimental data for several scenarios of stable and explosive hydrogen burning. In addition, the strength of the 259 keV resonance has been remeasured. The thermonuclear reaction rate has been calculated for temperatures 90–300×106 K, for the first time with negligible impact from extrapolations.

CNO reaction rates and chemical abundance variations in dense stellar plasma

In the hot interiors of dense stellar plasma, the equilibrium CNO cycle converts most of the carbon and oxygen into nitrogen. We discuss implications of new measurements concerning the modified thermonuclear CNO reaction rates and the chemical abundance evolution of the stellar core as a function of the temperature. We show that strong CNO abundance variations occur if non-extensive statistical effects, connected to memory plasma effects and long-range force, are taken into account.

Microscopic nuclear models for astrophysics: The Brussels BRUSLIB nuclear library and beyond

Astrophysics is in need of a broad variety of nuclear data. This concerns static ground state properties, characteristics of excited nuclei, spontaneous decay properties, or interactions of nuclei with (mainly) nucleons, α-particles or photons. A strong theoretical activity complementing laboratory efforts is also mandatory. A large variety of highly ‘exotic’ laboratory-unreachable nuclei are indeed involved in the astrophysics modelling. Even when laboratory-studied nuclei are considered, theory has very often to be called for. Mastering the huge volume of nuclear information and making it available in an accurate and usable form for incorporation into astrophysics models is clearly of pivotal importance. The recognition of this necessity has been the driving motivation for the construction of the Brussels library (BRUSLIB) of computed data of astrophysics relevance. It provides an extended information in tabular form on masses, nuclear level densities and partition functions, fission barriers, and thermonuclear reaction rates. In addition of the unprecedented broadness of its scope, BRUSLIB has the unique and most important feature of relying to the largest possible extent on global and coherent microscopic nuclear models. The models of this sort that we have developed to predict the basic properties of the nuclei and of their interactions are briefly reviewed. The content of the BRUSLIB library that relies on these models is described, as well as a user-friendly nuclear network generator (NETGEN) complementing BRUSLIB. Finally, an application of BRUSLIB and NETGEN to the p-process nucleosynthesis during He detonation in sub-Chandrasekhar CO white dwarfs is proposed.

F19αwidths and theF18+preaction rates

Understanding the properties of {sup 19}F levels in the range E{sub x}=6.4-7.5 MeV is important for constraining the contributions of {sup 19}Ne levels to the {sup 18}F(p,{alpha}){sup 15}O and {sup 18}F(p,{gamma}){sup 19}Ne thermonuclear reaction rates. We have reanalyzed {sup 15}N({alpha},{alpha}){sup 15}N data from H. Smotrich et al. [Phys. Rev. 122, 232 (1961)] to determine properties of {sup 19}F levels in this energy range. We find the energies and widths of broad levels to be different than previously reported and have set upper limits on the widths of postulated 3/2{sup +} resonances, analogs of which are important for the {sup 18}F+p rates.

Non-extensive resonant reaction rates in astrophysical plasmas

We study two different physical scenarios of thermonuclear reactions in stellar plasmas proceeding through a narrow resonance at low energy or through the low energy wing of a wide resonance at high energy. Correspondingly, we derive two approximate analytical formulae in order to calculate thermonuclear resonant reaction rates inside very coupled and non ideal astrophysical plasmas in which non-extensive effects are likely to arise. Our results are presented as simple first order corrective factors that generalize the well known classical rates obtained in the framework of Maxwell-Boltzmann statistical mechanics. As a possible application of our results, we calculate the dependence of the total corrective factor with respect to the energy at which the resonance is located, in an extremely dense and non ideal carbon plasma.

Explosive hydrogen burning of 17O in classical novae.

We report on the observation of a new resonance at E(lab)(R)=190 keV in the 17O(p,gamma)18F reaction. The measured resonance strength amounts to omegagamma(pgamma)=(1.2+/-0.2)x10(-6) eV. With this new value, the uncertainties in the 17O(p,gamma)18F and 17O(p,alpha)14N thermonuclear reaction rates are reduced by orders of magnitude at nova temperatures. Our significantly improved reaction rates have major implications for the galactic synthesis of 17O, the stellar production of the radioisotope 18F, and the predicted oxygen isotopic ratios in nova ejecta.

Resonances and thermonuclear reaction rates for charged particle collisions

We derive an approximate analytic expression for thermonuclear reaction rate for charged particles for the case that the cross section contains a single narrow or broad resonance described by a Breit-Wigner shape. An asymptotic series is obtained by making a Taylor series expansion which is exact at both the effective energy of the Gamow window and at the resonance energy. The resulting expression is uniformly valid as the effective energy and resonance energy coalesce or separate and as the resonance width is varied from narrow to broad. This is not true of conventional analytic approximations. We compare our uniform approximation with the exact reaction rate numerically and find it to be accurate over a large parameter range. We use our expressions to calculate the reaction rate for $^{12}\mathrm{C}(p,\ensuremath{\gamma})^{13}\mathrm{N}$.

Resonances and the thermonuclear reaction rate

We present an approximate analytic expression for thermonuclear reaction rate of charged particles when the cross section contains a single narrow or wide resonance described by a Breit-Wigner shape. The resulting expression is uniformly valid as the effective energy and resonance energy coalesce. We use our expressions to calculate the reaction rate for 12C(p,γ) 13N.

Analytic expansions of thermonuclear reaction rates

The evaluation of thermonuclear reaction rates requires the calculation of several thermonuclear functions. These functions can be written as the Laplace transform of locally integrable functions which have an asymptotic expansion in negative rational powers of their variable. In this paper we obtain asymptotic expansions of the Laplace transform of these kinds of functions for small values of the parameter of the transformation. Error bounds are obtained at any order of the approximation for a large family of Laplace transforms which include thermonuclear functions. Then we apply this asymptotic theory to the calculation of convergent expansions of four thermonuclear functions in powers of the dimensionless Sommerfeld parameter. Some of these expansions also involve logarithmic terms in the dimensionless Sommerfeld parameter. Accurate error bounds are given at any order of the approximation.

Light element nucleosynthesis from jet-cloud interactions in active galactic nuclei

The production of light nuclei via the interactions of jets from the central engines of active galactic nuclei (AGNs) and the surrounding medium are studied. Several environments ranging from hot, dense knots of gas near the central engine to the cold broad line region clouds are simulated by a nuclear reaction network that couples the thermonuclear processes in the cloud to the reactions between the jet particles and the cloud. Reaction products from the jet-cloud interactions are followed until they react or are thermalized, which may involve several subsequent reactions. Enhanced production of light nuclei well above their primordial abundances is possible even, under some conditions, of CNO nuclei. In these scenarios, the jets can enhance abundances of CNO nuclei by first producing excess amounts of nuclei with A<8, then by increasing the cloud density to the point at which the thermonuclear reaction rates become important. The comparison to observed abundances in quasars (QSOs) leads to the conclusion that the interactions of ejected matter from AGNs may be responsible for large observed abundances of light nuclei in addition to significant abundances of nuclei in the CNO region.

The 45V(p,γ) thermonuclear reaction rate relevant to 44Ti production rate in core-collapsed supernovae: a shell model analysis

The 45V(p,γ) thermonuclear reaction rate relevant to 44Ti production rate in core-collapsed supernovae: a shell model analysis

Enhancement of Resonant Thermonuclear Reaction Rates in Extremely Dense Stellar Plasmas

The enhancement factor of the resonant thermonuclear reaction rates is calculated for the extremely dense stellar plasmas in the liquid phase. In order to calculate the enhancement factor we use the screening potential which is deduced from the numerical experiment of the classical one-component plasma. It is found that the enhancement is tremendous for white dwarf densities if the ^{12}C + ^{12}C fusion cross sections show resonant behavior in the astrophysical energy range. We summarize our numerical results by accurate analytic fitting formulae.

The Effects of Thermonuclear Reaction‐Rate Variations on Nova Nucleosynthesis: A Sensitivity Study

We investigate the effects of thermonuclear reaction rate uncertainties on nova nucleosynthesis. One-zone nucleosynthesis calculations have been performed by adopting temperature-density-time profiles of the hottest hydrogen-burning zone (i.e., the region in which most of the nucleosynthesis takes place). We obtain our profiles from 7 different, recently published, hydrodynamic nova simulations covering peak temperatures in the range from Tpeak=0.145-0.418 GK. For each of these profiles, we individually varied the rates of 175 reactions within their associated errors and analyzed the resulting abundance changes of 142 isotopes in the mass range below A=40. In total, we performed 7350 nuclear reaction network calculations. We use the most recent thermonuclear reaction rate evaluations for the mass ranges A=1-20 and A=20-40. For the theoretical astrophysicist, our results indicate the extent to which nova nucleosynthesis calculations depend on presently uncertain nuclear physics input, while for the experimental nuclear physicist our results represent at least a qualitative guide for future measurements at stable and radioactive ion beam facilities. We find that present reaction rate estimates are reliable for predictions of Li, Be, C and N abundances in nova nucleosynthesis. However, rate uncertainties of several reactions have to be reduced significantly in order to predict more reliable O, F, Ne, Na, Mg, Al, Si, S, Cl and Ar abundances. Results are presented in tabular form for each adopted nova simulation.

Light‐Element Nucleosynthesis From Jet‐Cloud Interactions in Active Galactic Nuclei

The production of light nuclei via the interactions of jets from the central engines of active galactic nuclei and the surrounding medium is studied. Several environments ranging from hot, dense knots of gas near the central engine to the cold broad-line region clouds are simulated by a nuclear reaction network that couples the thermonuclear processes in the cloud to the reactions between the jet particles and the cloud. Reaction products from the jet-cloud interactions are followed until they react or are thermalized, which may involve several subsequent reactions. The effects of nucleosynthesis from the introduction of a jet into the cloud can result in enhanced production of light nuclei well above their primordial abundances, and enhancement of CNO nuclei is also predicted above thermally produced abundances. In these scenarios, the jets can enhance abundances of CNO nuclei by first producing excess amounts of nuclei with A < 8, then by increasing the cloud density to the point at which the thermonuclear reaction rates become important. The comparison to observed abundances in quasars leads to the conclusion that the interactions of ejected matter from AGNs may be responsible for large observed abundances of light nuclei in addition to significant abundances of nuclei in the CNO region.

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

We study the astrophysical reaction rate for the formation of 9Be 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 8Be, α+α⇌8Be(n,γ)9Be. Off-resonant and on-resonant contributions from the ground state in 8Be are taken into account. As input cross section, we adopt the latest experimental data by photodisintegration of 9Be with laser-electron photon beams, which covers all relevant resonances in 9Be. 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)9Be in the temperature range from T9=10−3 to T9=101 (T9 is the temperature in units of 109 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 9Be by Berman et al., is valid at T9>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 T9⩾0.1. The NACRE rate, which adopted different sources of experimental information on resonance states in 9Be, is 4–12 times larger than the present rate at T9⩽0.028, but is consistent with the present rate to within ±20% at T9⩾0.1.

Collective plasma corrections to thermonuclear reaction rates in dense plasmas

General kinetic equations are derived for nuclear reactions in dense plasmas by taking into account first-order collective plasma effects. We show that, apart from the corrections proportional to the product of the charges Z i and Z j of two reacting nuclei i and j, new corrections comparable in magnitude and proportional to the squares of the nuclear charges Z i 2 and Z j 2 arise. The Salpeter corrections [1] to the nuclear reaction probabilities due to the plasma screening of the interaction potential are shown to be at least a factor of r/d (r is the nuclear size and d is the Debye screening length) smaller than those assumed previously. These are zero in the approximation where the terms of order r/d are disregarded. The correlation corrections proportional to Z iZj have a different physical meaning than those in [1], can have a different sign, and arise for reactions with zero Salpeter corrections. For the correlation corrections that substitute for the previously used Salpeter corrections, strong correlations are difficult to describe analytically. The interpolation formulas between weak and strong Salpeter screenings previously used in many astrophysical applications are inapplicable, because the interpolation formulas between weak and strong correlations cannot yet be obtained. We found a new type of corrections that are proportional to the squares of the charges of reacting nuclei. These are attributable to a change in the collective electrostatic self-energy of the plasma system during nuclear reactions. Plasma corrections for the hydrogen-cycle nuclear reactions are numerically calculated for the temperature, density, and abundances in the solar interior.

Measurement of the nuclear reaction7Li(3He,p0)9Beat low energies

The nuclear reaction ${}^{7}\mathrm{Li}{(}^{3}\mathrm{He}{,p}_{0}{)}^{9}\mathrm{Be}$ was measured at effective center-of-mass energies of $E=106.3$ and $E=112.8\mathrm{keV}$ with the 180-kV Cockcroft-Walton accelerator at the Colorado School of Mines. As this reaction is a possible contributor to inhomogeneous big bang nucleosynthesis, all published data were compiled and used, together with our measurement, in a calculation of the thermonuclear reaction rate for temperatures up to ${10}^{9}\mathrm{K}.$

A Contribution of [TSUP]26[/TSUP]A[CLC]l[/CLC] to the O-A[CLC]l[/CLC] Anticorrelation in Globular Cluster Red Giants

We modify our combined (deep mixing plus primordial) scenario explaining the star-to-star abundance variations in globular cluster red giants in such a way that it confirms with new experimental data: (i) the new and better constrained (NACRE) thermonuclear reaction rates and (ii) a discovery of the O-Na anticorrelation in stars below the main-sequence turn-off in the cluster NGC6752. For the latter we propose that some main-sequence dwarfs in globular clusters accrete material lost by red giant primary components of close binaries during a common envelope event. As a consequence of the new reaction rates, we are drawn to the conclusion that the anomalies in [Al/Fe] in globular cluster red giants are in fact manifestations of 26Al (instead of the stable isotope 27Al) abundance variations produced by deep mixing.