Explosive hydrogen burning

Under astrophysical conditions of extreme temperature and density, nuclear reactions can occur with rates that are comparable to a dynamical free-fall time, i.e. on the order of seconds. Explosive hydrogen burning will take place in a number of sites, most notably in cataclysmic binary systems (including novae and some x-ray bursts), and during Type II supernovae. The former objects are thought to be thermonuclear outbursts triggered by mass accretion onto the surface of either a white dwarf or a neutron star. A knowledge of the relevant nuclear reaction cross sections is therefore critical to our understanding of the outburst phenomenon itself. In particular, this information determines the amount of energy generated to power the outburst and the inventory of elements produced. These results may be compared with direct observations to provide a tight constraint on models of these systems. Much useful information can be obtained from the nucleosynthesis itself. For example, measurements of absolute and relative elemental abundances, combined with nucleosynthesis calculations , could yield information regarding the physical conditions during the explosion. Also, if a detectable amount of a gamma-ray emitter such as 22Na or 26 Al is produced, then observations of the gamma-ray flux over time may shed some light on how the ejecta are mixed into the interstellar medium . The nuclei of active galaxies are thought to be powered by a similar mechanism, in this case mass accretion by massive black holes. As a result, much of what we learn by studying cataclysmic binaries might also be applied to models of active galaxies. In the case of supernovae, explosive hydrogen burning is incidental to the underlying explosion mechanism. However, nucleosynthetic yields are again useful in probing the explosion. In addition , since supernovae are major sources of heavy elements, explosive nucleosynthesis is responsible for much of galactic chemical evolution

Sodium enrichment in A-F type supergiants

We have investigated the nucleosynthesis of sodium (23Na) in stars of masses M = 5-19 M⊙ having solar-like initial chemical composition. The values obtained for the Na excess after the first dredge-up phase are in close agreement with recent observations suggesting a moderate Na excess in F-type supergiants. We also found a positive correlation between the overabundance factors [N/H] and [Na/H] which seems to indicate that Na enrichment originates from the Ne-Na cycle operating simultaneously with the CNO tri-cycle in these stars. We emphasize that our results were obtained on the basis of standard physical assumptions in the stellar model calculations, but with updated reaction rates for the reactions involved in the Ne-Na cycle which are presented in this work

Ne22(d,p)23Ne reaction and neutron balance in the s process

One possible source of neutrons for the astrophysical s process is the Ne22(n)25Mg reaction. However, the number of neutrons available to synthesize heavy elements may be limited by the rate of the Ne22(n,)23Ne reaction. To aid in the interpretation of recent (n,) measurements, we have used the Ne22(d,p)23Ne reaction to investigate the single-particle structure of states located near the Ne22+n threshold. No states that correspond to astrophysically significant resonances were found, and so the (n,) rate is effectively determined by direct capture

On the production of26A1 in the early solar system by low-energy oxygen cosmic rays

Clayton & Jin have proposed that the high abundance of 26Al found in meteorites was produced by cosmic rays in the early solar system through the 12C(16O,x)26Ales reaction. We have measured the yield of 26A1 in the ground state (i.e., 26Algs) from this reaction and find that, if this mechanism produced the meteoritic 26Al, a substantial fraction of the solar system oxygen must have entered the solar system as low-energy cosmic rays. This does not seem plausible. If the proto-Sun itself was the source of the oxygen cosmic rays, they must have carried off some 5% of the power of the protosolar wind for 1 Myr. This too seems unlikely. Although we do not address the role of other cosmic-ray species in the production of26 Al, it appears that 26A1 was produced in a stellar environment, and not by cosmic rays

Theoretical evaluation of the reaction rates for Al26(n,p)26Mg and Al26(n,α)23Na

The reactions that destroy Al26 in massive stars have significance in a number of astrophysical contexts. We evaluate the reaction rates of Al26(n,p)26Mg and Al26(n,α)23Na using cross sections obtained from the codes empire and talys. These have been compared to the published rates obtained from the non-smoker code and to some experimental data. We show that the results obtained from empire and talys are comparable to those from non-smoker. We also show how the theoretical results vary with respect to changes in the input parameters. Finally, we present recommended rates for these reactions using the available experimental data and our new theoretical results

Nuclear astrophysics in the laboratory and in the universe

Nuclear processes drive stellar evolution and so nuclear physics, stellar models and observations together allow us to describe the inner workings of stars and their life stories. This Information on nuclear reaction rates and nuclear properties are critical ingredients in addressing most questions in astrophysics and often the nuclear database is incomplete or lacking the needed precision. Direct measurements of astrophysically-interesting reactions are necessary and the experimental focus is on improving both sensitivity and precision. In the following, we review recent results and approaches taken at the Laboratory for Experimental Nuclear Astrophysics (LENA, http://research. physics.unc.edu/project/nuclearastro/Welcome.html)

Low-lying levels in Pm148

The Sm149(d,3He) reaction has been used to populate levels in Pm148. Nineteen new excited states have been observed below 1 MeV excitation energy in Pm148. The possible astrophysical implications of these results are discussed

Charged-particle thermonuclear reaction rates: III. Nuclear physics input

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

New recommended ωγ for the Er c. m. =458 keV resonance in Ne 22 (p,γ) Na 23

The Erc.m.=458 keV resonance in Ne22(p,γ)Na23 is an ideal reference resonance for measurements of cross sections and resonance strengths in noble gas targets. We report on a new measurement of the strength of this resonance. Data analysis employed the TFractionFitter class of root combined with geant simulations of potential decay cascades from this resonance. This approach allowed us to extract precise primary branching ratios for decays from the resonant state, including a new primary branch to the 7082-keV state in Na23. Our new resonance strength of ωγ(458 keV) = 0.583(43) eV is more than 1σ higher than a recent high-precision result that relied on literature branching ratios

Measurement of the ER=338 keV resonance strength for 23Na(p,a)20Ne

The absolute strength of the [Formula Presented] resonance for [Formula Presented] has been determined. The experiment was carried out by measuring the number of resonant [Formula Presented] particles, integrated over the yield curve, simultaneously with the number of Rutherford scattered protons. The method applied in the present work is independent of target stoichiometry, uniformity, stopping power, beam straggling, and current integration. For the resonance strength, we obtained a value of [Formula Presented] Previous results are systematically higher, because the change of target stoichiometry under proton bombardment was not taken into account. With proper consideration, the present method can also be applied to other low-energy [Formula Presented] resonances