37344886
Reaction rate for destruction of 7Li and primordial nucleosynthesis.
The rate for destruction of [sup 7]Li via deuteron-induced reactions is reexamined and is found to be appreciably larger than that previously used in primordial nucleosynthesis codes over most of the temperature region of interest. Numerous calculations were run to determine the significance of the new rate; it was found to change the predicted [sup 7]Li abundance by not more than 20% over the parameter space examined.
14018179
Evolution of massive stars up to the end of central oxygen burning
We present a detailed study of the evolution of massive stars of masses 15, 20, 25, and 30 M☉ assuming solar-like initial chemical composition. The stellar sequences were evolved through the advanced burning phases up to the end of core oxygen burning. We present a careful analysis of the physical characteristics of the stellar models. In particular, we investigate the effect of the still-unsettled reaction 12C(α,γ)16O on the advanced evolution by using recent compilations of this rate. We find that this rate has a significant impact on the evolution not only during the core helium burning phase but also during the late burning phases, especially the shell carbon burning. We have also considered the effect of different treatments of convective instability based on the Ledoux criterion in regions of varying molecular weight gradient during the hydrogen- and helium-burning phases. We compare our results with other investigations whenever available. Finally, our present study constitutes the basis of analyzing the nucleosynthesis processes in massive stars. In particular, we will present a detailed analysis of the s-process in a forthcoming paper.
53066200
Source of the Rare-Earth Element Peak in r-Process Nucleosynthesis
We use network calculations of r -process nucleosynthesis to pin down the origin of the peak in the solar r -process abundance distribution near nuclear mass number A{approx}160 . The peak is due to a subtle interplay of nuclear deformation and {beta} decay, and forms not in the steady phase of the r process, but only just prior to freeze-out, as the free neutrons rapidly disappear. Its existence should therefore help constrain the conditions under which the r process freezes out. {copyright} {ital 1997} {ital The American Physical Society}
120235748
Neutrino capture and r-process nucleosynthesis
Neutrino capture effects on free nucleons and heavy nuclei in r-process nucleosynthesis are discussed. Neutrino capture on heavy nuclei can “accelerate” the r-process; however, the dominant role neutrino capture plays is to set the neutron-to-proton ratio. In fact, network calculations indicate that neutrino capture on heavy nuclei is unlikely to be significant for r-process components that produce nuclei with mass number A near 195. The reason is that if the neutrino flux is sufficiently large to cause neutrino capture on heavy nuclei to be important, it was even larger in a earlier phase when 4He and neutrons dominated the abundances and capture on the free neutrons drastically reduced the neutron-to-seed-nucleus ratio.
121834079
General constraints on the age and chemical evolution of the Galaxy
The formalism of Schramm and Wasserburg (1970) for determining the mean age of the elements is extended. Model-independent constraints (constraints that are independent of a specific form for the effective nucleosynthesis rate and Galactic chemical evolution over time) are derived on the first four terms in the expansion giving the mean age of the elements, and from these constraints limits are derived on the total duration of nucleosynthesis. These limits require only input of the Schramm-Wasserburg parameter ..delta../sup max/ and of the ratio of the mean time for formation of the elements to the total duration of nucleosynthesis, t/sub nu//T. The former quantity is a function of nuclear input parameters. Limits on the latter are obtained from constraints on the relative rate of nucleosynthesis derived from the /sup 232/Th//sup 238/U, /sup 235/U//sup 238/U, and shorter-lived chronometric pairs. 65 refs.
121296909
MUONS PRODUCED BY ATMOSPHERIC NEUTRINOS: EXPERIMENT.
2491512
Space-time as a causal set.
We propose that space-time at the smallest scales is in reality a causal set: a locally finite set of elements endowed with a partial order corresponding to the macroscopic relation that defines past and future. We explore how a Lorentzian manifold can approximate a causal set, noting in particular that the thereby defined effective dimensionality of a given causal set can vary with length scale. Finally, we speculate briefly on the quantum dynamics of causal sets, indicating why an appropriate choice of action can reproduce general relativity in the classical limit.