Late-time dissipation of primordial baryon-number fluctuations and nucleosynthesis.
Author(s): Alcock, CR; Dearborn, DS; Fuller, GM; Mathews, GJ; Meyer, BS |  Primordial baryon-number fluctuations can be damped at temperatures 20 keV when the photon mean free path becomes larger than the high-density-region length scale. This dissipation process may result in mixing of the high- and low-density material on a time scale comparable to or shorter than that of the universal expansion. The nucleosynthesis yields in inhomogeneous cosmologies can be altered by this process for any ©b. Li7 can be reduced to an abundance consistent with observations of Population II halo stars and the abundances of Be9 and B10 can be reduced by several orders of magnitude.

title: Neutrino capture and r-process nucleosynthesis
abstract: 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.

title: Source of the Rare-Earth Element Peak in r-Process Nucleosynthesis
abstract: 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.

title: Evolution of massive stars up to the end of central oxygen burning
abstract: 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.

title: MUONS PRODUCED BY ATMOSPHERIC NEUTRINOS: EXPERIMENT.

title: General constraints on the age and chemical evolution of the Galaxy
abstract: 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.

title: Experimental study of muon bundles observed in the Fréjus detector.
abstract: The present study is based on a sample of 407 775 single muons and 12 559 muon bundles with zenith angles smaller than 60{degree}, observed in the 12.3 m{times}6 m{times}6 m Frejus proton-decay detector, at a depth of 4850 hg/cm{sup 2}. The variation of the vertical muon intensity with depth is given. Using a maximum-likelihood method, the muon lateral distribution of underground bundles is investigated as a function of muon multiplicity and zenith angle. The same method yields the true multiplicity distribution at the site depth, corrected for all detection effects.