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Angular Distribution Of Interstellar Al-26, Mark D. Leising, Donald D. Clayton
Angular Distribution Of Interstellar Al-26, Mark D. Leising, Donald D. Clayton
Publications
The angular distribution and local concentration of interstellar Al-26 are calculated for five theoretical models of its origin, as a guide for future observations. The models considered relate Al-26 to current star formation (with surface CO density as its indicator), treat Al-26 as a secondary-nucleosynthesis product on seed nuclei with the same metallicity gradient as O, assume the Al-26 ejection rate is proportional to present light output, make Al-26 synthesis depend on total H I + H2 gas density, or assume that Al-26 is formed mainly in novae. The local decay and production rates for the five models are found …
Astration Of Cosmological Deuterium, Donald D. Clayton
Astration Of Cosmological Deuterium, Donald D. Clayton
Publications
Attention is given to the degree of primordial deuterium's astration through the continuous galactic processes of star formation and chemical evolution. Exact analytic solutions are given for galactic chemical evolution when infall of constant composition occurs at a rate, f(t), which is presently defined. Solutions are given for the linear model with instantaneous recycling and with constant return fraction R. The results suggest that Big Bang D/H was at least three times larger than the largest values observed in today's solar neighborhood, and even larger if matter falling into the disk is already astrated.
Galactic Chemical Evolution And Nucleocosmochronology: Analytic Quadratic Models, Donald D. Clayton
Galactic Chemical Evolution And Nucleocosmochronology: Analytic Quadratic Models, Donald D. Clayton
Publications
The author presents a new analytic model of the chemical evolution of the galaxy. Explicit solutions for a gas mass, star mass, metallicity, and radiochronometers are obtained for models with parametrized galactic infall, and for which the star formation rate is proportional to the gas mass. Because all physically interesting observables have a simple explicit dependence on the parameters which themselves map a wide space of physical possibilites, the author suggests adopting this model as a reference standard for studies of chemical evolution.
Galactic Chemical Evolution And Nucleocosmochronology: Standard Model With Terminated Infall, Donald D. Clayton
Galactic Chemical Evolution And Nucleocosmochronology: Standard Model With Terminated Infall, Donald D. Clayton
Publications
Some exactly soluble families of models for the chemical evolution of the Galaxy are presented. The parameters considered include gas mass, the age-metallicity relation, the star mass vs. metallicity, the age distribution, and the mean age of dwarfs. A short BASIC program for calculating these parameters is given. The calculation of metallicity gradients, nuclear cosmochronology, and extinct radioactivities is addressed. An especially simple, mathematically linear model is recommended as a standard model of galaxies with truncated infall due to its internal consistency and compact display of the physical effects of the parameters.
Discovery Of S-Process Nd In Allende Residue, Donald D. Clayton
Discovery Of S-Process Nd In Allende Residue, Donald D. Clayton
Publications
New interpretation is given to the isotopic anomalies detected by Lugmair et al. in an acid-resistant residue of the Allende meteorite. If the 142Nd excess is due to 146Sm decay, as the discoverers proposed, the author argues that the decay has occurred in interstellar grains, so that the conclusion that 146Sm (1.03×108 yr) was alive in the solar system is premature. It is shown that the discovery is likely to be s-process Nd, confirming the survival of red-giant stardust in carbonaceous interstellar dust.
Extinct Radioactivities: A Three-Phase Mixing Model, Donald D. Clayton
Extinct Radioactivities: A Three-Phase Mixing Model, Donald D. Clayton
Publications
A new class of models is advanced for interpreting the relationship of radioactive abundances in the early solar system to their average concentration in the interstellar medium. The model assumes that fresh radioactivities are ejected from supernovae into the hot interstellar medium, and that the time scales for changes of phase into molecular clouds determine how much survives for formation therein of our solar system. A more realistic and physically motivated understanding of the low observed concentrations of 129I, 244Pu, and 107Pd may result.
S-Process Studies In The Light Of New Experimental Cross Sections: Distribution Of Neutron Fluences And R-Process Residuals, F Kaeppeler, H Beer, K Wisshak, Donald D. Clayton, R L. Macklin, Richard A. Ward
S-Process Studies In The Light Of New Experimental Cross Sections: Distribution Of Neutron Fluences And R-Process Residuals, F Kaeppeler, H Beer, K Wisshak, Donald D. Clayton, R L. Macklin, Richard A. Ward
Publications
A best set of neutron-capture cross sections has been evaluated for the most important s-process isotopes. With this data base, s-process studies have been carried out using the traditional model which assumes a steady neutron flux and an exponential distribution of neutron irradiations. The calculated sigma-N curve is in excellent agreement with the empirical sigma-N-values of pure s-process nuclei. Simultaneously, good agreement is found between the difference of solar and s-process abundances and the abundances of pure r-process nuclei. The abundance pattern of the iron group elements where s-process results complement the abundances obtained from explosive nuclear burning is discussed. …
Origin Of Ca-Al-Rich Inclusions. Ii. Sputtering And Collisions In The Three-Phase Interstellar Medium, Donald D. Clayton
Origin Of Ca-Al-Rich Inclusions. Ii. Sputtering And Collisions In The Three-Phase Interstellar Medium, Donald D. Clayton
Publications
The theory put forward by Clayton (1977) for the formation of the Ca-Al-rich inclusions within C3 meteorites is extended to an evolutionary history in a three-phase interstellar medium. Widespread supersonic turbulence in the hot interstellar medium is maintained by supernova shock waves, giving rise to heavy sputtering of the refractory dust. Subsequent reaccumulation with varying dust/gas ratios or varying particle sizes produces isotopically fractionated Ca-Al-rich accumulates. It is thought that the Ca-Al-rich inclusions themselves are formed by the following sequence in the solar system: (1) cold accumulation of larger-than-average Ca-Al-rich particles containing supernova condensate cores into macroscopic (approximately 1 cm) …
7li Gamma-Ray Lines From Novae, Donald D. Clayton
An Interpretation Of Special And General Isotopic Anomolies In R-Process Nuclei, Donald D. Clayton
An Interpretation Of Special And General Isotopic Anomolies In R-Process Nuclei, Donald D. Clayton
Publications
My analysis of new discoveries by McCulloch and Wasserburg of Ba and Nd isotopic anomalies in inclusions of the Allende meteorite argues that (1) these anomalies contain special extinct radioactivities resulting from radioactive decay within grains formed in and ejected from the supernova interior, (2) the inclusions studied are fused assemblies of interstellar grains that were never totally vaporized, and (3) theoretical separation into r and s abundances suggests that fluctuations between r and s components has occurred during the accumulation processes. These points lend support to a new chemical picture of the early solar system that I have developed, …
Author's Reply: Extinct Radioactivities As Trapped Residuals Of Presolar Grains, Donald D. Clayton
Author's Reply: Extinct Radioactivities As Trapped Residuals Of Presolar Grains, Donald D. Clayton
Publications
Trivedi's attempted disproof of presolar grains as carriers of special 129Xe* in meteorites is rejected on three grounds: (1) the high-T losses of 129Xe* and 1271 are tightly correlated, (2) the sharply isochronous meteorites are partially differentiated but not truly metamorphosed, and (3) evidence that much of solar 129Xe was trapped in presolar grains has strengthened the plausibility of the presolar-grain picture.
Gamma-Ray Emission And Nucleosynthesis Of Lithium By Young Pulsars, Donald D. Clayton, Eliahu Dwek
Gamma-Ray Emission And Nucleosynthesis Of Lithium By Young Pulsars, Donald D. Clayton, Eliahu Dwek
Publications
We propose that 7Li is produced in the Galaxy primarily by α-α collisions surrounding newly born pulsars. About 10 percent of the pulsar energy losses are converted to medium-energy α-particles which collide in a dominantly He nebula. The problem of the origin of lithium would be solved by the scenario, and clear-cut tests by nuclear γ-ray astronomy are described.
S-Process Studies: Branching And The Time Scale, Richard A. Ward, Michael J. Newman, Donald D. Clayton
S-Process Studies: Branching And The Time Scale, Richard A. Ward, Michael J. Newman, Donald D. Clayton
Publications
The theory of S-process heavy-element formation is reformulated to allow for competition between beta decay and neutron capture at various nuclei along the path. Solutions to the resulting branching network equations are presented (under the assumption of constant temperature and neutron flux) that do not require steady flow for the neutron current. Using the exponential exposure distribution rho (tau) =G exp(-tau/tau0) and recently calculated temperature-dependent beta-decay rates, comparison of several key branches yields the following average conditions for the solar-system S-process environment: Tapprox. =3.1 x 108 K, n/subn/approx. =1.6 x 107 neutrons cm-3. For tau0=0.25 n mb-1 we find that …
Extinct Radioactivities: Trapped Residuals Of Presolar Grains, Donald D. Clayton
Extinct Radioactivities: Trapped Residuals Of Presolar Grains, Donald D. Clayton
Publications
The xenon anomalies trapped in meteorites and the moon may have first been trapped in circumstellar grains formed in or outside of postexplosive stars. In that case, the initial solar nebula need not have contained most of their radioactive progenitors, and this would necessitate major revision of the history of solar system formation.
S-Process Studies: Exact Evaluation Of An Exponential Distrubution Of Exposures, Donald D. Clayton, Richard A. Ward
S-Process Studies: Exact Evaluation Of An Exponential Distrubution Of Exposures, Donald D. Clayton, Richard A. Ward
Publications
We show that the solution of the s-process chain can be easily evaluated exactly if the seed nuclei have been irradiated with an exponential distribution of exposures. For the same distribution of exposures, the shape of the akNk curve past the last seed is independent of the distribution of seed nuclei. Evaluation of these results confirms the accuracy of the well-known CFHZ approximation.
On The E-Process: Its Components And Their Neutron Excesses, Kem L. Hainebach, Donald D. Clayton, W David Arnett, S E. Woosley
On The E-Process: Its Components And Their Neutron Excesses, Kem L. Hainebach, Donald D. Clayton, W David Arnett, S E. Woosley
Publications
The pattern of abundances within the iron-abundance peak of the solar system is analyzed for various Cr, Fe, and Ni abundances, and a method is developed for finding the best fit to a given set of abundances with a chosen number of zones, i.e., mass contributions characterized by differing values of eta. This material can be synthesized by a superposition of e-process compositions in a low-eta region (eta = 0.003) and a high-eta region (eta = 0.065 -0.080) with at least 85% coming from the low-eta region. Addition of a third eta zone is unproductive. The applicability of the particle-poor …
S-Process Studies: Exact Solution To A Chain Having Two Distinct Cross-Section Values, Donald D. Clayton, Michael J. Newman
S-Process Studies: Exact Solution To A Chain Having Two Distinct Cross-Section Values, Donald D. Clayton, Michael J. Newman
Publications
We present the exact solution to an s-process chain having two distinct values for the cross-sections. The comparison of this exact solution with the CFHZ approximate solution to the same problem reveals that approximate solution to be adequate for most astrophysical problems.
Nucelosynthesis In White-Dwarf Atmospheres, Fred Hoyle, Donald D. Clayton
Nucelosynthesis In White-Dwarf Atmospheres, Fred Hoyle, Donald D. Clayton
Publications
Consideration of events by which both s- and r-process nucleosynthesis may occur on the surfaces of white-dwarf stars. The main requirement is that the accreted hydrogen be mixed with comparable numbers of C-12 (or other alpha nuclei) before a runaway capture of protons takes place. Subsequent events offer many possibilities for nucleosynthesis and stars of peculiar composition. A new mechanism for a surface s-process due to few-MeV protons is also described. Concluding comments concern cosmic gamma-ray bursts and the origin of anomalous low-energy galactic cosmic rays.
Coulomb De-Excitation Of C12 In A Helium Gas At High Density And Temperature, P B. Shaw, Donald D. Clayton
Coulomb De-Excitation Of C12 In A Helium Gas At High Density And Temperature, P B. Shaw, Donald D. Clayton
Publications
The report contains calculations of the extent to which the formation of C12 nuclei is speeded up in a dense hot helium plasma by the Coulomb de-excitation of its transiently formed excited states.