Stellar Abundances in the Early Galaxy and Two r-Process Components

We present quantitative predictions for the abundances of r-process elements in stars formed very early in the Galactic history using a phenomenological two-component r-process model based on the I129 and Hf182 inventory in the early solar system. This model assumes that a standard mass of the ISM dilutes the debris from an individual supernova. High frequency supernova H events and low frequency supernova L events are proposed in the model with characteristics determined by the meteoritic data on I129 and Hf182. The yields in an H or L event are obtained from these characteristics and the solar r-process abundances under the assumption that the yield template for the high mass (A > 130) nuclei associated with W182 or the low mass (A < or = 130) nuclei associated with I127 is the same for both the H and L events and follows the corresponding solar r-pattern in each mass region. The abundance of Eu, not Fe, is proposed as a key guide to the age of very metal-poor stars. We predict that stars with log epsilon (Eu) = -2.98 to -2.22 were formed from an ISM contaminated most likely by a single H event within the first 10**7 yr of the Galactic history and should have an Ag/Eu abundance ratio less than the corresponding solar r-process value by a factor of at least 10. Many of the very metal-poor stars observed so far are considered here to have been formed from an ISM contaminated by many (about 10) r-process events. Stars formed from an ISM contaminated only by a pure L event would have an Ag/Eu ratio higher than the corresponding solar r-process value but would be difficult to find due to the low frequency of the L events. However, variations in the relative abundances of the low and high mass regions should be detectable in very metal-poor stars.Comment: 46 pages, 19 figures, to appear in the Schramm Memorial Volume of Physics Report

Short-lived Nuclei in the Early Solar System: Possible AGB Sources

(Abridged) We review abundances of short-lived nuclides in the early solar system (ESS) and the methods used to determine them. We compare them to the inventory for a uniform galactic production model. Within a factor of two, observed abundances of several isotopes are compatible with this model. I-129 is an exception, with an ESS inventory much lower than expected. The isotopes Pd-107, Fe-60, Ca-41, Cl-36, Al-26, and Be-10 require late addition to the solar nebula. Be-10 is the product of particle irradiation of the solar system as probably is Cl-36. Late injection by a supernova (SN) cannot be responsible for most short-lived nuclei without excessively producing Mn-53; it can be the source of Mn-53 and maybe Fe-60. If a late SN is responsible for these two nuclei, it still cannot make Pd-107 and other isotopes. We emphasize an AGB star as a source of nuclei, including Fe-60 and explore this possibility with new stellar models. A dilution factor of about 4e-3 gives reasonable amounts of many nuclei. We discuss the role of irradiation for Al-26, Cl-36 and Ca-41. Conflict between scenarios is emphasized as well as the absence of a global interpretation for the existing data. Abundances of actinides indicate a quiescent interval of about 1e8 years for actinide group production in order to explain the data on Pu-244 and new bounds on Cm-247. This interval is not compatible with Hf-182 data, so a separate type of r-process is needed for at least the actinides, distinct from the two types previously identified. The apparent coincidence of the I-129 and trans-actinide time scales suggests that the last actinide contribution was from an r-process that produced actinides without fission recycling so that the yields at Ba and below were governed by fission.Comment: 92 pages, 14 figure files, in press at Nuclear Physics

Aquifer transport of Th, U, Ra, and Rn in solution and on colloids. 1998 annual progress report

'The investigation focuses on understanding the behavior of naturally occurring U, Th, Ra, and Rn isotopes in groundwater along with the supply rates of these isotopes by rock alteration, and utilizing these species as natural analogues for waste radionuclides, thereby providing a basis for predicting contaminant migration behavior in potentially impacted aquifers. The study examines the fundamental controls on natural radionuclide transport in specific aquifers by integrating aquifer sample analyses, focused laboratory experiments, field observations, and theoretical modeling.

Déterminations d'âges absolus dans le Nord du massif armoricain

National audienc

The Hamburg/ESO R-process Enhanced Star survey (HERES). I : Project description and discovery of two stars with strong enhancements of neutron-capture elements

Peer reviewe

'Domestic' origin of opaque assemblages in refractory inclusions in meteorites

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155827/1/Blum_et_al_1988_Domestic_origin.pd

Diffusion, phase equilibria and partitioning experiments in the Ni-Fe-Ru system

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155681/1/Blum_et_al_1989_Diffusion_phase_equilibria.pd