56 research outputs found
The Status and Future of Direct Nuclear Reaction Measurements for Stellar Burning
The study of stellar burning began just over 100 years ago. Nonetheless, we
do not yet have a detailed picture of the nucleosynthesis within stars and how
nucleosynthesis impacts stellar structure and the remnants of stellar
evolution. Achieving this understanding will require precise direct
measurements of the nuclear reactions involved. This report summarizes the
status of direct measurements for stellar burning, focusing on developments of
the last couple of decades, and offering a prospectus of near-future
developments.Comment: Accepted to Journal of Physics G as a Major Report. Corresponding
author: Zach Meisel ([email protected]
Catching Element Formation In The Act
Gamma-ray astronomy explores the most energetic photons in nature to address
some of the most pressing puzzles in contemporary astrophysics. It encompasses
a wide range of objects and phenomena: stars, supernovae, novae, neutron stars,
stellar-mass black holes, nucleosynthesis, the interstellar medium, cosmic rays
and relativistic-particle acceleration, and the evolution of galaxies. MeV
gamma-rays provide a unique probe of nuclear processes in astronomy, directly
measuring radioactive decay, nuclear de-excitation, and positron annihilation.
The substantial information carried by gamma-ray photons allows us to see
deeper into these objects, the bulk of the power is often emitted at gamma-ray
energies, and radioactivity provides a natural physical clock that adds unique
information. New science will be driven by time-domain population studies at
gamma-ray energies. This science is enabled by next-generation gamma-ray
instruments with one to two orders of magnitude better sensitivity, larger sky
coverage, and faster cadence than all previous gamma-ray instruments. This
transformative capability permits: (a) the accurate identification of the
gamma-ray emitting objects and correlations with observations taken at other
wavelengths and with other messengers; (b) construction of new gamma-ray maps
of the Milky Way and other nearby galaxies where extended regions are
distinguished from point sources; and (c) considerable serendipitous science of
scarce events -- nearby neutron star mergers, for example. Advances in
technology push the performance of new gamma-ray instruments to address a wide
set of astrophysical questions.Comment: 14 pages including 3 figure
Recommended from our members
The NOx System in Nuclear Waste
The objective of the project was to develop comprehensive quantitative understanding of the radiation-induced chemistry of the NOX system in waste simulants. Similarly, since the tanks' wastes are highly heterogeneous systems, the effects of particulate matter on the radiolytic yields were to be determined. When translated to site-specific concerns, quantitative modeling of these processes can be developed once the fundamental phenomena are understood. The results were to be transferred to site operators as soon as the experimental observations are confirmed to be reliable. Interpretation of the results and conclusions to specific issues, especially safety concerns, at the sites was a major goal
Recommended from our members
The NOx System in Homogeneous and Heterogeneous Nuclear Waste
This project focuses on the development of reliable theoretical and efficient computational descriptions of the chemistry of high-level waste simulants in highly concentrated solution and the experimental validation of this approach. It is an extension of previous work which: (a) Determined the mechanism of H{sub 2} formation in waste simulants allowing quantitative prediction of H{sub 2} generation in nuclear waste storage tanks; (b) Predicted and confirmed NO{sub 2} as a key oxidant in the tanks (c) Determined relative rates of reaction of NO{sub 2} with chelators thus helping to resolve the ''Organic Tanks'' safety issue; (d) Measured rates of NO{sub 2} and NO{sub 2}{sup -} with some model organic radicals; (e) Quantified the redox potentials of two major reductants, NO{sub 2}{sup -} and NO{sub 3}{sup -}; (f) Discovered a new radiolytic route to the reductant NO{sub 3}{sup 2-} and demonstrated its potential persistence in irradiated alkaline aqueous media; (g) Demonstrated that while radiolytic electrons escape from solid suspended silica particles to disrupt the surroundings, holes remain trapped thus storing oxidative equivalents
Recommended from our members
NOx and Heterogeneity Effects in High Level Waste (HLW)
We summarize contributions from our EMSP supported research to several field operations of the Office of Environmental Management (EM). In particular we emphasize its impact on safety programs at the Hanford and other EM sites where storage, maintenance and handling of HLW is a major mission. In recent years we were engaged in coordinated efforts to understand the chemistry initiated by radiation in HLW. Three projects of the EMSP (''The NOx System in Nuclear Waste,'' ''Mechanisms and Kinetics of Organic Aging in High Level Nuclear Wastes, D. Camaioni--PI'' and ''Interfacial Radiolysis Effects in Tanks Waste, T. Orlando--PI'') were involved in that effort, which included a team at Argonne, later moved to the University of Notre Dame, and two teams at the Pacific Northwest National Laboratory. Much effort was invested in integrating the results of the scientific studies into the engineering operations via coordination meetings and participation in various stages of the resolution of some of the outstanding safety issues at the sites. However, in this Abstract we summarize the effort at Notre Dame
Recommended from our members
Interfacial Radiolysis Effects in Tank Waste Speciation
The purpose of this project was to develop an understanding of radiolysis in systems relevant to nuclear wastes stored in tanks at DOE sites such as Hanford, Savannah River, and Idaho. Since these wastes are highly heterogeneous systems, determining the effects of particulate matter on the radiolytic yields was the main focus of interest. When translated to site-specific concerns, quantitative modeling of these processes can be developed once the fundamental phenomena are understood. Interpretation of the results and conclusions to specific issues, especially safety concerns, at the sites was a major goal. The results were transferred to site operators as soon as the experimental observations were confirmed to be reliable
- …