Download or read book Neutron Capture Reactions for Stockpile Stewardship and Basic Science written by and published by . This book was released on 2007 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt: The capture process is a nuclear reaction in which a target atom captures an incident projectile, e.g. a neutron. The excited-state compound nucleus de-excites by emitting photons. This process creates an atom that has one more neutron than the target atom, so it is a different isotope of the same element. With low energy (slow) neutron projectiles, capture is the dominant reaction, other than elastic scattering. However, with very heavy nuclei, fission competes with capture as a method of de-excitation of the compound nucleus. With higher energy (faster) incident neutrons, additional reactions are also possible, such as emission of protons or emission of multiple neutrons. The probability of a particular reaction occurring (such as capture) is referred to as the cross section for that reaction. Cross sections are very dependent on the incoming neutron's energy. Capture reactions can be studied either using monoenergetic neutron sources or 'white' neutron sources. A 'white' neutron source has a wide range of neutron energies in one neutron beam. The advantage to the white neutron source is that it allows the study of cross sections as they depend on neutron energies. The Los Alamos Neutron Science Center, located at Los Alamos National Laboratory, provides an intense white neutron source. Neutrons there are created by a high-energy proton beam from a linear accelerator striking a heavy metal (tungsten) target. The neutrons range in energy from subthermal up to very fast - over 100 MeV in energy. Low-energy neutron reaction cross sections fluctuate dramatically from one target to another, and they are very difficult to predict by theoretical modeling. The cross sections for particular capture reactions are important for defense sciences, advanced reactor concepts, transmutation of radioactive wastes and nuclear astrophysics. We now have a strong collaboration between Lawrence Livermore National Laboratory, Los Alamos National Laboratory, North Carolina State University and Charles University in Prague. In this paper, we report neutron capture studies that are of particular interest to Lawrence Livermore National Laboratory. In addition to determining neutron capture cross sections, we are also interested in the nuclear properties of the excited state compound nuclei created in the capture reactions. One model that describes the behavior of the nucleus is the statistical model. Our statistical studies included measuring the photon strength function, resonance parameters, level density and gamma-ray ([gamma]-ray) cascade multiplicity. The DANCE array allows the separation of cascades by the number of transitions (multiplicity) in the cascade, and this makes it possible to study detailed properties of the statistical cascade such as the relationship between multiplicity and energy distributions. The work reported here includes reaction on molybdenum targets, europium targets, gadolinium targets and the first americium-242m target. Our goal is to improve the accuracy and provide new measurements for stable and radioactive targets. We are especially interested in energy-dependent neutron capture cross sections. In all of our experiments, the photons emitted in the capture reactions are gamma rays, and they are detected by the barium fluoride crystal array named the Detector for Advanced Neutron Capture Experiments (DANCE) shown in Fig. 1. The detector array is made of 160 crystals arranged in a sphere around the target. There are four different crystal shapes, each of which covers an equal solid angle. This array was specifically designed to measure neutron capture cross sections with targets that were milligram sized or smaller, including radioactive targets. The barium fluoride crystals are scintillation (light generating) detectors with very fast response time, and are therefore suitable for high count rate experiments. Actual neutron capture events must be reliably distinguished from background [gamma]-rays, which are always present in neutron induced reactions. To reduce the background of scattered neutrons, a lithium hydride shell is placed inside the array. The purpose of using the spherical array of detectors is to cover all possible directions of emitted [gamma] rays, so we will come as close as possible to complete detection of all the prompt [gamma]-ray cascades emitted in a capture reaction. The sum of the energy of the [gamma] cascades is a measure of the binding energy of the capture neutron. The binding energy is the energy required to remove a bound neutron from the nucleus. The measured mass of the nucleus is smaller than the masses of the target nucleus plus the captured neutron, and the difference (converted to energy) is the binding energy of the capture neutron. Because the detector is segmented into a large number of independent detectors, additional information on event multiplicities (number of [gamma] rays emitted) and other properties can be determined.
Download or read book Review of Livermore Led Neutron Capture Studies Using DANCE written by and published by . This book was released on 2007 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: We have made neutron capture cross-section measurements using the white neutron source at the Los Alamos Science Center, the DANCE detector array (Detector for Advanced Neutron Capture Experiments) and targets important for basic science and stockpile stewardship. In this paper, we review results from (n, [gamma]) reactions on {sup 94,95}Mo, {sup 152,154,157,160,nat}Gd, {sup 151,153}Eu and {sup 242m}Am for neutron energies from
Download or read book FY07 LDRD Final Report Neutron Capture Cross Section Measurements at DANCE written by and published by . This book was released on 2008 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt: We have measured neutron capture cross sections intended to address defense science problems including mix and the Quantification of Margins and Uncertainties (QMU), and provide details about statistical decay of excited nuclei. A major part of this project included developing the ability to produce radioactive targets. The cross-section measurements were made using the white neutron source at the Los Alamos Neutron Science Center, the detector array called DANCE (The Detector for Advanced Neutron Capture Experiments) and targets important for astrophysics and stockpile stewardship. DANCE is at the leading edge of neutron capture physics and represents a major leap forward in capability. The detector array was recently built with LDRD money. Our measurements are a significant part of the early results from the new experimental DANCE facility. Neutron capture reactions are important for basic nuclear science, including astrophysics and the statistics of the [gamma]-ray cascades, and for applied science, including stockpile science and technology. We were most interested in neutron capture with neutron energies in the range between 1 eV and a few hundred keV, with targets important to basic science, and the s-process in particular. Of particular interest were neutron capture cross-section measurements of rare isotopes, especially radioactive isotopes. A strong collaboration between universities and Los Alamos due to the Academic Alliance was in place at the start of our project. Our project gave Livermore leverage in focusing on Livermore interests. The Lawrence Livermore Laboratory did not have a resident expert in cross-section measurements; this project allowed us to develop this expertise. For many radionuclides, the cross sections for destruction, especially (n, [gamma]), are not well known, and there is no adequate model that describes neutron capture. The modeling problem is significant because, at low energies where capture reactions are important, the neutron reaction cross sections show resonance behavior or follow 1/v of the incident neutrons. In the case of odd-odd nuclei, the modeling problem is particularly difficult because degenerate states (rotational bands) present in even-even nuclei have separated in energy. Our work included interpretation of the [gamma]-ray spectra to compare with the Statistical Model and provides information on level density and statistical decay. Neutron capture cross sections are of programmatic interest to defense sciences because many elements were added to nuclear devices in order to determine various details of the nuclear detonation, including fission yields, fusion yields, and mix. Both product nuclei created by (n,2n) reactions and reactant nuclei are transmuted by neutron capture during the explosion. Very few of the (n, [gamma]) cross sections for reactions that create products measured by radiochemists have ever been experimentally determined; most are calculated by radiochemical equivalences. Our new experimentally measured capture cross sections directly impact our knowledge about the uncertainties in device performances, which enhances our capability of carrying out our stockpile stewardship program. Europium and gadolinium cross sections are important for both astrophysics and defense programs. Measurements made prior to this project on stable europium targets differ by 30-40%, which was considered to be significantly disparate. Of the gadolinium isotopes, 151Gd is important for stockpile stewardship, and 153Gd is of high interest to astrophysics, and nether of these (radioactive) gadolinium (n, [gamma]) cross sections have been measured. Additional stable gadolinium isotopes, including {sup 157,160}Gd are of interest to astrophysics. Historical measurements of gadolinium isotopes, including {sup 152,154}Gd, had disagreements similar to the 30-40% disagreements found in the historical europium data. Actinide capture cross section measurements are important for both Stockpile Stewardship and for nuclear forensics. We focused on the {sup 242m}Am(n, [gamma]) measurement, as there was no existing capture measurement for this isotope. The cross-section measurements (cross section vs. E{sub n}) were made at the Detector for Advanced Neutron Capture Experiments. DANCE is comprised of a highly segmented array of barium fluoride (BaF2) crystals specifically designed for neutron capture-gamma measurements, using small radioactive targets (less than one milligram). A picture of half the array, along with a photo of one crystal, is shown in Fig. 1. DANCE provides the world's leading capability for measurements of neutron capture cross sections with radioactive targets. The DANCE is a 4[pi] calorimeter and uses the intense spallation neutron source the Lujan Center at the Los Alamos National Laboratory. The detector array consists of 159 barium fluoride crystals arranged in a sphere around the target.
Download or read book Nuclear Physics written by National Research Council and published by National Academies Press. This book was released on 2013-02-25 with total page 263 pages. Available in PDF, EPUB and Kindle. Book excerpt: The principal goals of the study were to articulate the scientific rationale and objectives of the field and then to take a long-term strategic view of U.S. nuclear science in the global context for setting future directions for the field. Nuclear Physics: Exploring the Heart of Matter provides a long-term assessment of an outlook for nuclear physics. The first phase of the report articulates the scientific rationale and objectives of the field, while the second phase provides a global context for the field and its long-term priorities and proposes a framework for progress through 2020 and beyond. In the second phase of the study, also developing a framework for progress through 2020 and beyond, the committee carefully considered the balance between universities and government facilities in terms of research and workforce development and the role of international collaborations in leveraging future investments. Nuclear physics today is a diverse field, encompassing research that spans dimensions from a tiny fraction of the volume of the individual particles (neutrons and protons) in the atomic nucleus to the enormous scales of astrophysical objects in the cosmos. Nuclear Physics: Exploring the Heart of Matter explains the research objectives, which include the desire not only to better understand the nature of matter interacting at the nuclear level, but also to describe the state of the universe that existed at the big bang. This report explains how the universe can now be studied in the most advanced colliding-beam accelerators, where strong forces are the dominant interactions, as well as the nature of neutrinos.
Download or read book Catalog of Federal Domestic Assistance written by and published by . This book was released on 2012 with total page 1512 pages. Available in PDF, EPUB and Kindle. Book excerpt: Identifies and describes specific government assistance opportunities such as loans, grants, counseling, and procurement contracts available under many agencies and programs.
Download or read book Nuclear Physics written by National Research Council and published by National Academies Press. This book was released on 1999-03-31 with total page 222 pages. Available in PDF, EPUB and Kindle. Book excerpt: Dramatic progress has been made in all branches of physics since the National Research Council's 1986 decadal survey of the field. The Physics in a New Era series explores these advances and looks ahead to future goals. The series includes assessments of the major subfields and reports on several smaller subfields, and preparation has begun on an overview volume on the unity of physics, its relationships to other fields, and its contributions to national needs. Nuclear Physics is the latest volume of the series. The book describes current activity in understanding nuclear structure and symmetries, the behavior of matter at extreme densities, the role of nuclear physics in astrophysics and cosmology, and the instrumentation and facilities used by the field. It makes recommendations on the resources needed for experimental and theoretical advances in the coming decade.
Download or read book Programmatic EIS for Stockpile Stewardship and Management written by and published by . This book was released on 1996 with total page 788 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Los Alamos Science written by and published by . This book was released on 2002 with total page 604 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Applications of Accelerators in Research and Industry Proceedings of the Fifteenth International Conference written by Jerome L. Duggan and published by American Institute of Physics. This book was released on 1999-06-18 with total page 662 pages. Available in PDF, EPUB and Kindle. Book excerpt: The papers in this proceedings volume describe the research and applications of low energy accelerators. The research is primarily in the field of nuclear and atomic physics. The applications are: ion implantation and all of the ion beam diagnostic techniques that are currently in use with small accelerators.
Download or read book International Conference on Nuclear Data for Science and Technology written by Robert C. Haight and published by American Institute of Physics. This book was released on 2005-06-24 with total page 1158 pages. Available in PDF, EPUB and Kindle. Book excerpt: All papers were peer reviewed. This conference focused on the broad field of nuclear data, their production, dissemination, and testing, with the goal of providing reliable data for applications such a nuclear fission and fusion energy, accelerators, spallation neutron sources, nuclear medicine, environment, space, non-proliferation, nuclear safety, astrophysics and cosmology, and basic research.
Download or read book Scientific Opportunities with a Rare Isotope Facility in the United States written by National Research Council and published by National Academies Press. This book was released on 2007-05-09 with total page 152 pages. Available in PDF, EPUB and Kindle. Book excerpt: Over ten years ago, U.S. nuclear scientists proposed construction of a new rare isotope accelerator in the United States, which would enable experiments to elucidate the important questions in nuclear physics. To help assess this proposal, DOE and NSF asked the NRC to define the science agenda for a next-generation U.S. Facility for Rare Isotope Beams (FRIB). As the study began, DOE announced a substantial reduction in the scope of this facility and put off its initial operation date by several years. The study focused on an evaluation of the science that could be accomplished on a facility reduced in scope. This report provides a discussion of the key science drivers for a FRIB, an assessment of existing domestic and international rare isotope beams, an assessment of the current U.S. position about the FRIB, and a set of findings and conclusions about the scientific and policy context for such a facility.
Download or read book Improving the Scientific Basis for Managing DOE s Excess Nuclear Materials and Spent Nuclear Fuel written by National Research Council and published by National Academies Press. This book was released on 2003-06-09 with total page 124 pages. Available in PDF, EPUB and Kindle. Book excerpt: The production of nuclear materials for the national defense was an intense, nationwide effort that began with the Manhattan Project and continued throughout the Cold War. Now many of these product materials, by-products, and precursors, such as irradiated nuclear fuels and targets, have been declared as excess by the Department of Energy (DOE). Most of this excess inventory has been, or will be, turned over to DOE's Office of Environmental Management (EM), which is responsible for cleaning up the former production sites. Recognizing the scientific and technical challenges facing EM, Congress in 1995 established the EM Science Program (EMSP) to develop and fund directed, long-term research that could substantially enhance the knowledge base available for new cleanup technologies and decision making. The EMSP has previously asked the National Academies' National Research Council for advice for developing research agendas in subsurface contamination, facility deactivation and decommissioning, high-level waste, and mixed and transuranic waste. For this study the committee was tasked to provide recommendations for a research agenda to improve the scientific basis for DOE's management of its high-cost, high-volume, or high-risk excess nuclear materials and spent nuclear fuels. To address its task, the committee focused its attention on DOE's excess plutonium-239, spent nuclear fuels, cesium-137 and strontium-90 capsules, depleted uranium, and higher actinide isotopes.
Download or read book Science and Technology written by United States. Office of Science and Technology Policy and published by . This book was released on 1997 with total page 156 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Celebrating 60 Years written by Los Alamos National Laboratory and published by . This book was released on 2003 with total page 260 pages. Available in PDF, EPUB and Kindle. Book excerpt: Accompanying CD-ROM ... "contains a PDF version of 'Celebrating 60 years"--Page [8] of booklet.
Download or read book Frontiers in Nuclear Structure Astrophysics and Reactions written by Paraskevi Demetriou and published by American Institute of Physics. This book was released on 2008-05-27 with total page 488 pages. Available in PDF, EPUB and Kindle. Book excerpt: Crete, Greece, 10-14 September 2007
Download or read book Frontiers in High Energy Density Physics written by National Research Council and published by National Academies Press. This book was released on 2003-05-11 with total page 177 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recent scientific and technical advances have made it possible to create matter in the laboratory under conditions relevant to astrophysical systems such as supernovae and black holes. These advances will also benefit inertial confinement fusion research and the nation's nuclear weapon's program. The report describes the major research facilities on which such high energy density conditions can be achieved and lists a number of key scientific questions about high energy density physics that can be addressed by this research. Several recommendations are presented that would facilitate the development of a comprehensive strategy for realizing these research opportunities.
Download or read book Science and Technology Shaping the Twenty first Century written by and published by . This book was released on 1997 with total page 156 pages. Available in PDF, EPUB and Kindle. Book excerpt:
