DOCSLIB.ORG

A Review of X-Ray Diffraction Studies in Uranium Alloys*

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
A Review of X-Ray Diffraction Studies in Uranium Alloys* A REVIEW OF X-RAY DIFFRACTION STUDIES IN URANIUM ALLOYS* Harry L. Yakel Metals and Ceramics Division Oak Ridge National Laboratory Oak Ridge, Tennessee 37830 The Physical Metallurgy of Uranium Alloys Conference Sponsored by the AEC Army Material and Mechanical Research Center, Vail, Colorado, Feb. 12-14, 1974. -NOTICE- This report was prepared as an account of work sponsored by the United States Government. Neither the United States nor the United States Atomic Energy Commission, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, com- pleteness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights. *Research sponsored by the U.S. Atomic Energy Commission under contract with the Union Carbide Corporation. ,-r-f OF THIS DOCUV.i-!'" -,ID! ! if I \ '-'I ' ' A REVIEW OF X-RAY DIFFRACTION STUDIES IN URANIUM ALLOYS Harry L. Yakel Metals and Ceramics Division Oak Ridge National Laboratory Oak Ridge, Tennessee 37830 ABSTRACT Results of x-ray diffraction experiments investigating equilibrium structures of uranium-base substitutional alloys and routes of transitions between equilibrium structures are critically reviewed. In the first section data on equilibrium alpha, beta, and gamma alloys are presented together with a resume1 of work on the crystal structures of relevant stable intermetallic compounds. Since many important physical and mechanical properties of practical uranium alloys are consequences of the production of metastable phases during heat-treatment or forming operations, the second part of the review is principally concerned with x-ray diffraction studies of such nonequi- librium phases — their structure and their mode of formation. Particular attention is given to the sequence of transitional phases found in gamma- quenched and aged uranium alloys, depending on aging time and temperature. The influence of external stresses imposed on the alloys before and during the transitions producing these phases is described in terms of the pre- ferred orientations that may be observed by x-ray diffraction methods. In the final section comparisons are drawn between the general structural behavior of uranium alloys and that of other alloy systems based on metals with allotropies similar to that of uranium. INTRODUCTION SCOPE AND OUTLINE An attempt to fully describe all investigations of uranium and its alloys that have employed x-ray diffraction methods in some aspect is clearly beyond the scope of this conference and its proceedings. I shall therefore focus attention on work in which x-ray techniques have been used as a primary tool to determine atomic arrangements in equilibrium and nonequiiibrium uranium-rich metallic phases. Crystallographic studies of modes of deformation and twinning, measurements of preferred orienta- tion, and determinations of structural effects of radiation damage in these materials will be mentioned only as they have relevance to this main area of interest. * Research sponsored by the U.S. Atomic Energy Commission under contract with the Union Carbide Corporation. In the following section, I summarize our current knowledge of the structures of equilibrium phases of elemental uranium and some of its sub- stitutional alloys. The alloy phases are selected on the basis of their relationship to the stable uranium allotropes and to the transitional structures often encountered in uranium-rich systems. Experimental and theoretical attempts to follow the course of transformations between these equilibrium phases are also briefly reviewed. Discussion of the phase transformations leads quite naturally to a consideration of the occurrence and structure of nonequilibrium transition phases in uranium-rich alloys. I review x~ray diffraction studies of such phases with special emphasis on those concerned with structures closely related to the y (A2-type1) configuration of uranium. Finally, and by way of summary, I compare the structural features of both equilibrium and nonequilibrium phases found in uranium-base metallic alloys with corresponding data for systems based on metals with similar allotropy. From this comparison, areas of unresolved problems and fields for future work emerge. SOME GENERAL REMARKS ON X-RAY METHODS While the results of x-ray diffraction experiments on uranium and its alloys have proven indispensable *-o an understanding of the structural phenomena observed in the materials, certain general problems have arisen that must be considered in any objecti. assessment of the state of our knowledge. The first has to do with the natural chemical reactivity of uranium in the metallic state. This reactivity often ensures that x-ray diffraction experiments carried out much above room temperature in a less- than-perfect vacuum or inert atmosphere have really studied materials contaminated by undesired and sometimes unknown impurities. The effects of these contaminants on the details of crystal structures, thermal expan- sion of lattices, or routes of transformation are usually indeterminate and probably significant. A second problem concerns the high linear photoelectric absorption coefficients of uranium and uranium-rich alloys for commonly used x-ray energies. With a value2 of 153 cm2/gm for the mass absorption coefficient of uranium for Mo Ka x rays (A » 0.7107 A), and assuming a density in the range of 15 to 20 gm/cm3, one may expect 99% of the incident x-ray intensity to be absorbed in a surface layer only 15 to 25 urn thick. This implies that results of x-ray diffraction experiments on such materials will be quite sensitive to surface aberrations, a condition suggesting interesting applications if it is the surface whose structural state is desired but creating potential pitfalls if it is the bulk material about which we wish to know. The large absorption corrections that must be applied to observed diffracted intensities before they can be compared to values predicted from a model structure also represent a serious uncertainty in the precise deri- vation of detailed crystal structures of uranium-rich phases. Lastly, the multiplicity of crystallographic orientations usually found on taking a single crystal through a phase transformation, espe- cially on cooling, constitutes a problem that must be recognized in analyzing x-ray scattering from the resulting composite. This is true of many systems, not only uranium alloys, and the literature contains several examples of errors that may occur if the situation is treated improperly.3 The hazards are more fully discussed by Curzon, Luhman and Silcock.4 STRUCTURAL STUDIES OF EQUILIBRIUM PHASES URANIUM ALLOTROPES Alpha Uranium The structure of uranium metal at room temperature and pressure, designated a, is stable up5 to 667.3 ± 1.3°C and down6 to about -231°C (42 K). Its atomic arrangement was first correctly determined by Jacob and Warren,7 who analyzed powder x-ray diffraction data, and then con- firmed by Lukesh8 from single-crystal data. The orthorhombic unit cell dimensions have been reported many times;7»9"15 best values14 would seem to be a = 2.8536 A, b - 5.8698 A, a * 4.9555 A (all ±0.0001 A) as determined from single crystals using a Bond16 goniometer. Four uranium atoms are located in this cell. They occupy the 4(e), (0, y, 1/4) etc., positions of space group Cmam with only a single posi- tional parameter y to be determined from the observed diffraction intensi- ties. The value of this parameter at room temperature and pressure has also been reported often;',11-13,15,17-20 t^e t,est value from x-ray diffraction experiments11*15 is 0.1025, while a recent neutron diffraction study20 gave 0.1027. Both results have uncertainties of 0.0001. The structure of a-uranium based on these best parameters is shown in Fig. 1. It is a rather severe distortion of an ideal hexagonal close- packed arrangement (jb:a - 2.0570 rather than 1.7321, a:a - 1.7366 rather than 1.6330). Each uranium atom has four near neighbors, two at 2.754 A, two at 2.854 A; the other eight atoms that would complete its nearest- neighbor shell in a dose-packed metal are at distances of 3.263 A (4) and 3.342 A (4). These four interatomic distances, labelled d\, d23 d$3 and <£it, respectively, are included in Table 1 together with values for a variety of other a-like phases. Note that do and c?3 depend only on the unit cell dimensions, while d\ and d^ also depend on y. The coordination geometry is unusual. Imagining the central uranium atom at the center of a sphere, two close contacts lie in the polar direc- tions (±a, respectively) and two lie on the equator at an angular separa- tion of 128.2°. The coordination polyhedron is roughly a trigonal bipyramid with one base atom missing. The disparity between the four short and the eight long contacts has suggested a stronger, more "covalent" character for the former and a weaker, more "metallic" character for the latter.21 ORNL-DWG 74-761 cum BETH URANIUM (Sfll KTB NCPTUNIUH SLPHR URANIUM BLPHfi NEPTUNIUM Fig. 1. Drawings of Equilibrium Structures of Uranium and Neptunium. For all but (3-uranium, close neighbor contacts are indicated by bonds; in the 3-uranium drawing these describe hexagonally connected main layers, and thicker bonds indicate abnormally short interatomic contacts. Unit cell edges appear as thin lines. For 3-uranium, a-neptunium, and 3- neptunium c is nearly vertical; for a-neptunium a is directed to the right; for~<x-uranium b is nearly vertical and a nearly horizontal. See text for references to parameters used in construction. Table 1. Near-Neighbor Separations in Alpha-Like Phases Temperature Atomic Distance, A Corrugation Material Angle, Reference (K) di d2 d* d, <!> (deg) a-U 873 2.813 2.911 3.263 3.355 127.24 10 a-U 298 2.754 2.854 3.263 3.342 128.19 14 a-U 50 2.7423 2.8364 3.2581 3.3352 128.32 15 a-U 4.2 2.7432 2.8444 3.2609 3.3322 128.02 15 ao-U-3.25 at.
Load more

Recommended publications
  • Table 2.Iii.1. Fissionable Isotopes1
    FISSIONABLE ISOTOPES Charles P. Blair Last revised: 2012 “While several isotopes are theoretically fissionable, RANNSAD defines fissionable isotopes as either uranium-233 or 235; plutonium 238, 239, 240, 241, or 242, or Americium-241. See, Ackerman, Asal, Bale, Blair and Rethemeyer, Anatomizing Radiological and Nuclear Non-State Adversaries: Identifying the Adversary, p. 99-101, footnote #10, TABLE 2.III.1. FISSIONABLE ISOTOPES1 Isotope Availability Possible Fission Bare Critical Weapon-types mass2 Uranium-233 MEDIUM: DOE reportedly stores Gun-type or implosion-type 15 kg more than one metric ton of U- 233.3 Uranium-235 HIGH: As of 2007, 1700 metric Gun-type or implosion-type 50 kg tons of HEU existed globally, in both civilian and military stocks.4 Plutonium- HIGH: A separated global stock of Implosion 10 kg 238 plutonium, both civilian and military, of over 500 tons.5 Implosion 10 kg Plutonium- Produced in military and civilian 239 reactor fuels. Typically, reactor Plutonium- grade plutonium (RGP) consists Implosion 40 kg 240 of roughly 60 percent plutonium- Plutonium- 239, 25 percent plutonium-240, Implosion 10-13 kg nine percent plutonium-241, five 241 percent plutonium-242 and one Plutonium- percent plutonium-2386 (these Implosion 89 -100 kg 242 percentages are influenced by how long the fuel is irradiated in the reactor).7 1 This table is drawn, in part, from Charles P. Blair, “Jihadists and Nuclear Weapons,” in Gary A. Ackerman and Jeremy Tamsett, ed., Jihadists and Weapons of Mass Destruction: A Growing Threat (New York: Taylor and Francis, 2009), pp. 196-197. See also, David Albright N 2 “Bare critical mass” refers to the absence of an initiator or a reflector.
    [Show full text]
  • FT/P3-20 Physics and Engineering Basis of Multi-Functional Compact Tokamak Reactor Concept R.M.O
    FT/P3-20 Physics and Engineering Basis of Multi-functional Compact Tokamak Reactor Concept R.M.O. Galvão1, G.O. Ludwig2, E. Del Bosco2, M.C.R. Andrade2, Jiangang Li3, Yuanxi Wan3 Yican Wu3, B. McNamara4, P. Edmonds, M. Gryaznevich5, R. Khairutdinov6, V. Lukash6, A. Danilov7, A. Dnestrovskij7 1CBPF/IFUSP, Rio de Janeiro, Brazil, 2Associated Plasma Laboratory, National Space Research Institute, São José dos Campos, SP, Brazil, 3Institute of Plasma Physics, CAS, Hefei, 230031, P.R. China, 4Leabrook Computing, Bournemouth, UK, 5EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon, UK, 6TRINITI, Troitsk, RF, 7RRC “Kurchatov Institute”, Moscow, RF [email protected] Abstract An important milestone on the Fast Track path to Fusion Power is to demonstrate reliable commercial application of Fusion as soon as possible. Many applications of fusion, other than electricity production, have already been studied in some depth for ITER class facilities. We show that these applications might be usefully realized on a small scale, in a Multi-Functional Compact Tokamak Reactor based on a Spherical Tokamak with similar size, but higher fields and currents than the present experiments NSTX and MAST, where performance has already exceeded expectations. The small power outputs, 20-40MW, permit existing materials and technologies to be used. The analysis of the performance of the compact reactor is based on the solution of the global power balance using empirical scaling laws considering requirements for the minimum necessary fusion power (which is determined by the optimized efficiency of the blanket design), positive power gain and constraints on the wall load. In addition, ASTRA and DINA simulations have been performed for the range of the design parameters.
    [Show full text]
  • ESTIMATION of FISSION-PRODUCT GAS PRESSURE in URANIUM DIOXIDE CERAMIC FUEL ELEMENTS by Wuzter A
    NASA TECHNICAL NOTE NASA TN D-4823 - - .- j (2. -1 "-0 -5 M 0-- N t+=$j oo w- P LOAN COPY: RET rm 3 d z c 4 c/) 4 z ESTIMATION OF FISSION-PRODUCT GAS PRESSURE IN URANIUM DIOXIDE CERAMIC FUEL ELEMENTS by WuZter A. PuuZson una Roy H. Springborn Lewis Reseurcb Center Clevelund, Ohio NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON, D. C. NOVEMBER 1968 i 1 TECH LIBRARY KAFB, NM I 111111 lllll IllH llll lilll1111111111111 Ill1 01317Lb NASA TN D-4823 ESTIMATION OF FISSION-PRODUCT GAS PRESSURE IN URANIUM DIOXIDE CERAMIC FUEL ELEMENTS By Walter A. Paulson and Roy H. Springborn Lewis Research Center Cleveland, Ohio NATIONAL AERONAUTICS AND SPACE ADMINISTRATION For sale by the Clearinghouse for Federal Scientific and Technical Information Springfield, Virginia 22151 - CFSTl price $3.00 ABSTRACl Fission-product gas pressure in macroscopic voids was calculated over the tempera- ture range of 1000 to 2500 K for clad uranium dioxide fuel elements operating in a fast neutron spectrum. The calculated fission-product yields for uranium-233 and uranium- 235 used in the pressure calculations were based on experimental data compiled from various sources. The contributions of cesium, rubidium, and other condensible fission products are included with those of the gases xenon and krypton. At low temperatures, xenon and krypton are the major contributors to the total pressure. At high tempera- tures, however, cesium and rubidium can make a considerable contribution to the total pressure. ii ESTIMATION OF FISSION-PRODUCT GAS PRESSURE IN URANIUM DIOXIDE CERAMIC FUEL ELEMENTS by Walter A. Paulson and Roy H.
    [Show full text]
  • Compilation and Evaluation of Fission Yield Nuclear Data Iaea, Vienna, 2000 Iaea-Tecdoc-1168 Issn 1011–4289
    IAEA-TECDOC-1168 Compilation and evaluation of fission yield nuclear data Final report of a co-ordinated research project 1991–1996 December 2000 The originating Section of this publication in the IAEA was: Nuclear Data Section International Atomic Energy Agency Wagramer Strasse 5 P.O. Box 100 A-1400 Vienna, Austria COMPILATION AND EVALUATION OF FISSION YIELD NUCLEAR DATA IAEA, VIENNA, 2000 IAEA-TECDOC-1168 ISSN 1011–4289 © IAEA, 2000 Printed by the IAEA in Austria December 2000 FOREWORD Fission product yields are required at several stages of the nuclear fuel cycle and are therefore included in all large international data files for reactor calculations and related applications. Such files are maintained and disseminated by the Nuclear Data Section of the IAEA as a member of an international data centres network. Users of these data are from the fields of reactor design and operation, waste management and nuclear materials safeguards, all of which are essential parts of the IAEA programme. In the 1980s, the number of measured fission yields increased so drastically that the manpower available for evaluating them to meet specific user needs was insufficient. To cope with this task, it was concluded in several meetings on fission product nuclear data, some of them convened by the IAEA, that international co-operation was required, and an IAEA co-ordinated research project (CRP) was recommended. This recommendation was endorsed by the International Nuclear Data Committee, an advisory body for the nuclear data programme of the IAEA. As a consequence, the CRP on the Compilation and Evaluation of Fission Yield Nuclear Data was initiated in 1991, after its scope, objectives and tasks had been defined by a preparatory meeting.
    [Show full text]
  • Uranium (Nuclear)
    Uranium (Nuclear) Uranium at a Glance, 2016 Classification: Major Uses: What Is Uranium? nonrenewable electricity Uranium is a naturally occurring radioactive element, that is very hard U.S. Energy Consumption: U.S. Energy Production: and heavy and is classified as a metal. It is also one of the few elements 8.427 Q 8.427 Q that is easily fissioned. It is the fuel used by nuclear power plants. 8.65% 10.01% Uranium was formed when the Earth was created and is found in rocks all over the world. Rocks that contain a lot of uranium are called uranium Lighter Atom Splits Element ore, or pitch-blende. Uranium, although abundant, is a nonrenewable energy source. Neutron Uranium Three isotopes of uranium are found in nature, uranium-234, 235 + Energy FISSION Neutron uranium-235, and uranium-238. These numbers refer to the number of Neutron neutrons and protons in each atom. Uranium-235 is the form commonly Lighter used for energy production because, unlike the other isotopes, the Element nucleus splits easily when bombarded by a neutron. During fission, the uranium-235 atom absorbs a bombarding neutron, causing its nucleus to split apart into two atoms of lighter mass. The first nuclear power plant came online in Shippingport, PA in 1957. At the same time, the fission reaction releases thermal and radiant Since then, the industry has experienced dramatic shifts in fortune. energy, as well as releasing more neutrons. The newly released neutrons Through the mid 1960s, government and industry experimented with go on to bombard other uranium atoms, and the process repeats itself demonstration and small commercial plants.
    [Show full text]
  • Nuclear Energy & the Environmental Debate
    FEATURES Nuclear energy & the environmental debate: The context of choices Through international bodies on climate change, the roles of nuclear power and other energy options are being assessed by Evelyne ^Environmental issues are high on international mental Panel on Climate Change (IPCC), which Bertel and Joop agendas. Governments, interest groups, and citi- has been active since 1988. Since the energy Van de Vate zens are increasingly aware of the need to limit sector is responsible for the major share of an- environmental impacts from human activities. In thropogenic greenhouse gas emissions, interna- the energy sector, one focus has been on green- tional organisations having expertise and man- house gas emissions which could lead to global date in the field of energy, such as the IAEA, are climate change. The issue is likely to be a driving actively involved in the activities of these bodies. factor in choices about energy options for elec- In this connection, the IAEA participated in the tricity generation during the coming decades. preparation of the second Scientific Assessment Nuclear power's future will undoubtedly be in- Report (SAR) of the Intergovernmental Panel on fluenced by this debate, and its potential role in Climate Change (IPCC). reducing environmental impacts from the elec- The IAEA has provided the IPCC with docu- tricity sector will be of central importance. mented information and results from its ongoing Scientifically there is little doubt that increas- programmes on the potential role of nuclear ing atmospheric levels of greenhouse gases, such power in alleviating the risk of global climate as carbon dioxide (CO2) and methane, will cause change.
    [Show full text]
  • Low Enriched Uranium Conversion Preliminary Safety Analysis Report for the MIT Research Reactor
    LEU PSAR 6 DEC 2017 TABLE OF CONTENTS TABLE OF CONTENTS .................................................................................................... a ••••••• i 1.0 MIT Research Reactor·······························································"······························· 1-1 1.1 Introduction .......................................................................................................... 1-1 1.2 Summary and Conclusions of Principal Safety Considerations .............................. 1-1 1.2.1 Consequences from Operation and Use ............................................................. 1-1 1.2.2 Safety Considerations on Choice of Site, Fue~ and Power Level.. ..................... 1-2 1.2.3 Inherent Safety Features ................................................................................... 1-3 1.2.4 Design Features for Safe Operation and Shutdown............................................ 1-4 1.2.5 Potential Accidents ........................................................................................... 1-5 1.3 General Description of the Facility ........................................................................ 1-6 1.4 Shared Facilities and Equipment.. ....................................................................... 1-10 1.5 Comparison with Similar Facilities ..................................................................... 1-11 1.6 Summary of Operation ......................................................................................... 1-11 1.7 Nuclear Waste Policy Act
    [Show full text]
  • CURIUM Element Symbol: Cm Atomic Number: 96
    CURIUM Element Symbol: Cm Atomic Number: 96 An initiative of IYC 2011 brought to you by the RACI ROBYN SILK www.raci.org.au CURIUM Element symbol: Cm Atomic number: 96 Curium is a radioactive metallic element of the actinide series, and named after Marie Skłodowska-Curie and her husband Pierre, who are noted for the discovery of Radium. Curium was the first element to be named after a historical person. Curium is a synthetic chemical element, first synthesized in 1944 by Glenn T. Seaborg, Ralph A. James, and Albert Ghiorso at the University of California, Berkeley, and then formally identified by the same research tea at the wartime Metallurgical Laboratory (now Argonne National Laboratory) at the University of Chicago. The discovery of Curium was closely related to the Manhattan Project, and thus results were kept confidential until after the end of World War II. Seaborg finally announced the discovery of Curium (and Americium) in November 1945 on ‘The Quiz Kids!’, a children’s radio show, five days before an official presentation at an American Chemical Society meeting. The first radioactive isotope of Curium discovered was Curium-242, which was made by bombarding alpha particles onto a Plutonium-239 target in a 60-inch cyclotron (University of California, Berkeley). Nineteen radioactive isotopes of Curium have now been characterized, ranging in atomic mass from 233 to 252. The most stable radioactive isotopes are Curium- 247 with a half-life of 15.6 million years, Curium-248 (half-life 340,000 years), Curium-250 (half-life of 9000 years), and Curium-245 (half-life of 8500 years).
    [Show full text]
  • Curium Is the First North American Manufacturer Offering Exclusively 100% LEU Generators
    FOR IMMEDIATE RELEASE January 16, 2018 Curium Is the First North American Manufacturer Offering Exclusively 100% LEU Generators (St. Louis - January 16, 2018) — Curium, a leading nuclear medicine solutions provider, announced today that the company is the first North American manufacturer to meet the deadline established by the American Medical Isotopes Production Act of 2012. This legislation effectively mandates the full conversion away from highly enriched uranium (HEU) as soon as possible and no later than January 2020. Curium’s multi-year project to transition its molybdenum-99 (Mo-99) processing facility from HEU to low enriched uranium (LEU) was completed in late-2017. This project makes Curium the only North American Technetium Tc 99m Generator manufacturer able to supply its customers exclusively with 100 percent LEU Tc 99m generators. Mo-99 is the parent isotope of Tc 99m, which is used in 30 to 40 million nuclear medicine procedures worldwide every year1. Curium is the world’s largest supplier of Tc 99m generators and the largest user of Mo- 99 in the world. “This milestone helps satisfy the goals set forth by the Department of Energy’s (DOE) National Nuclear Security Administration (NNSA) and confirms our support for the NNSA project to eliminate the use of weapons-grade uranium in the production of medical isotopes. We are eager to see others follow our lead and comply with the government’s call for full conversion as soon possible” says Curium North American CEO, Dan Brague. This project is the culmination of more than seven years of work, requiring close collaboration with Curium’s irradiation partners: the Dutch High Flux Reactor, the Polish MARIA reactor, and BR2 in Belgium, as well as, the DOE and NNSA.
    [Show full text]
  • Fission and Fusion Can Yield Energy
    Nuclear Energy Nuclear energy can also be separated into 2 separate forms: nuclear fission and nuclear fusion. Nuclear fusion is the splitting of large atomic nuclei into smaller elements releasing energy, and nuclear fusion is the joining of two small atomic nuclei into a larger element and in the process releasing energy. The mass of a nucleus is always less than the sum of the individual masses of the protons and neutrons which constitute it. The difference is a measure of the nuclear binding energy which holds the nucleus together (Figure 1). As figures 1 and 2 below show, the energy yield from nuclear fusion is much greater than nuclear fission. Figure 1 2 Nuclear binding energy = ∆mc For the alpha particle ∆m= 0.0304 u which gives a binding energy of 28.3 MeV. (Figure from: http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/nucbin.html ) Fission and fusion can yield energy Figure 2 (Figure from: http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/nucbin.html) Nuclear fission When a neutron is fired at a uranium-235 nucleus, the nucleus captures the neutron. It then splits into two lighter elements and throws off two or three new neutrons (the number of ejected neutrons depends on how the U-235 atom happens to split). The two new atoms then emit gamma radiation as they settle into their new states. (John R. Huizenga, "Nuclear fission", in AccessScience@McGraw-Hill, http://proxy.library.upenn.edu:3725) There are three things about this induced fission process that make it especially interesting: 1) The probability of a U-235 atom capturing a neutron as it passes by is fairly high.
    [Show full text]
  • EPA Facts About Plutonium
    EPA Facts about Plutonium What is Plutonium? Radiation is released during the decay process in the form of alpha and beta particles and gamma Plutonium is a radioactive metal that exists as a radiation. Alpha particles can travel only short solid under normal conditions. It is produced distances and generally will not penetrate when uranium absorbs an atomic particle such human skin; however, internal exposure to as a neutron. Small amounts of plutonium occur alpha radiation is a concern. Beta particles are naturally, but large amounts have been generally absorbed in the skin and do not pass produced in nuclear reactors as a result of through the entire body. Gamma radiation, neutron irradiation. however, can penetrate the body. Plutonium occurs in several forms called The time required for a radioactive substance to isotopes. The most common plutonium isotopes lose 50 percent of its radioactivity by decay is are plutonium-238, plutonium-239, and known as the half-life. Plutonium-238, plutonium-240. plutonium-239, and plutonium-240 are isotopes of plutonium, and have half-lives of 87 years for What are the uses of plutonium? plutonium-238, 24,065 years for plutonium-239, and 6,537 years for plutonium-240. Plutonium-238 is used as a source of heat to generate thermoelectric power for electronic How are people exposed to plutonium? systems in satellites and for heart pacemakers. Plutonium has been released to the Plutonium-239 is used primarily in nuclear environment primarily by atmospheric testing of weapons. Plutonium-239 and plutonium-240 are nuclear weapons and by accidents at facilities two of the most common byproducts of where plutonium is used.
    [Show full text]
  • Highlights in Early Stellarator Research at Princeton
    J. Plasma Fusion Res. SERIES, Vol.1 (1998) 3-8 Highlights in Early Stellarator Research at Princeton STIX Thomas H. Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08540, USA (Received: 30 September 1997/Accepted: 22 October 1997) Abstract This paper presents an overview of the work on Stellarators in Princeton during the first fifteen years. Particular emphasis is given to the pioneering contributions of the late Lyman Spitzer, Jr. The concepts discussed will include equilibrium, stability, ohmic and radiofrequency plasma heating, plasma purity, and the problems associated with creating a full-scale fusion power plant. Brief descriptions are given of the early Princeton Stellarators: Model A, Model B, Model B-2, Model B-3, Models 8-64 and 8-65, and Model C, and also of the postulated fusion power plant, Model D. Keywords: Spitzer, Kruskal, stellarator, rotational transform, Bohm diffusion, ohmic heating, magnetic pumping, ion cyclotron resonance heating (ICRH), magnetic island, tokamak On March 31 of this year, at the age of 82, Lyman stellarator was brought to the headquarters of the U.S. Spitzer, Jr., a true pioneer in the fields of astrophysics Atomic Energy Commission in Washington where it re- and plasma physics, died. I wish to dedicate this presen- ceived a favorable reception. Spitzer chose the name tation to his memory. "Project Matterhorn" for the project which was to be Forty-six years ago, in early 1951, Spitzer, then sited in the Princeton area, on the newly acquired For- chair of the Department of Astronomy at Princeton restal tract, and funding began on July 1 of that year University, together with Princeton physicist John 121- Wheeler, had been thinking about the physics of ther- Spitzer's earliest stellarator papers comprise a truly monoclear processes.
    [Show full text]