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Research in nuclear physics

Description: This report discusses the following topics: electron capture decay of {sup 179}Ta; search for 17-keV neutrinos in the Internal Bremsstrahlung Spectrum of {sup 125}I; and {beta}{sup +} decay and cosmic-ray half-life of {sup 91}Nb.
Date: June 1, 1992
Creator: Kozub, R.L. & Hindi, M.M.
Partner: UNT Libraries Government Documents Department

Lecture notes for introduction to nuclear engineering 101

Description: The lecture notes for introductory nuclear engineering are provided for Department of Energy personnel that are recent graduates, transfers from non-nuclear industries, and people with minimum engineering training. The material assumes a knowledge of algebra and elementary calculus. These notes support and supplement a three-hour lecture. The reader is led into the subject from the familiar macroscopic world to the microscopic world of atoms and the parts of atoms called elementary particles. Only a passing reference is made to the very extensive world of quarks and tansitory particles to concentrate on those associated with radioactivity and fission. The Einsteinian truth of mass-energy equivalence provides an understanding of the forces binding a nucleus with a resulting mass defect that results in fusion at one end of the mass spectrum and fission at the other. Exercises are provided in calculating the energy released in isotopic transformation, reading and understanding the chart of the nuclides. The periodic table is reviewed to appreciate that the noble elements are produced by quantum mechanical shell closings. Radioactive decay is calculated as well as nuclear penetration and shielding. The geometric attenuation of radiation is studied for personal protection; the use of shielding materials for radiation protection is presented along with the buildup factor that renders the shielding less effective than might be supposed. The process of fission is presented along with the fission products and energies produced by fission. The requirements for producing a sustained chain reactor are discussed. The lecture ends with discussions of how radiation and dose is measured and how dose is converted to measures of the damage of radiation to our bodies.
Date: March 1, 1992
Creator: Fullwood, R. & Cadwell, J.
Partner: UNT Libraries Government Documents Department

Muon transfer from hot muonic hydrogen atoms to neon

Description: A negative muon beam has been directed on adjacent solid layers of hydrogen and neon. Three targets differing by their deuterium concentration were investigated. Muonic hydrogen atoms can drift to the neon layer where the muon is immediately transferred. The time structure of the muonic neon X-rays follows the exponential law with a disappearance rate corresponding to the one of [mu][sup [minus]p] atoms in each target. The rates [lambda][sub pp[mu]] and [lambda][sub pd] can be extracted.
Date: January 1, 1992
Creator: Jacot-Guillarmod, R. (Fribourg Univ. (Switzerland). Inst. de Physique); Bailey, J.M. (Liverpool Univ. (United Kingdom)); Beer, G.A.; Knowles, P.E.; Mason, G.R.; Olin, A. (Victoria Univ., BC (Canada)) et al.
Partner: UNT Libraries Government Documents Department

From ground state to fission fragments: A complex, multi-dimensional multi-path problem

Description: Experimental results on the fission properties of nuclei close to {sup 264}Fm show sudden and large changes with a change of only one or two neutrons or protons. The nucleus {sup 258}Fm, for instance, undergoes symmetric fission with a half-life of about 0.4 ms and a kinetic-energy distribution peaked at about 235 MeV whereas {sup 256}Fm undergoes asymmetric fission with a half-life of about 3 h and a kinetic-energy distribution peaked at about 200 MeV. Qualitatively, these sudden changes have been postulated to be due to the emergence of fragment shells in symmetric-fission products close to {sup 132}Sn. Here we present a quantitative calculation that shows where high-kinetic-energy symmetric fusion occurs and why it is associated with a sudden and large decrease in fission half-lives. We base our study on calculations of potential-energy surfaces in the macroscopic-microscopic model and a semi-empirical model for the nuclear inertia. We use the three-quadratic-surface parameterization to generate the shapes for which the potential-energy surfaces are calculated. The use of this parameterization and the use of the finite-range macroscopic model allows for the study of two touching spheres and similar shapes. Since these shapes are thought to correspond to the scission shapes for the high-kinetic-energy events it is of crucial importance that a continuous sequence of shapes leading from the nuclear ground state to these configurations can be studied within the framework of the model. We present the results of the calculations in terms of potential-energy surfaces and fission half-lives for heavy even nuclei. The surfaces are displayed in the form of contour diagrams as functions of two moments of the shape. They clearly show the appearance of a second fission valley, which leads to scission configurations close to tow touching spheres, for fissioning systems in the vicinity of {sup 264}Fm.
Date: January 1, 1992
Creator: Moeller, P. (Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan)); Nix, J.R. (Los Alamos National Lab., NM (United States)) & Swiatecki, W.J. (Lawrence Berkeley Lab., CA (United States))
Partner: UNT Libraries Government Documents Department

Decay properties of nuclei at the end of the periodic system

Description: Recent studies of nuclear mass models show that it is essential to account for the Coulomb redistribution energy when calculating the nuclear potential energy in the heavy-element region. Results obtained by use of a mass model that includes Coulomb redistribution effects on analyzed. Q values of {alpha} and {beta} decay are calculated. Half-lives for {alpha} decay are estimated by use of the Viola-Seaborg systematics. For EC, {beta}{sup +} decay and {beta}{sup {minus}} decay, half-lives are calculated in a microscopic QRPA model. Calculated single-particle level structures in the heavy-element regions are presented. These indicate possible regions of isomers that would be unusually stable with respect to spontaneous fission and {alpha} decay. Finally, we discuss the implications of earlier extensive work on fission properties of nuclei in this region.
Date: January 24, 1992
Creator: Moeller, P. (Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan)) & Nix, J.R. (Los Alamos National Lab., NM (United States))
Partner: UNT Libraries Government Documents Department

[Molecular, genetic and physiological analysis of photoinhibition and photosynthetic]

Description: A major goal of this project is to use a combined molecular genetic, biochemical and physiological approach to understand the relationship between photosynthetic performance and the structure of the multifunctional D1 reaction center protein of Photosystem II encoded by the chloroplast psbA gene. Relative to other chloroplast proteins, turover of D1 is rapid and highly light dependent and de novo synthesis of D1 is required for a plant's recovery from short term exposure to irradiances which induce photoinhibitory damage. These observations have led to models for a damage/repair cycle of PSII involving the targeted degradation and replacement of photodamaged D1. To investigate the effects of perturbing the D1 cycle on photosynthesis and autotrophic growth under high and low irradiance, we have examined the consequences of site-specific mutations of the psbA and 16S rRNA genes affecting synthesis, maturation and function/stability of the D1 protein introduced into the chloroplast genome of wildtype strain of the green alga Chlamydomonas reinhardtii using biolistic transformation.
Date: January 1, 1992
Partner: UNT Libraries Government Documents Department

Results for f[sub B] and f[sub D] at [beta] = 6. 3

Description: We have computed the decay constants for the B and D mesons, using quenched lattices at [beta] = 6.3, by interpolating between the static approximation of Eichten and the conventional ( heavy'' Wilson fermion) method. A more careful treatment of the static result using better sources with longer time-displacements and a modification to the Wilson quark normalization to correct approximately for lattice effects in the large-am regime have led to the elimination of the large discrepancy between the two methods which had been previously observed. We report final results, with estimates of various systematic errors.
Date: January 1, 1992
Creator: Bernard, C. (Washington Univ., St. Louis, MO (United States). Dept. of Physics); Labrenz, J. (Washington Univ., Seattle, WA (United States). Dept. of Physics) & Soni, A. (Brookhaven National Lab., Upton, NY (United States))
Partner: UNT Libraries Government Documents Department