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  • 1
    Electronic Resource
    Electronic Resource
    Microdefects in Al2O3 films and interfaces revealed by positron lifetime spectroscopy (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 3165-3167 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied microdefects and interfaces of Al2O3 films on iron and nickel aluminide substrates using variable-energy positron lifetime spectroscopy. Di-vacancies, vacancy clusters, and microvoids were observed in the oxide scales. Their sizes and distributions were determined by the nature of the process used to synthesize the alumina film, and influenced by the composition of the alloy substrates. For oxide–iron aluminide interfaces, positron lifetimes are longer than those for the alumina layer itself, suggesting a greater defect concentration at such sites. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120278
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  • 2
    Electronic Resource
    Electronic Resource
    A quadratic potential time-of-flight mass spectrometer for use with slow positron ionization sources and other large-volume ion sources (1991)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 62 (1991), S. 2131-2137 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A time-of-flight spectrometer has been specially designed for measuring the masses of ions produced by low-energy positrons interacting with organic molecules in a Penning trap. To make the flight times insensitive to the starting positions of the ions in the trap, acceleration was done using a potential that varied as the square of the distance of the ion from the detector. The containment of the positrons in the Penning trap for extended time periods effected very long collision paths between the positrons and the molecules. The entire length of the Penning trap source could be sampled. These features produced high sensitivity, enabling the measurement of ionization processes with small cross sections. The spectrometer is useful for mass spectrometry of ions produced by processes other than positron interaction. Both large and small volume sources can be accommodated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142327
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Some etching studies of the microstructure and composition of large aluminosilicate particles in fly ash from coal-burning power plants (1980)
    s.l. : American Chemical Society
    Environmental science & technology 14 (1980), S. 965-970 
    Details
    ISSN: 1520-5851
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/es60168a013
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    ‘Spectacle’ array of 210 Po halo radiocentres in biotite: a nuclear geophysical enigma (1974)
    [s.l.] : Nature Publishing Group
    Nature 252 (1974), S. 564-566 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Generally, radiohaloes occur in one of several mineralogical contexts1,3,4. First, as single haloes around discrete inclusions well isolated from other mineral defects and haloes; second, as single haloes around discrete inclusions lodged in conduits or cleavage cracks; third, as single haloes ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/252564a0
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  • 5
    Electronic Resource
    Electronic Resource
    Analytical applications of positrons (1987)
    Springer
    Journal of radioanalytical and nuclear chemistry 110 (1987), S. 403-413 
    Details
    ISSN: 1588-2780
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract In using positrons as analytical tools the experimenter has two quite different options. The first and more obvious is to duplicate electron methods with positrons and see what differences (if any) result. The second is to exploit a unique characteristic of positrons, such as the formation and decay of the positronium atom, to study chemical composition and surface characteristics. Because positrons do not exist freely in our world, they must be obtained from radioactive sources or nuclear interactions. Source intensity has consequently been a limiting factor in experiments that attempt to duplicate electron applications. Some methods of producing and moderating positrons that have been developed here (and elsewhere) are described as well as results from studies using the sources. Surface measurements require less intense sources and yield useful data on materials such as xeolites, silica gels, graphite and alumina. Experimental apparatus, data and interpretation will be discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02035532
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  • 6
    Electronic Resource
    Electronic Resource
    The interaction of slow positrons with organic moecules above and below positronium formation thresholds (1996)
    Springer
    Journal of radioanalytical and nuclear chemistry 210 (1996), S. 309-325 
    Details
    ISSN: 1588-2780
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract A review is given of the ionization of organic moecules by monoenergetic positrons having energies in the range of 0.5–15 eV. Two mechanisms, unique to positrons, are described. If the kinetic energy of the positron is above the positronium formation threshold, such that electrons can be removed from the molecules to form free positronium atoms, the ionization/fragmentation behavior can be explained qualitatively by a modification of the Ore gap theory. To explain how positrons can ionize and fragment molecules when their kinetic energies are below the positronium formation threshold, it is necessary to assume that energy is transferred to the molecule by the annihilation process. Ionization cross sections for positrons having kinetic energies below the positronium formation threshold are sensitive to molecular size, structure and bond types. Continuing work involves a search for positronium compound formation and measurements of the kinetic energy distributions of ions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02056375
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  • 7
    Electronic Resource
    Electronic Resource
    The effect of source window material and thickness on the intensity of moderated positronsPaper presented at the Chemical and Physical Properties Solid Surfaces Conference, Lake Geneva, Wisconsin, USA, 29-31 October 1979. (1980)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 2 (1980), S. 204-206 
    Details
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: When fast positrons from a radioactive source such as 58Co or 22Na are impinged on a suitably prepared moderator surface a measurable fraction (∼0.1%) is re-emitted as a monoenergetic beam. Several groups have efforts underway to implement this phenomenon as a practical monoenergetic positron gun to be used for surface studies. To address the question that arises about the effects of the window of the capsule that contains the fast positron source, moderated positron intensities have been measured for windows constructed of several different materials of varying thicknesses. A semilog plot of the data approximates a universal curve, with all points on the same line regardless of material. A 58Co source can be masked by windows as thick as 22 µm Al or 11 µm Ti without decresasing the moderated positron intensity by more than 35%. Since 22Na has a similar fast β+ spectrum we have the implication that window effects for sources of this material will be of the same degree.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/sia.740020603
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  • 8
    Electronic Resource
    Electronic Resource
    Low energy positrons from metal surfacesPaper presented at the Chemical and Physical Properties of Solid Surfaces Conference, Lake Geneva, Wisconsin, USA, 29-31 October 1979. (1980)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 2 (1980), S. 199-203 
    Details
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: There is reason to believe that slow positron spectroscopy will have value for surface analyses, but in order to develop practical methods it is necessary to devise monoenergetic sources of positrons that output usable intensities. This paper describes how this can be achieved by preparing certain metal surfaces to act as moderators for fast positrons from radioactive sources. After entering the moderator, the positrons are thermalized and a certain fraction are re-emitted back into the vacuum. They can then be extracted by an electrostatic field and accelerated to any desired energy. Yields of low energy positrons were found to be generally large for certain metals having negative positron work functions (theoretically calculated). It is also necessary to minimize bulk defects, which act as positron traps. Tungsten and molybdenum are metals having negative work functions which can be easily prepared as effective moderators by simply heating in vacuum. This effects a cleaning by volatilizing oxides and anneals defects. The inertness of their surfaces towards oxidation allows them to maintain the negative work function effect which might otherwise be reduced by exposure to air and poor vacuum. These results have been utilized by the authors to design a monoenergetic positron gun to measure discrete energy losses in reflection spectra and threshold absorption effects. A Brandeis University group has used a tungsten moderator gun to make the first experimental measurements of low energy positron diffraction spectra.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/sia.740020602
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