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  • 1
    ISSN: 1432-0630
    Keywords: 61.70 ; 81
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract By means of an integrated source-specimen technique the temperature dependence of positron lifetimes and annihilation lineshapes has been measured, on the same specimens of gold and cadmium from 4.2K to the melting points, and also in electronirradiated and quenched gold. The anomalous temperature dependence of positron annihilation at intermediate temperatures (200 to 350 K in Cd, 270 to 750 K in Au) discovered by Lichtenberger, Schulte, and MacKenzie is confirmed. The data are incompatible with the idea that the intermediate temperature dependence is due to thermal expansion. They are well explained by an extension of the trapping model which includes the formation of metastable self-trapped positrons. From lineshape measurements after electron irradiation at 180 K and after quenching it is deduced that the trapping rate of positrons at vacancy-type defects in Au is temperature independent below room temperature.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0630
    Keywords: 78.70 ; 61.70 ; 07.77
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract A slow-positron source has been installed in the therminal of an electrostatic 6.5 MeV accelerator and provides a monoenergetic positron beam in the few-MeV range. It will be used to operate a “fast” positron lifetime spectrometer based onβ + γ coincidences. The properties of the beam, the expected performance of the spectrometer, its advantages over conventionalγγ lifetime measurements, a number of intended applications, as well as recent positron-electron scattering experiments and plans for positron channelling and channelling-radiation studies are outlined.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-0630
    Keywords: 06 ; 07 ; 61.70
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract A novel method is presented for measuring the spectral density of resistance fluctuations without the explicit determination of the voltage background noise (Johnson noise, pre-amplifier noise). The output of a standard ac bridge excited by a single-frequency alternating current is demodulated by two phase-sensitive detectors which operate in quadrature. When the phase difference between excitation and detection is properly set, the real part of the cross-spectral density of the two demodulators shows only the spectral density of the resistance fluctuations and not the disturbing background noise. The feasibility of our new method is demonstrated by measurements of 1/f noise of a thin-film A1 sample.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 22 (1980), S. 185-187 
    ISSN: 1432-0630
    Keywords: 06 ; 07 ; 61.70
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract New methods for thermal-equilibrium investigations of atomic vacancies or of dislocation movements in metals require measurements of minute resistance fluctuations. The accuracy of such measurements is limited by thermal noise from the resistor. The present paper proposes a method for analysing resistance fluctuations independent of voltage noise.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 30 (1983), S. 117-122 
    ISSN: 1432-0630
    Keywords: 61.70 ; 72.70
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Fluctuations in the number of vacancies in metals in thermal equilibrium lead to resistivity fluctuations. Analysis of these fluctuations permits measurement of both formation and migration enthalpy of the vacancies. The power spectrum of the fluctuations is calculated using a series of statistically independent pulses. It can be derived from the diffusion equation for any geometry of the vacancy sinks. Vacancy diffusion to the surface of a thin plate or of a sphere are treated as examples. The measurability of vacancy noise is assessed. It should also be possible to measure vacancy noise during irradiation. It is predicted that correlated vacancy creation, which may occur during irradiation, will cause an increase in the power spectrum.
    Type of Medium: Electronic Resource
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