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  • Artikel  (107)
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  • 78.70  (107)
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  • 1
    Digitale Medien
    Digitale Medien
    Crystallinity of pure silica glass studied by positron annihilation (1978)
    Springer
    Applied physics 16 (1978), S. 231-233 
    Details
    ISSN: 1432-0630
    Schlagwort(e): 78.70 ; 61.10 ; 81
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The crystallinity of silica glass fused from Brasilian quartz is demonstrated by positron annihilation lineshape measurements using a high resolution Ge(Li)-detector as well as by positron lifetime measurement.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00885117
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  • 2
    Digitale Medien
    Digitale Medien
    Phase transformations and vacancy formation energies of transition metals by positron annihilation (1979)
    Springer
    Applied physics 20 (1979), S. 135-140 
    Details
    ISSN: 1432-0630
    Schlagwort(e): 78.70 ; 71.60 ; 61.70
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The technique of the coincidence count rate at the peak of the angular correlation curve (CCR) in positron annihilation has been applied to the investigation of vacancy formation energies in thermal equilibrium in nickel, cobalt, and iron. The monovacancy formation energyE 1v/F has been determined to (1.55±0.05) eV and (1.34±0.07) eV for nickel and cobalt, and (1.60±0.10) eV for α-iron, and (1.40±0.15) eV for γ-iron, respectively. The structural phase transformations in cobalt (693 K) and iron (1183 K, 1663 K) are exhibited by discontinuities of the CCR. In the case of cobalt the CCR follows exactly the change of the thermal expansion at the transition temperature. The temperature dependence of the CCR in the prevacancy region is found to be proportional to the thermal expansion for all metals investigated.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00885934
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  • 3
    Digitale Medien
    Digitale Medien
    Annihilation gamma-ray lineshape parameters (1977)
    Springer
    Applied physics 13 (1977), S. 365-369 
    Details
    ISSN: 1432-0630
    Schlagwort(e): 78.70
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The S-parameter, introduced by MacKenzie et al., is now widely used to describe annihilation gamma-ray lineshapes recorded with Ge(Li) spectrometers. This paper discusses four descriptive parameters, their statistical properties and their sensitivity to positron trapping.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00882612
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  • 4
    Digitale Medien
    Digitale Medien
    A new positron source for positron annihilation lifetime experiments (1979)
    Springer
    Applied physics 18 (1979), S. 305-306 
    Details
    ISSN: 1432-0630
    Schlagwort(e): 06.60 ; 78.70 ; 71.60
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract A method using ion-implantation of Na22 to produce source-sample systems applicable to positron annihilation lifetime experiments at elevated temperatures in metals is presented.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00885519
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  • 5
    Digitale Medien
    Digitale Medien
    Positron trapping and self-diffusion activation energies in chromium (1979)
    Springer
    Applied physics 19 (1979), S. 149-152 
    Details
    ISSN: 1432-0630
    Schlagwort(e): 78.70 ; 66.30 F
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The activation energy for self-diffusion in chromium is found to be 3.51±0.13 eV from positron trapping measurements. The 4.51 eV activation energy seen in tracer diffusion work is therefore ascribed to divacancies, theQ 2/Q 1 ratio being typical of the bcc refractory group. The positron data give 0.55 for the ratioH 1v M /H 1v F of vacancy migration and formation energies, in agreement with quenching data for tungsten.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00932389
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  • 6
    Digitale Medien
    Digitale Medien
    Some investigations of moderators for slow positron beams (1979)
    Springer
    Applied physics 19 (1979), S. 247-255 
    Details
    ISSN: 1432-0630
    Schlagwort(e): 78.70 ; 82.65 ; 79.20
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Measurements were made on a low-energy positron beam apparatus in an attempt to increase the efficiency of the slow positron yield from radioisotopes. A study was made to sweep thermalized positrons to the surface of a silicon wafer with an applied electric field at 298 and 140 K. Temperature studies were also made on more conventional Pt and Pt+MgO powder moderators and the results are discussed. The role of the MgO powder has been clarified, though fundamental questions remain. The positron apparatus beam and relevant information regarding sources, temperature and magnetic fields are discussed in sufficient detail so that such a slow positron beam utilizing a “conventional” slow positron moderator could be easily duplicated for use in solid state studies.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00900467
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  • 7
    Digitale Medien
    Digitale Medien
    Positron annihilation in Ge-S glasses (1981)
    Springer
    Applied physics 26 (1981), S. 35-38 
    Details
    ISSN: 1432-0630
    Schlagwort(e): 78.70
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Positron lifetime and Doppler broadening measurements have been carried out on GeS1.375 and GeS1.5 glasses. A pronounced decrease of the mean lifetime was observed at crystallization of GeS1.375 glass into the GeS structure. Also the Doppler-broadened curves are strongly sensitive to this solid-solid phase transition. Unlike the situation for many metals, the positron annihilation parameters were found non-sensitive to fast neutron irradiation doses as high as 1019 n/cm2. No difference between positron annihilation parameters measured on GeS1.375 and GeS1.5 glasses was found. The state of the positron in the GeS glasses is discussed on the basis of these results. The idea is put forward, that the GeS-GeS2 system provides possibilities of sample parameter variations that might prove useful in the understanding of the positron state in non-metallic solids.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01197675
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  • 8
    Digitale Medien
    Digitale Medien
    Vacancy migration energy in quenched Al-Mg0.01 alloy by positron annihilation (1981)
    Springer
    Applied physics 26 (1981), S. 107-113 
    Details
    ISSN: 1432-0630
    Schlagwort(e): 61.70 ; 78.70
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The isothermal recovery rates of vacancy-impurity complexes in an aluminium-1% magnesium alloy are measured in situ at eight temperatures from variations of colinear annihilation γ-rays versus time. These data analysed in terms of a time dependant β+-trapping model yield two apparent migration energies of 0.8 eV±0.1 eV and 0.9 eV±0.05 eV. The nature of the complexes is discussed and their binding energy is estimated.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00616657
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  • 9
    Digitale Medien
    Digitale Medien
    Monte-Carlo calculations of keV electron and positron slowing down in solids (1983)
    Springer
    Applied physics 32 (1983), S. 95-106 
    Details
    ISSN: 1432-0630
    Schlagwort(e): 61.80 ; 78.70 ; 29.70
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract A Monte-Carlo simulation technique based on the screened Rutherford differential cross section for the elastic scattering and Gryzinski's semiempirical expression for the inelastic core and valence electron excitation is used to describe electrons and positrons slowing down in solids. The theoretical results are compared with the experimental backscattering, absorption and transmission results for aluminum, silicon, copper, and gold thin film and semi-infinite targets and good agreement is observed. The simulated stopping profiles are fitted with a simple analytic expression. The profiles are Laplace-transformed to give a useful data base for analyzing phenomena associated with slow positron re-emission from solids.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00617834
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  • 10
    Digitale Medien
    Digitale Medien
    On the effect of backscattering of γ quanta and statistics in positron-annihilation lifetime measurements (1981)
    Springer
    Applied physics 26 (1981), S. 255-259 
    Details
    ISSN: 1432-0630
    Schlagwort(e): 29 ; 78.70
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The contribution of backscattered, 1.27-MeVγ quanta to the coincidence counts in positron-annihilation lifetime measurements has been investigated. Depending on the energy window settings and geometry, as much as 20% of the coincidence counts was found to arise from backscattered events. Computer analysis of such spectra leads to erroneous results. Analysis of computer-generated lifetime spectra shows that good statistics is more important than good resolution power for the quality of the analysis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00617847
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