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Applied Physics A

, Volume 33, Issue 4, pp 255–263 | Cite as

Temperature dependence of positron annihilation parameters in neutron irradiated molybdenum

  • B. Pagh
  • H. E. Hansen
  • B. Nielsen
  • G. Trumpy
  • K. Petersen
Contributed Papers

Abstract

Positron lifetime measurements have been performed for molybdenum samples containing different densities of voids and dislocation loops. The samples consisted of single crystal molybdenum exposed to 2.7×1018 fast neutrons/cm2 at 60°C, and subsequently annealed at 650°, 725°, 800°, and 875°C in vacuum (p<10−7 Torr). After each annealing, where the densities of voids and loops were changed, positron lifetime measurements were performed in the temperature interval [−194°, 285°C]. In two-term fits of the measured spectra the longer lifetime, τe2-460 ps corresponds to an intensityIe2 increasing with sample temperature. The shorter lifetime τe1 decreases with increasing temperature. A three-state trapping model with and without detrapping is discussed, and appears to be incapable of explaining the observed temperature dependences. A four-state positron trapping model including detrapping is necessary and satisfactory. It describes positron trapping to voids and trapping to dislocation loops, which is followed by a competition between detrapping and positron transition to jogs or other dislocation-bound defects. Mathematical expressions of the four-state trapping model including detrapping are worked out and calculations of the intensityIe2 are compared with the experimental values ofIe2. By use of special models for the temperature dependence of trapping rates, numerical values can be determined for the positron-dislocation-binding energy and for specific positron trapping rates.

PACS

78.70 61.80 

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Copyright information

© Springer-Verlag 1984

Authors and Affiliations

  • B. Pagh
    • 1
  • H. E. Hansen
    • 1
  • B. Nielsen
    • 1
  • G. Trumpy
    • 1
  • K. Petersen
    • 1
  1. 1.Laboratory of Applied Physics IITechnical University of DenmarkLyngbyDenmark

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