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  • 1 High Energy Accelerator Research Organization (KEK) Department of Accelerator Science, The Graduate University for Advanced Studies Tsukuba, Ibaraki 305 Japan
  • | 2 High Energy Accelerator Research Organization (KEK) Radiation Science Center 305 Tsukuba, Ibaraki Japan
  • | 3 Tokyo Gakugei University Department of Physics 184 Koganei, Tokyo Japan
  • | 4 The University of Tokyo Research Center for Nuclear Science and Technology 319-11 Tokai, Ibaraki Japan
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Pulsed slow positrons were produced using a time-varying moderator bias with an interval of 82 ns; 97% of the positrons were compressed within 2 ns width at the target position. Both the positron annihilation lifetime and Doppler broadening of the positron annihilation radiation (DBPR) of polytetrafluoroethylene (PTFE) were measured as a function of the incident energy of slow positrons. It was shown that the lifetime and intensity of the long-lived component of positron annihilation are independent of the positron incident energy above 1.2 keV. However, the width of the Doppler-broadened annihilation γ-ray increased in the energy region below 1.2 keV.