Application of a pulsed slow-positron beam to polymers

Pulsed slow positrons were produced using a time-varying moderator bias wit h an interval of 82 ns; 97% of the positrons were compressed within 2 ns wi dth at the target position. Both the positron annihilation lifetime and Dop pler broadening of the positron annihilation radiation (DBPR) of polytetraf luoroethylene (PTFE) were measured as a function of the incident energy of slow positrons. It was shown that the lifetime and intensity of the long-li ved component of positron annihilation are independent of the positron inci dent energy above 1.2 keV. However, the width of the Doppler-broadened anni hilation gamma-ray increased in the energy region below 1.2 keV.