Pair production of a photon in the Coulomb field of an electron (often referred to as triplet pair production) despite the fact that it is a third-order QED process has a cross-section that exceeds the Compton cross-section for energies of collision equal to or greater than 250 m(e)c-squared. The present paper reexamines the problem of ultrarelativistic electrons entering a photon field by including triplet pair production as both an energy loss and reinjection mechanism for electrons. The steady state electron distribution and photon spectrum are calculated for monoenergetic and power-law electron injections, and a comparison is made with the results obtained in the pure Compton case, i.e., by ignoring triplet pair production.

The mixing and transport of cosmic rays accelerated by a pulsar inside an expanding supernova remnant are examined, and the resulting high-energy gamma-ray emission from nuclear interactions of these accelerated particles in the shell is investigated. Rayleigh-Taylor instability at the interface between a pulsar wind cavity and the inner supernova envelope is assumed to be the mixing mechanism. The analysis is applied to the model of Gaisser, Harding, and Stanev (1987), where protons are accelerated at the reverse shock in the pulsar wind. The instability time-scale is estimated from the dynamics of the pulsar wind cavity, and model the injection, diffusion, and interaction of protons in the shell. The resulting gamma-ray flux is lower than previous estimates due to proton adiabatic losses in the expanding pulsar wind. The protons mix and diffuse only into the innermost regions of the envelope before interacting. Energy-dependent diffusion causes the higher energy gamma-ray light curves to decay faster than those at lower energy.

The production of cosmic ray positrons by photon-photon pair production of high-energy gamma-rays on starlight photons is examined. Calculating the production rate as a function of positron energy and distance from the sun resulting from interactions with sunlight is the first step. The results are generalized to production on other types of star. The average production rate per unit volume averaged over the local region of the galaxy is calculated, and the contribution to the observed intensity from this process is estimated.