The purpose of this study was to observe the energy distribution of incident 511-keV photons produced as a result of annihilation effect e-+e+ γ+γ in three different electrodes (of aluminum, glass, and Bakelite). The transmission, absorption, and reflection of particles for 511-keV photons were examined using a thin or thick layer of electrodes. Moreover, the manner in which the energy spectrum of a single electrode changes with its thickness was explored. The positron range of the positron emission tomography (PET) radioisotopes is responsible for the production of highquality images in (PET) imaging reconstruction. As a result, the ranges and kinetic energies of positrons from three radioisotopes (F18, O15, I124) were calculated in this study using the Geant4 application for tomographic emission (GATE) simulation package. Notably, the ranges thereof were determined via their energies.Finally, the simulated ranges and kinetic energy values were compared with the literature values revealing a 0.5% difference

Keywords : Annihilation effect, Positron Emission Tomography (PET), Imaging reconstruction, Radioisotopes.