We study the effects of gamma-rays on different PEs using the ESR, FTIR and DSC. The changes in the ESR and FTIR spectra after irradiation is studied. We found that the chemical reactions produced during radiation as well as during the storage time are mainly scission and crosslinking and/or branching. The percentage of each of these reactions was determined by the Charlesby-Pinner equation and we concluded that they depend on the linearity of the PE.