Influence of ionizing radiation on the lifetime of polymers

The influence of gamma radiation on the temperature and time dependence of the strength of polyethylene terephthalate, polycaprolactam, and polystyrene has been investigated in the dose range up to 4 x 108 R. Irradiation has been carried out in air and under vacuum in the temperature ranges 20 to 120 0C (polyethylene terephthalate) and -20 to 80 0C (polycaprolactam and polystyrene). It has been found that the lifetime of the polymers can be described by the following equation: tau = C exp (U - ωβσ / kT), where C is a constant, U the energy of activation, ω and β material parameters, σ the tensile stress, k the Boltzmann constant, and T the absolute temperature. The parameters U, ω, and β depend on radiation dose and irradiation conditions