Secondary gamma and beta relaxations in polyethylene have been studied by photoluminescence of molecular probes dispersed in the polymer. The temperature of the gamma relaxation of low density polyethylene has been determined as -130-degrees-C by the phosphorescence emission of benzophenone. The temperature of the beta relaxation of the same polymer has been found to be -40-degrees-C by the fluorescence emission of anthracene. From the differences in the quenching processes for the phosphorescence and fluorescence of the molecular probes, it should be possible to discuss the mechanisms of both the gamma and beta relaxations depending on the size of the macromolecular segments involved in each process29912591264