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SYNOPSISThe ultrasonic pulse-echo technique and differential thermal analysis were utilized to characterize and to monitor the effect of y-irradiation on the sonic modulus and the heat effect of low-density polyethylene. The sonic wave velocity, sonic modulus, and specific gravity exhibit a minimum for samples irradiated at 10 Mrad. A minimum in the heat capacity was observed at 1 Mrad. The estimated relative change of the activation energy of ordering exhibits a minimum at 100 Mrad. Below 10 Mrad, the perturbation and the loss of the crystalline phase override the effect of radiation cross-linking. From 10 to 100 Mrad, the effect of cross-linking as well as that of crystallinity are prevailing. Oxidative degradation is dominating above 100 Mrad. 0 1993 John Wiley & Sons, Inc.

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