Ultrasonic pulse-echo technique, tensile testing and thermal gravimetric analysis have been utilised to characterise and monitor the effect of y irradiation on the physicomechanical properties of low density polyethylene LDPE, grade FB 5005. The sonic modulus, elastic modulus, rupture stress and decomposition temperature exhibit a minimum value at 2 Mrad irradiated samples, whereas, toughness and rupture strain exhibit a maximum at the same irradiation dose. The changes in mechanical properties (rupture stress and toughness) correlate well with decomposition temperature and the change in the sonic modulus correlates as well with elastic modulus for the tested material. The results are discussed in terms of cross-linking. Below 2 Mrad the loss of crystallinity overrides the effect of cross-linking, whereas above 2 Mrad the cross-linking dominates
