Orthopaedic grade ultra–high molecular weight polyethylene: some features of the main thermoluminescence glow curve

Abstract

Thermoluminescence (TL) characteristics of orthopaedic-grade ultra-high molecular weight polyethylene have been investigated between 20 and 200 degrees C. The TL at 1 degrees C s(-1) consists of two glow curves, a weaker intensity peak at 115 degrees C and the main peak at 70 degrees C, studied in this work. TL intensity increases with beta irradiation but with a dose-response influenced by heating rate. On the other hand, the peak maximum is affected by both irradiation and repeated use of a sample. The glow curve shifts to higher temperatures with increase in heating rate but only slightly so with change in beta irradiation dose, properties suggestive of first-order kinetics. Kinetic analysis for activation energy and order of kinetics, based on the discrete trap model, produce somewhat conflicting results. Whereas qualitative analysis of peak symmetry show that first-order kinetics apply, geometrical analysis of the peak shape suggests that the order of kinetics might be other than first-order. Values of activation energy evaluated using the initial rise method were found to be dose dependent and for a given beta dose are in agreement with calculations from peak shape and initial rise methods but less so with results from variable heating rate method.