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has been carried out in air, oxidative chain scission occurs as well as crosslinking (4]. The chain scission reactions are important because melt crystallisation in UHMWPE is diffusionally hindered and subsequent scission of interlamellae tie chains leads to both im- mediate and time dependent increases in crystallinity, modulus and brittleness (5-8). The approach to more stable grades has been through controlling irradiation conditions to drive molecular change in the direction of crosslinking and away from chain scis- sion. This has involved irradiation in the absence of oxygen, thermal annealing, two stage irradiation and melting routines, low irradi- ation dose rate procedures and the use of mechanical stress to kill radicals (9-11), and for reasons of commercial sensitivity many of these procedures have not been properly described in the litera- ture. However, despite the uncertainty about some of the pro- prietary methods of producing stable polymer very large numbers of publications have described the chemistry of the irradiation and photo-oxidation processes and have linked these processes to morphology change. It is usual to describe the morphology of UHMWPE in terms of crystalline and amorphous phases, with commercial compression moulded materials having crystallinity values in the range of 45- 60% depending upon molecular weight and history. However, it is the authors' view, based on experimental results already published and new results presented here, that such a description of the material is over simplistic and that a better description of the material can be given, which is relevant to the identified application It is well known that in structural analysis the results obtained are strongly influenced by the chosen technique. Differential