Yttrium doped glasses are of considerable interest due to their potential for use as in-vivo radioactive beta- emitters for localised treatment of liver cancer and other diseased organs. In order to model and predict the behaviour of these materials it is important to have a good understanding of the local structure, the network and the environment of the radioactive 90Y ions. We therefore propose to undertake a detailed study of these materials using a combination of neutron and X-ray diffraction and computer modelling using Molecular Dynamic simulations. Beam-time is requested for both GEM and the new ISIS Ag anode XRD system. The results will be combined to enable the yttrium correlations to be isolated from the more complex total structure factor and to aid the data analysis.