EPR study of gamma irradiated yttrium bioactive glasses and yttrium silica sol-gel microspheres

Silica bioactive glasses and sol-gel silica microspheres containing neutron activable yttrium were investigated as a potential material for internal radiotherapy of cancer. Yttrium bioactive glasses were obtained by melts annealing method while yttrium silica microspheres by sol-gel and spray-drying techniques. Information about the local structure of the samples was obtained by EPR investigation of the gamma radiation-induced paramagnetic defects in the structure of the samples. The EPR spectra of gamma irradiated the melted yttrium bioactive glasses indicate the presence of HC, and HC2 non-bridging oxygen hole centres in their structure. These defect centres are related to the presence of Q1 and Q2 units in the structure of the glasses. The presence of small amount of boron oxide, in some of the glasses induced the formation of boron oxygen hole centres (BOHC) and boron electron centres (E'). In the structure of sol-gel yttrium silica microspheres thermally treated at 700 deg C, two paramagnetic defect centres, non-bridging oxygen hole (NBOHC) and O2 centres, were evidenced after gamma irradiation.The presence of the EPR evidenced defects have to be taken into account as possible centres for glass dissolution in human body during the radiotherapy procedure.