PARAMAGNETIC CENTERS INDUCED BY GAMMA IRRADIATION OF BIOACTIVE SILICA GLASSES CONTAINING YTTRIUM

 D. Cacaina1, H.Ylänen2, S.Simon1

1 Babes-Bolyai University, Faculty of Physics, M. Kogalniceanu no 1, 400084, Cluj-Napoca, Romania, cdana@phys.ubbcluj.ro
2 Åbo Akademi University, Process Chemistry Centre, Biskopsgatan no.8, 20500, Turku, Finland 
     
     Silica bioactive glasses containing neutron activable yttrium were investigated as a potential material for internal radiotherapy of cancers. The silica glasses, containing yttrium oxide and different alkali and alkaline–earth oxides as network modifiers, were obtained by melts annealing method. The samples were exposed to gamma radiation from a  60Co source for up to 10 days irradiation time. 
   The radiation induced paramagnetic point defects in the irradiated glasses were analysed by Electron Paramagnetic Resonance (EPR). The EPR spectra of the silica glasses with different modifiers are characterised by a resonance line at g  2.024, slightly varying with the composition, attributed to a  non-bridging oxygen hole centres.  The addition of modifier oxides into glass network results in the formation of non-bridging oxygens that are locally charged compensated by modifier cations in neighbouring interstitial positions. The presence of small amount of boron oxide, up to 2.6 wt%, in some of the glasses induced the formation of boron oxygen hole centres that are the main EPR species in these irradiated glasses. 
  The presence of the EPR evidenced defects have to be taken into account as possible centres for glasses dissolution in human body during the radiotherapy procedure.