EFFECT OF ADSORBED IRON ON THERMOLUMINESCENCE AND ELECTRON SPIN RESONANCE SPECTRA OF Ca-Fe-EXCHANGED MONTMORILLONITE

Abstract- The electron spin resonance (ESR) spectra nd the natural and gamma-induced thermolumines-cence (TL) glow curves of a series of variably cation-exchanged Fe-Ca-clays prepared from SWy-1 mont-moriUonite were examined. The ESR signal (g = 2) intensity associated with the surface Fe was found to increase linearly with surface Fe content up to a nominal concentration f 50 % exchangeable F. At> 50% exchangeable F, no appreciable increase in the signal was noted. The TL intensity decreased linearly with increasing surface Fe up to 50 % nominal exchangeable F. At> 50%, the signal was not appreciably further diminished. The natural TL showed only a high-temperature p ak, but irradiation produced an additional low-temperature p ak. One month after gamma-irradiation, the integrated TL signal was still 10-100 times higher than that from the non-irradiated material. Thus, (1) surface iron clusters may form above a certain critical Fe concentration; (2)the Fe clusters are probably less effective in quenching TL than are single Fe atoms, implying interaction between surface Fe and the stored energy content of the material; and (3) the electronic energy stored in the material as the result of gamma-irradiation is only slowly dissipated. Key Words--Electron spin resonance, Iron, Montmorillonite, Surface adsorption, Thermoluminescence