title: Effect of adsorbed iron on thermoluminescence and electron spin resonance spectra of Ca-Fe-exchanged montmorillonite.
abstract: The electron spin resonance (ESR) spectra and the natural and gamma-induced thermoluminescence (TL) glow curves of a series of variably cation-exchanged Fe-Ca-clays prepared from SWy-1 montmorillonite 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 of 50% exchangeable Fe.  At > 50% exchangeable Fe, no appreciable increase in the signal was noted.  The TL intensity decreased linearly with increasing surface Fe up to 50% nominal exchangeable Fe.  At > 50%, the signal was not appreciably further diminished. The natural TL showed only a high-temperature peak, but irradiation produced an additional low-temperature peak.  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.
authors.affiliation: Department of Chemistry, San Jose State University, California 95192, USA.
authors.forename: L M
authors.initials: LM
authors.lastname: Coyne
authors.forename: A
authors.initials: A
authors.lastname: Banin
mesh_terms: D000327:Adsorption; D001546:Bentonite / Q000737:chemistry*; D002118:Calcium / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D005720:Gamma Rays; D007501:Iron / Q000737:chemistry*; D008163:Luminescent Measurements; D017785:Photons; D013499:Surface Properties; D013696:Temperature; D014959:Wyoming
chemical_list: D001546:Bentonite; D007501:Iron; D002118:Calcium