Oxygen-Effect in Annealing of Recoil Damage in Cobalt Chelates-Tris-Acetyl-Acetone Co(III) and Bis-Salicylaldehyde Triethylenetetramine Co(III) Chloride

Abstract

Summary: A marked 'oxygen effect' is observed for several cobalt complexes in thermal annealing. Kinetic data are reported for recoil damage, after ⁵⁹Co (γ, n) ⁵⁸Co and ⁵⁹Co (n, γ) ⁶⁰Co- reactions in trisacetylacetone Co (III) and bis-salicylaldehyde triethylenetetramine Co (III) chloride respectively. When the thermal treatment is carried out in N₂ or vacuum (viz., in absence of oxygen), the magnitude of Saturation anneal is considerably higher. Aliquots annealed to Saturation in presence of air can be made to undergo further annealing, if the thermal treatment is continued at the same temperature but in the absence of air (in vacuum or nitrogen). It is suggested that during an isothermal annealing run electrons are released from variable depth traps, and interact with the metastable species (damage centres) formed by virtue of interaction of recoil cobalt atom with a chelate molecule. The adsorbed oxygen on the surface acts as deep electron trap and suppresses annealing. Once it is displaced by N₂ (or vacuum), annealing proceeds further. The adsorbed oxygen is not found to affect the percentage contribution from individual rate processes (corresponding to different trapping centres) to an equal extent. This shows that the spatial distribution of different trapping centres in the bulk is not homogeneous.