Zur thermischen Ausheilung von Kernrückstoßdefekten in neutronenbestrahlten, kristallinen Ir(IV)- und Os(lV)-Hexahalogen-Komplexen

Abstract

The SZILARD-CHALMERS process of ligand and central atoms in neutron irradiated Na2IrCl6·6 H2O, K2IrBre, K2OsBr6 and (NH4)2OsBr6 has been investigated in some detail. Whereas in Na2IrCl6 · 6 H2O seven 192Ir-recoil species are formed, which show an individual annealing behaviour, recoil 82Br has been observed only in the chemical forms of Br- and the original hexabromocomplexes. The retention of the 192Ir central atom is only 3% in Na2IrCl6· 6 H2O and 38% in K2IrBr6. In contrast, we observed 80 — 90% 82Br-retention (R0) of the ligand atom. These high R0-values indicate an instantaneous annealing reaction, which might be explained by a billiard-ball mechanism and/or by activated exchange reactions. The thermal annealing of 82Br approaches a retention value of 100% quickly at high temperatures (∼ 200 °C) or for long heating times. The kinetics of 192Ir and 82Br annealing are discussed. For the fast annealing process of recoil-82Br an activation energy of about 3 — 4 kcal/mol was calculated. The results show, that physical models alone do not explain the annealing behaviour of the recoils satisfactorily. We must therefore assume, that also chemical reactions are important.