The fields of radiation chemistry and microdosimetry have produced models for the calculation of the extent of reactions involving radiation-produced ions. This paper presents a model based on ideas developed by Magee and coworkers which are in turn based on the old columnar recombination model of Jaffe. The key contribution of this model is a method for the determination of the spatial distribution of reactants into several differently shaped deposition regions. The implications of this multiple shape recombination (MSR) model for the treatment of electron-hole recombination in MOS oxides will be discussed. In addition, radiation damage in SiO2 appears to offer a better means for testing such a model than any which has been previously available. That is, the study of electronic devices is benefiting from ideas which originated in the fields of microdosimetry and radiation chemistry, and is in turn providing unique tests of such ideas.