Results are presented of a study undertaken to find a suitable isotope separation process for the /sup 13/C-/sup 12/C system that could be adapted to a multi-stage process for the commercial enrichment and separation of isotopes. Experiments reveal that solid porous silica provides an appropriate medium for the efficient enrichment of /sup 13/C via the photolysis of dibenzyl ketones (and related ketones). It is concluded that a system can be designed for the practical separation of /sup 13/C from /sup 12/C based on the photolysis in a magnetic field of ketones absorbed on solid porous silica.