Process of .sup.196 Hg enrichment

A process of producing mercury isotopically enriched in .sup.196 Hg isotope comprising forming a feedstock comprising a predetermined concentration of .sup.196 Hg isotope, flowing said feedstock through a reactor at a predetermined flow rate to isotopically enrich said isotope and yield a product enriched in said isotope, said reactor comprising a source of light in the form of a tube having a diameter of about 10 millimeters for producing mercury excitation radiation of about 2537 .ANG. and a glass reaction chamber for photochemically reacting mercury, said glass being selected so as to filter wavelengths below about 200 for reducing ozone formation wherein the exterior surface of said glass comprises a reflective coating formed thereon by the use of photoresist masking for completely coating the exterior surface without coating the interior surface, said reactor comprising a gas inlet and outlet ports situated so as to define a gas flow path along a reactor length of at least about 40 cm to about 150 cm, a filter arranged concentrically around the lamp, adjusting said predetermined flow rate of said feedstock for substantially maximizing said yield of a product enriched in said isotope for said reactor length, and selecting a reactor length for obtaining a desired yield of product enriched in said isotope wherein said yield increases with increasing reactor length.