Abstract: Apparatus to reduce pyrophoricity in deposits collected upon collection plates within a chamber employed for vapor deposition. The apparatus is preferably employed in a chamber utilized for isotopically selective photoexcitation, ionization and separation of metallic uranium vapor. The uranium vapor which collects on all surfaces exposed to it within the chamber is caused to collect in a relatively dense, non-porous body by maintaining a suitably elevated temperature for those surfaces while at the same time keeping the chamber itself cooled. The elevated temperature is achieved by baffles shielding the collection plates from the cooler chamber walls to reduce thermal radiation thereto and/or by applying additional thermal energy to the plates.