Fission Fragment Tracks as Uranium Tracers in Biological Electron Microscopy

Abstract

Fission fragment tracks from uranium-stained biological preparations have been observed in the electron microscope in a study of the feasibility of their use as tracers. Virus, DNA, and tissue sections were stained with uranium, prepared for electron microscopy, irradiated in the high thermal neutron flux of a nuclear reactor, and examined without further treatment in the electron microscope. Support films of 50 to 100 A of silicon monoxide and a conventional shadow layer of chromium revealed distinct fission fragment tracks with no other discernible damage to the specimen. Virus and DNA specimens were irradiated to 3 x 10(18) n/cm(2) (thermal) and tissue sections to 3 x 10(16) n/cm(2) (thermal). About (1/4) of the calculated number of fissions left detectable tracks. It is estimated that the position of a uranium atom on a DNA fibril may be determined to 50 A, and a uranium atom in a virus preparation or tissue section to about (1/2) micron