FEBRUARY, 1952
A STABLE RADIOACTIVE STANDARD JOHN P. BUTLER and JOHN N. MANDAS' Iowa State College, Ames, Iowa
DURIKG the course of radioactive investigations it was observed that ordinary black glazed porcelain ware exhibited residual activity. The source of such radioactivity was not at first readily apparent, but upon analysis it was found to lie in the hard black glaze as applied to such common laboratory utensils as evaporating dishes,-crucibles, etc. A communication from the Coors Porcelain Company, manufacturers of these items, revealed that the principal constituent used to impart this black glaze is uranium oxide of low percentage. The black oxide and other ingredients are sus~ended in water and the I
Present address: Western Cartridge Co., Alton, Illinois.
crucible or other piece dipped in the glazing mixture. The article is then fired at a temperature which vitrifies the body and melts the glaze leaving a hard, chemically resistant surface. The relative chemical inertness of the procelain ware, its ready availability, and the long half-life of the radioactive constituents of the black glaze make the laboratory pieces suitable for standards of activity. The amount of radiation emitted depends on the geometry of the surface and other factors, but it is on the order of 2 X lo-= microcuries/cm-2. Possible uses include those of Geiger-Miiller tube calibration, determination of tube geometry, and demonstration purposes.
