Improvements in radioactive sources

A radioactive source suitable for use under high mechanical stresses at high temperature and in corrosive atmospheres comprises a radioactive substance embedded or incorporated in a mass of pyroceram consisting of a crystalline glass containing 2-20% by weight of TiO2. As shown in Fig. 1 cobalt wire 1 is surrounded by ceramic glass material 2 containing SiO2, Al2O3, TiO2, ZnO, and MgO, and enclosed in a stainless steel container 3 which is disposed in an envelope 5 of sintered alumina. A seal between the alumina envelope 5 and closure plug 6 is effected by a high melting point glass containing large proportions of BeO and Al2O3, or by a ceramic glass composition containing SiO2, Al2O3, TiO2, and CoO. Before enclosing the tube 3, it is irradiated in a nuclear reactor to form cobalt-60. A wire of Ta 182 or Sb124 may be used instead of Co 60. Alternatively, Figs. 2 and 3 (not shown), the radioactive substance is incorporated in the ceramic glass mass, for example as CoO. The source may be used for controlling the thickness of a glass sheet 10, Fig. 4, as it is drawn from a furnace 8; radiation from the source 14 is detected at 15, and the rotation speed of rollers 11, 12 is regulated by electronic unit 15a. U.S.A. Specification 2,920,971 is referred to.