Cobalt-60, safety requirements

Safety requirements must be satisfied before a cobalt-60 source can be installed and licensed. Radiation-trained personnel must be on the staffbefore a license can be issued. At least 500,000-1,000,000 Ci (curies) of cobalt-60 are required in a production source for making wood-polymers, and at 1.00 or more per curie, a considerable investment must be made before production can begin. Besides cost considerations, the cobalt-60 radiation process does have some distinct advantages in making wood-polymer composites. Because the monomer is not catalyzed it can be stored at ambient conditions as long as the proper amount of inhibitor is maintained. The rate of free radical generation is constant for a given amount of cobalt-60 and does not increase with temperature. 

RBE is used to denote the experimentally determined ratio of the absorbed dose from one radiation type to the absorbed dose of a reference radiation required to produce an identical biologic effect under the same conditions. Gamma rays from cobalt-60 and 200-250 keV x-rays have been used as reference standards. The term RBE has been widely used in experimental radiobiology, and the term quality factor used in calculations of dose equivalents for radiation safety purposes (ICRP 1977 NCRP 1971 UNSCEAR 1982). RBE applies only to a specific biological end point, in a specific exposure, under specific conditions to a specific species. There are no generally accepted values of RBE. 

Although an excess of cobalt can be toxic to animals, there is a wide margin of safety between the nutritional requirement and the toxic level. Cobalt toxicosis is extremely unlikely to occur under practical farming conditions. Unlike copper, cobalt is poorly retained by the body tissues and an excess of the element is soon excreted. The toxic level of cobalt for cattle is 1 mg cobalt/kg body weight daily. Sheep are less susceptible to cobalt toxicosis than cattle and have been shown to tolerate levels up to 3.5 mg/kg. Excessive cobalt supplementation of ruminant diets can lead to the production of analogues of vitamin B12 and a reduction in the quantity of the true vitamin. Cobalt compounds pose a risk to human health as they cause cancer if inhaled and they irritate the skin for this reason, their use has been restricted in the... 

The new building took longer to finish than a normal structure because of the special features that had to be incorporated to accommodate all these activities. The handling of radioactive materials required more customized installations than did any other function, especially because significant improvements in safety standards were incorporated. The radioactive materials processing faciUties at Tunney s Pasture would segregate distina functions much more rigorously than thqr had ever been at Port Hope or Chalk River. Radium and cobalt-60 would each have a separate production line, and there would be a third line for all other isotopes. 

---