Understanding Neutron Radiography Reading V-Kodak Part 2 of 3

For instance, assume that in a particular radiographic department there are
two source containers, both at 100 feet from the film storage area. One
container holds 50 curies of cobalt 60 and the other an iridium 192 source
whose output is 5 roentgens per hour at 1 metre (5 Rhm). Since there are two
sources, the 5 curies of cobalt 60 will require the protection needed for a
"solitary" 100-curie source, and the iridium 192 source will need the same
protection as if a source whose output is 10 Rhm were alone irradiating the
stored film. The thicknesses of lead needed are shown to be 7.0 inches for
the 50 curies of cobalt 60 (Table VII) and 1.7 inches for the iridium 192 whose
emission is 5 Rhm (Table VIII). This method of determining the protective
requirements when multiple sources must be considered is based on two
facts.
Charlie Chong/ Fion Zhang
Radiography in Modern Industry. Rochester, NY: Eastman Kodak Co. 1980