How is a 60 Co source produced?

Cobalt-60 (60 Co) is produced through the activation of cobalt-59, which is a stable isotope. This process typically involves bombarding cobalt-59 with neutrons in a nuclear reactor. The interaction with neutrons transforms cobalt-59 into cobalt-60, which is radioactive. The terminology used in the chosen option reflects this process since "activating" small pellets or thin discs can refer to the cobalt-59 isotopes being prepared in such forms and then subjected to neutron capture, which is necessary for the conversion to 60 Co.

The other options do not accurately describe the method of producing cobalt-60:

• The mention of high-grade radioactive gases does not relate to the production of cobalt-60, as gaseous sources are not used for this isotope.

• Chemical reactions alone do not generate cobalt-60 since the transformation requires nuclear processes, not chemical ones.

• Heating metal rods beneath radiation does not describe the activation process needed to change cobalt-59 into cobalt-60. The production involves nuclear reactions rather than just heating or radiation exposure.

This understanding of the production method is critical in the context of medical dosimetry, particularly in the use of cobalt-60 for radiation therapy in treating cancer.