Which is a common source of gamma radiation?

Cobalt-60 is a well-known source of gamma radiation due to its radioactive decay process. When cobalt-60 decays, it emits high-energy gamma rays, which are a form of electromagnetic radiation. These gamma rays are particularly useful in various applications such as cancer treatment in radiation therapy, as well as in industrial radiography for non-destructive testing.

While other elements like uranium-235 and plutonium-239 are also radioactive and can emit radiation, they primarily emit alpha and beta particles rather than significant levels of gamma radiation. Radon, a noble gas, primarily emits alpha particles and has a different radiation profile compared to gamma-emitting isotopes. Therefore, cobalt-60 stands out as a common and significant source of gamma radiation, making it the correct choice in this context.