Question

What is the most common source of gamma rays?

Answer 1

radioisotopes

Answer 2

what is that?

Answer 3

for example \[_{27}^{60}Co\] that is cobalt with 60 nucleons (including 27 protons and 33 neutrons)
is an unstable form of cobalt that will emit gamma rays of 1.33 and 1.17 MeV