Balanced there are 2 Al, 6 oxygens on both sides.
Answer:
To the best of my knowledge, it is because of the amount of gamma rays is given off.
Explanation:
While both are isotopes, Potassium 40 gives off fewer gamma rays compared to Cobalt 60. Potassium 40 isn't really harmful to humans, but Cobalt 60 (I believe) is used in chemotherapy.
