"You are studying two radioisotopes, each of which contain the same number of undecayed atoms at the instant the activity of each is measured. Sample X has half life of 8 seconds, while sample Y has a half life of 1600 years. Which sample has the greatest activity? Explain." Im not sure. I would have said the 1600 year one, since it takes much longer for the activity to decrease, but im not sure. Any confirmation on this?