The half-life of cobalt-60 is 5.3 years,while that of strontium-90 is 28 years.Suppose that samples of cobalt-60 and strontium-90 are such that they initially have the same activity (number of decays per second).What is true about the initial numbers of cobalt-60 and strontium-90 nuclei in these samples?
A) There are more strontium-90 than cobalt-60 nuclei.
B) There are equal numbers of cobalt-60 and strontium-90 nuclei.
C) There are more cobalt-60 than strontium-90 nuclei.
D) It is not possible to compare numbers of nuclei without knowing the masses of the samples.

Question

Quizplus · Accepted Answer

Given that both samples have the same activity initially, and knowing that activity is directly proportional to the number of radioactive nuclei and inversely proportional to the half-life, a sample with a longer half-life (strontium-90) must have more nuclei to have the same activity as a sample with a shorter half-life (cobalt-60).

The Half-Life of Cobalt-60 Is 5