The half-life of cobalt-60 is 5.3 years,while that of strontium-90 is about 29 years.Suppose you have samples of both isotopes,and that they initially have the same activity (number of decays per second).What must be true of the 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

Since cobalt-60 has a shorter half-life than strontium-90, it decays faster. For both samples to have the same activity initially, there must be more strontium-90 nuclei to compensate for its slower decay rate.

The Half-Life of Cobalt-60 Is 5