Two radioactive isotopes, X and Y, both decay to stable products. The half-life of X is about a day, while that of Y is about a week. Suppose a radioactive sample consists of a mixture of these two
Nuclides. If the mixture is such that the activities arising from X and Y are initially equal, then a few
Days later the activity of the sample will be due
A) predominantly to Y.
B) predominantly to X.
C) to X and Y equally.
D) entirely to Y.

Question

Quizplus · Accepted Answer

Since the half-life of X is about a day, its activity will decrease much faster than that of Y, whose half-life is about a week. A few days later, the activity of X will have decreased significantly, while Y's activity will have decreased much less, making the sample's activity predominantly due to Y.

Two Radioactive Isotopes, X and Y, Both Decay to Stable