The half life of Sr-90 is 28 years.After 56 years of decay only 0.40 g of a sample remains.What was the mass of the original sample?

Question

Quizplus · Accepted Answer

Since the half-life of Sr-90 is 28 years, after 56 years, two half-lives have passed. This means that the amount of Sr-90 remaining is 1/4 of the original amount, since 2^(number of half-lives) = 2^2 = 4.

Let X be the original mass of the sample. We know that:

0.40g = X/4

Multiplying both sides by 4 gives:

1.60g = X

Therefore, the original mass of the sample was 1.6g, which is choice C.

The Half Life of Sr-90 Is 28 Years