31.5 Exercise 16

Data from the appendices and the periodic table may be needed for these problems.

(a) Natural potassium contains $^{\text{40}} \text{K}$, which has a half-life of $1 . \text{277} \times \text{10}^{9}$ y. What mass of $^{\text{40}} \text{K}$ in a person would have a decay rate of 4140 Bq? (b) What is the fraction of $^{\text{40}} \text{K}$ in natural potassium, given that the person has 140 g in his body? (These numbers are typical for a 70-kg adult.)