31.5 Exercise 14

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

Mantles for gas lanterns contain thorium, because it forms an oxide that can survive being heated to incandescence for long periods of time. Natural thorium is almost 100% $^{\text{232}} \text{Th}$, with a half-life of $1 . \text{405} \times \text{10}^{\text{10}} \text{y}$. If an average lantern mantle contains 300 mg of thorium, what is its activity?