What is the alpha activity of a 10-kg sample of { }^{235} U that is used in a nuclear reactor?

**Strategy** We find the number of radioactive atoms by using Avogadro’s number and the gram-molecular weight. We find in Appendix 8 that { }^{235} U has a half-life for emitting α particles of t_{1 / 2}=7.04 \times 10^{8} y. Then we use Equation (12.22) to find the activity.

R=\lambda N(t) (12.22)