Question

Uranium-232 has a half-life of 72 years. How many years will it take for a sample of uranium-232 to decay to 80% of its initial quantity?

Answer 1

\[A_0e^{rt}=A\]
\[e^{r(72)}=1/2\]
\[ln(e^{72r})=ln(1/2)\]
\[72rln(e)=ln(1/2)\]
\[72r=ln(1/2)\]

Answer 2

Thanks :/