Question

What is the half-life of an isotope if it decays to 12.5% of its radioactivity in 18 minutes?

Answer 1

ln(100/12.5) = k*18
Solve for k, then
k = 0.693/t(sub>1/2</sub>.
Solve for t_1/2.

Answer 2

k = 0.693/t_1/2