Question

Iron-59 has a half-life of 45.1 days. How old is an iron nail if the Fe-59 content is 25% that of a new sample of iron?

Answer 1

The equation for half-life decay is:

\[m=m_0 \left( {1 \over 2} \right)^{t \over t_{0.5}}\]
Where m is the final mass, m(0) is the starting mass, t is the total time elapsed, and t(0.5) is the length of the half-life. You're given t(0.5) in the question, and you're also told that m=0.25m(0). Using this information and the equation above, you should be able to calculate t.