Use the exponential growth model #P(t) = P_0e^(kt)#. The half-life of thorium-229 is 7,340 years. How long will it take for a sample of this substance to decay to 20% of its original amount?
We first find the original amt. of thorium-229, i.e., its amt.
We are given that, its, Half-life is
Using this data in
What we require, now, is time
Thus, it will take (approx.)
20% of its original amt.