Plutonium-241 is an isotope of plutonium that is highly radioactive and is used in some nuclear reactors and many nuclear weapons. It has a half-life of 14.4 years. If 1000g of Pu-241 is placed in storage at a weapons plant, how much will still be remaining after 28.8 years?

We use the radioactive decay equation for this problem which is expressed as:

An = Aoe^-kt

An is the remaining amount after time t, Ao is the initial amount and k is a constant.

First, we determine the k from the half life as follows:

An/Ao = 1/2 = e^-k (14.4)

k = 0.04814

Then, we can calculate An after 28.8 yr.

An = 1000 e^-0.04814 (28.8)

An = 250 g