Question

Plutonium-239 undergoes alpha decay and has a half-life of 24, 000 years . After 72, 000 years, how much of an initial 100.0 sample will remain?

Answer 1

Hey there!

A half-life means after a certain amount of time, half of that substance will have decayed after that time.

There are 3 half-lives in 72,000 years because 72,000 ÷ 24,000 = 3.

So, we divide the 100g sample in half 3 times.

100 ÷ 2 = 50

50 ÷ 2 = 25

25 ÷ 2 = 12.5

There will be 12.5g of the radioactive sample remaining after 72,000 years.

Hope this helps!