Question

Plutonium isotope ${}^{239}Pu$ decays by alpha decay with a half life of 24 100 y. How many milligrams of helium are produced by an initially pure 12.0 g of ${}^{239}Pu$ at the end of 20000 y? (Consider only the helium produced directly by the plutonium and not by any by-products of the decay process.)

Answer 1

The energy released is
$Q=-△m{c}^2=-(m_{H}e-m_{H}2-m_{H}1)c^2$
= -(3.016029 u – 2.014102 u – 1.007825 u)(931.5 MeV/u)
= 5.49 MeV.