|Destruction of a heavy nucleus by fission|
Fission is an excellent way of destroying a very long-lived heavy nucleus. Here a fissile uranium-235 nucleus captures a neutron and splits into two highly radioactive fragments. At the end of a decay chain these become stable. The fragment with 143 nucleons takes about a fortnight to become stable, while the fragment with 90 nucleons takes around 30 years because of the strontium-90. Around 30 years is much less than the 700 million years that uranium-235 lives for. Isotopes of plutonium and the minor actinides can be destroyed by fission.