An isotope used in nuclear reactors is U-238. The energy comes from

high-energy neutrons
the loss of mass during nuclear reactions***
carefully controlled chemical reactions
tiny nuclear explosions encased in huge domes

The way radioisotopes are useful in treating cancer is due to
being easy to detect
killing actively growing cancer cells***
only affecting cancer and not healthy cells
being able to react chemically with tumors

1 answer

I agree with both answers