An isotope of ______ is used as a fuel in nuclear reactors.
Uranium
Uranium-235 is fissile and is used as fuel in many nuclear fission reactors. Its controlled chain reaction releases energy.
Nuclear energy is generated by
A positron is an anti-particle of an electron, having the same mass but opposite charge to electron. Then, the minimum energy released in annihilation of matter of a pair of an electron and a positron is nearly: