In a nuclear reactor,the chain reaction is controlled by introducing:

Nuclei tend to have more neutrons than protons at high mass numbers because

$A$ possible material for use in nuclear reactors as a fuel is

The nucleus of a radioactive element possesses:

The calculated mass of ${}_{20}Ca^{40}$ is $40.328 \ u$. It releases $306.3 \ MeV$ energy in a nuclear process. Its isotopic mass is

When nuclear energy is intended to be harnessed for the generation of electricity,the potentially destructive neutrons released in a nuclear reactor are absorbed by: