Under precise conditions, we can split an atom's nucleus by striking it with small particles called neutrons. Splitting certain very heavy atoms, such as some forms of uranium, into lighter atoms allows additional neutrons and energy to be produced. Under the right circumstances, these neutrons will strike other uranium atoms, causing more atoms to fission. When this takes place as a continuous chain reaction under controlled conditions, it releases heat in useful amounts. It also makes the uranium and some fissioned atoms intensely radioactive.
Radiation is a natural energy force that has always existed on earth and throughout the cosmos.
It is energy transferred over distance through waves or particles. The term radiation can include such things as light and radio waves, but it usually refers to ionizing radiation. We cannot detect ionizing radiation with any of our five senses. It is made up of energized particles or waves of pure energy. Its name refers to its ability to ionize, or electrically charge, stable atoms.