Nuclear Radiation: Nuclear Fission

Nuclear Radiation: Nuclear Fission

Nuclear Fission

Definition and Mechanism

• Nuclear fission is a nuclear reaction in which heavy nuclei split into two roughly equal fragments, accompanied by the release of energy.
• It can be spontaneous, but is usually triggered by the absorption of a neutron by a heavy nucleus like uranium-235 or plutonium-239.

Energy Release

• A lot of energy is released during fission as the binding energy of the resulting nuclei is less than that of the original nucleus. It can be calculated by using Einstein’s mass-energy equivalence equation, E=mc^2.
• The energy is released in various forms including kinetic energy of the fission fragments and emitted neutrons, instantly emitted gamma photons, and energy from series of beta and gamma radiations emitted by the fission products.

Chain Reaction

• Fission reaction of uranium-235 and plutonium-239 is characterised by the release of more than one neutron per fission.
• These neutrons can induce fission in other adjacent heavy nuclei causing a self-sustaining chain reaction. This chain reaction forms the basis for nuclear reactors and atomic bombs.
• The level of chain reaction can be controlled in a nuclear reactor by using control rods that absorb excess neutrons.

Fission Products

• Nuclear fission of a heavy nucleus produces a wide range of lighter nuclei as fission products along with neutrons and radioactive isotopes.
• These fission products are often radioactive due to their unstable combinations of neutrons and protons. They can cause potential radiation hazard.

Criticality

• In a nuclear reaction, if each fission triggers, on average, exactly one more fission, the reaction is said to be critical.
• If each fission causes less than one additional fission, the reaction is described as subcritical.
• If each fission causes more than one additional fission, the reaction is supercritical. This is the condition in a nuclear bomb.

Commercial Application

• The most common use of nuclear fission is in nuclear power plants where it serves as a source of heat to generate electricity.
• The splitting of uranium-235 or plutonium-239 in a nuclear reactor produces a vast amount of heat which is used to produce steam, the steam is then used to drive turbines which generate electricity.

Environmental Impacts

• While nuclear fission provides a substantial amount of energy without producing carbon dioxide, it does result in the creation of radioactive waste.
• This waste remains hazardous for many years and disposing of it represents a major environmental challenge.