Nuclear Fission

Definition of Nuclear Fission

Nuclear fission is the process where a large, unstable atomic nucleus splits into two smaller nuclei. This splitting releases a significant amount of energy. The smaller nuclei produced are called fission products. This process is fundamental in nuclear power generation and certain types of nuclear weapons.

Process of Nuclear Fission

Nuclear fission begins when a neutron is absorbed by a large nucleus, such as uranium-235 or plutonium-239. This absorption makes the nucleus unstable, causing it to split into two smaller nuclei. Along with these smaller nuclei, a few neutrons and a large amount of energy are released.

The emitted neutrons can then be absorbed by other nearby nuclei, causing them to split as well, which leads to a chain reaction (covered in a separate topic; see the "Chain Reactions" section for more details).

The energy released in fission is mainly kinetic energy of the fission fragments and the emitted neutrons, which is later converted to heat.

For instance, when a uranium-235 nucleus absorbs a neutron, it can split into two smaller nuclei such as barium-141 and krypton-92, releasing three neutrons and energy:

$$\mathrm{^{235}U} + \mathrm{n} \rightarrow \mathrm{^{141}Ba} + \mathrm{^{92}Kr} + 3\mathrm{n} + \text{energy}$$

Energy Released in Fission

The energy released during nuclear fission comes from the conversion of some of the mass of the original nucleus into energy, as described by Einstein’s equation:

$$E = mc^2$$

Here, m is the mass lost during the fission process and c is the speed of light (approximately $3 \times 10^8 \, \mathrm{m/s}$). Even a tiny amount of mass converted to energy produces a huge amount of energy.

This large energy output is harnessed in nuclear power stations to generate electricity. The heat produced by fission is used to produce steam, which drives turbines connected to electricity generators.

For example, if the mass lost in a fission reaction is $0.2 \, \mathrm{g}$, the energy released can be calculated as:

$$E = 0.0002 \, \mathrm{kg} \times (3 \times 10^8 \, \mathrm{m/s})^2 = 1.8 \times 10^{13} \, \mathrm{J}$$

This is an enormous amount of energy from a very small mass! Typical mass losses in fission are very small, but due to the speed of light squared in the equation, even these tiny losses produce huge energy outputs.

For instance, calculating the energy released from a mass loss of 0.1 g would yield similarly large energy values, illustrating the power of nuclear fission.

For instance, if a uranium-235 nucleus absorbs a neutron and splits, releasing neutrons that then cause further fission events, the reaction can continue and produce a large amount of energy.