A chain reaction
Firstly it must be able to capture neutrons which then have a high probability of causing its nuclei to undergo fission or splitting, and the fissions must produce enough further neutrons so that for every fission that occurs, another one will follow.
Neutron-rich nuclei could be said to be atomic nuclei that have a large number of neutrons. The term, however, is generally used in conjunction with the physics of nuclear fission, or the nuclear chain reaction. Fission relies on the production of neutrons to build or maintain the chain reaction (depending on the application - reactor or bomb). Neutrons are let loose in nuclear fission. But if some other materials can be included in the construction of the fission device so that they, too, contribute neutrons to help build the chain, then that would be helpful. (That's what the German heavy water project was all about.) Generally, neutron-rich nuclei are atomic nuclei that can contribute, can add to, the number of neutrons available to support a chain reaction.
Uranium-235
It is not a chemical reaction! You can write U-235, with atomic number 92, plus a neutron, produces two fission product nuclei (which can be various combinations) plus two or three free neutrons. The limitations of notation on this site does not allow to show this properly. If you look up nuclear fission in Wikipedia you will see how such a reaction is written.
The process is called nuclear fission. When uranium-235 splits, it releases a large amount of energy along with smaller nuclei and multiple neutrons. This chain reaction continues as these neutrons can cause additional uranium-235 atoms to undergo fission.
In a fission reaction, energy is released when a heavy nucleus splits into lighter nuclei and neutrons. In a fusion reaction, energy is released when light nuclei combine to form a heavier nucleus. Both reactions release a large amount of energy due to the difference in binding energy between the initial and final nuclei.
Neutrons are the particles captured by other nuclei in a nuclear chain reaction. When these neutrons are absorbed by other nuclei, it can trigger additional fission events, leading to a self-sustaining chain reaction.
Under bombardment with thermal neutrons a nuclear fission is produced with the isotopes 235U and 233U; a formidable energy is released after fission.
A fission reaction is initiated by bombarding a heavy atomic nucleus, like uranium or plutonium, with a neutron. This causes the nucleus to split into two smaller nuclei, releasing more neutrons and a large amount of energy. To sustain the reaction, these released neutrons must continue to collide with other nuclei, causing them to split and release more neutrons, creating a chain reaction. This process is carefully controlled in nuclear reactors to generate heat for electricity production.
A typical uranium fission event produces 2 to 3 neutrons. These neutrons are moderated (slowed down) and go on to initiate the fission of more uranium. On average, in a controlled reaction that is maintained at normal criticality (KEffective = 1), each fission creates exactly one neutron that is used to produce another fission.
Firstly it must be able to capture neutrons which then have a high probability of causing its nuclei to undergo fission or splitting, and the fissions must produce enough further neutrons so that for every fission that occurs, another one will follow.
A nuclear chain reaction occurs when a nucleus undergoes fission, releasing energy and more neutrons. These neutrons can then collide with other nuclei, causing them to also undergo fission and release additional neutrons. This process continues in a chain reaction, leading to the release of large amounts of energy.
Nuclear fission reactions typically occur in the core of a nuclear reactor. This is where the fissionable material, such as uranium-235, is bombarded with neutrons, causing the nuclei to split and release more neutrons and energy in a chain reaction.
Neutron-rich nuclei could be said to be atomic nuclei that have a large number of neutrons. The term, however, is generally used in conjunction with the physics of nuclear fission, or the nuclear chain reaction. Fission relies on the production of neutrons to build or maintain the chain reaction (depending on the application - reactor or bomb). Neutrons are let loose in nuclear fission. But if some other materials can be included in the construction of the fission device so that they, too, contribute neutrons to help build the chain, then that would be helpful. (That's what the German heavy water project was all about.) Generally, neutron-rich nuclei are atomic nuclei that can contribute, can add to, the number of neutrons available to support a chain reaction.
Fission is not a particle. It is a nuclear reaction in which the nucleus of an atom splits into two or more smaller nuclei, along with the release of a large amount of energy and usually some neutrons.
Uranium-235
A fission equation describes the splitting of an atomic nucleus into two or more smaller nuclei, accompanied by the release of a large amount of energy. An example of a fission reaction is the splitting of a uranium nucleus into two smaller nuclei, along with the release of neutrons and energy.