An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

1) The act or process of splitting or breaking into parts.
2) Splitting of the nucleus of an atom into two or more fragments of comparable size, usually as the result of the impact of a neutron on the nucleus. Same as → nuclear fission.

Fission, from L. fissionem "a breaking up, cleaving," from root of findere "to split."

Šekâft, stem of šekâftan "to split, break, tear," akin to kaftan, kâftan "to split; to dig," Parthian Mid.Pers. q'f- "to split;" Sogdian kβ "to split;" Chorasmian kf- "to split, be split;" Proto-Iranian *kap-, *kaf- "to split."

Nuclides generated by the fission of higher mass elements or by subsequent radioactive decay of nuclides directly generated by fission.

→ fission; → product.

A theory that suggests the Moon was formed at the same time as Earth. A spinning Earth ejected a large piece of its material into space which then developed into the shape and orbit of the Moon. This event was also thought to be at the origin of the Pacific Ocean. This first modern idea about the formation of the Moon is due to George Darwin, the son of the great naturalist Charles Darwin. The fission theory explained the lack of volatile substances on the Earth. The volatile materials on the Earth would have been thrown out into space The fission theory is almost completely abandoned today. The analysis of lunar rocks brought to Earth by NASA astronauts showed that the Moon rocks are older than the rocks at the bottom of the Pacific Ocean. Moreover, modern → plate tectonics gives a better explanation of the origin of the Pacific Ocean. See also → giant impact hypothesis, → capture theory, → co-formation theory.

→ fission; → theory.

The material that can be fissioned by fast neutrons, such as uranium-238. Commonly used as a synonym for → fissile material.

From → fission + → -able.

Fission which takes place when a nucleon is bombarded with neutrons or high-energy radiation (gamma rays).

Induced, p.p. of → induce; → fission.

A → nuclear reaction in which a heavy atomic nucleus splits into two or more approximately equal parts, usually as the result of the capture of a slow, or → thermal neutron by the nucleus. It is normally accompanied by the emission of further neutrons or → gamma rays and very large amounts of energy. The neutrons can continue the process as a → chain reaction, so that it becomes the source of energy in a → nuclear reactor or an atomic bomb. It may also be a trigger for → nuclear fusion in a hydrogen bomb. Fission occurs spontaneously in nuclei of uranium-235, the main fuel used in nuclear reactors.

→ nuclear; → fission.