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Neutron radiation is a form of ionizing radiation that presents as free neutrons.Typical phenomena are nuclear fission or nuclear fusion causing the release of free neutrons, which then react with nuclei of other atoms to form new nuclides—which, in turn, may trigger further neutron radiation.
Ionizing subatomic particles include alpha particles, beta particles, and neutrons. These particles are created by radioactive decay , and almost all are energetic enough to ionize. There are also secondary cosmic particles produced after cosmic rays interact with Earth's atmosphere, including muons , mesons , and positrons .
Free neutrons do not directly ionize atoms, but they do indirectly cause ionizing radiation, so they can be a biological hazard, depending on dose. A small natural "neutron background" flux of free neutrons exists on Earth, caused by cosmic ray showers , and by the natural radioactivity of spontaneously fissionable elements in the Earth's crust .
In addition, high-energy (high-speed) neutrons have the ability to directly ionize atoms. One mechanism by which high energy neutrons ionize atoms is to strike the nucleus of an atom and knock the atom out of a molecule, leaving one or more electrons behind as the chemical bond is broken. This leads to production of chemical free radicals. In ...
Radioactive decay is a random process at the level of single atoms. According to quantum theory, it is impossible to predict when a particular atom will decay, regardless of how long the atom has existed. [2] [3] [4] However, for a significant number of identical atoms, the overall decay rate can be expressed as a decay constant or as a half-life.
Six important long-lived radioactive isotopes (54 Mn, 55 Fe, 60 Co, 65 Zn, 133 Ba, and 152 Eu) can be found within concrete nuclei affected by neutrons. [3] The residual radioactivity is predominantly due to trace elements present, and thus the amount of radioactivity derived from cyclotron activation is minuscule, i.e., pCi/g or Bq/g.
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When 14 N was proposed to consist of 3 pairs each of protons and neutrons, with an additional unpaired neutron and proton each contributing a spin of 1 ⁄ 2 ħ in the same direction for a total spin of 1 ħ, the model became viable. [70] [71] [72] Soon, neutrons were used to naturally explain spin differences in many different nuclides in the ...