Nucleogenic
Encyclopedia
A nucleogenic isotope
or nuclide, is one that is produced by a natural terrestrial nuclear reaction
, other than a reaction beginning with cosmic rays (the latter nuclides by convention are called by the different term cosmogenic). The nuclear reaction that produces nucleogenic nuclides is usually interaction with an alpha particle or the capture of fission or thermal neutron
. Some nucleogenic isotopes are stable and others are radioactive.
An example of a nucleogenic nuclide would be neon-21 produced from neon-20 that absorbs a thermal neutron, to become stable neon-21 (some neon-21 is also primordial). Other nucleogenic reactions that produce heavy neon isotopes are (fast neutron capture, alpha emission) reactions, starting with magnesium-24 and magnesium-25, respectively. The source of the neutrons in these reactions is often secondary neutrons produced by alpha radiation from natural uranium
and thorium
in rock.
Because nucleogenic isotopes have been produced later than the birth of the solar system (and the nucleosynthetic events that preceded it) nucleogenic isotopes by definition not primordial nuclide
s. However, nucleogenic isotopes should not be confused with much more common radiogenic nuclides that are also younger than primordial nuclides, but which arise as simple daughter isotopes from radioactive decay
. Nucleogenic isotopes, as noted, are the result of a more complicated nuclear reaction
, although such reactions may begin with a radioactive decay event.
Alpha particles that produce nucleogenic reactions come from natural alpha particle
emitters in uranium and thorium decay chains. Neutrons to produce nucleogenic nuclides may be produced by a number of processes, but due to the short half-life of free neutrons, all of these reactions occur on Earth. Among the most common are cosmic ray
spallation production of neutrons from elements near the surface of the Earth. Alpha emission produced by some radioactive decay also produces neutrons by spallation knockout of neutron rich isotopes, such as the reaction of alpha particles with oxygen-18. Neutrons are also produced by the neutron emission
type of radioactive decay, and also from spontaneous fission of fissile elements on Earth, particularly uranium-235.
Nucleogenesis (also known as nucleosynthesis
) as a general phenomenon is a process usually associated with production of nuclides in the Big Bang
or in stars, by nuclear reactions there. Some of these neutron reactions (such as the r-process
and s-process
) involve absorption by atomic nuclei of high-temperature (high energy) neutrons from the star. These processes produce most of the chemical element
s in the universe heavier than zirconium
(element 40), because nuclear fusion processes become increasingly inefficient and unlikely, for elements heavier than this. By convention, such heavier elements produced in normal elemental abundance, are not referred to as "nucleogenic." Instead, this term is reserved for nuclides (isotopes) made on Earth from natural nuclear reactions.
Also, the term "nucleogenic" by convention excludes artificially produced radionuclide
s, for example tritium
, many of which are produced in large amounts by a similar artificial processes, but using the copious neutron flux produced by conventional nuclear reactor
s.
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
or nuclide, is one that is produced by a natural terrestrial nuclear reaction
Nuclear reaction
In nuclear physics and nuclear chemistry, a nuclear reaction is semantically considered to be the process in which two nuclei, or else a nucleus of an atom and a subatomic particle from outside the atom, collide to produce products different from the initial particles...
, other than a reaction beginning with cosmic rays (the latter nuclides by convention are called by the different term cosmogenic). The nuclear reaction that produces nucleogenic nuclides is usually interaction with an alpha particle or the capture of fission or thermal neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
. Some nucleogenic isotopes are stable and others are radioactive.
An example of a nucleogenic nuclide would be neon-21 produced from neon-20 that absorbs a thermal neutron, to become stable neon-21 (some neon-21 is also primordial). Other nucleogenic reactions that produce heavy neon isotopes are (fast neutron capture, alpha emission) reactions, starting with magnesium-24 and magnesium-25, respectively. The source of the neutrons in these reactions is often secondary neutrons produced by alpha radiation from natural uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
and thorium
Thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....
in rock.
Because nucleogenic isotopes have been produced later than the birth of the solar system (and the nucleosynthetic events that preceded it) nucleogenic isotopes by definition not primordial nuclide
Primordial nuclide
In geochemistry and geonuclear physics, primordial nuclides or primordial isotopes are nuclides found on the earth that have existed in their current form since before Earth was formed. Only 288 such nuclides are known...
s. However, nucleogenic isotopes should not be confused with much more common radiogenic nuclides that are also younger than primordial nuclides, but which arise as simple daughter isotopes from radioactive decay
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...
. Nucleogenic isotopes, as noted, are the result of a more complicated nuclear reaction
Nuclear reaction
In nuclear physics and nuclear chemistry, a nuclear reaction is semantically considered to be the process in which two nuclei, or else a nucleus of an atom and a subatomic particle from outside the atom, collide to produce products different from the initial particles...
, although such reactions may begin with a radioactive decay event.
Alpha particles that produce nucleogenic reactions come from natural alpha particle
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name...
emitters in uranium and thorium decay chains. Neutrons to produce nucleogenic nuclides may be produced by a number of processes, but due to the short half-life of free neutrons, all of these reactions occur on Earth. Among the most common are cosmic ray
Cosmic ray
Cosmic rays are energetic charged subatomic particles, originating from outer space. They may produce secondary particles that penetrate the Earth's atmosphere and surface. The term ray is historical as cosmic rays were thought to be electromagnetic radiation...
spallation production of neutrons from elements near the surface of the Earth. Alpha emission produced by some radioactive decay also produces neutrons by spallation knockout of neutron rich isotopes, such as the reaction of alpha particles with oxygen-18. Neutrons are also produced by the neutron emission
Neutron emission
Neutron emission is a type of radioactive decay of atoms containing excess neutrons, in which a neutron is simply ejected from the nucleus. Two examples of isotopes which emit neutrons are helium-5 and beryllium-13...
type of radioactive decay, and also from spontaneous fission of fissile elements on Earth, particularly uranium-235.
Nucleogenesis (also known as nucleosynthesis
Nucleosynthesis
Nucleosynthesis is the process of creating new atomic nuclei from pre-existing nucleons . It is thought that the primordial nucleons themselves were formed from the quark–gluon plasma from the Big Bang as it cooled below two trillion degrees...
) as a general phenomenon is a process usually associated with production of nuclides in the Big Bang
Big Bang
The Big Bang theory is the prevailing cosmological model that explains the early development of the Universe. According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the young Universe to cool and resulted in...
or in stars, by nuclear reactions there. Some of these neutron reactions (such as the r-process
R-process
The r-process is a nucleosynthesis process, likely occurring in core-collapse supernovae responsible for the creation of approximately half of the neutron-rich atomic nuclei that are heavier than iron. The process entails a succession of rapid neutron captures on seed nuclei, typically Ni-56,...
and s-process
S-process
The S-process or slow-neutron-capture-process is a nucleosynthesis process that occurs at relatively low neutron density and intermediate temperature conditions in stars. Under these conditions the rate of neutron capture by atomic nuclei is slow relative to the rate of radioactive beta-minus decay...
) involve absorption by atomic nuclei of high-temperature (high energy) neutrons from the star. These processes produce most of the chemical element
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...
s in the universe heavier than zirconium
Zirconium
Zirconium is a chemical element with the symbol Zr and atomic number 40. The name of zirconium is taken from the mineral zircon. Its atomic mass is 91.224. It is a lustrous, grey-white, strong transition metal that resembles titanium...
(element 40), because nuclear fusion processes become increasingly inefficient and unlikely, for elements heavier than this. By convention, such heavier elements produced in normal elemental abundance, are not referred to as "nucleogenic." Instead, this term is reserved for nuclides (isotopes) made on Earth from natural nuclear reactions.
Also, the term "nucleogenic" by convention excludes artificially produced radionuclide
Radionuclide
A radionuclide is an atom with an unstable nucleus, which is a nucleus characterized by excess energy available to be imparted either to a newly created radiation particle within the nucleus or to an atomic electron. The radionuclide, in this process, undergoes radioactive decay, and emits gamma...
s, for example tritium
Tritium
Tritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons...
, many of which are produced in large amounts by a similar artificial processes, but using the copious neutron flux produced by conventional nuclear reactor
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...
s.