A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is an atom that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transferred to one of its electrons to release it as a conversion electron; or used to create and emit a new particle (alpha particle or beta particle) from the nucleus. During those processes, the radionuclide is said to undergo radioactive decay.These emissions are considered ionizing radiation because they are powerful enough to liberate an electron from another atom. The radioactive decay can produce a stable nuclide or will sometimes produce a new unstable radionuclide which may undergo further decay. Radioactive decay is a random process at the level of single atoms: it is impossible to predict when one particular atom will decay. However, for a collection of atoms of a single element the decay rate, and thus the half-life (t1/2) for that collection can be calculated from their measured decay constants. The range of the half-lives of radioactive atoms have no known limits and span a time range of over 55 orders of magnitude.
An atom is the smallest constituent unit of ordinary matter that has the properties of a chemical element. Every solid, liquid, gas, and plasma is composed of neutral or ionized atoms. Atoms are extremely small; typical sizes are around 100 picometers.
The electron is a subatomic particle, symbol
, whose electric charge is negative one elementary charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no known components or substructure. The electron has a mass that is approximately 1/1836 that of the proton. Quantum mechanical properties of the electron include an intrinsic angular momentum (spin) of a half-integer value, expressed in units of the reduced Planck constant, ħ. As it is a fermion, no two electrons can occupy the same quantum state, in accordance with the Pauli exclusion principle. Like all elementary particles, electrons exhibit properties of both particles and waves: they can collide with other particles and can be diffracted like light. The wave properties of electrons are easier to observe with experiments than those of other particles like neutrons and protons because electrons have a lower mass and hence a longer de Broglie wavelength for a given energy.
Internal conversion is a radioactive decay process wherein an excited nucleus interacts electromagnetically with one of the orbital electrons of the atom. This causes the electron to be emitted (ejected) from the atom. Thus, in an internal conversion process, a high-energy electron is emitted from the radioactive atom, but not from the nucleus. For this reason, the high-speed electrons resulting from internal conversion are not called beta particles, since the latter come from beta decay, where they are newly created in the nuclear decay process.
Radionuclides occur naturally or are artificially produced in nuclear reactors, cyclotrons, particle accelerators or radionuclide generators. There are about 730 radionuclides with half-lives longer than 60 minutes (see list of nuclides). Thirty-two of those are primordial radionuclides that were created before the earth was formed. At least another 60 radionuclides are detectable in nature, either as daughters of primordial radionuclides or as radionuclides produced through natural production on Earth by cosmic radiation. More than 2400 radionuclides have half-lives less than 60 minutes. Most of those are only produced artificially, and have very short half-lives. For comparison, there are about 253 stable nuclides. (In theory, only 146 of them are stable, and the other 107 are believed to decay (alpha decay or beta decay or double beta decay or electron capture or double electron capture))
A nuclear reactor, formerly known as an atomic pile, is a device used to initiate and control a self-sustained nuclear chain reaction. Nuclear reactors are used at nuclear power plants for electricity generation and in propulsion of ships. Heat from nuclear fission is passed to a working fluid, which in turn runs through steam turbines. These either drive a ship's propellers or turn electrical generators' shafts. Nuclear generated steam in principle can be used for industrial process heat or for district heating. Some reactors are used to produce isotopes for medical and industrial use, or for production of weapons-grade plutonium. Some are run only for research. As of early 2019, the IAEA reports there are 454 nuclear power reactors and 226 nuclear research reactors in operation around the world.
A cyclotron is a type of particle accelerator invented by Ernest O. Lawrence in 1929-1930 at the University of California, Berkeley, and patented in 1932. A cyclotron accelerates charged particles outwards from the center along a spiral path. The particles are held to a spiral trajectory by a static magnetic field and accelerated by a rapidly varying electric field. Lawrence was awarded the 1939 Nobel prize in physics for this invention.
A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to very high speeds and energies, and to contain them in well-defined beams.
All chemical elements can exist as radionuclides. Even the lightest element, hydrogen, has a well-known radionuclide, tritium. Elements heavier than lead, and the elements technetium and promethium, exist only as radionuclides. (In theory, elements heavier than dysprosium exist only as radionuclides, but the half-life for some such elements (e.g. gold and platinum) are too long to found)
A chemical element is a species of atom having the same number of protons in their atomic nuclei. For example, the atomic number of oxygen is 8, so the element oxygen consists of all atoms which have exactly 8 protons.
Hydrogen is a chemical element with symbol H and atomic number 1. With a standard atomic weight of 1.008, hydrogen is the lightest element in the periodic table. Its monatomic form (H) is the most abundant chemical substance in the Universe, constituting roughly 75% of all baryonic mass. Non-remnant stars are mainly composed of hydrogen in the plasma state. The most common isotope of hydrogen, termed protium, has one proton and no neutrons.
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. Naturally occurring tritium is extremely rare on Earth, where trace amounts are formed by the interaction of the atmosphere with cosmic rays. It can be produced by irradiating lithium metal or lithium-bearing ceramic pebbles in a nuclear reactor. Tritium is used as a radioactive tracer, in radioluminescent light sources for watches and instruments, and, along with deuterium, as a fuel for nuclear fusion reactions with applications in energy generation and weapons. The name of this isotope is derived from Greek, Modern τρίτος (trítos), meaning 'third'.
Unplanned exposure to radionuclides generally has a harmful effect on living organisms including humans, although low levels of exposure occur naturally without harm. The degree of harm will depend on the nature and extent of the radiation produced, the amount and nature of exposure (close contact, inhalation or ingestion), and the biochemical properties of the element; with increased risk of cancer the most usual consequence. However, radionuclides with suitable properties are used in nuclear medicine for both diagnosis and treatment. An imaging tracer made with radionuclides is called a radioactive tracer. A pharmaceutical drug made with radionuclides is called a radiopharmaceutical.
Nuclear medicine is a medical specialty involving the application of radioactive substances in the diagnosis and treatment of disease. Nuclear medicine, in a sense, is "radiology done inside out" or "endoradiology" because it records radiation emitting from within the body rather than radiation that is generated by external sources like X-rays. In addition, nuclear medicine scans differ from radiology as the emphasis is not on imaging anatomy but the function and for such reason, it is called a physiological imaging modality. Single photon emission computed tomography (SPECT) and positron emission tomography (PET) scans are the two most common imaging modalities in nuclear medicine.
A radioactive tracer, or radioactive label, is a chemical compound in which one or more atoms have been replaced by a radionuclide so by virtue of its radioactive decay it can be used to explore the mechanism of chemical reactions by tracing the path that the radioisotope follows from reactants to products. Radiolabeling is thus the radioactive form of isotopic labeling.
Radiopharmaceuticals, or medicinal radiocompounds, are a group of pharmaceutical drugs which have radioactivity. Radiopharmaceuticals can be used as diagnostic and therapeutic agents. Radiopharmaceuticals emit radiation themselves, which is different from contrast media which absorb or alter external electromagnetism or ultrasound. Radiopharmacology is the branch of pharmacology that specializes in these agents.
On Earth, naturally occurring radionuclides fall into three categories: primordial radionuclides, secondary radionuclides, and cosmogenic radionuclides.
Stellar nucleosynthesis is the theory explaining the creation (nucleosynthesis) of chemical elements by nuclear fusion reactions between atoms within stars. Stellar nucleosynthesis has occurred continuously since the original creation of hydrogen, helium and lithium during the Big Bang. It is a highly predictive theory that today yields excellent agreement between calculations based upon it and the observed abundances of the elements. It explains why the observed abundances of elements in the universe grow over time and why some elements and their isotopes are much more abundant than others. The theory was initially proposed by Fred Hoyle in 1946, who later refined it in 1954. Further advances were made, especially to nucleosynthesis by neutron capture of the elements heavier than iron, by Margaret Burbidge, Geoffrey Burbidge, William Alfred Fowler and Hoyle in their famous 1957 B2FH paper, which became one of the most heavily cited papers in astrophysics history.
Uranium is a chemical element with symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weakly radioactive because all isotopes of uranium are unstable, with half-lives varying between 159,200 years and 4.5 billion years. The most common isotopes in natural uranium are uranium-238 and uranium-235. Uranium has the highest atomic weight of the primordially occurring elements. Its density is about 70% higher than that of lead, and slightly lower than that of gold or tungsten. It occurs naturally in low concentrations of a few parts per million in soil, rock and water, and is commercially extracted from uranium-bearing minerals such as uraninite.
Thorium is a weakly radioactive metallic chemical element with symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately hard, malleable, and has a high melting point. Thorium is an electropositive actinide whose chemistry is dominated by the +4 oxidation state; it is quite reactive and can ignite in air when finely divided.
Many of these radionuclides exist only in trace amounts in nature, including all cosmogenic nuclides. Secondary radionuclides will occur in proportion to their half-lives, so short-lived ones will be very rare. Thus polonium can be found in uranium ores at about 0.1 mg per metric ton (1 part in 1010). Further radionunclides may occur in nature in virtually undetectable amounts as a result of rare events such as spontaneous fission or uncommon cosmic ray interactions.
Radionuclides are produced as an unavoidable result of nuclear fission and thermonuclear explosions. The process of nuclear fission creates a wide range of fission products, most of which are radionuclides. Further radionuclides can be created from irradiation of the nuclear fuel (creating a range of actinides) and of the surrounding structures, yielding activation products. This complex mixture of radionuclides with different chemistries and radioactivity makes handling nuclear waste and dealing with nuclear fallout particularly problematic.
Synthetic radionuclides are deliberately synthesised using nuclear reactors, particle accelerators or radionuclide generators:
Radionuclides are used in two major ways: either for their radiation alone (irradiation, nuclear batteries) or for the combination of chemical properties and their radiation (tracers, biopharmaceuticals).
The following table lists properties of selected radionuclides illustrating the range of properties and uses.
|Mode of formation||Comments|
|Tritium (3H)||1||2||12.3 y||β−||19||Cosmogenic||lightest radionuclide, used in artificial nuclear fusion, also used for radioluminescence and as oceanic transient tracer. Synthesized from neutron bombardment of lithium-6 or deuterium|
|Beryllium-10||4||6||1,387,000 y||β−||556||Cosmogenic||used to examine soil erosion, soil formation from regolith, and the age of ice cores|
|Carbon-14||6||8||5,700 y||β−||156||Cosmogenic||used for radiocarbon dating|
|Fluorine-18||9||9||110 min||β+, EC||633/1655||Cosmogenic||positron source, synthesised for use as a medical radiotracer in PET scans.|
|Aluminium-26||13||13||717,000 y||β+, EC||4004||Cosmogenic||exposure dating of rocks, sediment|
|Chlorine-36||17||19||301,000 y||β−, EC||709||Cosmogenic||exposure dating of rocks, groundwater tracer|
|Potassium-40||19||21||1.24×109 y||β−, EC||1330 /1505||Primordial||used for potassium-argon dating, source of atmospheric argon, source of radiogenic heat, largest source of natural radioactivity|
|Calcium-41||20||21||102,000 y||EC||Cosmogenic||exposure dating of carbonate rocks|
|Cobalt-60||27||33||5.3 y||β−||2824||Synthetic||produces high energy gamma rays, used for radiotherapy, equipment sterilisation, food irradiation|
|Strontium-90||38||52||28.8 y||β−||546||Fission product||medium-lived fission product; probably most dangerous component of nuclear fallout|
|Technetium-99||43||56||210,000 y||β−||294||Fission product||commonest isotope of the lightest unstable element, most significant of long-lived fission products|
|Technetium-99m||43||56||6 hr||γ,IC||141||Synthetic||most commonly used medical radioisotope, used as a radioactive tracer|
|Iodine-129||53||76||15,700,000 y||β−||194||Cosmogenic||longest lived fission product; groundwater tracer|
|Iodine-131||53||78||8 d||β−||971||Fission product||most significant short term health hazard from nuclear fission, used in nuclear medicine, industrial tracer|
|Xenon-135||54||81||9.1 h||β−||1160||Fission Product||strongest known "nuclear poison" (neutron-absorber), with a major effect on nuclear reactor operation.|
|Caesium-137||55||82||30.2 y||β−||1176||Fission Product||other major medium-lived fission product of concern|
|Gadolinium-153||64||89||240 d||EC||Synthetic||Calibrating nuclear equipment, bone density screening|
|Bismuth-209||83||126||1.9×1019y||α||3137||Primordial||long considered stable, decay only detected in 2003|
|Polonium-210||84||126||138 d||α||5307||Decay Product||Highly toxic, used in poisoning of Alexander Litvinenko|
|Radon-222||86||136||3.8d||α||5590||Decay Product||gas, responsible for the majority of public exposure to ionizing radiation, second most frequent cause of lung cancer|
|Thorium-232||90||142||1.4×1010 y||α||4083||Primordial||basis of thorium fuel cycle|
|Uranium-235||92||143||7×108y||α||4679||Primordial||fissile, main nuclear fuel|
|Uranium-238||92||146||4.5×109 y||α||4267||Primordial||Main Uranium isotope|
|Plutonium-238||94||144||87.7 y||α||5593||Synthetic||used in radioisotope thermoelectric generators (RTGs) and radioisotope heater units as an energy source for spacecraft|
|Plutonium-239||94||145||24110 y||α||5245||Synthetic||used for most modern nuclear weapons|
|Americium-241||95||146||432 y||α||5486||Synthetic||used in household smoke detectors as an ionising agent|
|Californium-252||98||154||2.64 y||α/SF||6217||Synthetic||undergoes spontaneous fission (3% of decays), making it a powerful neutron source, used as a reactor initiator and for detection devices|
Key: Z = atomic number; N = neutron number; DM = decay mode; DE = decay energy; EC = electron capture
Radionuclides are present in many homes as they are used inside the most common household smoke detectors. The radionuclide used is americium-241, which is created by bombarding plutonium with neutrons in a nuclear reactor. It decays by emitting alpha particles and gamma radiation to become neptunium-237. Smoke detectors use a very small quantity of 241Am (about 0.29 micrograms per smoke detector) in the form of americium dioxide. 241Am is used as it emits alpha particles which ionise the air in the detector's ionization chamber. A small electric voltage is applied to the ionised air which gives rise to a small electric current. In the presence of smoke some of the ions are neutralized, thereby decreasing the current, which activates the detector's alarm.
Radionuclides that find their way into the environment may cause harmful effects as radioactive contamination. They can also cause damage if they are excessively used during treatment or in other ways exposed to living beings, by radiation poisoning. Potential health damage from exposure to radionuclides depends on a number of factors, and "can damage the functions of healthy tissue/organs. Radiation exposure can produce effects ranging from skin redness and hair loss, to radiation burns and acute radiation syndrome. Prolonged exposure can lead to cells being damaged and in turn lead to cancer. Signs of cancerous cells might not show up until years, or even decades, after exposure."
Following is a summary table for the total list of nuclides with half-lives greater than one hour. Ninety of these 989 nuclides are theoretically stable, except to proton-decay (which has never been observed). About 253 nuclides have never been observed to decay, and are classically considered stable.
The remaining 662 radionuclides have half-lives longer than 1 hour, and are well-characterized (see list of nuclides for a complete tabulation). They include 28 nuclides with measured half-lives longer than the estimated age of the universe (13.8 billion years), and another 4 nuclides with half-lives long enough (> 100 million years) that they are radioactive primordial nuclides, and may be detected on Earth, having survived from their presence in interstellar dust since before the formation of the solar system, about 4.6 billion years ago. Another 60+ short-lived nuclides can be detected naturally as daughters of longer-lived nuclides or cosmic-ray products. The remaining known nuclides are known solely from artificial nuclear transmutation.
Numbers are not exact, and may change slightly in the future, as "stable nuclides" are observed to be radioactive with very long half-lives.
This is a summary tablefor the 988 nuclides with half-lives longer than one hour (including those that are stable), given in list of nuclides.
|Stability class||Number of nuclides||Running total||Notes on running total|
|Theoretically stable to all but proton decay||90||90||Includes first 40 elements. Proton decay yet to be observed.|
|Theoretically stable to alpha decay, beta decay, isomeric transition, and double beta decay but not spontaneous fission, which is possible for "stable" nuclides ≥ niobium-93||56||146||All nuclides that are possible completely stable (spontaneous fission has never been observed for nuclides with mass number < 232).|
|Energetically unstable to one or more known decay modes, but no decay yet seen. All considered "stable" until decay detected.||107||253||Total of classically stable nuclides.|
|Radioactive primordial nuclides.||33||286||Total primordial elements include uranium, thorium, bismuth, rubidium-87, potassium-40, tellurium-128 plus all stable nuclides.|
|Radioactive nonprimordial, but naturally occurring on Earth.||61||347||Carbon-14 (and other isotopes generated by cosmic rays) and daughters of radioactive primordial elements, such as radium, polonium, etc. 41 of these have a half life of greater than one hour.|
|Radioactive synthetic half-life ≥ 1.0 hour). Includes most useful radiotracers.||662||989||These 989 nuclides are listed in the article List of nuclides.|
|Radioactive synthetic (half-life < 1.0 hour).||>2400||>3300||Includes all well-characterized synthetic nuclides.|
This list covers common isotopes, most of which are available in very small quantities to the general public in most countries. Others that are not publicly accessible are traded commercially in industrial, medical, and scientific fields and are subject to government regulation.
|Barium-133||9694 TBq/kg (262 Ci/g)||10.7 years||81.0, 356.0|
|Cadmium-109||96200 TBq/kg (2600 Ci/g)||453 days||88.0|
|Cobalt-57||312280 TBq/kg (8440 Ci/g)||270 days||122.1|
|Cobalt-60||40700 TBq/kg (1100 Ci/g)||5.27 years||1173.2, 1332.5|
|Europium-152||6660 TBq/kg (180 Ci/g)||13.5 years||121.8, 344.3, 1408.0|
|Manganese-54||287120 TBq/kg (7760 Ci/g)||312 days||834.8|
|Sodium-22||237540 Tbq/kg (6240 Ci/g)||2.6 years||511.0, 1274.5|
|Zinc-65||304510 TBq/kg (8230 Ci/g)||244 days||511.0, 1115.5|
|Technetium-99m||×1071.95 TBq/kg (5.27 × 105 Ci/g)||6 hours||140|
|Strontium-90||5180 TBq/kg (140 Ci/g)||28.5 years||546.0|
|Thallium-204||17057 TBq/kg (461 Ci/g)||3.78 years||763.4|
|Carbon-14||166.5 TBq/kg (4.5 Ci/g)||5730 years||49.5 (average)|
|Tritium (Hydrogen-3)||357050 TBq/kg (9650 Ci/g)||12.32 years||5.7 (average)|
|Polonium-210||166500 TBq/kg (4500 Ci/g)||138.376 days||5304.5|
|Uranium-238||12580 KBq/kg (0.00000034 Ci/g)||4.468 billion years||4267|
|Isotope||Activity||Half-life||Radiation types||Energies (keV)|
|Caesium-137||3256 TBq/kg (88 Ci/g)||30.1 years||Gamma & beta||G: 32, 661.6 B: 511.6, 1173.2|
|Americium-241||129.5 TBq/kg (3.5 Ci/g)||432.2 years||Gamma & alpha||G: 59.5, 26.3, 13.9 A: 5485, 5443|
Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms or 'decays' into a different atomic nucleus, with a mass number that is reduced by four and an atomic number that is reduced by two. An alpha particle is identical to the nucleus of a helium-4 atom, which consists of two protons and two neutrons. It has a charge of +2 e and a mass of 4 u. For example, uranium-238 decays to form thorium-234. Alpha particles have a charge +2 e, but as a nuclear equation describes a nuclear reaction without considering the electrons – a convention that does not imply that the nuclei necessarily occur in neutral atoms – the charge is not usually shown.
Neutron activation analysis (NAA) is a nuclear process used for determining the concentrations of elements in a vast amount of materials. NAA allows discrete sampling of elements as it disregards the chemical form of a sample, and focuses solely on its nucleus. The method is based on neutron activation and therefore requires a source of neutrons. The sample is bombarded with neutrons, causing the elements to form radioactive isotopes. The radioactive emissions and radioactive decay paths for each element are well known. Using this information, it is possible to study spectra of the emissions of the radioactive sample, and determine the concentrations of the elements within it. A particular advantage of this technique is that it does not destroy the sample, and thus has been used for analysis of works of art and historical artifacts. NAA can also be used to determine the activity of a radioactive sample.
A synthetic radioisotope is a radionuclide that is not found in nature: no natural process or mechanism exists which produces it, or it is so unstable that it decays away in a very short period of time. Examples include technetium-95 and promethium-146. Many of these are found in, and harvested from, spent nuclear fuel assemblies. Some must be manufactured in particle accelerators.
A nuclide is an atomic species characterized by the specific constitution of its nucleus, i.e., by its number of protons Z, its number of neutrons N, and its nuclear energy state.
Radioactive decay is the process by which an unstable atomic nucleus loses energy by emitting radiation, such as an alpha particle, beta particle with neutrino or only a neutrino in the case of electron capture, or a gamma ray or electron in the case of internal conversion. A material containing such unstable nuclei is considered radioactive. Certain highly excited short-lived nuclear states can decay through neutron emission, or more rarely, proton emission.
In nuclear science, the decay chain refers to a series of radioactive decays of different radioactive decay products as a sequential series of transformations. It is also known as a "radioactive cascade". Most radioisotopes do not decay directly to a stable state, but rather undergo a series of decays until eventually a stable isotope is reached.
Nuclear fission products are the atomic fragments left after a large atomic nucleus undergoes nuclear fission. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons, the release of heat energy, and gamma rays. The two smaller nuclei are the fission products..
Radiochemistry is the chemistry of radioactive materials, where radioactive isotopes of elements are used to study the properties and chemical reactions of non-radioactive isotopes. Much of radiochemistry deals with the use of radioactivity to study ordinary chemical reactions. This is very different from radiation chemistry where the radiation levels are kept too low to influence the chemistry.
There are 37 known isotopes of iodine (53I) from 108I to 144I; all undergo radioactive decay except 127I, which is stable. Iodine is thus a monoisotopic element.
Caesium (55Cs) has 40 known isotopes, making it, along with barium and mercury, the element with the most isotopes. The atomic masses of these isotopes range from 112 to 151. Only one isotope, 133Cs, is stable. The longest-lived radioisotopes are 135Cs with a half-life of 2.3 million years, 137Cs with a half-life of 30.1671 years and 134Cs with a half-life of 2.0652 years. All other isotopes have half-lives less than 2 weeks, most under an hour.
Naturally occurring zirconium (40Zr) is composed of four stable isotopes (of which one may in the future be found radioactive), and one very long-lived radioisotope (96Zr), a primordial nuclide that decays via double beta decay with an observed half-life of 2.0×1019 years; it can also undergo single beta decay, which is not yet observed, but the theoretically predicted value of t1/2 is 2.4×1020 years. The second most stable radioisotope is 93Zr, which has a half-life of 1.53 million years. Twenty-seven other radioisotopes have been observed. All have half-lives less than a day except for 95Zr (64.02 days), 88Zr (83.4 days), and 89Zr (78.41 hours). The primary decay mode is electron capture for isotopes lighter than 92Zr, and the primary mode for heavier isotopes is beta decay.
Radionuclides which emit gamma radiation are valuable in a range of different industrial, scientific and medical technologies. This article lists some common gamma-emitting radionuclides of technological importance, and their properties.
Iodine-125 (125I) is a radioisotope of iodine which has uses in biological assays, nuclear medicine imaging and in radiation therapy as brachytherapy to treat a number of conditions, including prostate cancer, uveal melanomas, and brain tumors. It is the second longest-lived radioisotope of iodine, after iodine-129.
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 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.
Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number. All isotopes of a given element have the same number of protons but different numbers of neutrons in each atom.
Alpha particles, also called alpha ray or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay, but may also be produced in other ways. Alpha particles are named after the first letter in the Greek alphabet, α. The symbol for the alpha particle is α or α2+. Because they are identical to helium nuclei, they are also sometimes written as He2+
indicating a helium ion with a +2 charge. If the ion gains electrons from its environment, the alpha particle becomes a normal helium atom 4
In geochemistry, geophysics and geonuclear physics, primordial nuclides, also known as primordial isotopes, are nuclides found on Earth that have existed in their current form since before Earth was formed. Primordial nuclides were present in the interstellar medium from which the solar system was formed, and were formed in, or after, the Big Bang, by nucleosynthesis in stars and supernovae followed by mass ejection, by cosmic ray spallation, and potentially from other processes. They are the stable nuclides plus the long-lived fraction of radionuclides surviving in the primordial solar nebula through planet accretion until the present. Only 286 such nuclides are known.
Nuclear transmutation is the conversion of one chemical element or an isotope into another chemical element. Because any element is defined by its number of protons in its atoms, i.e. in the atomic nucleus, nuclear transmutation occurs in any process where the number of protons or neutrons in the nucleus is changed.
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