A radioactive tracer, radiotracer, or radioactive label is a

synthetic Synthetic may refer to: Science * Synthetic biology * Synthetic chemical or compound, produced by the process of chemical synthesis * Synthetic elements, chemical elements that are not naturally found on Earth and therefore have to be created in ...

derivative of a

natural compound A natural product is a natural compound or substance produced by a living organism—that is, found in nature. In the broadest sense, natural products include any substance produced by life. Natural products can also be prepared by chemical s ...

in which one or more atoms have been replaced by a

radionuclide A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess numbers of either neutrons or protons, giving it excess nuclear energy, and making it unstable. This excess energy can be used in one of three ...

(a radioactive atom). By virtue of its

radioactive decay Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...

, it can be used to explore the mechanism of chemical reactions by tracing the path that the radioisotope follows from reactants to products. Radiolabeling or radiotracing is thus the radioactive form of isotopic labeling. In biological contexts, experiments that use radioisotope tracers are sometimes called radioisotope feeding experiments. Radioisotopes of

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

carbon Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...

phosphorus Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...

sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...

, and

iodine Iodine is a chemical element; it has symbol I and atomic number 53. The heaviest of the stable halogens, it exists at standard conditions as a semi-lustrous, non-metallic solid that melts to form a deep violet liquid at , and boils to a vi ...

have been used extensively to trace the path of biochemical reactions. A radioactive tracer can also be used to track the distribution of a substance within a natural system such as a cell or tissue, or as a flow tracer to track

fluid flow In physics, physical chemistry and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids – liquids and gases. It has several subdisciplines, including (the study of air and other gases in motion ...

. Radioactive tracers are also used to determine the location of fractures created by

hydraulic fracturing Fracking (also known as hydraulic fracturing, fracing, hydrofracturing, or hydrofracking) is a well stimulation technique involving the fracturing of Formation (geology), formations in bedrock by a pressurized liquid. The process involves the ...

in natural gas production.Reis, John C. (1976). ''Environmental Control in Petroleum Engineering.'' Gulf Professional Publishers. Radioactive tracers form the basis of a variety of imaging systems, such as,

PET scan Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in Metabolism, metabolic processes, and in other physiological activities including bloo ...

s, SPECT scans and technetium scans.

Radiocarbon dating Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for Chronological dating, determining the age of an object containing organic material by using the properties of carbon-14, radiocarbon, a radioactive Isotop ...

uses the naturally occurring

carbon-14 Carbon-14, C-14, C or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic matter is the basis of the radiocarbon dating method pioneered by Willard Libby and coll ...

isotope as an isotopic label. In radiopharmaceutical sciences some misuse of established scientific terms exist. Therefore an international "Working Group on Nomenclature in Radiopharmaceutical Chemistry and Related Areas" was formed in 2015 by the Society of Radiopharmaceutical Sciences (SRS). Their goal was to clarify terminology and to establish a standardized nomenclature through global consensus, ensuring consistency and accuracy within the discipline.

Methodology

Isotope Isotopes are distinct nuclear species (or ''nuclides'') of the same chemical element. They have the same atomic number (number of protons in their Atomic nucleus, nuclei) and position in the periodic table (and hence belong to the same chemica ...

s of a

chemical element A chemical element is a chemical substance whose atoms all have the same number of protons. The number of protons is called the atomic number of that element. For example, oxygen has an atomic number of 8: each oxygen atom has 8 protons in its ...

differ only in the mass number. For example, the isotopes of

can be written as ¹H, ²H and ³H, with the mass number superscripted to the left. When the

atomic nucleus The atomic nucleus is the small, dense region consisting of protons and neutrons at the center of an atom, discovered in 1911 by Ernest Rutherford at the Department_of_Physics_and_Astronomy,_University_of_Manchester , University of Manchester ...

of an isotope is unstable, compounds containing this isotope are

radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...

Tritium Tritium () or hydrogen-3 (symbol T or H) is a rare and radioactive isotope of hydrogen with a half-life of ~12.33 years. The tritium nucleus (t, sometimes called a ''triton'') contains one proton and two neutrons, whereas the nucleus of the ...

is an example of a radioactive isotope. The principle behind the use of radioactive tracers is that an

atom Atoms are the basic particles of the chemical elements. An atom consists of a atomic nucleus, nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished fr ...

in a

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

is replaced by another atom, of the same chemical element. The substituting atom, however, is a radioactive isotope. This process is often called radioactive labeling. The power of the technique is due to the fact that radioactive decay is much more energetic than chemical reactions. Therefore, the radioactive isotope can be present in low concentration and its presence detected by sensitive radiation detectors such as

Geiger counter A Geiger counter (, ; also known as a Geiger–Müller counter or G-M counter) is an electronic instrument for detecting and measuring ionizing radiation with the use of a Geiger–Müller tube. It is widely used in applications such as radiat ...

s and

scintillation counter A scintillation counter is an instrument for detecting and measuring ionizing radiation by using the Electron excitation, excitation effect of incident radiation on a Scintillation (physics), scintillating material, and detecting the resultant li ...

George de Hevesy George Charles de Hevesy (born György Bischitz; ; ; 1 August 1885 – 5 July 1966) was a Hungarian radiochemist and Nobel Prize in Chemistry laureate, recognized in 1943 for his key role in the development of radioactive tracers to study ch ...

won the 1943

Nobel Prize for Chemistry The Nobel Prize in Chemistry () is awarded annually by the Royal Swedish Academy of Sciences to scientists in the various fields of chemistry. It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895, awarded for outst ...

"for his work on the use of isotopes as tracers in the study of chemical processes". There are two main ways in which radioactive tracers are used # When a labeled chemical compound undergoes chemical reactions one or more of the products will contain the radioactive label. Analysis of what happens to the radioactive isotope provides detailed information on the mechanism of the chemical reaction. # A radioactive compound is introduced into a living organism and the radio-isotope provides a means to construct an image showing the way in which that compound and its reaction products are distributed around the organism.

Production

The commonly used radioisotopes have short half lives and so do not occur in nature in large amounts. They are produced by

nuclear reaction In nuclear physics and nuclear chemistry, a nuclear reaction is a process in which two atomic nucleus, nuclei, or a nucleus and an external subatomic particle, collide to produce one or more new nuclides. Thus, a nuclear reaction must cause a t ...

s. One of the most important processes is absorption of a neutron by an atomic nucleus, in which the mass number of the element concerned increases by 1 for each neutron absorbed. For example, : ¹³C + n → ¹⁴C In this case the atomic mass increases, but the element is unchanged. In other cases the product nucleus is unstable and decays, typically emitting protons, electrons (

beta particle A beta particle, also called beta ray or beta radiation (symbol β), is a high-energy, high-speed electron or positron emitted by the radioactive decay of an atomic nucleus, known as beta decay. There are two forms of beta decay, β− decay and � ...

) or

alpha particle Alpha particles, also called alpha rays 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 produce ...

s. When a nucleus loses a proton the

atomic number The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of its atomic nucleus. For ordinary nuclei composed of protons and neutrons, this is equal to the proton number (''n''p) or the number of pro ...

decreases by 1. For example, : ³²S + n → ³²P + p Neutron irradiation is performed in a

nuclear reactor A nuclear reactor is a device used to initiate and control a Nuclear fission, fission nuclear chain reaction. They are used for Nuclear power, commercial electricity, nuclear marine propulsion, marine propulsion, Weapons-grade plutonium, weapons ...

. The other main method used to synthesize radioisotopes is proton bombardment. The proton are accelerated to high energy either in a

cyclotron A cyclotron is a type of particle accelerator invented by Ernest Lawrence in 1929–1930 at the University of California, Berkeley, and patented in 1932. Lawrence, Ernest O. ''Method and apparatus for the acceleration of ions'', filed: Januar ...

or a

linear accelerator A linear particle accelerator (often shortened to linac) is a type of particle accelerator that accelerates charged subatomic particles or ions to a high speed by subjecting them to a series of oscillating electric potentials along a linear ...

Tracer isotopes

Hydrogen

(hydrogen-3) is produced by neutron irradiation of ⁶Li: : ⁶Li + n → ⁴He + ³H Tritium has a

half-life Half-life is a mathematical and scientific description of exponential or gradual decay. Half-life, half life or halflife may also refer to: Film * Half-Life (film), ''Half-Life'' (film), a 2008 independent film by Jennifer Phang * ''Half Life: ...

days (approximately 12.32 years) and it decays by

beta decay In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which an atomic nucleus emits a beta particle (fast energetic electron or positron), transforming into an isobar of that nuclide. For example, beta decay of a neutron ...

. The

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

s produced have an average energy of 5.7 keV. Because the emitted electrons have relatively low energy, the detection efficiency by scintillation counting is rather low. However, hydrogen atoms are present in all organic compounds, so tritium is frequently used as a tracer in

biochemical Biochemistry, or biological chemistry, is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology, ...

studies.

Carbon

¹¹C decays by

positron emission Positron emission, beta plus decay, or β+ decay is a subtype of radioactive decay called beta decay, in which a proton inside a radionuclide nucleus is converted into a neutron while releasing a positron and an electron neutrino (). Positron emi ...

with a half-life of ca. 20 min. ¹¹C is one of the isotopes often used in

positron emission tomography Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in metabolic processes, and in other physiological activities including blood flow, r ...

.Fowler J. S. and Wolf A. P. (1982) The synthesis of carbon-11, fluorine-18 and nitrogen-13 labeled radiotracers for biomedical applications. Nucl. Sci. Ser. Natl Acad. Sci. Natl Res. Council Monogr. 1982. ¹⁴C decays by

, with a half-life of 5730 years. It is continuously produced in the upper atmosphere of the earth, so it occurs at a trace level in the environment. However, it is not practical to use naturally-occurring ¹⁴C for tracer studies. Instead it is made by neutron irradiation of the isotope ¹³C which occurs naturally in carbon at about the 1.1% level. ¹⁴C has been used extensively to trace the progress of organic molecules through metabolic pathways.

Nitrogen

¹³N decays by

with a half-life of 9.97 min. It is produced by the nuclear reaction : ¹H + ¹⁶O → ¹³N + ⁴He ¹³N is used in

(PET scan).

Oxygen

¹⁵O decays by positron emission with a half-life of 122 seconds. It is used in positron emission tomography.

Fluorine

¹⁸F decays predominantly by β emission, with a half-life of 109.8 min. It is made by proton bombardment of ¹⁸O in a cyclotron or

linear particle accelerator A linear particle accelerator (often shortened to linac) is a type of particle accelerator that accelerates charged subatomic particles or ions to a high speed by subjecting them to a series of Oscillation, oscillating electric potentials along ...

. It is an important isotope in the

radiopharmaceutical Radiopharmaceuticals, or medicinal radiocompounds, are a group of pharmaceutical drugs containing radioactive isotopes. Radiopharmaceuticals can be used as diagnostic and therapeutic agents. Radiopharmaceuticals emit radiation themselves, which ...

industry. For example, it is used to make labeled fluorodeoxyglucose (FDG) for application in PET scans.

Phosphorus

³²P is made by neutron bombardment of ³²S : ³²S + n → ³²P + p It decays by beta decay with a half-life of 14.29 days. It is commonly used to study protein phosphorylation by

kinases In biochemistry, a kinase () is an enzyme that catalysis, catalyzes the transfer of phosphate groups from High-energy phosphate, high-energy, phosphate-donating molecules to specific Substrate (biochemistry), substrates. This process is known as ...

in biochemistry. ³³P is made in relatively low yield by neutron bombardment of ³¹P. It is also a beta-emitter, with a half-life of 25.4 days. Though more expensive than ³²P, the emitted electrons are less energetic, permitting better resolution in, for example, DNA sequencing. Both isotopes are useful for labeling

nucleotide Nucleotides are Organic compound, organic molecules composed of a nitrogenous base, a pentose sugar and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both o ...

s and other species that contain a

phosphate Phosphates are the naturally occurring form of the element phosphorus. In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthop ...

group.

Sulfur

³⁵S is made by neutron bombardment of ³⁵Cl : ³⁵Cl + n → ³⁵S + p It decays by beta-decay with a half-life of 87.51 days. It is used to label the sulfur-containing amino-acids

methionine Methionine (symbol Met or M) () is an essential amino acid in humans. As the precursor of other non-essential amino acids such as cysteine and taurine, versatile compounds such as SAM-e, and the important antioxidant glutathione, methionine play ...

and

cysteine Cysteine (; symbol Cys or C) is a semiessential proteinogenic amino acid with the chemical formula, formula . The thiol side chain in cysteine enables the formation of Disulfide, disulfide bonds, and often participates in enzymatic reactions as ...

. When a sulfur atom replaces an oxygen atom in a

group on a

a thiophosphate is produced, so ³⁵S can also be used to trace a phosphate group.

Technetium

^99mTc is a very versatile radioisotope, and is the most commonly used radioisotope tracer in medicine. It is easy to produce in a

technetium-99m generator A technetium-99m generator, or colloquially a technetium cow or moly cow, is a device used to extract the metastable isotope 99mTc of technetium from a decaying sample of molybdenum-99. 99Mo has a half-life of 66 hours and can be easily tran ...

, by decay of ⁹⁹Mo. :⁹⁹Mo → ^99mTc + + The molybdenum isotope has a half-life of approximately 66 hours (2.75 days), so the generator has a useful life of about two weeks. Most commercial ^99mTc generators use

column chromatography Column chromatography in chemistry is a chromatography method used to isolate a single chemical compounds, chemical compound from a mixture. Chromatography is able to separate substances based on differential absorption of compounds to the adsorbe ...

, in which ⁹⁹Mo in the form of molybdate, MoO₄²⁻ is adsorbed onto acid alumina (Al₂O₃). When the ⁹⁹Mo decays it forms pertechnetate TcO₄⁻, which because of its single charge is less tightly bound to the alumina. Pulling normal saline solution through the column of immobilized ⁹⁹Mo elutes the soluble ^99mTc, resulting in a saline solution containing the ^99mTc as the dissolved sodium salt of the pertechnetate. The pertechnetate is treated with a

reducing agent In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ). Examples of substances that are common reducing agents include hydrogen, carbon ...

such as Sn²⁺ and a

ligand In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's el ...

. Different ligands form

coordination complex A coordination complex is a chemical compound consisting of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of chemical bond, bound molecules or ions, that are in turn known as ' ...

es which give the technetium enhanced affinity for particular sites in the human body. ^99mTc decays by gamma emission, with a half-life: 6.01 hours. The short half-life ensures that the body-concentration of the radioisotope falls effectively to zero in a few days.

Iodine

¹²³I is produced by proton irradiation of ¹²⁴ Xe. The

caesium Caesium (IUPAC spelling; also spelled cesium in American English) is a chemical element; it has Symbol (chemistry), symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of , which makes it one of only f ...

isotope produced is unstable and decays to ¹²³I. The isotope is usually supplied as the iodide and hypoiodate in dilute sodium hydroxide solution, at high isotopic purity. ¹²³I has also been produced at Oak Ridge National Laboratories by proton bombardment of ¹²³Te. ¹²³I decays by

electron capture Electron capture (K-electron capture, also K-capture, or L-electron capture, L-capture) is a process in which the proton-rich nucleus of an electrically neutral atom absorbs an inner atomic electron, usually from the K or L electron shells. Th ...

with a half-life of 13.22 hours. The emitted 159 keV

gamma ray A gamma ray, also known as gamma radiation (symbol ), is a penetrating form of electromagnetic radiation arising from high energy interactions like the radioactive decay of atomic nuclei or astronomical events like solar flares. It consists o ...

is used in

single-photon emission computed tomography Single-photon emission computed tomography (SPECT, or less commonly, SPET) is a nuclear medicine tomography, tomographic imaging technique using gamma rays. It is very similar to conventional nuclear medicine planar imaging using a gamma camera ...

(SPECT). A 127 keV gamma ray is also emitted. ¹²⁵I is frequently used in

radioimmunoassay A radioimmunoassay (RIA) is an immunoassay that uses radioactive tracer, radiolabeled molecules in a stepwise formation of immune complexes. A RIA is a very sensitive in vitro assay technique used to measure concentrations of substances, usually m ...

s because of its relatively long half-life (59 days) and ability to be detected with high sensitivity by gamma counters. ¹²⁹I is present in the environment as a result of the testing of

nuclear weapons A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either nuclear fission, fission (fission or atomic bomb) or a combination of fission and nuclear fusion, fusion reactions (thermonuclear weap ...

in the atmosphere. It was also produced in the Chernobyl and Fukushima disasters. ¹²⁹I decays with a

of 15.7 million years, with low-energy

beta Beta (, ; uppercase , lowercase , or cursive ; or ) is the second letter of the Greek alphabet. In the system of Greek numerals, it has a value of 2. In Ancient Greek, beta represented the voiced bilabial plosive . In Modern Greek, it represe ...

and

gamma Gamma (; uppercase , lowercase ; ) is the third letter of the Greek alphabet. In the system of Greek numerals it has a value of 3. In Ancient Greek, the letter gamma represented a voiced velar stop . In Modern Greek, this letter normally repr ...

emissions. It is not used as a tracer, though its presence in living organisms, including human beings, can be characterized by measurement of the gamma rays.

Other isotopes

Many other isotopes have been used in specialized radiopharmacological studies. The most widely used is ⁶⁷Ga for

gallium scan A gallium scan is a type of nuclear medicine diagnostic investigation that uses either a gallium-67 (67Ga) or gallium-68 (68Ga) radiopharmaceutical to obtain images of a specific type of tissue, or disease state of tissue. The gamma emission o ...

s. ⁶⁷Ga is used because, like ^99mTc, it is a gamma-ray emitter and various ligands can be attached to the Ga³⁺ ion, forming a

which may have selective affinity for particular sites in the human body. An extensive list of radioactive tracers used in hydraulic fracturing can be found below.

Applications

metabolism Metabolism (, from ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the co ...

research, tritium and ¹⁴C-labeled glucose are commonly used in glucose clamps to measure rates of glucose uptake,

fatty acid synthesis In biochemistry, fatty acid synthesis is the creation of fatty acids from acetyl-CoA and NADPH through the action of enzymes. Two ''De novo synthesis, de novo'' fatty acid syntheses can be distinguished: cytosolic fatty acid synthesis (FAS/FASI) ...

, and other metabolic processes. While radioactive tracers are sometimes still used in human studies,

stable isotope Stable nuclides are Isotope, isotopes of a chemical element whose Nucleon, nucleons are in a configuration that does not permit them the surplus energy required to produce a radioactive emission. The Atomic nucleus, nuclei of such isotopes are no ...

tracers such as ¹³C are more commonly used in current human clamp studies. Radioactive tracers are also used to study

lipoprotein A lipoprotein is a biochemical assembly whose primary function is to transport hydrophobic lipid (also known as fat) molecules in water, as in blood plasma or other extracellular fluids. They consist of a triglyceride and cholesterol center, sur ...

metabolism in humans and experimental animals. In

medicine Medicine is the science and Praxis (process), practice of caring for patients, managing the Medical diagnosis, diagnosis, prognosis, Preventive medicine, prevention, therapy, treatment, Palliative care, palliation of their injury or disease, ...

, tracers are applied in a number of tests, such as ^99mTc in autoradiography and

nuclear medicine Nuclear medicine (nuclear radiology, nucleology), is a medical specialty involving the application of radioactivity, radioactive substances in the diagnosis and treatment of disease. Nuclear imaging is, in a sense, ''radiology done inside out'', ...

, including

(SPECT), positron emission tomography (PET) and

scintigraphy Scintigraphy (from Latin ''scintilla'', "spark"), also known as a gamma scan, is a diagnostic test in nuclear medicine, where radioisotopes attached to drugs that travel to a specific organ or tissue (radiopharmaceuticals) are taken internally a ...

. The

urea breath test The urea breath test is a rapid diagnostic procedure used to identify infections by ''Helicobacter pylori'', a spiral bacterium implicated in gastritis, gastric ulcer, and peptic ulcer disease. It is based upon the ability of ''H. pylori'' to ...

for

helicobacter pylori ''Helicobacter pylori'', previously known as ''Campylobacter pylori'', is a gram-negative, Flagellum#bacterial, flagellated, Bacterial cellular morphologies#Helical, helical bacterium. Mutants can have a rod or curved rod shape that exhibits l ...

commonly used a dose of ¹⁴C labeled urea to detect h. pylori infection. If the labeled urea was metabolized by h. pylori in the stomach, the patient's breath would contain labeled carbon dioxide. In recent years, the use of substances enriched in the non-radioactive isotope ¹³C has become the preferred method, avoiding patient exposure to radioactivity. In

, radioactive tracer isotopes are injected with hydraulic fracturing fluid to determine the injection profile and location of created fractures. Tracers with different half-lives are used for each stage of hydraulic fracturing. In the United States amounts per injection of radionuclide are listed in the US

Nuclear Regulatory Commission The United States Nuclear Regulatory Commission (NRC) is an independent agency of the United States government tasked with protecting public health and safety related to nuclear energy. Established by the Energy Reorganization Act of 1974, the ...

(NRC) guidelines. According to the NRC, some of the most commonly used tracers include

antimony-124 Antimony (Sb) occurs in two stable isotopes, Sb and Sb. There are 37 artificial radioactive isotopes, the longest-lived of which are Sb, with a half-life of 2.75856 years; Sb, with half-life 60.2 days; and Sb, with half-life 12.35 days. All other ...

, bromine-82,

iodine-125 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 tumor ...

, iodine-131, iridium-192, and scandium-46. A 2003 publication by the

International Atomic Energy Agency The International Atomic Energy Agency (IAEA) is an intergovernmental organization that seeks to promote the peaceful use of nuclear technology, nuclear energy and to inhibit its use for any military purpose, including nuclear weapons. It was ...

confirms the frequent use of most of the tracers above, and says that manganese-56,

sodium-24 There are 20 isotopes of sodium (11Na), ranging from to (except for the still-unknown 36Na and 38Na), and five isomers (two for , and one each for , , and ). is the only stable (and the only primordial) isotope. It is considered a monoisotopi ...

technetium-99m Technetium-99m (99mTc) is a metastable nuclear isomer of technetium-99 (itself an isotope of technetium), symbolized as 99mTc, that is used in tens of millions of medical diagnostic procedures annually, making it the most commonly used Radiophar ...

, silver-110m, argon-41, and xenon-133 are also used extensively because they are easily identified and measured.

References

External links

National Isotope Development Center
U.S. Government resources for radioisotopes - production, distribution, and information
Isotope Development & Production for Research and Applications (IDPRA)
U.S. Department of Energy program sponsoring isotope production and production research and development {{DEFAULTSORT:Radioactive Tracer Radiobiology Radiology Radiopharmaceuticals Radioactivity Biochemistry methods Medicinal radiochemistry