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.
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))
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)
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.
On Earth, naturally occurring radionuclides fall into three categories: primordial radionuclides, secondary radionuclides, and cosmogenic radionuclides.
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|
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.
|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||1.95×107 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|
Cardiac ventriculography is a medical imaging test used to determine a person's heart function in the right, or left ventricle. Cardiac ventriculography involves injecting contrast media into the heart's ventricle(s) to measure the volume of blood pumped. Cardiac ventriculography can be performed with a radionuclide in radionuclide ventriculography or with an iodine-based contrast in cardiac chamber catheterization.
The 3 major measurements obtained by cardiac ventriculography are:
Cardiac OutputThese three measurements share a commonality of ratios between end systolic volume and end diastolic volume and all lend mathematical structure to the common medical term systole.DMSA scan
A DMSA scan is a radionuclide scan that uses dimercaptosuccinic acid (DMSA) in assessing renal morphology, structure and function. Radioactive technetium-99m is combined with DMSA and injected into a patient, followed by imaging with a gamma camera after 2-3 hours. A DMSA scan is usually static imaging, other radiotracers like DTPA & MAG3 are usually used for dynamic imaging to assess renal excretion.The major clinical indications for this investigation are
Detection and/or evaluation of a renal scar especially in patients having vesicoureteric reflux (VUR).
Small or absent kidney (renal agenesis),
Ectopic kidneys (sometimes cannot be visualized by ultrasonography of abdomen due to intestinal gas)
Evaluation of an occult duplex system,
Characterization of certain renal masses,
Evaluation of systemic hypertension especially young hypertensive and in cases of suspected vasculitis.
It is sometimes used as a test for the diagnosis of acute pyelonephritis. However, the sensitivity of DMSA scan for acute pyelonephritis may be as low as 46%.
Procedure: Patient is injected with 2-5 mCi of Technetium-99m DMSA intravenously and static imaging is done using Gamma camera after 2-3 hours. Imaging time is approximately 5 - 10 minutes depending on the views take. Usually posterior and oblique views are must for better interpretation of the scan. Patient is asked to maintain good hydration before and after the radiotracer injection by drinking water or intravenous fluid administration, if patient cannot drink water for any reason. Usually fasting in not required for scanning purpose and patients can have light breakfast in the morning of the scan day.
The technetium-99m DMSA binds to the proximal convoluted tubules in kidney so the excretion pattern of the kidneys cannot be assessed by this for which renal dynamic scans using radiotracers like DTPA, MAG3 are used.Extinct radionuclide
An extinct radionuclide is a radionuclide that was formed by nucleosynthesis before the formation of the Solar System, about 4.6 billion years ago, and incorporated into it, but has since decayed to virtually zero abundance, due to having a half-life shorter than about 100 million years.
Short-lived radioisotopes that are found in nature are continuously generated or replenished by natural processes, such as cosmic rays (cosmogenic nuclides), background radiation, or the decay chain or spontaneous fission of very long-lived isotopes such as uranium or thorium.
Short-lived isotopes that are not generated or replenished by natural processes are not found in nature, so they are known as extinct radionuclides. Their former existence is inferred from a superabundance of their stable decay products.
Examples of extinct radionuclides include iodine-129 (the first to be noted in 1960, inferred from excess xenon-129 concentrations in meteorites, in the xenon-iodine dating system), aluminium-26 (inferred from extra magnesium-26 found in meteorites), and iron-60.
The Solar System and Earth formed from primordial nuclides and extinct nuclides. Extinct nuclides have decayed away, but primordial nuclides still exist in their original state (undecayed). There are 253 stable primordial nuclides, and remainders of 33 primordial radionuclides that have very long half-lives.Indium (111In) capromab pendetide
Indium (111In) capromab pendetide (trade name Prostascint) is used to image the extent of prostate cancer. Capromab is a mouse monoclonal antibody which recognizes a protein found on both prostate cancer cells and normal prostate tissue. It is linked to pendetide, a derivative of DTPA. Pendetide acts as a chelating agent for the radionuclide indium-111. Following an intravenous injection of Prostascint, imaging is performed using single photon emission computed tomography (SPECT).Early trials with yttrium (90Y) capromab pendetide were also conducted.Indium (111In) satumomab pendetide
Indium (111In) satumomab pendetide (trade name OncoScint CR103) is a mouse monoclonal antibody which is used for cancer diagnosis. The antibody, satumomab, is linked to pendetide, a derivative of DTPA. Pendetide acts as a chelating agent for the radionuclide indium-111.Lymphogram
Lymphography is a medical imaging technique in which a radiocontrast agent is injected, and then an X-ray picture is taken to visualize structures of the lymphatic system, including lymph nodes, lymph ducts, lymphatic tissues, lymph capillaries and lymph vessels. Lymphangiography is the same procedure, used only to visualize the lymph vessels. The X-ray film or image of the vessels and nodes is called a lymphogram or a lymphangiogram.
Radiographs can be taken after injection of a radiopaque contrast medium into small lymphatic vessels (these are made visible by prior subcutaneous injection of patent blue dye). The resulting lymphogram is used to find the locations of large vessels and nodes, and to identify sites of blockage in lymphatic drainage.
Lymph nodes can also be detected via radionuclide imaging after injection of radioactive colloids. Macrophages phagocytose these foreign bodies and sequester in the nodes.Nuclear medicine
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.Peptide receptor radionuclide therapy
Peptide receptor radionuclide therapy (PRRT) is a type of unsealed source radiotherapy, using a radiopharmaceutical which targets peptide receptors to deliver localised treatment, typically for neuroendocrine tumours (NETs).Perfusion scanning
Perfusion is the passage of fluid through the lymphatic system or blood vessels to an organ or a tissue. The practice of perfusion scanning, is the process by which this perfusion can be observed, recorded and quantified. The term perfusion scanning encompasses a wide range of medical imaging modalities.Primordial nuclide
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.Radionuclide angiography
Radionuclide angiography is an area of nuclear medicine which specialises in imaging to show the functionality of the right and left ventricles of the heart, thus allowing informed diagnostic intervention in heart failure. It involves use of a radiopharmaceutical, injected into a patient, and a gamma camera for acquisition. A MUGA scan (multigated acquisition) involves an acquisition triggered (gated) at different points of the cardiac cycle. MUGA scanning is also called equilibrium radionuclide angiocardiography, radionuclide ventriculography (RNVG), or gated blood pool imaging, as well as SYMA scanning (synchronized multigated acquisition scanning).
This mode of imaging uniquely provides a cine type of image of the beating heart, and allows the interpreter to determine the efficiency of the individual heart valves and chambers. MUGA/Cine scanning represents a robust adjunct to the now more common echocardiogram. Mathematics regarding acquisition of cardiac output (Q) is well served by both of these methods as well as other inexpensive models supporting ejection fraction as a product of the heart/myocardium in systole. The advantage of a MUGA scan over an echocardiogram or an angiogram is its accuracy. An echocardiogram measures the shortening fraction of the ventricle and is limited by the user's ability. Furthermore, an angiogram is invasive and, often, more expensive. A MUGA scan provides a more accurate representation of cardiac ejection fraction.Radionuclide ventriculography
Radionuclide ventriculography, a type of cardiac ventriculography, is a form of nuclear imaging, where a gamma camera is used to create an image following injection of radioactive material, usually Technetium-99m (99mTc) labeled red blood cells. In radionuclide ventriculography, the radionuclide has the property of circulating through the cardiac chambers, availing for studies of the pumping function of the heart. In contrast, in myocardial perfusion imaging, the radionuclide is taken up by the myocardial cells, making its presence correlating with myocardial perfusion or viability of the cells.Radionuclide ventriculography is done to evaluate coronary artery disease (CAD), valvular heart disease, congenital heart diseases, cardiomyopathy, and other cardiac disorders. It exposes patients to less radiation than do comparable chest x-ray studies. However, the radioactive material is retained in the patient for several days after the test, during which sophisticated radiation alarms may be triggered, such as in airports. Radionuclide ventriculography has largely been replaced by echocardiography, which is less expensive, and does not require radiation exposure. Radionuclide ventriculography gives a much more precise measurement of left ventricular ejection fraction (LVEF) than a transthoracic echocardiogram (TTE). Transthoracic echocardiogram is highly operator dependant, therefore radionuclide ventriculography is a more reproducible measurement of LVEF. Its primary use today is in monitoring cardiac function in patients receiving certain chemotherapeutic agents (anthracyclines: doxorubicin or daunorubicin) which are cardiotoxic. The chemotherapy dose is often determined by the patient's cardiac function. In this setting, a much more accurate measurement of ejection fraction, than a transthoracic echocardiogram can provide, is necessary.Radiopharmacology
Radiopharmacology is radiochemistry applied to medicine and thus the pharmacology of radiopharmaceuticals (medicinal radiocompounds, that is, pharmaceutical drugs that are radioactive). Radiopharmaceuticals are used in the field of nuclear medicine as radioactive tracers in medical imaging and in therapy for many diseases (for example, brachytherapy). Many radiopharmaceuticals use technetium-99m (Tc-99m) which has many useful properties as a gamma-emitting tracer nuclide. In the book Technetium a total of 31 different radiopharmaceuticals based on Tc-99m are listed for imaging and functional studies of the brain, myocardium, thyroid, lungs, liver, gallbladder, kidneys, skeleton, blood and tumors.The term radioisotope, which in its general sense refers to any radioactive isotope (radionuclide), has historically been used to refer to all radiopharmaceuticals, and this usage remains common. Technically, however, many radiopharmaceuticals incorporate a radioactive tracer atom into a larger pharmaceutically-active molecule, which is localized in the body, after which the radionuclide tracer atom allows it to be easily detected with a gamma camera or similar gamma imaging device. An example is fludeoxyglucose in which fluorine-18 is incorporated into deoxyglucose. Some radioisotopes (for example gallium-67, gallium-68, and radioiodine) are used directly as soluble ionic salts, without further modification. This use relies on the chemical and biological properties of the radioisotope itself, to localize it within the body.Secular equilibrium
In nuclear physics, secular equilibrium is a situation in which the quantity of a radioactive isotope remains constant because its production rate (e.g., due to decay of a parent isotope) is equal to its decay rate.Single-photon emission computed tomography
Single-photon emission computed tomography (SPECT, or less commonly, SPET) is a nuclear medicine tomographic imaging technique using gamma rays. It is very similar to conventional nuclear medicine planar imaging using a gamma camera (that is, scintigraphy). but is able to provide true 3D information. This information is typically presented as cross-sectional slices through the patient, but can be freely reformatted or manipulated as required.
The technique requires delivery of a gamma-emitting radioisotope (a radionuclide) into the patient, normally through injection into the bloodstream. On occasion, the radioisotope is a simple soluble dissolved ion, such as an isotope of gallium(III). Most of the time, though, a marker radioisotope is attached to a specific ligand to create a radioligand, whose properties bind it to certain types of tissues. This marriage allows the combination of ligand and radiopharmaceutical to be carried and bound to a place of interest in the body, where the ligand concentration is seen by a gamma camera.Specific activity
Specific activity is the activity per quantity of a radionuclide and is a physical property of that radionuclide.Activity is a quantity related to radioactivity. The SI unit of activity is the becquerel (Bq), equal to one reciprocal second. The becquerel is defined as the number of radioactive transformations per second that occur in a particular radionuclide. Its related non-SI unit equivalent is the Curie (Ci) which is 3.7×1010 transformations per second.
Since the probability of radioactive decay for a given radionuclide is a fixed physical quantity (with some slight exceptions, see changing decay rates), the number of decays that occur in a given time of a specific number of atoms of that radionuclide is also a fixed physical quantity (if there are large enough numbers of atoms to ignore statistical fluctuations).
Thus, specific activity is defined as the activity per quantity of atoms of a particular radionuclide. It is usually given in units of Bq/g, but another commonly used unit of activity is the curie (Ci) allowing the definition of specific activity in Ci/g.Surface exposure dating
Surface exposure dating is a collection of geochronological techniques for estimating the length of time that a rock has been exposed at or near Earth's surface. Surface exposure dating is used to date glacial advances and retreats, erosion history, lava flows, meteorite impacts, rock slides, fault scarps, cave development, and other geological events. It is most useful for rocks which have been exposed for between 10 years and 30,000,000 years.Synthetic radioisotope
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.Targeted alpha-particle therapy
Targeted alpha-particle therapy (or TAT) is an in-development method of targeted radionuclide therapy of various cancers. It employs radioactive substances which undergo alpha decay to treat diseased tissue at close proximity. It has the potential to provide highly targeted treatment, especially to microscopic tumour cells. Targets include leukemias, lymphomas, gliomas, melanoma, and peritoneal carcinomatosis. As in diagnostic nuclear medicine, appropriate radionuclides can be chemically bound to a targeting biomolecule which carries the combined radiopharmaceutical to a specific treatment point.It has been said that "α-emitters are indispensable with regard to optimisation of strategies for tumour therapy".
Radiation (physics and health)
|Central nervous system|