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Radiochemistry is the chemistry of
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 consid ...
materials, where radioactive isotopes of elements are used to study the properties and
chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breakin ...
s of non-radioactive isotopes (often within radiochemistry the absence of radioactivity leads to a substance being described as being ''inactive'' as the isotopes are ''stable''). Much of radiochemistry deals with the use of radioactivity to study ordinary
chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breakin ...
s. This is very different from
radiation chemistry Radiation chemistry is a subdivision of nuclear chemistry which is the study of the chemical effects of radiation on matter; this is very different from radiochemistry as no radioactivity needs to be present in the material which is being chemical ...
where the radiation levels are kept too low to influence the chemistry. Radiochemistry includes the study of both natural and man-made radioisotopes.


Main decay modes

All radioisotopes are unstable isotopes of elements— that undergo
nuclear 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 consid ...
and emit some form of radiation. The radiation emitted can be of several types including
alpha Alpha (uppercase , lowercase ; grc, ἄλφα, ''álpha'', or ell, άλφα, álfa) is the first letter of the Greek alphabet. In the system of Greek numerals, it has a value of one. Alpha is derived from the Phoenician letter aleph , whic ...
,
beta Beta (, ; uppercase , lowercase , or cursive ; grc, βῆτα, bē̂ta or ell, βήτα, víta) is the second letter of the Greek alphabet. In the system of Greek numerals, it has a value of 2. In Modern Greek, it represents the voiced labiod ...
, gamma radiation, proton, and neutron emission along with neutrino and
antiparticle In particle physics, every type of particle is associated with an antiparticle with the same mass but with opposite physical charges (such as electric charge). For example, the antiparticle of the electron is the positron (also known as an antie ...
emission decay pathways. 1. α (alpha) radiation—the emission of an
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 ...
(which contains 2 protons and 2 neutrons) from an atomic nucleus. When this occurs, the atom's
atomic mass The atomic mass (''m''a or ''m'') is the mass of an atom. Although the SI unit of mass is the kilogram (symbol: kg), atomic mass is often expressed in the non-SI unit dalton (symbol: Da) – equivalently, unified atomic mass unit (u). 1&nbs ...
will decrease by 4 units and the
atomic number The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei, this is equal to the proton number (''n''p) or the number of protons found in the nucleus of every ...
will decrease by 2. 2. β (beta) radiation—the transmutation of a neutron into an electron and a proton. After this happens, the electron is emitted from the nucleus into the electron cloud. 3. γ (gamma) radiation—the emission of electromagnetic energy (such as
gamma rays A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically sh ...
) from the nucleus of an atom. This usually occurs during alpha or beta radioactive decay. These three types of radiation can be distinguished by their difference in penetrating power. Alpha can be stopped quite easily by a few centimetres of air or a piece of paper and is equivalent to a helium nucleus. Beta can be cut off by an aluminium sheet just a few millimetres thick and are electrons. Gamma is the most penetrating of the three and is a massless chargeless high-energy photon. Gamma radiation requires an appreciable amount of heavy metal radiation shielding (usually lead or
barium Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element. The ...
-based) to reduce its intensity.


Activation analysis

By neutron irradiation of objects, it is possible to induce radioactivity; this activation of stable isotopes to create radioisotopes is the basis of
neutron activation analysis Neutron activation analysis (NAA) is the nuclear process used for determining the concentrations of elements in many materials. NAA allows discrete sampling of elements as it disregards the chemical form of a sample, and focuses solely on atomic ...
. A high-energy most interesting object which has been studied in this way is the hair of Napoleon's head, which has been examined for its
arsenic Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, but ...
content. A series of different experimental methods exist, these have been designed to enable the measurement of a range of different elements in different matrices. To reduce the effect of the matrix it is common to use the chemical extraction of the wanted element ''and/or'' to allow the radioactivity due to the matrix elements to decay before the measurement of the radioactivity. Since the matrix effect can be corrected by observing the decay spectrum, little or no sample preparation is required for some samples, making neutron activation analysis less susceptible to contamination. The effects of a series of different cooling times can be seen if a hypothetical sample that contains sodium, uranium, and cobalt in a 100:10:1 ratio was subjected to a very short pulse of thermal neutrons. The initial radioactivity would be dominated by the 24Na activity (
half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...
15 h) but with increasing time the 239Np (half-life 2.4 d after formation from parent 239U with half-life 24 min) and finally the 60Co activity (5.3 yr) would predominate.


Biology applications

One biological application is the study of DNA using radioactive phosphorus-32. In these experiments, stable phosphorus is replaced by the chemically identical radioactive P-32, and the resulting radioactivity is used in the analysis of the molecules and their behaviour. Another example is the work that was done on the methylation of elements such as sulfur, selenium,
tellurium Tellurium is a chemical element with the symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur, all three of which are chalcogens. It is occasionally fou ...
, and
polonium Polonium is a chemical element with the symbol Po and atomic number 84. Polonium is a chalcogen. A rare and highly radioactive metal with no stable isotopes, polonium is chemically similar to selenium and tellurium, though its metallic character ...
by living organisms. It has been shown that bacteria can convert these elements into volatile compounds, it is thought that
methylcobalamin Methylcobalamin (mecobalamin, MeCbl, or MeB) is a cobalamin, a form of vitamin B. It differs from cyanocobalamin in that the cyano group at the cobalt is replaced with a methyl group. Methylcobalamin features an octahedral cobalt(III) centre and c ...
( vitamin B12) alkylates these elements to create the dimethyls. It has been shown that a combination of Cobaloxime and inorganic polonium in sterile water forms a volatile polonium compound, while a control experiment that did not contain the
cobalt Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, pro ...
compound did not form the volatile polonium compound. For the sulfur work, the isotope 35S was used, while for polonium 207Po was used. In some related work by the addition of 57Co to the bacterial culture, followed by isolation of the cobalamin from the bacteria (and the measurement of the radioactivity of the isolated cobalamin) it was shown that the bacteria convert available cobalt into methylcobalamin. In medicine PET (Positron Emission Tomography) scans are commonly used for diagnostic purposes in. A radiative tracer is injected intravenously into the patient and then taken to the PET machine. The radioactive tracer releases radiation outward from the patient and the cameras in the machine interpret the radiation rays from the tracer. PET scan machines use solid state scintillation detection because of their high detection efficiency, NaI(Tl) crystals absorb the tracer's radiation and produce photons that get converted into an electrical signal for the machine to analyze.


Environmental

Radiochemistry also includes the study of the behaviour of radioisotopes in the environment; for instance, a forest or grass fire can make radioisotopes mobile again. In these experiments, fires were started in the exclusion zone around Chernobyl and the radioactivity in the air downwind was measured. It is important to note that a vast number of processes can release radioactivity into the environment, for example, the action of cosmic rays on the air is responsible for the formation of radioisotopes (such as 14C and 32P), the decay of 226Ra forms 222Rn which is a gas which can diffuse through rocks before entering buildings and dissolve in water and thus enter drinking water In addition, human activities such as bomb tests, accidents, and normal releases from industry have resulted in the release of radioactivity.


Chemical form of the actinides

The environmental chemistry of some radioactive elements such as plutonium is complicated by the fact that solutions of this element can undergo disproportionation and as a result, many different oxidation states can coexist at once. Some work has been done on the identification of the oxidation state and coordination number of plutonium and the other actinides under different condition

This includes work on both solutions of relatively simple complexes and work on
colloids A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid, while others extend ...
Two of the key matrixes are soil/
rock Rock most often refers to: * Rock (geology), a naturally occurring solid aggregate of minerals or mineraloids * Rock music, a genre of popular music Rock or Rocks may also refer to: Places United Kingdom * Rock, Caerphilly, a location in Wales ...
s and concrete, in these systems the chemical properties of plutonium have been studied using methods such as EXAFS and XANESbr>
http://www.lanl.gov/orgs/nmt/nmtdo/AQarchive/02spring/synchrotron.html]


Movement of colloids

While binding of a metal to the surfaces of the soil particles can prevent its movement through a layer of soil, it is possible for the particles of soil that bear the radioactive metal can migrate as colloidal particles through the soil. This has been shown to occur using soil particles labeled with 134Cs, these are able to move through cracks in the soil.


Normal background

Radioactivity is present everywhere (and has been since the formation of the earth). According to the
International Atomic Energy Agency The International Atomic Energy Agency (IAEA) is an intergovernmental organization that seeks to promote the peaceful use of nuclear energy and to inhibit its use for any military purpose, including nuclear weapons. It was established in 195 ...
, one kilogram of soil typically contains the following amounts of the following three natural radioisotopes 370 Bq 40K (typical range 100–700 Bq), 25 Bq 226Ra (typical range 10–50 Bq), 25 Bq 238U (typical range 10–50 Bq) and 25 Bq 232Th (typical range 7–50 Bq).


Action of microorganisms

The action of micro-organisms can fix uranium;
Thermoanaerobacter ''Thermoanaerobacter'' is a genus in the phylum Bacillota ( Bacteria). Members of this genus are thermophilic and anaerobic, several of them were previously described as ''Clostridium'' species and members of the now obsolete genera ''Acetogeni ...
can use
chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hardne ...
(VI), iron(III),
cobalt Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, pro ...
(III), manganese(IV), and uranium(VI) as electron acceptors while
acetate An acetate is a salt formed by the combination of acetic acid with a base (e.g. alkaline, earthy, metallic, nonmetallic or radical base). "Acetate" also describes the conjugate base or ion (specifically, the negatively charged ion called an ...
, glucose, hydrogen,
lactate Lactate may refer to: * Lactation, the secretion of milk from the mammary glands * Lactate, the conjugate base of lactic acid Lactic acid is an organic acid. It has a molecular formula . It is white in the solid state and it is miscible with w ...
, pyruvate, succinate, and xylose can act as electron donors for the metabolism of the bacteria. In this way, the metals can be reduced to form
magnetite Magnetite is a mineral and one of the main iron ores, with the chemical formula Fe2+Fe3+2O4. It is one of the oxides of iron, and is ferrimagnetic; it is attracted to a magnet and can be magnetized to become a permanent magnet itself. With the ...
(Fe3O4), siderite (FeCO3), rhodochrosite (MnCO3), and uraninite (UO2). Other researchers have also worked on the fixing of uranium using bacteri

http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371%2Fjournal.pbio.004028

Francis R. Livens ''et al.'' (Working at Manchester) have suggested that the reason why ''Geobacter sulfurreducens'' can reduce cations to
uranium dioxide Uranium dioxide or uranium(IV) oxide (), also known as urania or uranous oxide, is an oxide of uranium, and is a black, radioactive, crystalline powder that naturally occurs in the mineral uraninite. It is used in nuclear fuel rods in nuclear react ...
is that the bacteria reduce the uranyl cations to which then undergoes disproportionation to form and UO2. This reasoning was based (at least in part) on the observation that is not converted to an insoluble neptunium oxide by the bacteria.


Education

Despite the growing use of nuclear medicine, the potential expansion of nuclear power plants, and worries about protection against nuclear threats and the management of the nuclear waste generated in past decades, the number of students opting to specialize in nuclear and radiochemistry has decreased significantly over the past few decades. Now, with many experts in these fields approaching retirement age, action is needed to avoid a workforce gap in these critical fields, for example by building student interest in these careers, expanding the educational capacity of universities and colleges, and providing more specific on-the-job training. Nuclear and Radiochemistry (NRC) is mostly being taught at the university level, usually first at the Master- and PhD-degree level. In Europe, substantial effort is being done to harmonize and prepare the NRC education for the industry's and society's future needs. This effort is being coordinated in projects funded by the Coordinated Action supported by the European Atomic Energy Community's 7th Framework Program: The CINCH-II project - Cooperation in education and training In Nuclear Chemistry.


References


External links


ACS radioelectrochemistry
{{Authority control Nuclear chemistry Radioactivity