Isotope

When isotopes are called nuclides in their relation to each other when their atomic nuclei equal number of protons ( same atomic number ) but different numbers of neutrons contain. Then make one and the same element that, that are chemically almost identical, but have different mass numbers. The term isotope is older than the more general term nuclide and is therefore still often used as a synonym nuclide.

The name (from the Greek ἴσος isos "equal" and τόπος, tópos " location, location " ) comes from the fact that the isotopes of an element in the periodic table are in the same place. Separated from each other, they are shown in a chart of nuclides.

The term isotope was coined by Frederick Soddy, who received the Nobel Prize in Chemistry for his work and findings in the area of ​​isotopes and radionuclides 1921.

In general, each naturally occurring element has one or a few stable isotopes, while his remaining radioactive isotopes (ie, unstable ), and sooner or later fall apart. However, there are elements in which all isotopes are unstable.

Notation for isotopes

To identify a specific isotope of an element, the mass number is added to the element symbol on the top left. The atomic number is already given by the name (the element symbol ), but can also be written on the bottom left of the element symbol, if they - for example, in nuclear reactions - is of interest, as in

In running text, the mass number is often simply added to the element symbol or the full element name with hyphen, eg U -235, uranium -235, C -14, carbon-14, which was also the speech.

If in the name of another m (eg 16m1N ), this refers to a Kernisomer. If behind the m is a number, this is a numbering if multiple isomers exist.

Chemical reactions of isotopes

In their chemical behavior to isotopes of an element do not differ in the types of possible reactions, but also in their response speed because these weakly depends on the mass.

For heavy elements, however, the relative mass difference is very small. For example, the ratio of the atomic masses of the uranium -238 and uranium -235 1:1,013; in their chemical behavior is not a noticeable difference, to separate physical methods must be used (see enrichment). In the lithium isotopes Li -7 and Li -6, the ratio 1:1.17; here physicochemical separation methods are already available (see lithium). In the three hydrogen isotopes, the mass differences are very large (1H: 2H: 3H as 1:2:3 ), which is why they react chemically slightly different and even got its own name and element symbols:

• By far the most common hydrogen isotope 1H is also known as protium, or light hydrogen.
• 2H, the isotope is also referred to as deuterium or heavy hydrogen. Element symbol: D.
• 3H, the isotope is also referred to as tritium or heavy hydrogen. Element symbol: T.

An example of the different chemical behavior of H and D occurs in the electrolysis of water, in the preferred water with the normal 1H reacts and decomposes into hydrogen and oxygen, while water molecules containing D (2H deuterium, heavy hydrogen), the residual water enriched ( compared to the natural ratio of about 1:7000 ).

Stable isotopes

Stable isotopes are the isotopes of an element that are not radioactive, so do not fall apart. Most on earth naturally occurring isotopes are stable or have extremely long half-lives. Examples of such extremely long-lived isotopes 232Th and 209Bi, whose radioactivity was detected only in 2003. Nuclides with such a long half-lives and stable nuclides are known as primordial nuclides.

The chart of nuclides stable isotopes are commonly found in a central region between the beta plus and beta minus emitters.

With 10 stable isotopes of tin has the most naturally occurring isotopes.

Of the 22 pure elements or anisotopen elements exists only one stable or very long-lived isotope. These are: beryllium fluoride, sodium, aluminum, phosphorus, scandium, manganese, cobalt, arsenic, yttrium, niobium, rhodium, iodine, cesium, praseodymium, terbium, holmium, thulium, gold, bismuth, thorium and plutonium.

The naturally occurring isotopes of the latter three elements, 209Bi, 232Th and 244Pu, have half-lives of 1.9 x 1019 years 1.4 × 1010 years, or 8 × 107 years.

Known isotopes

Hydrogen

Deuterium (2H or deuterium ) is used in the heavy-water reactor as moderator. About Heavy hydrogen ( 3H or tritium) is radioactive. It arises, for example, in the atmosphere by cosmic radiation and also in nuclear reactors. Tritium was used between about 1960 and 1998 in light colors for clock dials etc.. In larger amounts, it is to be produced and used in the future as a part of the fuel for nuclear fusion reactors.

Carbon

A well-known isotope is the radioactive 14C, which is used to determine the age of organic materials (archeology) ( radiocarbon method). Carbon (C) is mainly present in the stable isotope 12 C and 13C.

Oxygen

For the investigation of paleo- temperatures, especially the ratio of the two stable oxygen isotopes 18O and 16O is taken.

Uranium

The isotope 235U is used as fuel in nuclear power plants. For most reactor types, the natural uranium must be enriched to in U235. Almost pure 235U is used in nuclear weapons. In most nuclear weapons, however, plutonium is used today, as it can be obtained without additional enrichment process from spent nuclear reactor fuel.

Plutonium

239Pu has the same use as 235U. 238Pu is because of its radioactive decay heat in space to generate electricity in radioisotope generators used if because solar cells are no longer applicable to a large distance from the sun.

Isotopes in analytics

( See also isotope study )

In measurements of the optical spectrum with sufficient resolution isotopes of an element can be distinguished by their spectral ( isotope ).

The isotopic composition of a sample is usually determined with a mass spectrometer, in the case of trace isotopes by accelerator mass spectrometry.

Radioactive isotopes can often be identified by their degradation products or the emitted ionizing radiation.

Isotopes also play a role in NMR spectroscopy. The concentration of 13C is measured, for example, in NMR spectroscopy of organic compounds, since it, in contrast to more common isotope 12 C has a non-zero nuclear spin, and hence a magnetic moment.

Isotopes are also used in the elucidation of reaction mechanisms or metabolisms using the so-called isotope labeling.

Isotopic composition of water and different characteristic in different parts of the world. These differences allow for example in foods such as wine or cheese to review the declaration of the place of origin.

The investigation of certain isotope patterns (especially 13C isotope patterns ) in organic molecules is called isotopomers analysis. It also allows for the determination of intracellular fluxes in living cells. In addition, the analysis of 13C/12C, 15N/14N- and 34S/32S-Verhältnissen in ecology is widely used today. Based on the fractionation can keep track of material flows in food webs or determine the trophic levels of individual species.

In hydrology it is to draw conclusions on hydrological processes possible by the ratio of isotopes. Stable isotopes are used as natural tracers. Here, the Vienna Standard Mean Ocean Water ( VSMOV ) serves mostly as a reference. The fractionation, ie the ratio of heavy to light isotopes is influenced by different effects. The water cycle accompanies most fluxes above and below the earth.

The geochemistry is concerned with their isotopes in minerals, rocks, soil, water and atmosphere.