A nuclide (a type of atom) is called a radionuclide or radioactive nuclide if it is unstable and therefore radioactive .
The formulaic designation is the same as for stable nuclides, e.g. B. for the radionuclide cobalt -60:
in the running text also:
- Co-60, Co60 or 60Co.
A special designation for radioactive is not provided. The almost always radioactive core isomers are excluded . To distinguish them from their basic state, they are given a superscript m after the mass number, e.g. B. . Until 1960 the spelling or was common.
The previously common term radioisotope instead of radionuclide should only be used if, in addition to radioactivity, the association with a certain element is important. However, the term isotope can still be found instead of nuclide or especially radionuclide as part of many technical terms such as “isotope laboratory”, “ isotope method ” or “ radioisotope generator ”.
Every radionuclide has its characteristic decay properties such as half-life , type (s) of decay and decay energy. During the decay, alpha or beta radiation and / or gamma radiation are usually produced . The "speed" of this decay is described by the half-life T ½ : after one half-life half of all the atoms initially present have not yet decayed, after two half-lives only a quarter, etc.
On the one hand, radionuclides can be classified according to their type of decay (alpha emitters, beta emitters, etc.) or according to the order of magnitude of their half-life.
On the other hand, a distinction can be made between natural and artificial radionuclides. However, all of the radionuclides naturally occurring on earth today can also be produced artificially; therefore, the incidence of some of them has increased since the beginning of the nuclear age. Examples are carbon-14 ( 14 C) and tritium ( 3 H), which are produced as by-products of the use of nuclear energy.
Natural radionuclides occur in the biosphere or in the earth. Some of them come from the reservoir of the nuclides formed during stellar nucleosynthesis , especially the heavy mineral radionuclides such as uranium-235. These so-called primordial radionuclides must have correspondingly long half-lives. Since the proportion of nuclides formed during nucleosynthesis can be modeled arithmetically and the radionuclides among them decay according to their half-lives, the proportions measured today can be used to infer the age of the matter forming the earth.
Another part of the natural radionuclides is continuously high energy by the interaction of cosmic rays ( cosmic radiation ) with the atmosphere formed. These radionuclides are called cosmogenic. The radioactive carbon isotope 14 C (half-life approx. 5730 years) is the best-known representative of this genus. See radiocarbon method .
The rest of the natural radionuclides are formed by the radioactive decay products of the first genus. These radionuclides are called radiogenic.
Artificial radionuclides are understood to be those that arise from human-induced nuclear reactions . Many artificial radionuclides do not occur in noticeable amounts in nature due to their short half-lives.
- by isolation from the fission product mixture of nuclear reactors ;
- by neutron irradiation in nuclear reactors or with other neutron sources , e.g. B.
- C-14 by reaction 14 N (n, p) 14 C;
- P-32 by the reaction 35 Cl (n, α) 32 P;
- by irradiation with charged particles in accelerators, so-called cyclotron radionuclides, e.g. B.
- F-18 by reaction 18 O (p, n) 18 F;
- O-15 by reaction 14 N (d, n) 15 O.
Some artificial radionuclides, for example for medical use, cannot be transported far and kept in storage because of their short half-life. Instead, they are first separated from their longer-lived mother nuclide in a radionuclide generator for use. Suitable solvents or binders ( elution ) are used for this. A frequently used generator is the 99 Mo- 99m Tc generator.
Overview of the classification of radionuclides
Fission products from nuclear reactors:
|Oxygen -15||2 min|
|Carbon -11||20 min|
|Fluorine -18||110 min|
|Technetium -99m||6 h|
|Iodine -123||13 h|
|Indium -111||2.80 d|
|Phosphorus -32||14.26 d|
|Cobalt -60||5.27 a|
|Chrome -51||28 d|
|Copper -64||12 h|
|Mercury -197||2.7 d|
|Ytterbium -169||30 d|
|Selenium -75||120 d|
Radionuclides are used in many areas of technology and science as well as in medicine. When handling it, make sure that all necessary measures for radiation protection are observed and complied with, applicable law must be taken into account.
In chemistry (more precisely radiochemistry ), for example, radionuclides are used as radio indicators . Connections are marked with radionuclides, that is, radionuclides are built into the connection ( guide isotopes ) in order to carry out changes over time or place (for example, quantity determinations). One advantage of this method is that the radioactively labeled compounds experience the same chemical reactions as their non-radioactive equivalents, but are much easier to distinguish and find (even at low concentrations).
Analogous to this, biology and medicine use similar methods to make metabolic processes in the living organism visible and to examine them ( autoradiography , radiochromatography ). In radiation therapy , enclosed radionuclides are used, for example 60 Co (" cobalt cannon "); see. Nuclear medicine . In addition, radionuclide therapy offers a variety of treatment options. The table on the right shows an example of a selection of some radionuclides and their half-lives . a. can also be used in radiation therapy for cancer. For investigations in vivo , the half-lives should be as short as possible in order to minimize the risk potential for the body.
In technology, for example, radionuclides are used as an energy source (see nuclear power plant , radionuclide battery ).
The German Radiation Protection Ordinance divides radionuclides into four classes depending on the hazard potential.
- Hans Götte, Gerhard Kloss: Nuclear Medicine and Radiochemistry . In: Angewandte Chemie . tape 85 , no. 18 , 1973, p. 793-802 , doi : 10.1002 / anie.19730851803 .
- C. Keller: Fundamentals of Radiochemistry. 3rd edition, Salle & Sauerländer, 1993, ISBN 3-7935-5487-2 .
- C. Keller (Ed.): Experiments on radiochemistry. Diesterweg & Salle & Sauerländer, 1980, ISBN 3-425-05453-8 .
- ↑ a b Chemistry Explained - Indium ( English ) Retrieved August 31, 2011: "Indium-113 is used to examine the liver, spleen, brain, pulmonary (" breathing ") system, and heart and blood system. Indium-111 is used to search for tumors, internal bleeding, abscesses, and infections and to study the gastric (stomach) and blood systems. "