Isotopes are varieties of any chemical element in the periodic system, D. I. Mendeleev, having a different atomic weight. Different isotopes of any chemical element have the same number of protons in the nucleus and the same number of electron shells of atoms that have the same atomic number and hold certain specific chemical element, designated in table D. I. Mendeleev.
The difference in atomic weight of the isotopes due to the fact that the kernel of their atoms contain different numbers of neutrons.
Isotopes of radioactive isotopes of any element of the periodic system D. I. Mendeleev, the atoms which have an unstable nucleus and move in a steady state by radioactive decay, accompanied by radiation (see Radioactivity). The elements with atomic number greater than 82 all isotopes and radioactive decay by alpha or beta decay. This is the so - called natural radioactive isotopes, found normally in nature. Atoms formed during the breakdown of these elements if they ordinal above 82, in turn exposed to radioactive decay products of which can also be radioactive. It turns out as though the sequential chain, or the so-called family of radioactive isotopes.
There are three natural radioactive family, called the first element of a number of families of uranium, thorium and actinouranium (or sea anemone). To the family of uranium are radium (see) and radon (see). The last element of each row becomes a result of the collapse in one of the stable isotopes of lead with a serial number 82. In addition to these collections, known individual of natural radioactive isotopes of elements with atomic numbers less 82. It potassium-40 and some others. Of them important potassium-40, as it is contained in any living organism.
Radioactive isotopes of all chemical elements can be obtained artificially. It is artificial radioactive isotopes. There are several ways of receiving them. Radioactive isotopes of elements such as strontium, iodine, bromine and other, which occupies a middle place in the periodic system are products of the fission of the uranium nucleus. Of a mixture of these products received in a nuclear reactor (see nuclear Reactors), they emit, using radiochemical and other methods. Radioactive isotopes of almost all items can be obtained on the accelerator of charged particles (see) by bombing sustainable certain atoms, protons or deuterons.
Common method of obtaining radioactive isotopes of the stable isotopes of the same element by their irradiation with neutrons in a nuclear reactor. The method is based on the so-called radiation capture. If the substance is irradiated with neutrons, the latter, without charge, are free to approach the nucleus of an atom and how to "stick" to it, forming a new kernel of the same element, but with one extra neutron. Allocates a certain amount of energy in the form of gamma radiation (see)why the process is called radiative capture. Nuclei with an excess of neutrons are unstable, so the resulting radioactive isotope. With rare exceptions, this way you can get a radioactive isotope of each element.
In the decay of the isotope can be formed isotope, also radioactive. For example, strontium-90 turns into yttrium-90, barium-140 - lanthanum-140, etc.
Artificially were obtained not known in nature transuranium elements with atomic number greater than 92 (neptunium, plutonium, americium, curium, and so on), all isotopes are radioactive. One of them giving rise to yet another radioactive family - the family of neptunium.
When working reactors and accelerators radioactive isotopes are formed in the materials and the details of these facilities and surrounding equipment. This "induced activity", remaining more or less long time after cessation of operation, is undesirable radiation source. Induced activity occurs and in the living organism exposed to neutrons, for example when an accident or during a nuclear explosion.
Activity of the radioactive isotopes measured in units Curie (see "Units") or a derivative of millicurie, microcurie.
Detect and measure the quantity of radioactive isotopes in their radiation, using for this purpose the usual way of measuring radioactivity (see Dosimetry, ionizing radiation). These methods allow to measure the activity about hundredths and thousandths of mikrochori, which corresponds to the weight of the number of isotope less billionths of shares milligrams. This shows that insignificant admixture of radioactive isotopes of an element to its sustainable atoms makes it easy to find this item. Its atoms, thus labelled atoms. Their label is radiation.
Chemical and physico-chemical properties of the radioactive isotopes do not differ from natural elements; their admixture to any substance does not change its behavior in a living organism.
Can such tagged atoms replace stable isotopes in various chemical compounds. The properties of the last will not change, and if you type them in the body, they will behave as usual, its substance. However, due to the radiation easy to detect their presence in the blood, tissues, cells, etc., Radioactive isotopes in these substances are, therefore, indicators or indicators, distribution and fate introduced into the body substances. Therefore they are called "radioactive indicators". Synthesized many inorganic and organic compounds labeled with different radioactive isotopes, for radioisotope diagnostics (see) and for various experimental studies.
Many radioactive isotopes (iodine-131, phosphorus-32, gold-198 and others) are used for radiation therapy (see).
Artificially radioactive isotopes (cobalt-60, cesium-137, and some others, which is the gamma emitters) completely replaced radium, previously used as a radiation source (see Gamma-ray devicesfor medical and technical purposes. Cm. articles by title elements.