CERIUM (Cerium, Xie) radioactive — chemical element III of group of a periodic system of D. I. Mendeleyev, belongs to ceric subgroup of family of lanthanides (rare earths). Sequence number 58, atomic weight (weight) 140, 12. Cerium is the most widespread element from among lanthanides (see). Its content in crust apprx. 7-10“ 3% on weight. It meets in the minerals containing monazites, bastnasites, cerites and allanites.
C. — plastic, soft metal of silver-white color, its density of 6,657 g! cm3 at 20 °, t 798 °,
t ° ° 3257 °. It has high hi-
michesky activity, in connections of three - or chetyrekhvalenten.
There are 4 stable nuclides of natural C. with mass numbers 136 (0,19%), 138 (0,25%), 140
(88,5%) and 142 ~ 11,1%). 20 radioisotopes C are received by an artificial way. with mass numbers from 128 to 151, three of to-rykh have nuclear isomers (see the Isomerism, an isomerism of atomic kernels). Majority of radioisotopes of C. and its isomers are ultra - and short-lived with hour, minute and second half-lives, the others possess the half-lives exceeding days. Nek-ry radionuclides C. found practical application, mainly as radio tracers, including during the studying of metabolism of C. in an organism and in ra-diotoksikologichesky researches. Marked connections with C. are issued in the form of nitrate, chloride and dioxide of cerium.
139 Of Xie (T x / 2=137,6 days), 141 Xie (T1/2=32,5 days) and 143 Xie (T1/2 =
33 hours) receive radiation of compounds of cerium neutrons in the nuclear reactor, and 139 Xie without carrier with high specific activity and radionuclide purity allocate from the l-An-Tat irradiated on a cyclotron. This radionuclide which is breaking up by electron capture and letting out monoenergetic ^-radiation with energy of Eu = 165,85 kev is used, e.g., in a set of model spectrometer gamma sources, to-ry it is applied, in particular, to quality control of radio of pharmaceuticals (see). 144 You
delyat Xie (T1/2 = 284 days) from cleavage products of heavy elements.
141 Xie, 143 Xie and 144 Xie undergo a beta decay and at the same time let out ^-radiation, on their Krom usually and detect. 144 Xie, breaking up, forms short-lived affiliated radionuclide 144rg (T1/2 = 17,3 min.) with high boundary energy of beta radiation (E0 = 3 Mei) in this connection 144 Xie use as a maternal nuclide of the corresponding isotope generator (see Generators of radioisotopes).
At nuclear explosions radioactive C. comes to the environment and can get into a human body through respiratory organs, skin, and also with food stuffs. The radioactive C which got to an organism. the hl is found. obr. in a liver (apprx. 50%) and a skeleton (to 35%); it is allocated from an organism with a stake and in insignificant quantity with urine.
According to standards of radiation safety (NRB-76), on of 141 Xie's radio toxicity, 143 Xie and 144 Xie carry to group B, i.e. open drugs of these radionuclides activity not higher than 10 mkkyura (370 kBq) can be in a workplace without the permission of a sanepidsluzhba.
Admissible concentration 144 Xie in water of open reservoirs 1,2-10“ 8 curies/l (~ 0,44 kBq/l), in air of workrooms of 6,4*10-12 curies! l (~ 0,24 Bq/l) and in free air 2,2-10 ~ 13 curies! l (8,14 • 10” 3 Bq/l).
See also Isotopes.
Bibliography: JI e in and V. I N. Receiving ra’ dioaktivny isotopes, M., 1972; Standards of radiation safety of NRB-76, M, 1978; Distribution, biological effect, acceleration of removal of radioisotopes, under the editorship of Yu. I. Moskalyov, M., 1964; Table of isotopes, ed. by C. M. Lede-rer a. V. S. Shirley, N. Y., 1978.
V. V. Bochkaryov.