KALIFORNY (Californium; Cf) — artificially received radioactive chemical element VII of group of a periodic system of D. I. Mendeleyev, from family of actinides, sequence number 98. The most stable state California — trivalent.
To. it was for the first time found in 1950 by Thompson, Giorzo, Strit and Siborg (S. G. Thompson, A. Ghiorso, To. Strit, G. Seaborg) in products of radiation of curium (atomic number 96) alpha particles. It is called in the place of opening (the State of California, the USA). It were two isotopes received on nuclear reactions 242 Cm (alpha, 2n) 244 Cf and 242 Cm (alpha, n) 245 Cf. In 1952 at thermonuclear explosion isotope 252Cf was discovered. 15 isotopes K are known. with mass numbers from 242 to 256. Stable isotopes To. has no. Including in medicine, found the greatest practical application 252 Cf as small-size source of intensive neutron emission (see), let out by it at spontaneous division.
Four isotopes K. with mass numbers 249, 250, 251 and 252 are rather steady and can be received in weight quantities by long radiation of uranium or plutonium in the nuclear reactor by a neutron flow of high density on repeated reaction of neutron capture. 252 Cf can be received also on accelerators during the bombing of uranium by heavy ions, napr, kernels of nitrogen, and radiation of an uranium target at thermonuclear explosions.
From among these isotopes 251 Cf is alpha-radioactive (T 1/2 ~ 800 years), and the others experience radioactive transformations as by alpha decay (with T 1/2 249 Cf, 250 Cf, 252 Cf, equal 360 years, 13,2 years and 2,65 years respectively), and spontaneous division (with T 1/2 1,5*10 9 years, 1,7*10 4 years and 85 years respectively).
252 Cf lets out the alpha radiation (97%) with energy of particles of 6,08 and 6,12 MEV and undergoes spontaneous division (3%) with emission 2,3*10 12 neutrons / sek-g. Neutron sources with 252 Cf apply in medicine to an interstitial and contact therapy of malignant new growths, and also to radiography in the form of cores active part long of 4 — 30 mm and to dia. 0,8 — 1,2 mm concluded in a cocoon from platinoiridiyevy alloy or stainless steel. Each source contains 0,5 — 1 mkg 252 Cf, i.e. lets out 1 — 2*10 6 neutrons in 1 sec. Such sources are entered to the patient by means of hollow needles (intrastat) or gather in flexible teflon tubes (see. Neutron therapy ).
On radio toxicity isotopes California, including 252 Cf, concern to group A. Minimum significant activity which is not demanding registration or obtaining permission of bodies State a dignity. supervision, 0,1 mkkyur.
See also Isotopes .
Bibliography: Vdovenko V. M. Modern radiochemistry, page 370, M., 1969; Moskalyov Yu. I. and d river. Biological effect California-252, Radiobiology, t. 14, century 2, page 266, 1974; With and - about r G. T. and Katz of D. D. Himiya of aktinidny elements, the lane with English, M., 1960; Atkins H. L. Possibility of tumor therapy with of £f 252 radiation, Isotopes Rad. Technol., v. 6, p. 410, 1969.
V. V. Bochkaryov.