berkelium Chemische Eigenschaften,Einsatz,Produktion Methoden
Physikalische Eigenschaften
Berkelium is a metallic element located in group 11 (IB) of the transuranic subseries of theactinide series. Berkelium is located just below the rare-earth metal terbium in the lanthanideseries of the periodic table. Therefore, it has many chemical and physical properties similar toterbium (
65Tb). Its isotopes are very reactive and are not found in nature. Only small amountshave been artificially produced in particle accelerators and by alpha and beta decay.
Its melting point is ～1050°C, its boiling point is unknown, and its density is 14g/cm
3.
Isotopes
There are a total of 23 isotopes of berkelium, none of which are found innature or are stable. Their half-lives range from 600 nanoseconds for Bk-242 to 1,389years for Bk-247, which is also the most stable isotope that by alpha decay transmutatesinto americium-243.
Origin of Name
Named after the nuclear laboratory and the town in which the laboratory
is located: Berkeley, California.
Occurrence
The pure metal of berkelium does not exist in nature and has never been directly artificiallyproduced, although the first isotope of berkelium produced was berkelium-243. It was artificiallyformed by bombarding americium-241 with the nuclei of helium (alpha particles), asfollows:
241Am+(alpha particle = 2 protons + 2 neutron)→
243Bk. (Note: Two protons as wellas two neutrons are found in the nucleus of helium, and thus the two protons changed theatomic number of americium [
95Am] to berkelium [
97Bk].) Today a different process is used toproduce berkelium in small amounts, as follows:
244Cm+(5n = neutrons & λ = gamma rays)→ (becomes)
249Cm →
249Bk + β- = (beta-minus decay).
History
Berkelium, the eighth member of the actinide transition
series, was discovered in December 1949 by Thompson,
Ghiorso, and Seaborg, and was the fifth transuranium element
synthesized. It was produced by cyclotron bombardment of
milligram amounts of 241Am with helium ions at Berkeley,
California. The first isotope produced had a mass number of
243 and decayed with a half-life of 4.5 hours. Thirteen isotopes
are now known and have been synthesized. The existence of
249Bk, with a half-life of 320 days, makes it feasible to isolate
berkelium in weighable amounts so that its properties can be
investigated with macroscopic quantities. One of the first visible
amounts of a pure berkelium compound, berkelium chloride,
was produced in 1962. It weighed 3 billionth of a gram.
Berkelium probably has not yet been prepared in elemental
form, but it is expected to be a silvery metal, easily soluble
in dilute mineral acids, and readily oxidized by air or oxygen
at elevated temperatures to form the oxide. X-ray diffraction
methods have been used to identify the following compounds:
BkO2, BkO3, BkF3, BkCl, and BkOCl. As with other actinide
elements, berkelium tends to accumulate in the skeletal system.
The maximum permissible body burden of 249Bk in the
human skeleton is about 0.0004 μg. Because of its rarity,
berkelium presently has no commercial or technological
use. Berkelium most likely resembles terbium with respect
to chemical properties. Berkelium-249 is available from
O.R.N.L. at a cost of $185/μg plus packing charges.
Charakteristisch
Only milligram amounts of
249Bk have been produced, and most of its other isotopes haveshort half-lives. Therefore, not all of its properties and characteristics and fully known.
Verwenden
Because such small amounts of berkelium have been produced, not many uses for it havebeen found. One use is as a source for producing the element californium by bombardingisotopes of berkelium with high-energy neutrons in nuclear reactors. Berkelium is also usedin some laboratory research.
Definition
Synthetic radioactive element with atomic number 97, first produced (1949) as the 243 isotope by bombarding americium with helium ions in a cyclotron. The chemical properties of berkelium have been studied by tracer techniques and are similar to those of the other transuranium elements. Its oxidation behavior is similar to that of the rare earth cerium. It has a mp of 986C. There are 8 isotopes ranging from 243 to 250; the 249 isotope has been made by neutron bombardment of curium 244. Atomic weight is generally accepted as 249. The following compounds have been identified by X-ray diffraction: berkelium dioxide (BkO2), berkelium sesquioxide (Bk2O 3 ), berkelium trifluoride (BkF3), berkelium trichloride (BkCl 3 ), and berkelium oxychloride (BkOCl).
Hazard
Like the radioactive isotopes of berkelium, its compounds are also extremely dangerousradioactive poisons. Because of the extremely small amounts of berkelium isotopes and compoundsthat exist and are produced, it is unlikely that many people will be exposed to them.
berkelium Upstream-Materialien And Downstream Produkte
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