berkelium

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/cm³.

• 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).

• Definition

  A silvery radioactive transuranic element of the actinoid series of metals, not found naturally on Earth. Several radioisotopes have been synthesized. The metal reacts with oxygen, steam, and acids.

• Definition

  berkelium: Symbol Bk. A radioactivemetallic transuranic elementbelonging to the actinoids; a.n. 97;mass number of the most stable isotope247 (half-life 1.4 × 103 years); r.d.(calculated) 14. There are eightknown isotopes. It was first producedby G. T. Seborg and associates in1949 by bombarding americium–241with alpha particles.

• 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.

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