actinium Chemische Eigenschaften,Einsatz,Produktion Methoden
Physikalische Eigenschaften
Actinium is an extremely radioactive, silvery-white, heavy metal that glows in the dark withan eerie bluish light. It decays rapidly which makes it difficult to study, given that it changesinto thorium and francium through electron capture and alpha decay. Its melting point is1,051°C, its boiling point is 3,198°C, and its density is 10.07g/cm
3.
Isotopes
There are a total of 35 isotopes of actinium, none of which are stable. All areradioactive, and none exist in the Earth’s crust in any large amounts, although a few canbe extracted from large quantities of pitchblende and other minerals. All are extremelyscarce. Those produced artificially in nuclear reactors, cyclotrons, or linear acceleratorshave relatively short half-lives, ranging from 69 nanoseconds to 21 years.
Origin of Name
The name “actinium” is derived from the Greek word(s) aktis or aktinos,
meaning “beam” or “ray.”
Occurrence
Actinium is a rare element that is found in very small amounts in uranium ore (pitchblende),making it difficult and expensive to extract even a small quantity. It is less expensiveand easier to produce small amounts by bombarding the element radium with neutrons in anuclear reactor. Actinium has few commercial uses.
History
Its presence in air was suspected by Cavendish in 1785, discovered by Lord Rayleigh and Sir William Ramsay in 1894.
The gas is prepared by fractionation of liquid air, the atmosphere
containing 0.94% argon. The atmosphere of Mars contains
1.6% of 40Ar and 5 p.p.m. of 36Ar. Argon is two and one
half times as soluble in water as nitrogen, having about the
same solubility as oxygen. It is recognized by the characteristic
lines in the red end of the spectrum. It is used in electric light
bulbs and in fluorescent tubes at a pressure of about 400 Pa,
and in filling photo tubes, glow tubes, etc. Argon is also used
as an inert gas shield for arc welding and cutting, as a blanket
for the production of titanium and other reactive elements,
and as a protective atmosphere for growing silicon and germanium
crystals. Argon is colorless and odorless, both as a
gas and liquid. It is available in high-purity form. Commercial
argon is available at a cost of about 3￠ per cubic foot. Argon
is considered to be a very inert gas and is not known to form
true chemical compounds, as do krypton, xenon, and radon.
However, it does form a hydrate having a dissociation pressure
of 105 atm at 0°C. Ion molecules such as (ArKr)+, (ArXe)+,
(NeAr)+ have been observed spectroscopically. Argon also
forms a clathrate with β-hydroquinone. This clathrate is stable
and can be stored for a considerable time, but a true chemical
bond does not exist. Van der Waals’ forces act to hold the argon.
In August 2000, researchers at the University of Helsinki,
Finland reported they made a new argon compound HArF
4-4 The Elements
by shining UV light on frozen argon that contained a small
amount of HF. Naturally occurring argon is a mixture of three
isotopes. Seventeen other radioactive isotopes are now known
to exist. Commercial argon is priced at about $70/300 cu. ft.
or 8.5 cu. meters.
Charakteristisch
Actinium is the last (bottom) member of group 3 (IIIB) of elements in the periodic tableand the first of the actinide series of metallic elements that share similar chemical and physicalcharacteristics. Actinium is also closely related in its characteristics to the element lanthanum,which is located just above it in group 3. The elements in this series range from atomic number89 (actinium) through 103 (lawrencium). Actinium’s most stable isotope is actinium-227,with a half-life of about 22 years. It decays into Fr-223 by alpha decay and Th-227 throughbeta decay, and both of these isotopes are decay products from uranium-235.
Verwenden
There are no significant uses for actinium because of its scarcity and the expense of producingit. The only practical use for small amounts of actinium is as a tracer in medicine andindustry. It is too difficult to produce in substantial quantities to make it useful. Actiniumcan be used as a source of neutrons to bombard other elements to produce isotopes of thoseelements, but other neutron sources are less expensive.
Definition
actinium: Symbol Ac. A silveryradioactive metallic element belongingto group 3 (formerly IIIA) of theperiodic table; a.n. 89; mass numberof most stable isotope 227 (half-life21.7 years); m.p. 1050 ± 50°C; b.p.3200°C (estimated). Actinium–227 occursin natural uranium to an extentof about 0.715%. Actinium-228 (halflife6.13 hours) also occurs in nature.There are 22 other artificial isotopes,all radioactive and all with very shorthalf-lives. Its chemistry is similar tothat of lanthanum. Its main use is asa source of alpha particles. The elementwas discovered by A. Debiernein 1899.
Hazard
Most of the radioactive isotopes of actinium pose an extreme radiation hazard. They arebone-seeking radioactive poisons.
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