| Identification | Back Directory | [Name]
americium | [CAS]
7440-35-9 | [Synonyms]
95Am
Americio
Amerizium
americium
NSC 612825
Chebi:33389
americium atom
americium ISO 9001：2015 REACH | [EINECS(EC#)]
231-144-4 | [Molecular Formula]
C5H12 | [MOL File]
7440-35-9.mol | [Molecular Weight]
72.1488 |
| Chemical Properties | Back Directory | [Melting point ]
1175℃ | [Boiling point ]
bp (calc) 2067° | [density ]
13.671 | [solubility ]
soluble in acid solutions | [form ]
silvery metal | [color ]
silvery metal; hexagonal, hexane or
cubic | [Water Solubility ]
soluble dilute acids [CRC10] | [History]
Americium was the fourth transuranium element to be
discovered; the isotope 241 Am was identified by Seaborg,
James, Morgan, and Ghiorso late in 1944 at the wartime
Metallurgical Laboratory of the University of Chicago as the
result of successive neutron capture reactions by plutonium
isotopes in a nuclear reactor:
239Pu(n,γ)→240Pu(n,γ)→241Pu?β →83Am
Since the isotope 241Am can be prepared in relatively pure form
by extraction as a decay product over a period of years from
strongly neutron-bombarded plutonium, 241Pu, this isotope is
used for much of the chemical investigation of this element.
Better suited is the isotope 243Am due to its longer half-life
(7.37 × 103 years as compared to 432.2 years for 241Am). A mixture
of the isotopes 241Am, 242Am, and 243Am can be prepared
by intense neutron irradiation of 241Am according to the reactions
241Am (n, γ) → 242Am (n, γ) → 243Am. Nearly isotopically
pure, 243Am can be prepared by a sequence of neutron
bombardments and chemical separations as follows: neutron
bombardment of 241Am yields 242Pu by the reactions 241Am (n,
γ) → 242Am → 242Pu, after chemical separation the 242Pu can
be transformed to 243Am via the reactions 242Pu (n, γ) → 243Pu
→ 243Am, and the 243Am can be chemically separated. Fairly
pure 242Pu can be prepared more simply by very intense neutron
irradiation of 239Pu as the result of successive neutroncapture
reactions. Seventeen radioactive isotopes and isomers
are now recognized. Americium metal has been prepared by
reducing the trifluoride with barium vapor at 1000 to 1200°C
or the dioxide by lanthanum metal. The luster of freshly prepared
americium metal is white and more silvery than plutonium
or neptunium prepared in the same manner. It appears
to be more malleable than uranium or neptunium and
tarnishes slowly in dry air at room temperature. Americium
is thought to exist in two forms: an alpha form which has a
double hexagonal close-packed structure and a loose-packed
cubic beta form. Americium must be handled with great care
to avoid personal contamination. As little as 0.03 μCi of 241Am
is the maximum permissible total body burden. The alpha activity
from 241Am is about three times that of radium. When
gram quantities of 241Am are handled, the intense gamma activity
makes exposure a serious problem. Americium dioxide,
AmO2, is the most important oxide. AmF3, AmF4, AmCl3,
AmBr3, AmI3, and other compounds have been prepared. The
isotope 241Am has been used as a portable source for gamma
radiography. It has also been used as a radioactive glass thickness
gage for the flat glass industry, and as a source of ionization
for smoke detectors. Americum-243 (99%) is available
from the Oak Ridge National Laboratory at a cost of about
$750/g plus packing charges. | [EPA Substance Registry System]
Americium (7440-35-9) |
| Hazard Information | Back Directory | [Chemical Properties]
silvery metal with two forms; α-Am: hexagonal, a=0.3468 nm, c=1.1241 nm; β-Am: cub, a=0.4894 nm; t1/2 241Am=433 years, t1/2242Am=152 h, t1/2 243Am=7400 years; Am+++ stable in aqueous solution; enthalpy of vaporization 230 kJ/mol; enthalpy of fusion 14.4 kJ/mol; enthalpy of sublimation 276 kJ/mol; ionic radius of Am+++ is 0.0982nm; can be prepared from 241Pu; used to diagnose thyroid disorders [KIR78] [CIC73] | [Uses]
Gamma radiography, radiochemical research, diagnostic aid, electronic devices. | [Definition]
Am. A synthetic radioactive element of atomic number 95, a member of the actinide series; aw 241; 14 isotopes of widely varying half-life; valence 3, but divalent, tetravalent, and higher valencies exist. α and γ emitter, forms compounds with oxygen, halides, lithium, etc. Metallic americium is silver-white crystalline, d 13.6, mp approximately 100C. Half-life of 241 Am is 458 years. | [Hazard]
A radioactive poison. | [Physical properties]
All the isotopes of americium belonging to the transuranic subseries of the actinide seriesare radioactive and are artificially produced. Americium has similar chemical and physicalcharacteristics and is homologous to europium, located just above it in the rare-earth (lanthanide)series on the periodic table. It is a bright-white malleable heavy metal that is somewhatsimilar to lead. Americium’s melting point is 1,176°C, its boiling point is 2,607°C, and itsdensity is 13.68g/cm3. | [Isotopes]
There are 24 isotopes of americium. All are radioactive with half-lives rangingfrom 72 microseconds to over 7,000 years. Five of americium’s isotopes are fissionablewith spontaneous alpha decay. | [Origin of Name]
Named after the continent America because Europium was named
after the European continent. | [Occurrence]
Americium does not exist in nature. All of its isotopes are man-made and radioactive.Americium-241 is produced by bombarding plutonium-239 with high-energy neutrons,resulting in the isotope plutonium-240 that again is bombarded with neutrons and resultsin the formation of plutonium-241, which in turn finally decays into americium-241 by theprocess of beta decay. Both americium-241 and americium-243 are produced within nuclearreactors. The reaction is as follows: 239Pu + (neutron and λ gamma rays) → 240Pu + (neutronand λ gamma rays) → 241Pu→ 241Am + beta minus (β-); followed by 241Am→ 93Np-237 +4He2 (helium nuclei). | [Characteristics]
Although americium’s main valence (oxidation state) is +3, it is tetravalent. It can formcompounds with its ions of +4, +5, and +6, particularly when oxidized. Its most stable isotopeis americium-243, with a half-life of 7,379 years, which, over time through alpha decay,transmutates into neptunium-239. |
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