Americium (Am)
actinideSolid
Masse atomique relative standard
[243]Configuration électronique
[Rn] 7s2 5f7Point de fusion
1175,85 °CPoint d’ébullition
2010,85 °CMasse volumique
1,369e+4 kg/m³États d’oxydation
+2, +3, +4, +5, +6, +7Électronégativité (Pauling)
1,3Énergie d’ionisation (1re)
5,97381 eVAnnée de découverte
1944Rayon atomique
175 pmDétails
Americium is a synthetic transuranium actinide made mainly by neutron capture in plutonium during reactor operation. It is radioactive, silvery in metal form, and chemically resembles other mid-actinides more than the lanthanides only superficially. The most accessible isotope, ²⁴¹Am, has a half-life of about 432 years and is important because it can be isolated from aged plutonium and used as a compact alpha and gamma source.
Americium does not occur naturally in the Earth’s crust. In 1944, it was first synthesized by Glenn T. Seaborg and his team at the University of California Laboratory in Berkeley via multiple neutron capture reaction on 239Pu to produce 241Am : 239Pu (n, γ) 240Pu, 240Pu (n, γ) 241Pu, and 241Pu→ 241Am+β −.
The initial americium samples weighed a few micrograms; they were barely visible and were identified by their radioactivity. The first substantial amounts of metallic americium were not prepared until 1951 via reduction of americium(III) fluoride with barium metal in high vacuum at 1100 °C, producing up to 200 milligrams. 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. In solution, oxidation states III, IV, V, and VI are known and there is an unsubstantiated claim of the existence of Am(VII). Am(IV) is unstable in acidic media but in strongly basic carbonate solutions Am(IV) is stable. In fact, in carbonate solutions, americium has been shown to be the second element after plutonium to have in coexistence all four oxidation states simultaneously. There are numerous compounds of americium. Its oxides have the most practical applications.
Americium was discovered in 1944 by the American scientists Glenn T. Seaborg, Ralph A. James, Leon O. Morgan and Albert Ghiorso. They produced americium by bombarding plutonium-239, an isotope of plutonium, with high energy neutrons. This formed plutonium-240, which was itself bombarded with neutrons. The plutonium-240 changed into plutonium-241, which then decayed into americium-241 through beta decay. This work was carried out at the University of Chicago's Metallurgical Laboratory, now known as Argonne National Laboratory. Americium's most stable isotope, americium-243, has a half-life of about 7,370 years. It decays into neptunium-239 through alpha decay.
Americium was the fourth synthetic transuranic element to be discovered and was named after the continent of North America by analogy to its lighter lanthanide homologue, europium, which was named after Europe, its continent of discovery. Americium was made by Glenn Seaborg, Ralph James, Leon Morgan, and Albert Ghiorso late in 1944 at the wartime metallurgical laboratory at the University of Chicago. It was made as the result of successive neutron capture reactions by plutonium isotopes in a nuclear reactor. The product element was quite difficult to separate based on its anticipated properties, which were incorrect as it turned out. Unlike the lighter previously discovered transuranium elements placed in the main block of the periodic table, americium behaved chemically like the lanthanide series of elements. It exhibited, for example, the trivalent state as the most stable in aqueous solutions. This behavior and the similar behavior of the newly discovered element, curium, prompted Glenn Seaborg to boldly and radically revise the periodic table and create the actinide series of elements.
The first americium isotope identified was that of 241Am, which has an alpha decay half-life of 432.2 years to daughter neptunium-237. The initial discovery was classified as secret as part of the Manhattan Project during World War II, but the discovery was later declassified. Seaborg announced the discovery of elements 95, americium 96, and curium on the U.S. children’s radio show,"The Quiz Kids" five days before his planned presentation at an American Chemical Society meeting in November 1945. His announcement resulted when one of the young listeners asked whether any new transuranium element beside plutonium and neptunium had been discovered.
Pure americium metal has been prepared in milligram quantities. It is a silvery-white, lustrous, radioactive metal that slowly tarnishes in air. Its radioactivity produces self-heating, so macroscopic handling and property measurements require shielding and contamination control.
The principal established use of americium is in sealed ²⁴¹Am sources for ionization smoke detectors, where alpha particles ionize air in a small chamber. ²⁴¹Am is also used in industrial gauges, thickness or density measurements, and as a low-energy gamma source for calibration and analytical instruments. Mixed with beryllium, it has served as a neutron source through alpha-induced reactions. Americium has no structural or bulk-material use.
Americium can be produced in kilogram quantities and has a few practical uses. It is used in smoke detectors and can be used as a portable source of gamma rays. Americium-241, with a half-life of 432.2 years, is used in these products because it is easier to produce relatively pure samples of this isotope.
There are many commercial applications for americium isotopes. Americium-241 has been used as a portable source of both gamma rays and alpha particles for a number of medical and industrial uses. The 60-keV gamma ray emissions from 241Am in such sources can be used for indirect analysis of materials in radiography and X-ray fluorescence spectroscopy, as well as for quality control in fixed nuclear density gauges and nuclear densometers. For example, americium has been employed to gauge glass thickness to help create flat glass. Americium-241 is also suitable for calibration of gamma-ray spectrometers in the low-energy range, since its spectrum consists of nearly a single gamma peak. Americium-241 is also used as the ionization source in commercial smoke detectors. Several unusual applications, such as a nuclear battery or fuel for space ships with nuclear propulsion, have been proposed for the isotope 242mAm, but they are as yet hindered by the scarcity and high price of this isomer.
Isotopes in Industry
241Am (with a half-life of 433 days) is used in smoke detectors as an ionization source to detect smoke (Fig. IUPAC.95.1). A small piece of 241Am oxide is housed inside ionizing smoke detectors. The americium compound emits alpha particles that strike air molecules in their path, causing them to ionize. The ions carry a current from one plate in the detector to a second plate. Current flows continuously until smoke disrupts the current between the two plates. The alarm sounds when the current is disrupted by smoke [75] J. Peterson, M. McDonell, L. Haroun, F. Monette, R. D. Hildebrand, A. Taboas. Radiological and Chemical Fact Sheets to Support Health Risk Analyses for Contaminated Areas, Prepared by Argonne National Laboratory Environmental Science Division in collaboration with U.S. Department of Energy, Richland Operations Office and Chicago Operations Office (2014), Feb. 22; http://www.remm.nlm.gov/ANL_ContaminantFactSheets_All_070418.pdf., [614] Institute of Physics. Episode 509: Radioactive Background and Detectors, Institute of Physics (2014), Feb. 25; http://tap.iop.org/atoms/radioactivity/509/page_47071.html., [615] US Environmental Protection Agency. Americium in Smoke Detectors, US Environmental Protection Agency (2017), April 8; https://www3.epa.gov/radtown/docs/americium-smoke-detectors.pdf..
241Am is used for the control and measurement of industrial material thickness and product quality. In manufacturing, for example, a small piece of 241Am is placed above a conveyer belt and a Geiger counter (used to count alpha particles) is placed below the conveyor belt. A specific quantity of radiation is expected to be measured by the Geiger counter. If the product being manufactured (i.e. glass) is thicker than expected, less radiation will be measured, and the product will be rejected [75] J. Peterson, M. McDonell, L. Haroun, F. Monette, R. D. Hildebrand, A. Taboas. Radiological and Chemical Fact Sheets to Support Health Risk Analyses for Contaminated Areas, Prepared by Argonne National Laboratory Environmental Science Division in collaboration with U.S. Department of Energy, Richland Operations Office and Chicago Operations Office (2014), Feb. 22; http://www.remm.nlm.gov/ANL_ContaminantFactSheets_All_070418.pdf.. The gamma radiation of 241Am is also used in a variety of gauges. Thickness gauges, fluid-density gauges, aircraft fuel gauges, and distance-sensing devices use the density-measuring capabilities of the emitting gamma rays and radiation detector to function.
When 241Am is mixed with beryllium (241AmBe), it emits neutrons at a high rate. This high rate of neutron generation is useful in oil-well operations to monitor the rate of oil production, and it can also be used in well logging to log the porosity (fraction of void volume to total volume of a material) of the geologic units along the sides of a borehole. Gamma rays from 241Am are also used as portable X-ray machines to determine where new wells should be drilled. When a small pellet of 241Am is placed in a sealed titanium capsule, it can serve as a portable source for gamma radiography, which is more penetrating than X-rays, to test various materials for defects, such as invisible cracks or faulty welds in pipelines [75] J. Peterson, M. McDonell, L. Haroun, F. Monette, R. D. Hildebrand, A. Taboas. Radiological and Chemical Fact Sheets to Support Health Risk Analyses for Contaminated Areas, Prepared by Argonne National Laboratory Environmental Science Division in collaboration with U.S. Department of Energy, Richland Operations Office and Chicago Operations Office (2014), Feb. 22; http://www.remm.nlm.gov/ANL_ContaminantFactSheets_All_070418.pdf., [614] Institute of Physics. Episode 509: Radioactive Background and Detectors, Institute of Physics (2014), Feb. 25; http://tap.iop.org/atoms/radioactivity/509/page_47071.html., [616] J. E. Strain, G. W. Leddicotte. The Preparation, Properties, and Uses of Americium-241, Alpha-, Gamma-, and Deutron Sources, ORNL-3335, p. 68. Oak Ridge National Laboratory (1962)..
Isotopes in Medicine
Gamma-ray emissions from 241Am have been used as a radiation source for medical diagnostic tests. In particular, 241Am has helped to provide accurate diagnoses of thyroid function, but this use of americium is now obsolete [617] US Environmental Protection Agency. EPA Facts About Americium-241, US Environmental Protection Agency (2017), April 8; https://semspub.epa.gov/work/HQ/176296.pdf..
Americium chemistry is dominated by the +3 oxidation state in aqueous solution, giving pink to reddish Am³⁺ salts and complexes. Higher oxidation states, including +4, +5, and +6, are known under oxidizing conditions but are less stable than the corresponding states of some lighter actinides. Important compounds include americium dioxide, AmO₂, americium sesquioxide, Am₂O₃, americium trichloride, AmCl₃, and americium nitrate, Am(NO₃)₃. Its coordination chemistry is central to actinide separation research.
See more information at the Americium compound page.
Americium is hazardous chiefly because of ionizing radiation and radiotoxicity after intake. ²⁴¹Am is an alpha emitter with associated gamma emission; external exposure from sealed sources is usually dominated by the gamma component, while inhaled or ingested material can irradiate tissues internally. Americium compounds and contaminated dust require strict containment, shielding, monitoring, and licensed handling.
Americium occurs in the environment only in trace anthropogenic amounts from nuclear weapons fallout, reactor operations, waste processing, and accidental releases. In soils and sediments it commonly binds strongly to mineral surfaces and organic matter, limiting mobility, although complexing agents and colloids can affect transport. It can be taken up by organisms, but it has no known biological role.
Americium is not traded as a normal commodity. It is produced as a by-product of neutron irradiation of plutonium and heavier actinide buildup in nuclear reactors, then recovered by specialized radiochemical processing. Supply is constrained by isotope availability, regulatory controls, waste-handling requirements, and the small number of facilities able to purify and fabricate sealed sources. Demand is limited mainly to smoke detectors, radiation sources, calibration, and research, with substitution often possible where regulatory or disposal costs are high.
Produced by bombarding plutonium with neutrons.
Americium has no stable isotopes and is not a primordial element in measurable natural abundance. In stars it would be made, if at all, only in small amounts during rapid neutron-capture nucleosynthesis and would decay on timescales short compared with the age of the Solar System. Any natural americium on Earth is transient and produced by human nuclear activity rather than inherited cosmic inventory.
- Americium was first identified in plutonium irradiated in a nuclear reactor.
- The element is named after the Americas, by analogy with europium.
- ²⁴¹Am emits a useful 59.5 keV gamma ray.
- Aged plutonium accumulates americium as ²⁴¹Pu decays to ²⁴¹Am.
- Microgram amounts of ²⁴¹Am can be visibly warm in well-insulated conditions.
- Americium is one of the few transuranium elements encountered in consumer products, but only in sealed sources.
Images
Propriétés
Propriétés physiques
- Rayon atomique (empirique)
- 175 pm Comparer : Rayon atomique (empirique) de tous les éléments →
- Rayon covalent
- 180 pm Comparer : Rayon covalent de tous les éléments →
- Rayon de van der Waals
- 244 pm Comparer : Rayon de van der Waals de tous les éléments →
- Masse volumique
- 1,369 × 104 kg/m³ Comparer : Masse volumique de tous les éléments →
- Volume molaire
- 0,0208 L/mol
- Phase aux CNTP
- Solide Comparer : Phase aux CNTP de tous les éléments →
- Point de fusion
- 1175,85 °C Comparer : Point de fusion de tous les éléments →
- Point d’ébullition
- 2010,85 °C Comparer : Point d’ébullition de tous les éléments →
Propriétés chimiques
- Électronégativité (Pauling)
- 1,3 Comparer : Électronégativité (Pauling) de tous les éléments →
- Affinité électronique
- 0,1 eV
- Énergie d’ionisation (1re)
- 5,97381 eV Comparer : Énergie d’ionisation (1re) de tous les éléments →
- Énergie d’ionisation (2e)
- 11,70004 eV Comparer : Énergie d’ionisation (2e) de tous les éléments →
- Énergie d’ionisation (3e)
- 21,700075 eV Comparer : Énergie d’ionisation (3e) de tous les éléments →
- Énergie d’ionisation (4e)
- 36,800127 eV Comparer : Énergie d’ionisation (4e) de tous les éléments →
- Énergie d’ionisation (5e)
- 50,000172 eV Comparer : Énergie d’ionisation (5e) de tous les éléments →
- États d’oxydation
- +2, +3, +4, +5, +6, +7 Comparer : États d’oxydation de tous les éléments →
- Électrons de valence
- 3 Comparer : Électrons de valence de tous les éléments →
- Configuration électronique
- [Rn] 7s2 5f7
Propriétés thermodynamiques
- Enthalpie de fusion
- 0,14914235 eV Comparer : Enthalpie de fusion de tous les éléments →
- Enthalpie de vaporisation
- 2,471887 eV Comparer : Enthalpie de vaporisation de tous les éléments →
- Enthalpie de sublimation
- 2,943463 eV
- Enthalpie d’atomisation
- 2,943463 eV
- Enthalpie d’atomisation
- 2,943463 eV
Propriétés nucléaires
- Protons
- 95 Comparer : Protons de tous les éléments →
- Neutrons
- 148 Comparer : Neutrons de tous les éléments →
- Isotopes connus
- 27 Comparer : Isotopes connus de tous les éléments →
- Isotopes stables
- 0 Comparer : Isotopes stables de tous les éléments →
- Nombre de masse (isotope le plus stable)
- 243
- Isotope le plus stable
- Am-243
- Année de découverte
- 1944
Abondance
N/D
Structure cristalline
N/D
Structure électronique
- Électrons par couche
- 2, 8, 18, 32, 25, 8, 2 Comparer : Électrons par couche de tous les éléments →
Identifiants
- Numéro CAS
- 7440-35-9 Comparer : Numéro CAS de tous les éléments →
- Symbole de terme
- 8S°7/2
- InChI
- InChI=1S/Am
- Clé InChI
- LXQXZNRPTYVCNG-UHFFFAOYSA-N
Configuration électronique Mesuré
Am: 5f⁷ 7s²[Rn] 5f⁷ 7s²1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 4f¹⁴ 5d¹⁰ 6s² 6p⁶ 5f⁷ 7s²Modèle atomique
Les isotopes diffèrent par leur nombre de neutrons, leur masse et leur stabilité — pas par la configuration électronique de l’atome neutre.
Modèle atomique schématique, non à l’échelle.
Empreinte atomique
Spectre d’émission / d’absorption
Distribution isotopique
Aucun isotope stable.
| Nombre de masse | Masse atomique (u) | Abondance naturelle | Demi-vie |
|---|---|---|---|
| 241 Radioactif | 241,0568293 ± 0,0000019 | N/D | 432.6 années |
| 225 Radioactif | 225,045508 ± 0,000429 | N/D | 100 us |
| 226 Radioactif | 226,04613 ± 0,000322 | N/D | 100 us |
| 228 Radioactif | 228,046001 ± 0,000215 | N/D | 100 ms |
| 238 Radioactif | 238,051985 ± 0,000054 | N/D | 98 minutes |
Phase / État
Explication: 1150,8 °C en dessous du point de fusion (1175,85 °C)
Schématique, non à l’échelle
Points de transition de phase
Énergies de transition
Énergie nécessaire pour faire fondre 1 mol au point de fusion
Énergie nécessaire pour vaporiser 1 mol au point d’ébullition
Énergie nécessaire pour sublimer 1 mol au point de sublimation
Masse volumique
Dans les conditions standard
Dans les conditions standard
Spectres atomiques
Affichage de 10 sur 95. Tri par charge ionique croissante.
Raies répertoriées ?
| Ion | Charge | Nombre total de raies | Probabilités de transition | Désignations des niveaux |
|---|---|---|---|---|
| Am I | 0 | 27 | 0 | 0 |
| Am II | +1 | 67 | 0 | 0 |
Niveaux répertoriés ?
| Ion | Charge | Niveaux |
|---|---|---|
| Am I | 0 | 2 |
| Am II | +1 | 2 |
| Am III | +2 | 2 |
| Am IV | +3 | 2 |
| Am V | +4 | 2 |
| Am VI | +5 | 2 |
| Am VII | +6 | 2 |
| Am VIII | +7 | 2 |
| Am IX | +8 | 2 |
| Am X | +9 | 2 |
Données de structure cristalline indisponibles
Rayons ioniques
| Charge | Coordinence | Spin | Rayon |
|---|---|---|---|
| +2 | 7 | N/D | 121 pm |
| +2 | 8 | N/D | 126 pm |
| +2 | 9 | N/D | 131 pm |
| +3 | 6 | N/D | 97.5 pm |
| +3 | 8 | N/D | 109.00000000000001 pm |
| +3 | 9 | N/D | 115.7 pm |
| +4 | 6 | N/D | 85 pm |
| +4 | 8 | N/D | 95 pm |
Composés
Isotopes (5)
About 19 isotopes and 8 nuclear isomers are known for americium. There are two long-lived alpha-emitters, 241Am and 243Am with half-lives of 432.2 and 7,370 years, respectively, and the nuclear isomer 242Am has a half-life of 141 years. The half-lives of other isotopes and isomers range from 0.64 microseconds for 245Am to 50.8 hours for 240Am. As with most other actinides, the isotopes of americium with odd number of neutrons have relatively high rate of nuclear fission and low critical mass. High purity kilogram quantities are now available for the longer lived isotopes, 241Am and 243Am.
| Nombre de masse | Masse atomique (u) | Abondance naturelle | Demi-vie | Mode de désintégration | |
|---|---|---|---|---|---|
| 241 Radioactif | 241,0568293 ± 0,0000019 | N/D | 432.6 années | α =100%SF =3.6e-10±0.9% | |
| 225 Radioactif | 225,045508 ± 0,000429 | N/D | 100 us | α ?SF ? | |
| 226 Radioactif | 226,04613 ± 0,000322 | N/D | 100 us | α ?SF ? | |
| 228 Radioactif | 228,046001 ± 0,000215 | N/D | 100 ms | α ?SF ? | |
| 238 Radioactif | 238,051985 ± 0,000054 | N/D | 98 minutes | β+ =100%α =1.0e-4±0.4% |
Propriétés étendues
Rayons covalents (données étendues)
- Rayon covalent (Pyykkö)
- 166 pm
- Rayon covalent (Pyykkö, liaison double)
- 135 pm
Rayons de van der Waals
- Alvarez
- 283 pm
- UFF
- 338,1 pm
Rayons atomiques et métalliques
- Rayon atomique (Rahm)
- 276 pm
Échelles de numérotation
- Mendeleev
- 26
- Pettifor
- 42
- Glawe
- 39
Échelles d’électronégativité
- Ghosh
- 0
Polarisabilité et dispersion
- Polarisabilité dipolaire
- 131 a.u.
- Polarisabilité dipolaire (incertitude)
- 25 a.u.
Transitions de phase et allotropes
| Point de fusion | 1449,15 K |
Catégories d’états d’oxydation
Données de référence avancées
Détail des rayons cristallins (8)
| Charge | CN | Spin | rcrystal (pm) | Origine |
|---|---|---|---|---|
| 2 | VII | 135 | ||
| 2 | VIII | 140 | ||
| 2 | IX | 145 | ||
| 3 | VI | 111,5 | from r^3 vs V plots, | |
| 3 | VIII | 123 | ||
| 4 | VI | 99 | from r^3 vs V plots, | |
| 4 | VIII | 109 | ||
| 3 | IX | — | 129,7 |
Modes de désintégration des isotopes (50)
| Isotope | Mode | Intensité |
|---|---|---|
| 223 | A | 100% |
| 223 | B+ | — |
| 224 | A | — |
| 224 | SF | — |
| 225 | A | — |
| 225 | SF | — |
| 226 | A | — |
| 226 | SF | — |
| 227 | A | — |
| 227 | SF | — |
Données complémentaires
Estimated Crustal Abundance
The estimated element abundance in the earth's crust.
Not Applicable
Références (1)
- [5] Americium https://education.jlab.org/itselemental/ele095.html
Estimated Oceanic Abundance
The estimated element abundance in the earth's oceans.
Not Applicable
Références (1)
- [5] Americium https://education.jlab.org/itselemental/ele095.html
Références
(9)
Data deposited in or computed by PubChem
The half-life and atomic mass data was provided by the Atomic Mass Data Center at the International Atomic Energy Agency.
Element data are cited from the Atomic weights of the elements (an IUPAC Technical Report). The IUPAC periodic table of elements can be found at https://iupac.org/what-we-do/periodic-table-of-elements/. Additional information can be found within IUPAC publication doi:10.1515/pac-2015-0703 Copyright © 2020 International Union of Pure and Applied Chemistry.
The information are cited from Pure Appl. Chem. 2018; 90(12): 1833-2092, https://doi.org/10.1515/pac-2015-0703.
Thomas Jefferson National Accelerator Facility (Jefferson Lab) is one of 17 national laboratories funded by the U.S. Department of Energy. The lab's primary mission is to conduct basic research of the atom's nucleus using the lab's unique particle accelerator, known as the Continuous Electron Beam Accelerator Facility (CEBAF). For more information visit https://www.jlab.org/
The periodic table at the LANL (Los Alamos National Laboratory) contains basic element information together with the history, source, properties, use, handling and more. The provenance data may be found from the link under the source name.
The periodic table contains NIST's critically-evaluated data on atomic properties of the elements. The provenance data that include data for atomic spectroscopy, X-ray and gamma ray, radiation dosimetry, nuclear physics, and condensed matter physics may be found from the link under the source name. Ref: https://www.nist.gov/pml/atomic-spectra-database
This section provides all form of data related to element Americium.
The element property data was retrieved from publications.