Americium

properties
[ Rn ] 5 f 7 7 s 2 95 am Periodic table
General
Name , symbol , atomic number	Americium, Am, 95
Element category	Actinoids
Group , period , block	Ac , 7 , f
Appearance	silvery white metal
CAS number	7440-35-9
EC number	231-144-4
ECHA InfoCard	100.028.313
Atomic
Atomic mass	243.061375 u
Atomic radius	184 pm
Van der Waals radius	228.5 pm
Electron configuration	[ Rn ] 5 f 7 7 s 2
1. Ionization energy	5.97381 (25) eV ≈ 576.38 kJ / mol
2. Ionization energy	11.7 (4) eV ≈ 1 130 kJ / mol
3. Ionization energy	21st.7 (4) eV ≈ 2 090 kJ / mol
4. Ionization energy	36.8 (4) eV ≈ 3 550 kJ / mol
5. Ionization energy	50.0 (1.9) eV ≈ 4 820 kJ / mol
Physically
Physical state	firmly
Crystal structure	hexagonal
density	13.67 g / cm 3
magnetism	paramagnetic ( Χ m = 7.1 · 10 −4 )
Melting point	1449 K (1176 ° C)
boiling point	2880 (2607 ° C)
Molar volume	1.778 10 −5 m 3 mol −1
Heat of evaporation	238.5 kJ / mol
Heat of fusion	14.4 kJ mol −1
Specific heat capacity	0.11 J kg −1 K −1
Electric conductivity	147.1 A V −1 m −1 at 293.15 K.
Thermal conductivity	10 W m −1 K −1 at 300 K
Chemically
Oxidation states	+2, +3 , +4, +5, +6, (+7)
Normal potential	−2.070  V (Am 3+ + 3 e - → Am)
Electronegativity	1.3 ( Pauling scale )
Isotopes
isotope NH t 1/2 ZA ZE (M eV ) ZP 238 On {syn.} 98  min ε  (≈ 100%) 238 Pu α  (1.0 · 10 −4  %) 234 Np 239 On {syn.} 11.9  h ε  (≈ 100%) 239 Pu α  (0.010%) 235 Np 240 am {syn.} 50.8  h ε  (≈ 100%) 240 pu α  (1.9 · 10 −4  %) 236 Np 241 On {syn.} 432.2  a α  (≈ 100%) 5.486 237 Np SF  (4.3 · 10 −10  %) ? ? 242 On {syn.} 16.02  h β -  (82.7%) 0.665 242 cm ε  (17.3%) 0.751 242 Pu 242 m 1 am {syn.} 141  a IT  (≈ 100%) 0.049 242 On α  (0.45%) 5.637 238 Np SF  (4.7 · 10 −9  %) ? ? 242 m 2 Am {syn.} 14.0 m s SF  (≈ 100%) ? ? α 7.788 238 Np IT 2.2 242 On 243 On {syn.} 7370  a α  (≈ 100%) 5.438 239 Np SF  (4.7 · 10 −9  %) ? ? 244 On {syn.} 10.1  h β -  (100%) 244 cm
For other isotopes see list of isotopes
Hazard and safety information
Radioactive
GHS hazard labeling no classification available
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Americium ( listen ^{? / I} ) is a chemical element with the element symbol Am and the atomic number 95. In the periodic table it is in the group of actinides ( 7th period , f-block ) and is also one of the transuranic elements . Besides europium, americium is the only element named after a continent . It is an easily deformable radioactive metal with a silvery-white appearance.

There is no stable isotope of americium . On earth it occurs exclusively in an artificially produced form. The element was first created in late autumn 1944, but the discovery was not initially published. Curiously, its existence was revealed to the public on an American radio show for children by the explorer Glenn T. Seaborg , the show's guest.

Americium is formed in nuclear reactors , and one tonne of spent nuclear fuel contains an average of about 100 g of the element. It is used as a source of ionizing radiation, e.g. B. in fluorescence spectroscopy and in ionization smoke detectors . The americium isotope ²⁴¹ Am was proposed because of its significantly longer half-life of 432.2 years compared to plutonium ( ²³⁸ Pu) for filling radionuclide batteries (RTG) for space probes , which would then provide electrical energy for operation for hundreds of years.

history

Glenn T. Seaborg

60 inch cyclotron

Americium was discovered in the late autumn of 1944 by Glenn T. Seaborg , Ralph A. James , Leon O. Morgan and Albert Ghiorso in the 60-inch cyclotron at the University of California at Berkeley and at the Metallurgical Laboratory of the University of Chicago (today: Argonne National Laboratory ) generated. After neptunium and plutonium , americium was the fourth transuranic uranium to be discovered since 1940; the curium , which is one atomic number higher , was the third produced in the summer of 1944. The name for the element was chosen based on the continent America - in analogy to europium , the rare earth metal that is exactly above americium in the periodic table : The name americium (after the Americas) and the symbol Am are suggested for the element on the basis of its position as the sixth member of the actinide rare-earth series, analogous to europium, Eu, of the lanthanide series.

As a rule, the oxides of the starting elements were used to create the new element . For this purpose, plutonium nitrate solution (with the isotope ²³⁹ Pu) was first applied to a platinum foil of about 0.5 cm ² ; the solution then evaporated and the residue then calcined to oxide (PuO ₂ ). After the bombardment in the cyclotron, the coating was dissolved using nitric acid, then again precipitated as the hydroxide using a concentrated aqueous ammonia solution; the residue was dissolved in perchloric acid. The further separation took place with ion exchangers . In their series of experiments, four different isotopes were generated in sequence: ²⁴¹ Am, ²⁴² Am, ²³⁹ Am and ²³⁸ Am.

They isolated ²⁴¹ Am as the first isotope from a plutonium sample that was irradiated with neutrons . It breaks down into ²³⁷ Np when an α particle is emitted. The half-life of this α-decay was initially determined to be 510 ± 20 years; the value generally accepted today is 432.2 a.

${\displaystyle \mathrm {^{239}_{\ 94}Pu\ {\xrightarrow {(n,\gamma )}}\ _{\ 94}^{240}Pu\ {\xrightarrow {(n,\gamma )}}\ _{\ 94}^{241}Pu\ {\xrightarrow[{14,35\ a}]{\beta ^{-}}}\ _{\ 95}^{241}Am\ \left(\ {\xrightarrow[{432,2\ a}]{\alpha }}\ _{\ 93}^{237}Np\right)} }$

The times given are half-lives .

As a second isotope, ²⁴² Am was found by renewed neutron bombardment of the previously generated ²⁴¹ Am. The subsequent rapid β-decay results in ²⁴² cm, the previously discovered curium . The half-life of this β-decay was initially determined to be 17 hours; the value determined to be valid today is 16.02 hours.

${\displaystyle \mathrm {^{241}_{\ 95}Am\ {\xrightarrow {(n,\gamma )}}\ _{\ 95}^{242}Am\ \left(\ {\xrightarrow[{16,02\ h}]{\beta ^{-}}}\ _{\ 96}^{242}Cm\right)} }$

The discovery of the element was first made public in the American radio program Quiz Kids on November 11, 1945 by Glenn T. Seaborg, even before the actual announcement at a symposium of the American Chemical Society : One of the young listeners asked the show's guest, Seaborg whether new elements were discovered during the course of research into nuclear weapons during World War II . Seaborg answered yes and at the same time revealed the discovery of the next higher element, curium .

Americium ( ²⁴¹ Am and ²⁴² Am) and its production was later patented under the name "Element 95 and method of producing said element" , with only Glenn T. Seaborg being named as the inventor.

It was first represented in elemental form in 1951 by reducing americium (III) fluoride with barium .

Occurrence

Americium isotopes arise in the r process in supernovae and do not occur naturally on Earth because of their half-life, which is too short compared to the age of the Earth .

Nowadays, however, americium is bred as a by-product in nuclear power plants ; the americium isotope ²⁴¹ Am arises as a decay product (e.g. in spent fuel rods ) from the plutonium isotope ²⁴¹ Pu. One tonne of spent nuclear fuel contains, on average, about 100 g of different isotopes of americium. These are mainly the α-emitters ²⁴¹ Am and ²⁴³ Am, which are undesirable in final disposal due to their relatively long half-lives and are therefore part of the transuranium waste . A reduction in long-term radio toxicity in nuclear repositories would be possible by separating long-lived isotopes from spent nuclear fuel. The partitioning & transmutation strategy is currently being investigated to eliminate the americium .

Extraction and presentation

Extraction of americium isotopes

Americium is produced in small quantities in nuclear reactors . Today it is available in quantities of a few kilograms. Due to the complex extraction from spent fuel rods , it has a very high price. Since its market launch in 1962, americium (IV) oxide with the isotope ²⁴¹ Am has been said to have been priced at around 1500  US dollars per gram . The americium isotope ²⁴³ Am is produced in smaller quantities in the reactor from ²⁴¹ Am and is therefore even more expensive at 160 US dollars per milligram of ²⁴³ Am.

Americium is inevitably produced via the plutonium isotope ²³⁹ Pu in nuclear reactors with a high ²³⁸ U content, as it is produced from this through neutron capture and two subsequent β decays (over ²³⁹ U and ²³⁹ Np).

${\displaystyle \mathrm {^{238}_{\ 92}U\ {\xrightarrow {(n,\gamma )}}\ _{\ 92}^{239}U\ {\xrightarrow[{23,5\ min}]{\beta ^{-}}}\ _{\ 93}^{239}Np\ {\xrightarrow[{2,3565\ d}]{\beta ^{-}}}\ _{\ 94}^{239}Pu} }$

The times given are half-lives .

Thereafter, if nuclear fission does not occur, ²³⁹ Pu, along with other nuclides, is hatched through gradual neutron capture (n, γ) and subsequent β-decay ²⁴¹ Am or ²⁴³ Am.

${\displaystyle \mathrm {^{239}_{\ 94}Pu\ {\xrightarrow {2(n,\gamma )}}\ _{\ 94}^{241}Pu\ {\xrightarrow[{14,35\ a}]{\beta ^{-}}}\ _{\ 95}^{241}Am} }$

The plutonium, which can be obtained from spent fuel rods in power reactors, consists of about 12% of the isotope ²⁴¹ Pu. This is why the spent fuel rods only reach their maximum content of ²⁴¹ Am; 70 years after the breeding process has ended ; thereafter the content decreases again (more slowly than the increase).

The resulting ²⁴¹ Am can be converted into ²⁴² Am through further neutron capture in the reactor . In the case of light water reactors , the ²⁴¹ Am should be 79% ²⁴² Am and 10% ^{242 m} Am:

to 79%: ${\displaystyle \mathrm {^{241}_{\ 95}Am\ {\xrightarrow {(n,\gamma )}}\ _{\ 95}^{242}Am} }$

to 10%: ${\displaystyle \mathrm {^{241}_{\ 95}Am\ {\xrightarrow {(n,\gamma )}}\ _{\ \ \ 95}^{242m}Am} }$

For the breeding of ²⁴³ Am a quadruple neutron capture of the ²³⁹ Pu is necessary:

${\displaystyle \mathrm {^{239}_{\ 94}Pu\ {\xrightarrow {4(n,\gamma )}}\ _{\ 94}^{243}Pu\ {\xrightarrow[{4,956\ h}]{\beta ^{-}}}\ _{\ 95}^{243}Am} }$

Depiction of elemental americiums

Metallic americium can be obtained from its compounds by reduction . First americium (III) fluoride was used for reduction. For this purpose, this is caused to react with elemental barium in reaction apparatuses made of tantalum and tungsten in an environment free of water and oxygen .

${\displaystyle {\ce {2 AmF3 + 3 Ba -> 2 Am + 3 BaF2}}}$

The reduction of americium (IV) oxide using lanthanum or thorium also produces metallic americium.

${\displaystyle {\ce {3 AmO2 + 4 La -> 3 Am + 2 La2O3}}}$

properties

Am-241 under the microscope

Double-hexagonal close packing of spheres with the layer sequence ABAC in the crystal structure of α-Am (A: green; B: blue; C: red).

In the periodic table , americium with atomic number 95 is in the series of actinides, its predecessor is plutonium, the following element is curium. Its analogue in the series of lanthanides is europium .

Physical Properties

Americium is a radioactive metal. Freshly made americium is a silver-white metal that slowly becomes matt at room temperature . It is easily deformable. Its melting point is 1176 ° C, the boiling point is 2607 ° C. The density is 13.67 g cm ⁻³ . It occurs in two modifications.

The α-Am modification, which is stable under standard conditions, crystallizes in the hexagonal crystal system in the space group P 6 ₃ / mmc (space group no. 194) with the lattice parameters a  = 346.8  pm and c  = 1124 pm and four formula units per unit cell . The crystal structure consists of a double hexagonal close packing of spheres (i.e. hcp) with the layer sequence ABAC and is therefore isotypic to the structure of α-La .

At high pressure, α-Am changes to β-Am. The β-modification crystallizes in the cubic crystal system in the space group  Fm 3 m (No. 225) with the lattice parameter a  = 489 pm, which corresponds to a face-centered cubic lattice (fcc) or a cubic closest packing of spheres with the stacking sequence ABC.

The enthalpy of solution of americium metal in hydrochloric acid under standard conditions is −620.6 ± 1.3 kJ mol ⁻¹ . Based on this value, the standard enthalpy of formation (Δ _f H ⁰ ) was calculated for the first time from Am ³⁺ _(aq) to −621.2 ± 2.0 kJ mol ⁻¹ and the standard ^potential Am ³⁺  / Am ⁰ to −2, 08 ± 0.01 V.

Chemical properties

Americium is a very reactive element that reacts with atmospheric oxygen and dissolves well in acids . It is stable to alkalis .

The most stable oxidation state for americium is +3, the Am (III) compounds are very stable against oxidation and reduction. The americium is the first representative of the actinides, which behaves more like the lanthanoids than the d-block elements.

It can also be found in oxidation states +2 as well as +4, +5, +6 and +7. Depending on the oxidation number , the color of americium varies in aqueous solution as well as in solid compounds :
Am ³⁺  (yellow-pink), Am ⁴⁺  (yellow-red), Am ^V O ₂ ⁺  (yellow), Am ^VI O ₂ ²⁺  (lemon yellow), Am ^VII O ₆ ⁵⁻  (dark green).

In contrast to the homologous europium - americium has an electron configuration analogous to europium - Am ³⁺ can not be reduced to Am ²⁺ in aqueous solution .

Compounds with americium from oxidation number +4 upwards are strong oxidizing agents , comparable to permanganate ion (MnO ₄ ^- ) in acidic solution.

The Am ⁴⁺ ions, which are not stable in aqueous solution , can only be produced from Am (III) using strong oxidizing agents. Two compounds of americium in the +4 oxidation state are known in solid form: americium (IV) oxide (AmO ₂ ) and americium (IV) fluoride (AmF ₄ ).

The pentavalent oxidation state was first observed in americium in 1951. In aqueous solution are primarily AmO ₂ ⁺ ions (acid) or AmO ₃ ^- ions (alkaline) before, but these are unstable and rapid disproportionation subject:

${\displaystyle {\ce {3 AmO2^+ + 4 H^+ -> 2 AmO2^2+ + Am^3+ + 2 H2O}}}$

First of all, a disproportionation to the oxidation state +6 and +4 can be assumed:

${\displaystyle {\ce {2 Am (V) -> Am (VI) + Am (IV)}}}$

The americium (VI) compounds are somewhat more stable than Am (IV) and Am (V). They can be prepared from Am (III) by oxidation with ammonium peroxodisulfate in dilute nitric acid. The typical pink tone disappears towards a strong yellow color. In addition, the oxidation with silver (I) oxide in perchloric acid can be achieved quantitatively. In sodium carbonate or sodium hydrogen carbonate solutions, oxidation with ozone or sodium peroxodisulfate is also possible.

• 

  Americium (III)
  in 2 M Na ₂ CO ₃ solution

• 

  Americium (IV)
  in 2 M Na ₂ CO ₃ solution

• 

  Americium (IV) and (VI)
  in 2 M Na ₂ CO ₃ solution

Biological aspects

A biological function of americium is not known. The use of immobilized bacterial cells to remove americium and other heavy metals from rivers has been proposed. Thus, enteric bacteria of the genus Citrobacter by the phosphatase activity in their cell wall precipitate certain Americiumnuklide from aqueous solution and bind as a metal-phosphate complex. The factors that influence the biosorption and bioaccumulation of americium by bacteria and fungi were also examined .

Cleavage

The isotope ^{242 m 1} Am has the highest thermal gap cross-section measured to date (10/2008) at around 5700  barn . This is accompanied by a small critical mass , which is why ^{242 m 1} Am was proposed as fissile material, for example to power spaceships with nuclear energy propulsion.

In principle, this isotope is also suitable for the construction of nuclear weapons . The critical mass of a pure ^{242 m 1} Am sphere is about 9-14 kg. The uncertainties of the available cross- sections currently do not allow a more precise statement. With the reflector, the critical mass is around 3–5 kg. In aqueous solution it is again greatly reduced. In this way, very compact warheads could be built. According to the state of public knowledge, no nuclear weapons from ^{242 m 1} Am have been built so far , which can be explained by the low availability and the high price.

For the same reasons, ^{242 m 1} Am is also not used as a nuclear fuel in nuclear reactors , although in principle it would be suitable for this in both thermal and fast reactors ., The two other more commonly available isotopes, ²⁴¹ Am and ²⁴³ Am, can also be used in a fast reactor maintain a chain reaction. However, the critical masses are very high here. Unreflected, they are 57.6–75.6 kg at ²⁴¹ Am and 209 kg at ²⁴³ Am so that their use does not result in any advantages over conventional fissile materials.

Correspondingly, americium is not legally assigned to nuclear fuels in accordance with Section 2 (1) of the Atomic Energy Act . However, there are proposals to construct very compact reactors with an americium inventory of just 20 g, which can be used in hospitals as a neutron source for neutron capture therapy.

Isotopes

16 isotopes and 11 nuclear isomers with half-lives between fractions of microseconds and 7370 years are known of americium . There are two long-lived α-emitting isotopes ²⁴¹ Am with 432.2 and ²⁴³ Am with 7370 years half-life. In addition, the core isomer ^{242 m 1} Am has a long half-life of 141 years. The remaining core isomers and isotopes have short half-lives of 0.64 µs at ^{245 m 1} Am to 50.8 hours at ²⁴⁰ Am.

²⁴¹ Am is the most frequently incubated americium isotope and belongs to the Neptunium series . It decays with a half-life of 432.2 years with an α-decay to ²³⁷ Np. ²⁴¹ Am emits the entire decay energy with the α-particle with a probability of 0.35%, but mostly emits one or more gamma quanta .

²⁴² Am is short-lived and, with a half-life of 16.02 h, decays 82.7% through β-decay to ²⁴² Cm and 17.3% through electron capture to ²⁴² Pu. The ²⁴² cm decays to ²³⁸ Pu and this further to ²³⁴ U, which is on the uranium-radium series . The ²⁴² Pu decays via the same chain of decay as ²³⁸ Pu. However, while ²³⁸ Pu joins the decay chain as a side arm of ²³⁴ U, ²⁴² Pu is still before ²³⁸ U. ²⁴² Pu decays through α decay into ²³⁸ U, the beginning of the natural uranium-radium series.

^{242 m 1} Am decays with a half-life of 141 years to 99.541% by internal conversion to ²⁴² Am and to 0.459% by α-decay to ²³⁸ Np. This decays to ²³⁸ Pu and then further to ²³⁴ U, which is on the uranium-radium series .

With a half-life of 7,370 years, ²⁴³ Am is the longest-lived americium isotope. It is first converted into ²³⁹ Np by α radiation , which further decays to ²³⁹ Pu by β decay . The ²³⁹ Pu decays through α-radiation to uranium ²³⁵ U, the official beginning of the uranium actinium series .

The americium isotopes with an odd number of neutrons , i.e. an even mass number , can be easily split by thermal neutrons .

→ List of americium isotopes

use

The two most long-lived isotopes ²⁴¹ Am and ²⁴³ Am are of particular interest for the use of americium . Usually it is used in the form of the oxide (AmO ₂ ).

Americium 241 in a smoke alarm

Ionization smoke detector

The α radiation from the ²⁴¹ Am is used in ionization smoke detectors . It is preferred over ²²⁶ Ra because it emits comparatively little γ radiation . To do this, however, the activity against radium must be about five times as much. The decay series of ²⁴¹ Am “ends” for the period of use almost immediately after its α decay at ²³⁷ Np , which has a half-life of around 2.144 million years.

Radionuclide batteries

Because of its significantly longer half-life compared to ²³⁸ Pu, ²⁴¹ Am was proposed for filling radionuclide batteries (RTG) of space probes . Thanks to its half-life of 432.2 years, an RTG with a ²⁴¹ Am filling could provide electrical energy to operate a space probe for hundreds of years - instead of just a few decades (as with a ²³⁸ Pu filling). It is expected to be used in the radionuclide batteries that ESA is considering developing and that could be completed in the 2020s.

Neutron sources

²⁴¹ Am pressed as oxide with beryllium represents a neutron source that is used, for example, for radiochemical investigations. For this purpose, the high cross-section of beryllium is used for (α, n) nuclear reactions, with americium serving as the producer of the α particles. The corresponding reaction equations are:

${\displaystyle \mathrm {^{241\!\,}_{\ 95}Am\ \longrightarrow \ _{\ 93}^{237}Np\ +\ _{2}^{4}He\ +\ \gamma } }$

${\displaystyle \mathrm {^{9}_{4}Be\ +\ _{2}^{4}He\ \longrightarrow \ _{\ 6}^{12}C\ +\ _{0}^{1}n\ +\ \gamma } }$

Such neutron sources are used, for example, in neutron radiography and tomography .

Ionizer

Americium 241 in the brush head

In addition to the frequently used ²¹⁰ Po as an ionizer to remove unwanted electrostatic charge , ²⁴¹ Am was also used. For this purpose z. B. the source is mounted on the head of a brush with which one slowly stroked the surfaces to be treated and thus could avoid re-contamination by electrostatically attracted dust particles.

Manufacture of other items

Americium is the starting material for the production of higher transuranic elements and also the transactinoids . From ²⁴² On arises to 82.7% curium ( ²⁴² Cm) and 17.3% plutonium ( ²⁴² Pu). In the nuclear reactor the ²⁴⁴ Am is inevitably hatched in small quantities by neutron capture from ²⁴³ Am , which decays to the curium isotope ²⁴⁴ Cm through β-decay .

${\displaystyle \mathrm {^{243}_{\ 95}Am\ {\xrightarrow {(n,\gamma )}}\ _{\ 95}^{244}Am\ {\xrightarrow[{10,1\ h}]{\beta ^{-}}}\ _{\ 96}^{244}Cm} }$

In particle accelerators , for example, bombardment of ²⁴¹ Am with carbon nuclei ( ¹² C) or neon nuclei ( ²² Ne) leads to the elements Einsteinium ²⁴⁷ Es and Dubnium ²⁶⁰ Db.

spectrometer

With its intense gamma radiation - spectral line at 60  keV is suitable ²⁴¹ On well as a radiation source for X-ray fluorescence spectroscopy . This is also used for calibration of gamma spectrometers used in the low energy region, since the adjacent lines are relatively weak and formed as a single peak standing. In addition, the peak is only negligibly disturbed by the Compton continuum of higher-energy lines, since these also occur at most with an intensity that is at least three orders of magnitude lower.

Safety instructions and dangers

Classifications according to the CLP regulation are not available because they only include chemical hazard, which plays a completely subordinate role compared to the hazards based on radioactivity . There is only a chemical hazard at all if it concerns a relevant amount of substance.

Since americium only has radioactive isotopes, it and its compounds may only be handled in suitable laboratories under special precautions. Most common americium isotopes are alpha emitters, which is why incorporation must be avoided. The broad spectrum of daughter nuclides, which are usually also radioactive, represents a further risk that must be taken into account when choosing safety precautions. ²⁴¹ Am emits large amounts of relatively soft gamma radiation during radioactive decay, which can be shielded well.

According to research by the researcher Arnulf Seidel from the Institute for Radiation Biology at the Karlsruhe Nuclear Research Center , americium (like plutonium ), when absorbed into the body, generates more bone tumors than the same dose of radium .

The biological half-life of ²⁴¹ Am is 50 years in the bones and 20 years in the liver . In contrast, it apparently remains permanently in the gonads .

links

→ Category: Americium compound

Oxides

Americium has oxides of oxidation states +3 (Am ₂ O ₃ ) and +4 (AmO ₂ ).

Americium (III) oxide (Am ₂ O ₃ ) is a red-brown solid and has a melting point of 2205 ° C.

Americium (IV) oxide (AmO ₂ ) is the main compound of this element. Almost all applications of this element are based on this connection. It occurs implicitly in nuclear reactors when irradiating uranium dioxide (UO ₂ ) or plutonium dioxide (PuO ₂ ) with neutrons. It is a black solid and crystallizes - like the other actinide (IV) oxides - in the cubic crystal system in the fluorite structure.

Halides

Halides are known for their oxidation states +2, +3 and +4. The most stable level +3 is known for all compounds from fluorine to iodine and is stable in aqueous solution.

Oxidation number	F.	Cl	Br	I.
+4	Americium (IV) fluoride AmF 4 pale pink
+3	Americium (III) fluoride AmF 3 pink	Americium (III) chloride AmCl 3 pink	Americium (III) bromide AmBr 3 light yellow	Americium (III) iodide AmI 3 light yellow
+2		Americium (II) chloride AmCl 2 black	Americium (II) bromide AmBr 2 black	Americium (II) iodide AmI 2 black

Americium (III) fluoride (AmF ₃ ) is sparingly soluble and can be produced by the reaction of an aqueous americium solution with fluoride salts in a weakly acidic solution:

${\displaystyle \mathrm {Am^{3+}\ _{(aq)}+\ 3\ F^{-}\ _{(aq)}\longrightarrow \ AmF_{3}\ _{(s)}\downarrow } }$

The tetravalent americium (IV) fluoride (AmF ₄ ) is accessible through the reaction of americium (III) fluoride with molecular fluorine :

${\displaystyle \mathrm {2\ AmF_{3}\ +\ F_{2}\ \longrightarrow \ 2\ AmF_{4}} }$

The tetravalent americium was also observed in the aqueous phase.

Americium (III) chloride (AmCl ₃ ) forms pink hexagonal crystals. Its crystal structure is isotype with uranium (III) chloride . The melting point of the compound is 715 ° C. The hexahydrate (AmCl ₃ · 6 H ₂ O) has a monoclinic crystal structure.

Am (II) salts are accessible by reduction with Na amalgam from Am (III) compounds: the black halides AmCl ₂ , AmBr ₂ and AmI ₂ . They are very sensitive to oxygen and oxidise to Am (III) compounds in water, releasing hydrogen.

Chalcogenides and pentelides

The following are known of the chalcogenides : the sulfide (AmS ₂ ), two selenides (AmSe ₂ and Am ₃ Se ₄ ) and two tellurides (Am ₂ Te ₃ and AmTe ₂ ).

The pentelids of americium ( ²⁴³ Am) of the type AmX have been shown for the elements phosphorus , arsenic , antimony and bismuth . They crystallize in the NaCl grid.

Silicides and borides

Americium monosilicide (AmSi) and americium "disilicid" (AmSi _x with: 1.87 <x <2.0) were obtained by reducing americium (III) fluoride with elemental silicon in a vacuum at 1050 ° C (AmSi) and 1150– 1200 ° C (AmSi _x ) shown. AmSi is a black mass, isomorphic with LaSi. AmSi _x is a light silver compound with a tetragonal crystal lattice.

Borides of the compositions AmB ₄ and AmB ₆ are also known.

Organometallic compounds

Analogous to uranocene , an organometallic compound in which uranium is complexed by two cyclooctatetraene ligands, the corresponding complexes of thorium , protactinium , neptunium, plutonium and also of americium, (η ⁸ -C ₈ H ₈ ) ₂ Am, were prepared.

literature

• Wolfgang H. Runde, Wallace W. Schulz: Americium , in: Lester R. Morss, Norman M. Edelstein, Jean Fuger (Eds.): The Chemistry of the Actinide and Transactinide Elements , Springer, Dordrecht 2006; ISBN 1-4020-3555-1 , pp. 1265-1395 ( doi: 10.1007 / 1-4020-3598-5_8 ).
• Gmelin's Handbook of Inorganic Chemistry , System No. 71, Transurane: Part A 1 I, pp. 30-34; Part A 1 II, pp. 18, 315-326, 343-344; Part A 2, pp. 42-44, 164-175, 185-188; Part B 1, pp. 57-67.

Web links

Commons : Americium  - collection of images, videos, and audio files

Wiktionary: Americium  - explanations of meanings, word origins, synonyms, translations

• Entry to americium. In: Römpp Online . Georg Thieme Verlag, accessed on January 3, 2015.
• Rachel Sheremeta Pepling: Americium. Chemical & Engineering News, 2003.

Individual evidence

1. ↑ The values ​​of the atomic and physical properties (info box) are taken from www.webelements.com (Americium) , unless otherwise stated .
2. ↑ ^{a b c d e f} Harry H. Binder: Lexicon of the chemical elements , S. Hirzel Verlag, Stuttgart 1999, ISBN 3-7776-0736-3 , pp. 18-23.
3. ↑ ^{a b c d e} entry on americium in Kramida, A., Ralchenko, Yu., Reader, J. and NIST ASD Team (2019): NIST Atomic Spectra Database (ver. 5.7.1) . Ed .: NIST , Gaithersburg, MD. doi : 10.18434 / T4W30F ( https://physics.nist.gov/asd ). Retrieved June 13, 2020.
4. ↑ ^{a b c d e} entry on americium at WebElements, https://www.webelements.com , accessed on June 13, 2020.
5. ↑ Robert C. Weast (Ed.): CRC Handbook of Chemistry and Physics . CRC (Chemical Rubber Publishing Company), Boca Raton 1990, ISBN 0-8493-0470-9 , pp. E-129 to E-145. The values ​​there are based on g / mol and are given in cgs units. The value specified here is the SI value calculated from it, without a unit of measure.
6. ↑ ^{a b c d e f g h} G. Audi, O. Bersillon, J. Blachot, AH Wapstra: The NUBASE evaluation of nuclear and decay properties , in: Nuclear Physics A , 729, 2003, pp. 3–128. doi : 10.1016 / j.nuclphysa.2003.11.001 . ( PDF ; 1.0 MB).
7. ↑ The hazards emanating from radioactivity do not belong to the properties to be classified according to the GHS labeling. With regard to other hazards, this element has either not yet been classified or a reliable and citable source has not yet been found.
8. ↑ GT Seaborg, RA James, LO Morgan: The New Element Americium (Atomic Number 95) , NNES PPR (National Nuclear Energy Series, Plutonium Project Record) , Vol. 14 B The Transuranium Elements: Research Papers , Paper No. 22.1, McGraw-Hill Book Co., Inc., New York, 1949 ( abstract ; machine script (January 1948) ).
9. ↑ K. Street, Jr., A. Ghiorso, GT Seaborg: The Isotopes of Americium , in: Physical Review , 1950 , 79  (3), pp. 530-531 ( doi: 10.1103 / PhysRev.79.530 ; Maschinoscript (11. April 1950) ).
10. ↑ Translation: The name Americium (after the two Americas) and the symbol Am are proposed for the element - based on its position as the sixth member of the actinide rare earth series, by analogy with Europium, Eu, from the lanthanide series .
11. ↑ Rachel Sheremeta Pepling: Americium. Chemical & Engineering News, 2003.
12. ↑ Patent US3156523 : Element 95 and method of producing said element. Registered on August 23, 1946 , published November 10, 1964 , inventor: Glenn T. Seaborg. ‌
13. ^ ^{A b} Edgar F. Westrum, Jr., LeRoy Eyring: The Preparation and Some Properties of Americium Metal , in: J. Am. Chem. Soc. , 1951 , 73  (7), pp. 3396-3398 ( doi: 10.1021 / ja01151a116 ).
14. ↑ Klaus Hoffmann: Can you make gold? Crooks, jugglers and scholars. From the history of the chemical elements , Urania-Verlag; Leipzig, Jena, Berlin 1979, DNB 800228367 , p. 233.
15. ↑ LH Baetsle: Application of Partitioning / Transmutation of Radioactive Materials in Radioactive Waste Management ( Memento of April 26, 2005 in the Internet Archive ) (PDF; 2.4 MB), September 2001.
16. ↑ Gabriele Fioni, Michel Cribier, Frédéric Marie: Can the minor actinide, americium-241, be transmuted by thermal neutrons? .
17. ^ ^{A b c} Smoke Detectors and Americium. ( Memento from November 12, 2010 in the Internet Archive )
18. ↑ Information on the element americium at www.speclab.com (Engl.) ; Accessed October 8, 2008.
19. ↑ BREDL Southern Anti-plutonium Campaign ( Memento of 29 April 2015, Internet Archive ).
20. ↑ Akihiro Sasahara, Tetsuo Matsumura, Giorgos Nicolaou, Dimitri Papaioannou: Neutron and Gamma Ray Source Evaluation of LWR High Burn-up UO ₂ and MOX Spent Fuels , in: Journal of Nuclear Science and Technology , 2004 , 41  (4), p. 448-456 ( doi: 10.1080 / 18811248.2004.9715507 ).
21. ↑ ^{a b c} Gmelin's Handbook of Inorganic Chemistry , System No. 71, Transurane, Part B 1, pp. 57-67.
22. ^ ^{A b c} W. Z. Wade, T. Wolf: Preparation and Some Properties of Americium Metal , in: J. Inorg. Nucl. Chem. , 1967 , 29  (10), pp. 2577-2587 ( doi: 10.1016 / 0022-1902 (67) 80183-0 ).
23. ^ ^{A b c} D. B. McWhan, BB Cunningham, JC Wallmann: Crystal Structure, Thermal Expansion and Melting Point of Americium Metal , in: J. Inorg. Nucl. Chem. , 1962 , 24  (9), pp. 1025-1038 ( doi: 10.1016 / 0022-1902 (62) 80246-2 ).
24. ↑ JU Mondal, DL Raschella, RG Haire, JR Peterson: The Enthalpy of Solution of ²⁴³ Am Metal and the Standard Enthalpy of Formation of Am ³⁺ (aq) , in: Thermochim. Acta , 1987 , 116 , pp. 235-240 ( doi: 10.1016 / 0040-6031 (87) 88183-2 ).
25. ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 1956.
26. ^ LB Werner, I. Perlman: The Pentavalent State of Americium , in: J. Am. Chem. Soc. , 1951 , 73  (1), pp. 495-496 ( doi: 10.1021 / ja01145a540 ).
27. ^ GR Hall, TL Markin: The Self-reduction of Americium (V) and (VI) and the Disproportionation of Americium (V) in Aqueous Solution , in: J. Inorg. Nucl. Chem. , 1957 , 4  (5-6), pp. 296-303 ( doi: 10.1016 / 0022-1902 (57) 80011-6 ).
28. ↑ James S. Coleman: The Kinetics of the Disproportionation of Americium (V) , in: Inorg. Chem. , 1963 , 2  (1), pp. 53-57 ( doi: 10.1021 / ic50005a016 ).
29. ^ LB Asprey, SE Stephanou, RA Penneman: A New Valence State of Americium, Am (VI) , in: J. Am. Chem. Soc. , 1950 , 72  (3), pp. 1425-1426 ( doi: 10.1021 / ja01159a528 ).
30. ^ LB Asprey, SE Stephanou, RA Penneman: Hexavalent Americium , in: J. Am. Chem. Soc. , 1951 , 73  (12), pp. 5715-5717 ( doi: 10.1021 / ja01156a065 ).
31. ↑ JS Coleman, TK Keenan, LH Jones, WT Carnall, RA Penneman: Preparation and Properties of Americium (VI) in Aqueous Carbonate Solutions , in: Inorg. Chem. , 1963 , 2  (1), pp. 58-61 ( doi: 10.1021 / ic50005a017 ).
32. ^ The Biochemical Periodic Tables - Americium .
33. ↑ LE Macaskie, BC Jeong, MR Tolley: Enzymically Accelerated Biomineralization of Heavy Metals: Application to the removal of americium and plutonium from Aqueous flows , in: FEMS Microbiol. Rev. , 1994 , 14  (4), pp. 351-367 ( PMID 7917422 ).
34. ^ EA Wurtz, TH Sibley, WR Schell: Interactions of Escherichia coli and Marine Bacteria with ²⁴¹ Am in Laboratory Cultures , in: Health Phys. , 1986 , 50  (1), pp. 79-88 ( PMID 3511007 ).
35. ^ AJ Francis, JB Fillow, CJ Dodge, M. Dunn, K. Mantione, BA Strietelmeier, ME Pansoy-Hjelvik, HW Papenguth: Role of Bacteria as Biocolloids in the Transport of Actinides from a Deep Underground Radioactive Waste Repository , in: Radiochimica Acta , 1998 , 82 , pp. 347-354 ( abstract and PDF download ).
36. ↑ N. Liu, Y. Yang, S. Luo, T. Zhang, J. Jin, J. Liao, X. Hua: Biosorption of ²⁴¹ Am by Rhizopus arrihizus: Preliminary Investigation and Evaluation , in: Appl. Radiate. Isot. , 2002 , 57  (2), pp. 139-143 ( PMID 12150270 ).
37. ↑ G. Pfennig, H. Klewe-Nebenius, W. Seelmann-Eggebert (Eds.): Karlsruher Nuklidkarte , 7th edition 2006.
38. ↑ Science daily: Extremely Efficient Nuclear Fuel Could Take Man To Mars In Just Two Weeks , January 3, 2001.
39. ↑ H. Dias, N. Tancock, A. Clayton: Critical Mass Calculations for ²⁴¹ Am, ^242m Am and ²⁴³ Am , in: Nippon Genshiryoku Kenkyujo JAERI, Conf , 2003 , pp. 618-623 ( abstract ; PDF ).
40. ↑ Y. Ronen, M. AboudY, D. Regev: A novel method for energy production using ^242m Am as a nuclear fuel , in: Nuclear technology , in 2000 , 129  (3), pp 407-417 ( Abstract ).
41. ↑ Institut de Radioprotection et de Sûreté Nucléaire : Evaluation of nuclear criticality safety data and limits for actinides in transport , p. 16 ( PDF ( Memento from August 22, 2011 on WebCite )).
42. ↑ Y. Ronen, M. AboudY, D. Regev: Homogeneous ^242m Am-Fueled Reactor for Neutron Capture Therapy , in: Nuclear Science and Engineering , 2001 , 138  (3), pp 295-304 ( Abstract ).
43. ↑ α-decay of ²⁴¹ Am with the formation of gamma rays ( memento from June 24, 2008 in the Internet Archive ).
44. ↑ Nuclides for RTGs (PDF; 297 kB) last page.
45. ↑ Stephen Clark: Space agencies tackle waning plutonium stockpiles , in: Spaceflight Now , July 9, 2010.
46. ↑ Nuclear Data Viewer 2.4, NNDC, accessed on September 11, 2008; Search input .
47. ↑ Lenntech: americium (Am) .
48. ↑ Public Health Statement for Americium Section 1.5.
49. ^ Franz Frisch: Klipp und klar, 100 x Energie , Bibliographisches Institut AG, Mannheim 1977, ISBN 3-411-01704-X , p. 184.
50. ^ Division of Environmental Health, Office of Radiation Protection, Fact Sheet # 23 (November 2002): Americium-241 ( Memento of February 18, 2011 on WebCite ).
51. ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 1972.
52. ^ ^{A b} A. F. Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 1969.
53. Jump up ↑ LB Asprey, TK Keenan, FH Kruse: Crystal Structures of the Trifluorides, Trichlorides, Tribromides, and Triiodides of Americium and Curium , in: Inorg. Chem. , 1965 , 4  (7), pp. 985-986 ( doi: 10.1021 / ic50029a013 ).
54. ↑ LB Asprey: New Compounds of Quadrivalent Americium, AmF ₄ , KAmF ₅ , in: J. Am. Chem. Soc. , 1954 , 76  (7), pp. 2019-2020 ( doi: 10.1021 / ja01636a094 ).
55. ^ LB Asprey, RA Penneman: First Observation of Aqueous Tetravalent Americium , in: J. Am. Chem. Soc. , 1961 , 83  (9), pp. 2200-2200 ( doi: 10.1021 / ja01470a040 ).
56. ↑ John H. Burns, Joseph Richard Peterson: The Crystal Structures of Americium Trichloride Hexahydrate and Berkelium Trichloride Hexahydrate , in: Inorg. Chem. , 1971 , 10  (1), pp. 147-151 ( doi: 10.1021 / ic50095a029 ).
57. ^ ^{A b} D. Damien, J. Jove: Americium Disulfide and Diselenide , in: Inorg. Nucl. Chem. Lett. , 1971 , 7  (7), pp. 685-688 ( doi: 10.1016 / 0020-1650 (71) 80055-7 ).
58. ↑ ^{a b} J. W. Roddy: Americium Metallides: AmAs, AmSb, AmBi, Am ₃ Se ₄ , and AmSe ₂ , in: J. Inorg. Nucl. Chem. , 1974 , 36  (11), pp. 2531-2533 ( doi: 10.1016 / 0022-1902 (74) 80466-5 ).
59. ↑ D. Damien: Americium Tritelluride and Ditelluride , in: Inorg. Nucl. Chem. Lett. , 1972 , 8  (5), pp. 501-504 ( doi: 10.1016 / 0020-1650 (72) 80262-9 ).
60. ↑ JP Charvillat, D. Damien: Americium Monoarsenide in: Inorg. Nucl. Chem. Lett. , 1973 , 9  (5), pp. 559-563 ( doi: 10.1016 / 0020-1650 (73) 80191-6 ).
61. ↑ F. Weigel, FD Wittmann, R. Marquart: Americium Monosilicide and “Disilicide” , in: Journal of the Less Common Metals , 1977 , 56  (1), pp. 47-53 ( doi: 10.1016 / 0022-5088 (77 ) 90217-X ).
62. ↑ Harry A. Eick, RNR Mulford: Americium and Neptunium Borides , in: J. Inorg. Nucl. Chem. , 1969 , 31  (2), pp. 371-375 ( doi: 10.1016 / 0022-1902 (69) 80480-X ).
63. ↑ Christoph Elschenbroich : Organometallchemie , 6th edition, Wiesbaden 2008, ISBN 978-3-8351-0167-8 , p. 589.

This article was added to the list of excellent articles on January 8, 2010 in this version .