The atomic bomb dropped on Nagasaki had a plutonium charge.^[1]

The actinide or actinoid (IUPAC nomenclature) series encompasses the 15 chemical elements with atomic numbers from 89 to 103, actinium to lawrencium.^[2] The actinide series derives its name from the group 3 element actinium; although actinoid (actinide) means "actinium-like" and therefore should exclude actinium, it is usually included in the series for the purpose of comparison.^[3] Only thorium and uranium occur in more than trace quantities in nature; the other actinides are synthetic elements.^[4] The actinides are usually considered to be f-block elements; they show much more variable valence than the lanthanides. All actinides are radioactive and release energy upon radioactive decay; uranium, thorium, and plutonium, the most abundant actinides on Earth, are used in nuclear reactors and nuclear weapons.

[edit] Synthesis

Like lanthanides, actinides form a family of elements with similar properties. Within actinides, there are two overlapping groups: transuranium elements, which follow uranium in the periodic table—and transplutonium elements, which follow plutonium. Compared to the lanthanides, which (except for promethium) are found in nature in appreciable quantities, most actinides are rare. The most abundant, or easy to synthesize actinides are uranium and thorium, followed by plutonium, americium, actinium, protactinium and neptunium.

At present, there are two major methods of producing isotopes of transplutonium elements: irradiation of the lighter elements with neutrons or accelerated charged particles. The first method is most important for applications, as only neutron irradiation using nuclear reactors allows to produce sizeable amounts of synthetic actinides; however, it is limited to relatively light elements. The advantage of the second method is that it allows obtaining elements heavier than plutonium, as well as neutron-deficient isotopes, which are not formed during neutron irradiation.^[7]

In 1962–1966, there were attempts in the United States to produce transplutonium isotopes using a series of 6 underground nuclear explosions. Small samples of rock were extracted from the blast area immediately after the test to study the explosion products, but no isotopes with mass number greater than 257 could be detected, despite predictions that such isotopes would have relatively long half-lives of α-decay. This inobservation was attributed to spontaneous fission owing to the large speed of the products and to other decay channels, such as neutron emission and nuclear fission.^[7]

The existence of transuranium elements was suggested by Enrico Fermi based on his experiments in 1934,^[8][9] and the terms "actinides" (and "lanthanides"; from Greek éidos meaning "type") were proposed in 1948 by Sergey Shchukarev.^[10]

[edit] From actinium to neptunium

Enrico Fermi suggested the existence of transuranium elements in 1934.

Uranium and thorium were the first actinides discovered. Uranium was identified in 1789 by the German chemist Martin Heinrich Klaproth in pitchblende ore. He named it after the planet Uranus,^[4] which had been discovered only eight years earlier. Klaproth was able to precipitate a yellow compound (likely sodium diuranate) by dissolving pitchblende in nitric acid and neutralizing the solution with sodium hydroxide. He then reduced the obtained yellow powder with charcoal, and extracted a black substance that he mistook for metal. Only 60 years later, the French scientist Eugène-Melchior Péligot identified it with uranium oxide.^[11] He also isolated the first sample of uranium metal by heating uranium tetrachloride with potassium.^[12] The atomic mass of uranium was then calculated as 120, but Dmitri Mendeleev in 1872 corrected it to 240 using his periodicity laws. This value was confirmed experimentally in 1882 by K. Zimmerman.^[13][14]

Thorium oxide was discovered by Friedrich Wöhler in the mineral, which was found in Norway (1827).^[15] Jöns Jacob Berzelius characterized this material in more detail by in 1828. By reduction of thorium tetrachloride with potassium, he isolated the metal and named it thorium after the Norse god of thunder and lightning Thor.^[16][17] The same isolation method was later used by Péligot for uranium.^[4]

Actinium was discovered in 1899 by André-Louis Debierne, an assistant of Marie Curie, in the pitchblende waste left after removal of radium and polonium. He described the substance (in 1899) as similar to titanium^[18] and (in 1900) as similar to thorium.^[19] The discovery of actinium by Debierne was however questioned in 1971^[20] and 2000,^[21] arguing that Debierne's publications in 1904 contradict to his earlier work of 1899–1900. The name for word actinium comes from the Greek aktis, aktinos (ακτίς, ακτίνος), meaning beam or ray. This metal was discovered not by its own radiation but by the radiation of the daughter products.^[15][22] Owing to the close similarity of actinium and lanthanum and low abundance, pure actinium could only be produced in 1950.

Protactinium was possibly isolated in 1900 by William Crookes.^[23] It was first identified in 1913, when Kasimir Fajans and Oswald Helmuth Göhring encountered the short-lived isotope ^234mPa (half-life 1.17 minutes) during their studies of the ²³⁸U decay. They named the new element brevium (from Latin brevis meaning brief);^[24][25] the name was changed to protoactinium (from Greek πρῶτος + ἀκτίς meaning "first beam element") in 1918 when two groups of scientists, led by Otto Hahn and Lise Meitner of Germany and Frederick Soddy and John Cranston of Great Britain, independently discovered ²³¹Pa. The name was shortened to Protactinium in 1949. This element was little characterized until 1960, when A. G. Maddock and co-workers in UK produced 130 grams of protactinium from 60 tonnes of waste left after extraction of uranium from its ore.^[26]

Neptunium (named for the planet Neptune, the next planet out from Uranus, after which uranium was named) was discovered by Edwin McMillan and Philip H. Abelson in 1940 in Berkeley, California.^[27] They produced the ²³⁹Np isotope (half-life 2.4 days) by bombarding uranium with slow neutrons.^[26] It was the first transuranium element produced synthetically.^[28]

[edit] Plutonium and above

Glenn T. Seaborg and his group at the University of California at Berkeley synthesized Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No and element 106, which was later named seaborgium in his honor while he was still living. They also developed more than 100 atomic actinide isotopes.

Transuranium elements do not occur in sizeable quantities in nature and are commonly synthesized via nuclear reactions conducted with nuclear reactors. For example, under irradiation with reactor neutrons, uranium-238 partially converts to plutonium-239:

In this way, Enrico Fermi with collaborators, using the first nuclear reactor Chicago Pile-1, obtained significant amounts of plutonium-239, which were then used in nuclear weapons.^[29]

Actinides with the highest mass numbers are synthesized by bombarding uranium, plutonium, curium and californium with ions of nitrogen, oxygen, carbon, neon or boron in a particle accelerator. So, nobelium was produced by bombarding uranium-238 with neon-22 as

.

First isotopes of transplutonium elements, americium-241 and curium-242, were synthesized in 1944 by Glenn T. Seaborg, Ralph A. James and Albert Ghiorso.^[30] Curium-242 was obtained by bombarding plutonium-239 with 32-MeV α-particles

.

The americium-241 and curium-242 isotopes also were produced by irradiating plutonium in a nuclear reactor.^[7] The latter element was named after Marie Curie and her husband Pierre who are noted for discovering radium and for their work in radioactivity.

Bombarding curium-242 with α-particles resulted in an isotope of californium ²⁴⁵Cf (1950), and a similar procedure yielded in 1949 berkelium-243 from americium-241.^[31] The new elements were named after Berkeley, California, by analogy with its lanthanide homologue terbium, which was named after the village of Ytterby in Sweden.^[32]

Americium hydroxide

In 1945, B. B. Cunningham obtained the first bulk chemical compound of a transplutonium element, namely americium hydroxide.^[33] Over the next 3–4 years, milligram quantities of americium and microgram amounts of curium were accumulated that allowed production of isotopes of berkelium (Thomson, 1949)^[34][35] and californium (Thomson, 1950).^[36][37][38] Sizeable amounts of these elements were produced only in 1958 (Burris B. Cunningham and Stanley G. Thomson),^[39] and the first californium compound (0.3 µg of CfOCl) was obtained only in 1960 by B. B. Cunningham and J. C. Wallmann).^[40]

Einsteinium and fermium were identified in 1952–1953 in the fallout from the "Ivy Mike" nuclear test (1 November 1952), the first successful test of a hydrogen bomb. Instantaneous exposure of uranium-238 to a large neutron flux resulting from the explosion produced heavy isotopes of uranium, including uranium-253 and uranium-255, and their β-decay yielded einsteinium-253 and fermium-255. The discovery of the new elements and the new data on neutron capture were initially kept secret on the orders of the U.S. military until 1955 due to Cold War tensions.^[41][42] Nevertheless, the Berkeley team were able to prepare einsteinium and fermium by civilian means, through the neutron bombardment of plutonium-239, and published this work in 1954 with the disclaimer that it was not the first studies that had been carried out on the elements.^[43][44] The "Ivy Mike" studies were declassified and published in 1955.^[41] The first significant (submicrograms) amounts of einsteinium were produced in 1961 by Cunningham and colleagues, but this has not been done for fermium yet.^[45]

The first isotope of mendelevium, ²⁵⁶Md (half-life 87 min), was synthesized by Albert Ghiorso, Glenn T. Seaborg, Gregory R. Choppin, Bernard G. Harvey and Stanley G. Thompson when they bombarded an ²⁵³Es target with alpha particles in the Berkeley Radiation Laboratory's 60-inch cyclotron; this was the first isotope of any element to be synthesized one atom at a time.^[46]

There were several attempts to obtain isotopes of nobelium by Swedish (1957) and American (1958) groups, but the first reliable results was the synthesis of ²⁵⁶No by the Russian group (Georgy Flyorov et al.) in 1965, as acknowledges by the IUPAC in 1992. In their experiments, Flyorov et al. bombarded uranium-238 with neon-22.^[5]

In 1961, Ghiorso et al. obtained the first isotope of lawrencium by irradiating californium (mostly californium-252) with boron-10 and boron-11 ions.^[5] The mass number of this isotope was not clearly established (possibly 258 or 259) at the time. In 1965, ²⁵⁶Lr were synthesized by Flyorov et al. from ²⁴³Am and ¹⁸O. Thus IUPAC recognized the nuclear physics teams at Dubna and Berkeley as the co-discoverers of lawrencium.

[edit] Isotopes

Most actinides have 89 to 103 protons and 117 to 159 neutrons.

Thirty one isotopes of actinium and 8 excited isomeric states of some of its nuclides were identified by 2010.^[47] Three isotopes, ²²⁵Ac, ²²⁷Ac and ²²⁸Ac, were found in nature and the others were produced in the laboratory; only the three natural isotopes are used in applications. Actinium-225 is a member of radioactive neptunium series;^[50] it was first discovered in 1947 as a fission product of uranium-233, it is an α-emitter with a half-life of 10 days. Actinium-225 is less available than actinium-228, but is more promising in radiotracer applications.^[22] Actinium-227 (half-life 21.77 years) occurs in all uranium ores, but in small quantities. One gram of uranium (in radioactive equilibrium) contains only 2×10⁻¹⁰ gram of ²²⁷Ac.^[22][47] Actinium-228 is a member of radioactive thorium series formed by the decay of ²²⁸Ra;^[50] it is a β^– emitter with a half-life of 6.15 hours. In one tonne of thorium there is 5×10⁻⁸ gram of ²²⁸Ac. It was discovered by Otto Hahn in 1906.^[22]

Twenty nine isotopes of protactinium are known with mass numbers 212–240^[47] as well as three excited isomeric states. Only ²³¹Pa and ²³⁴Pa have been found in nature. All the isotopes have short lifetime, except for protactinium-231 (half-life 32,760 years). The most important isotopes are ²³¹Pa and ²³³Pa, which is an intermediate product in obtaining uranium-233 and is the most affordable among artificial isotopes of protactinium. ²³³Pa has convenient half-life and energy of γ-radiation, and thus was used in most studies of protactinium chemistry. Protactinium-233 is a β-emitter with a half-life of 26.97 days.^[47][51]

Uranium has the highest number (25) of both natural and synthetic isotopes. They have mass numbers of 217–242,^[48] and three of them, ²³⁴U, ²³⁵U and ²³⁸U, are present in appreciable quantities in nature. Among others, the most important is ²³³U, which is a final product of transformations of ²³²Th irradiated by slow neutrons. ²³³U has a very higher fission efficiency by low-energy (thermal) neutrons, compared e.g. with ²³⁵U. Most uranium chemistry studies were carried out on uranium-238 owing to its long half-life of 4.4×10⁹ years.^[52]

There are 19 isotopes of neptunium with mass numbers from 225 to 244;^[48] they are all highly radioactive. The most popular among scientists are long-lived ²³⁷Np (t_½ = 2.20×10⁶ years) and short-lived ²³⁹Np, ²³⁸Np (t_½ ~ 2 days).^[28]

Sixteen isotopes of americium are known with mass numbers from 232 to 248.^[48] The most important are ²⁴¹Am and ²⁴³Am, which are alpha-emitters and also emit soft, but intense γ-rays; both of them can be obtained in an isotopically pure form. Chemical properties of americium were first studied with ²⁴¹Am, but later shifted to ²⁴³Am, which is almost 20 times less radioactive. The disadvantage of ²⁴³Am is production of the short-lived daughter isotope ²³⁹Np, which has to be considered in the data analysis.^[7]

Among 19 isotopes of curium,^[48] the most accessible are ²⁴²Cm and ²⁴⁴Cm; they are α-emitters, but with much shorter lifetime than the americium isotopes. These isotopes emit almost no γ-radiation, but undergo spontaneous fission with the associated emission of neutrons. More long-lived isotopes of curium (^245–248Cm, all α-emitters) are formed as a mixture during neutron irradiation of plutonium or americium. Upon short irradiation, this mixture is dominated by curium-246, and then curium-248 begins to accumulate. Both of these isotopes, especially ²⁴⁸Cm, have a longer half-life (3.48×10⁵ years) and are much more convenient for carrying out chemical research than ²⁴²Cm and ²⁴⁴Cm, but they also have a rather high rate of spontaneous fission. ²⁴⁷Cm has the longest lifetime among isotopes of curium (1.56×10⁷ years), but is not formed in large quantities because of the strong fission induced by thermal neutrons.

Fourteen isotopes of berkelium were identified with mass numbers 238–252.^[48] Only ²⁴⁹Bk is available in large quantities; it has a relatively short half-life of 330 days and emits mostly soft β-particles, which are inconvenient for detection. Its alpha radiation is rather weak (1.45×10⁻³% with respect to β-radiation), but is sometimes used to detect this isotope. ²⁴⁷Bk is an alpha-emitter with a long half-life of 1,380 years, but it is hard to obtain in appreciable quantities; it is not formed upon neutron irradiation of plutonium because of the β-stability of isotopes of curium isotopes with mass number below 248.^[7]

Isotopes of californium with mass numbers 237–256 are formed in nuclear reactors;^[48] californium-253 is a β-emitter and the rest are α-emitters. The isotopes with even mass numbers (²⁵⁰Cf, ²⁵²Cf and ²⁵⁴Cf) have a high rate of spontaneous fission, especially ²⁵⁴Cf of which 99.7% decays by spontaneous fission. Californium-249 has a relatively long half-life (352 years), weak spontaneous fission and strong γ-emission that facilitates its identification. ²⁴⁹Cf is not formed in large quantities in a nuclear reactor because of the slow β-decay of the parent isotope ²⁴⁹Bk and a large cross section of interaction with neutrons, but it can be accumulated in the isotopically pure form as the β-decay product of (pre-selected) ²⁴⁹Bk. Californium produced by reactor-irradiation of plutonium mostly consists of ²⁵⁰Cf and ²⁵²Cf, the latter being predominant for large neutron fluences, and its study is hindered by the strong neutron radiation.^[7]

Among the 16 known isotopes of einsteinium with mass numbers from 241 to 257^[48] the most affordable is ²⁵³Es. It is an α-emitter with a half-life of 20.47 days, a relatively weak γ-emission and small spontaneous fission rate as compared with the isotopes of californium. Prolonged neutron irradiation also produces a long-lived isotope ²⁵⁴Es (t_½ = 275.5 days).^[7]

Nineteen isotopes of fermium are known with mass numbers of 242–260. ²⁵⁴Fm, ²⁵⁵Fm and ²⁵⁶Fm are α-emitters with a short half-life (hours), which can be isolated in significant amounts. ²⁵⁷Fm (t_½ = 100 days) can accumulate upon prolonged and strong irradiation. All these isotopes are characterized by high rates of spontaneous fission.^[7][53]

Among the 15 known isotopes of mendelevium (mass numbers from 245 to 260),^[48] the most studied is ²⁵⁶Md, which mainly decays through the electron capture (α-radiation is ≈10%) with the half-life of 77 minutes. Another alpha emitter, ²⁵⁸Md, has a half-life of 53 days. Both these isotopes are produced from rare einsteinium (²⁵³Es and ²⁵⁵Es respectively), that limits their so their availability.^[47]

Long-lived isotopes of nobelium and isotopes of lawrencium (and of heavier elements) have relatively small half-lives. For nobelium 11 isotopes are known with mass numbers 250–260 and 262. Chemical properties of nobelium and lawrencium were studied with ²⁵⁵No (t_½ = 3 min) and ²⁵⁶Lr (t_½ = 35 s). The longest-lived nobelium isotope ²⁵⁹No has a half-life of 1.5 hours.^[47]

[edit] Distribution in nature

Unprocessed uranium ore

Thorium and uranium are the most abundant actinides in nature with the respective mass concentrations of 1.6×10⁻³% and 4×10⁻⁴%.^[54] Uranium mostly occurs in the Earth's crust as a mixture of its oxides in the minerals uraninite, which is also called pitchblende because of its black color. There are several dozens of other uranium minerals such as carnotite (KUO₂VO₄·3H₂O) and autunite (Ca(UO₂)₂(PO₄)₂·nH₂O). The isotopic composition of natural uranium is ²³⁸U (relative abundance 99.2742%), ²³⁵U (0.7204%) and ²³⁴U (0.0054%); of these ²³⁸U has the largest half-life of 4.51×10⁹ years.^[55][56] The worldwide production of uranium in 2009 amounted to 50,572 tonnes, of which 27.3% was mined in Kazakhstan. Other important uranium mining countries are Canada (20.1%), Australia (15.7%), Namibia (9.1%), Russia (7.0%), and Niger (6.4%).^[57]

The most abundant thorium minerals are thorianite (ThO₂), thorite (ThSiO₄) and monazite, ((Th, Ca, Ce)PO₄). Most thorium minerals contain uranium and vice versa; and they all have significant fraction of lanthanides. Rich deposits of thorium minerals are located in the United States (440,000 tonnes), Australia and India (~300,000 tonnes each) and Canada (~100,000 tonnes).^[58]

The abundance of actinium in the Earth's crust is only about 5×10⁻¹⁵%.^[51] Actinium is mostly present in uranium-containing, but also in other minerals, though in much smaller quantities. The content of actinium in most natural objects corresponds to the isotopic equilibrium of parent isotope ²³⁵U, and it is not affected by the weak Ac migration.^[22] Protactinium is more abundant (10⁻¹²%) in the Earth's crust than actinium. It was discovered in the uranium ore in 1913 by Fajans and Göhring.^[24] As actinium, the distribution of protactinium follows that of ²³⁵U.^[51]

The half-life of the longest-lived isotope of neptunium, ²³⁷Np, is negligible compared to the age of the Earth. Thus neptunium is present in nature in negligible amounts produced as intermediate decay products of other isotopes.^[28] Traces of plutonium in uranium minerals were first found in 1942, and the more systematic results on ²³⁹Pu are summarized in the table (no other plutonium isotopes could be detected in those samples). The upper limit of abundance of the longest-living isotope of plutonium, ²⁴⁴Pu, is 3×10⁻²⁰%. Plutonium could not be detected in samples of lunar soil. Owing to its scarcity in nature, most plutonium is produced synthetically.^[59]

[edit] Extraction

Monazite—a major thorium mineral

Owing to the low abundance of actinides, their extraction is a complex, multistep process. Fluorides of actinides are usually used because they are insoluble in water and can be easily separated with redox reactions. Fluorides are reduced with calcium, magnesium or barium:^[15]

Among the actinides, thorium and uranium are the easiest to isolate. Thorium is extracted mostly from monazite: thorium diphosphate (Th(PO₄)₂) is reacted with nitric acid, and the produced thorium nitrate treated with tributyl phosphate. Rare-earth impurities are separated by increasing the pH in sulfate solution.

Monazite is decomposed with a 45% aqueous solution of sodium hydroxide at 140 °C. Mixed metal hydroxides are extracted first, filtered at 80 °C, washed with water and dissolved with concentrated hydrochloric acid. Next, the acidic solution is neutralized with hydroxides to pH = 5.8 that results in precipitation of thorium hydroxide (Th(OH)₄) contaminated with ~3% of rare-earth hydroxides; the rest of rare-earth hydroxides remains in solution. Thorium hydroxide is dissolved in an inorganic acid and then purified from the rare earth elements. An efficient method is the dissolution of thorium hydroxide in nitric acid, because the resulting solution can be purified by extraction with organic solvents:^[15]

Separation of uranium and plutonium from nuclear fuel^[60]

Th(OH)₄ + 4 HNO₃ → Th(NO₃)₄ + 4 H₂O

Metallic thorium is separated from the anhydrous oxide, chloride or fluoride by reacting it with calcium in an inert atmosphere:^[61]

ThO₂ + 2 Ca → 2 CaO + Th

Sometimes thorium is extracted by electrolysis of a fluoride in a mixture of sodium and potassium chloride at 700–800 °C in a graphite crucible. Highly pure thorium can be extracted from its iodide with the crystal bar process.^[62]

Uranium is extracted from its ores in various ways. In one method, the ore is burned and then reacted with nitric acid to convert uranium into a dissolved state. Treating the solution with a solution of tributyl phosphate (TBP) in kerosene transforms uranium into an organic form UO₂(NCS)₂·2TBP. The insoluble impurities are filtered and the uranium is extracted by reaction with hydroxides as (NH₄)₂U₂O₇ or with hydrogen peroxide as UO₄·2H₂O.^[15]

When the uranium ore is rich in such minerals as dolomite, magnesite, etc., those minerals consume much acid. In this case, the carbonate method is used for uranium extraction. Its main component is an aqueous solution of sodium carbonate, which converts uranium into a complex [UO₂(CO₃)₃]^4–, which is stable in aqueous solutions at low concentrations of hydroxide ions. The advantages of the sodium carbonate method are that the chemicals have low corrosivity (compared to nitrates) and that most non-uranium metals precipitate from the solution. The disadvantage is that tetravalent uranium compounds precipitate as well. Therefore, the uranium ore is treated with sodium carbonate at elevated temperature and under oxygen pressure:

2 UO₂ + O₂ + 6 CO₃^2– → 2 [UO₂(CO₃)₃]^4–

This equation suggests that the best solvent for the uranium carbonate processing is a mixture of carbonate with bicarbonate. At high pH, this results in precipitation of diuranate, which is treated with hydrogen in the presence of nickel yielding an insoluble uranium tetracarbonate.^[15]

Another separation method uses polymeric resins as a polyelectrolyte. Ion exchange processes in the resins result in separation of uranium. Uranium from resins is washed with a solution of ammonium nitrate or nitric acid that yields uranyl nitrate, UO₂(NO₃)₂·6H₂O. When heated, it turns into UO₃, which is converted to UO₂ with hydrogen:

UO₃ + H₂ → UO₂ + H₂O

Reacting uranium dioxide with fluoric acid changes it to uranium tetrafluoride, which yields uranium metal upon reaction with magnesium metal:^[61]

4 HF + UO₂ → UF₄ + 2 H₂O

To extract plutonium, neutron-irradiated uranium is dissolved in nitric acid, and a reducing agent (FeSO₄, or H₂O₂) is added to the resulting solution. This addition changes the oxidation state of plutonium from +6 to +4, while uranium remains in the form of uranyl nitrate (UO₂(NO₃)₂). The solution is treated with a reducing agent and neutralized with ammonium carbonate to pH = 8 that results in precipitation of Pu⁴⁺ compounds.^[15]

In another method, Pu⁴⁺and UO₂²⁺ are first extracted with tributyl phosphate, then reacted with hydrazine washing out the recovered plutonium.^[15]

The major difficulty in separation of actinium is the similarity of its properties with those of lanthanum. Thus actinium is either synthesized in nuclear reactions from isotopes of radium or separated using ion-exchange procedures.^[22]

[edit] Properties

Actinides have similar properties to lanthanides. The 6d and 7s electronic shells are completed in actinium and thorium, and the 5f shell is being filled with further increase in atomic number; the 4f shell is filled in the lanthanides. The first experimental evidence for the filling of the 5f shell in actinides was obtained by McMillan and Abelson in 1940.^[63] As in lanthanides (see lanthanide contraction), the ionic radius of actinides monotonically decreases with atomic number (see also Aufbau principle).^[15]

[edit] Physical properties

Major crystal structures of some actinides vs. temperature	Metallic and ionic radii of actinides[64]

A pellet of ²³⁸PuO₂ to be used in a radioisotope thermoelectric generator for either the Cassini or Galileo mission. The pellet produces 62 watts of heat and glows because of the heat generated by the radioactive decay (primarily α). Photo is taken after insulating the pellet under a graphite blanket for minutes and removing the blanket.

Thorium

Actinides are typical metals. All of them are soft and have a silvery color (but tarnish in air),^[67] relatively high density and plasticity. Some of them can be cut with a knife. Their electrical resistivity varies between 15 and 150 µOhm·cm.^[64] The hardness of thorium is similar to that of soft steel, so heated pure thorium can be rolled in sheets and pulled into wire. Thorium is nearly half as dense as uranium and plutonium, but is harder than either of them. All actinides are radioactive, paramagnetic, and, with the exception of actinium, have several crystalline phases: plutonium has seven, and uranium, neptunium and californium three. Crystal structures of protactinium, uranium, neptunium and plutonium do not have clear analogs among the lanthanide and are more similar to those of the 3d-transition metals.^[56]

All actinides are pyrophoric, especially when finely divided, that is, they spontaneously ignite upon reaction with air.^[67] The melting point of actinides does not have a clear dependence on the number of f-electrons. The unusually low melting point of neptunium and plutonium (~640 °C) is explained by hybridization of 5f and 6d orbitals and the formation of directional bonds in these metals.^[56]

[edit] Chemical properties

Like the lanthanides, all actinides are highly reactive with halogens and chalcogens; however, actinides react more easily. Actinides, especially those with a small number of 5f-electrons, are prone to hybridization. This is explained by the similarity of the electron energies at the 5f, 7s and 6d shells.^[15] Most actinides exhibit a larger variety of valence states, and the most stable are +6 for uranium, +5 for protactinium and neptunium, +4 for thorium and plutonium and +3 for actinium and other actinides.^[15]

Chemically, actinium is similar to lanthanum, which is explained by their similar ionic radii and electronic structure. Like lanthanum, actinium has oxidation of +3, but it is less reactive and has more pronounced basic properties. Among other trivalent actinides Ac³⁺ is least acidic, i.e. has the weakest tendency to hydrolyze in aqueous solutions.^[22][56]

Thorium is rather active chemically. Owing to lack of electrons on 6d-and 4f-orbitals, the tetravalent thorium compounds are colorless. At pH < 3, the solutions of thorium salts are dominated by the cations [Th(H₂O)₈]⁴⁺. The Th⁴⁺ ion is relatively large, and depending on the coordination number can have a radius between 0.95 and 1.14 Å. As a result, thorium salts have a weak tendency to a hydrolysis. The distinctive ability of thorium salts is their high solubility, not only in water, but also in polar organic solvents.^[56]

Protactinium exhibits two valence states; the +5 is stable, and the +4 state easily oxidizes to protactinium(V). Thus tetravalent protactinium in solutions is obtained by the action of strong reducing agents in a hydrogen atmosphere. Tetravalent protactinium is chemically similar to U^IV and thorium. Fluorides, phosphates, hypophosphate, iodate and phenylarsonates of Pa^IV are insoluble in water and dilute acids. Protactinium forms soluble carbonates. The hydrolytic properties of pentavalent protactinium are close to those of tantalum(V) and niobium(V). The complex chemical behavior of protactinium is a consequence of the start of the filling of the 5f shell in this element.^[51]

Uranium has a valence from 3 to 6, the last being most stable. In the hexavalent state, uranium is very similar to the sixth group elements. Many compounds of uranium(IV) and uranium(VI) are nonstoichiometric, i.e. have variable composition. For example, the actual chemical formula of uranium dioxide is UO_2+x, where x varies between −0.4 and 0.32. Uranium(VI) compounds are weak oxidants. Most of them contain the linear "uranyl" group, UO₂²⁺. Between 4 to 6 ligands can be accommodated in an equatorial plane perpendicular to the uranyl group. The uranyl group acts as a hard acid and forms stronger complexes with oxygen-donor ligands than with nitrogen-donor ligands. NpO₂²⁺ and PuO₂²⁺ are also the common form of Np and Pu in the +6 oxidation state. Uranium(IV) compounds exhibit reducing properties, e.g., they are easily oxidized by atmospheric oxygen. Uranium(III) is a very strong reducing agent. Owing to the presence of d-shell, uranium (as well as many other actinides) forms organometallic compounds, such as U^III(C₅H₅)₃ and U^IV(C₅H₅)₄.^[56][68]

Neptunium has valence states from 3 to 7, which can be simultaneously observed in solutions. The most stable state in solution is +5, but the valence +4 is preferred in solid neptunium compounds. Neptunium metal is very reactive. Ions of neptunium are prone to hydrolysis and formation of coordination compounds.^[28]

Plutonium also exhibits the valence between 3 and 7, and thus is chemically similar to neptunium and uranium. It is highly reactive, and quickly forms an oxide film in air. Plutonium reacts with hydrogen even at temperatures as low as 25–50 °C; it also easily forms halides and intermetallic compounds. Hydrolysis reactions of plutonium ions of different oxidation states are quite diverse. Plutonium(V) can enter polymerization reactions.^[69][70]

The largest chemical diversity among actinides is observed in americium, which can have valence between 2 and 6. Divalent americium is obtained only in dry compounds and non-aqueous solutions (acetonitrile). Oxidation states +3, +5 and +6 are typical for aqueous solutions, but also in the solid state. Tetravalent americium forms stable solid compounds (dioxide, fluoride and hydroxide) as well as complexes in aqueous solutions. It was reported that in alkaline solution americium can be oxidized to the heptavalent state, but these data proved to be erroneous. The most stable valence of americium is 3 in the aqueous solutions and 3 or 4 in solid compounds.^[7]

Valence 3 is dominant in all subsequent elements up to lawrencium (maybe except for nobelium). Curium can be tetravalent in solids (fluoride, dioxide). Berkelium, along with a valence of +3, also shows the valence of +4, more stable than that of curium; the valence 4 is observed in solid fluoride and dioxide. The stability of Bk⁴⁺ in aqueous solution is close to that of Ce⁴⁺. Only valence 3 was observed for californium, einsteinium and fermium. Bivalent state is proven for mendelevium and nobelium, and in nobelium it is more stable than the trivalent state. Lawrencium shows valence 3 both in solutions and solids. Rutherfordium chloride behaves similar to hafnium chloride, i.e. might contain tetravalent rutherfordium.^[7]

The redox potential increases from −0.32 V in uranium, through 0.34 V (Np) and 1.04 V (Pu) to 1.34 V in americium revealing the increasing reduction ability of the An⁴⁺ ion from americium to uranium. All actinides form AnH₃ hydrides of black color with salt-like properties. Actinides also produce carbides with the general formula of AnC or AnC₂ (U₂C₃ for uranium) as well as sulfides An₂S₃ and AnS₂.^[15]

[edit] Compounds

[edit] Oxides and hydroxides

Oxides of actinides^{[7][22][28][51][71]}

Compound	Color	Crystal symmetry, type	Lattice constants, Å			Density, g/cm3	Temperature, °C
			a	b	c
Ac2O3	White	Hexagonal, La2O3	4.07	-	6.29	9.19	–
PaO2	-	Cubic, CaF2	5.505	-	-	-	-
Pa2O5	White	cubic, CaF2 Cubic Tetragonal Hexagonal Rhombohedral Orthorhombic	5.446 10.891 5.429 3.817 5.425 6.92	- - - - - 4.02	- 10.992 5.503 13.22 - 4. 18	-	700 700–1100 1000 1000–1200 1240–1400 –
ThO2	Colorless	Cubic	5.59	-	-	9.87	–
UO2	Black-brown	Cubic	5.47	-	-	10.9	–
NpO2	Greenish-brown	Cubic, CaF2	5.424	-	-	11.1	–
PuO	Black	Cubic, NaCl	4.96	-	-	13.9	–
PuO2	Olive green	Cubic	5.39	-	-	11.44	–
Am2O3	Red-brown Red-brown	Cubic, Mn2O3 Hexagonal, La2O3	11.03 3.817	-	- 5.971	10.57 11.7	–
AmO2	Black	Cubic, CaF2	5.376	-	-	-	-
Cm2O3	White [72] - -	Cubic, Mn2O2 Hexagonal, LaCl3 Monoclinic, Sm2O3	11.01 3.80 14.28	- - 3.65	- 6 8.9	11.7	–
CmO2	Black	Cubic, CaF2	5.37	-	-	-	-
Bk2O3	Light brown	Cubic, Mn2O3	10.886	-	-	-	-
BkO2	Red-brown	Cubic, CaF2	5.33	-	-	-	-
Cf2O3[73]	Colorless Yellowish -	Cubic, Mn2O3 Monoclinic, Sm2O3 Hexagonal, La2O3	10.79 14.12 3.72	- 3.59 -	- 8.80 5.96	-	-
CfO2	Black	Cubic	5.31	-	-	-	-
Es2O3	-	Cubic, Mn2O3 Monoclinic Hexagonal, La2O3	10.07 14.1 3.7	- 3.59 -	- 8.80 6	-	-

Approximate colors of actinide oxides (most stable are bolded)^[74]

Oxidation state	89	90	91	92	93	94	95	96	97	98	99
+3						Pu2O3	Am2O3	Cm2O3	Bk2O3	Cf2O3	Es2O3
+4		ThO2	PaO2	UO2	NpO2	PuO2	AmO2	CmO2	BkO2	CfO2
+5			PaO2+	U2O5	Np2O5
+6				U3O8
				UO3

Dioxides of some actinides^[75]

Chemical formula	ThO2	PaO2	UO2	NpO2	PuO2	AmO2	CmO2	BkO2	CfO2
CAS-number	1314-20-1	12036-03-2	1344-57-6	12035-79-9	12059-95-9	12005-67-3	12016-67-0	12010-84-3	12015-10-0
PubChem	14808		10916
Molar mass	264.04	263.035	270.03	269.047	276.063	275.06	270–284**	279.069	283.078
Melting point	3390 °C		2878 °C	2600 °C	2400 °C	2050 °C
Boiling point	4400 °C				2800 °C
structure	An4+: __  /  O2−: __
Space group	Fm3m
Coordination number	An[8], O[4]

An – actinide
**Depending on the isotopes

Some actinides can exists in various oxide forms: An₂O₃, AnO₂, An₂O₅ and AnO₃. For all actinides, oxides AnO₃ are amphoteric and An₂O₃, AnO₂ and An₂O₅ are basic, they easily react with water, forming bases:^[15]

An₂O₃ + 3 H₂O → 2 An(OH)₃.

These bases are poorly soluble in water and by their activity are close to the hydroxides of rare-earth metals. The strongest base is of actinium. All compounds of actinium are colorless, except for black actinium sulfide (Ac₂S₃).^[15] Dioxides of tetravalent actinides crystallize in the cubic system, same as in calcium fluoride.

Thorium reacting with oxygen exclusively forms dioxide:

Thorium dioxide is a refractory material with the highest melting point among any known oxide (3390 °C).^[74] Adding 0.8–1% ThO₂to tungsten stabilizes its structure, so the doped filaments have better mechanical stability to vibrations. To dissolve ThO₂acids, it is heated to 500–600 °C; heating above 600 °C produces a very resistant to acids and other reagents form of ThO₂. Small addition of fluoride ions catalyses dissolution of thorium dioxide in acids.

Two protactinium oxides were obtained: PaO₂ (black) and Pa₂O₅(white); the former is isomorphic with ThO₂ and the latter is easier to obtain. Both oxides are basic, and Pa(OH)₅ is a weak, poorly soluble base.^[15]

Decomposition of certain salts of uranium, for example UO₂(NO₃)·6H₂O in air at 400 °C, yields orange or yellow UO₃.^[74] This oxide is amphoteric and forms several hydroxides, the most stable being UO₂(OH)₂. Reaction of uranium(VI) oxide with hydrogen results in uranium dioxide, which is similar in its properties with ThO₂. This oxide is also basic and corresponds to the uranium hydroxide (U(OH)₄).^[15]

Plutonium, neptunium and americium form two basic oxides: An₂O₃ and AnO₂. Neptunium trioxide is unstable, thus only Np₃O₈ could be obtained so far. However, the oxides of plutonium and neptunium with the chemical formula AnO₂ and An₂O₃ are well characterized.^[15]

[edit] Salts

Trichlorides of some actinides^[75][76]

Chemical formula	AcCl3	UCl3	NpCl3	PuCl3	AmCl3	CmCl3	BkCl3	CfCl3
CAS-number	22986-54-5	10025-93-1	20737-06-8	13569-62-5	13464-46-5	13537-20-7	13536-46-4	13536-90-8
PubChem		167444
Molar mass	333.386	344.387	343.406	350.32	349.42	344–358**	353.428	357.438
Melting point		837 °C	800 °C	767 °C	715 °C	695 °C	603 °C	545 °C
Boiling point		1657 °C		1767 °C	850 °C
Crystal structure	An3+: __  /  Cl−: __
Space group	P63/m
Coordination number	An*[9], Cl [3]
Lattice constants	a = 762 pm c = 455 pm	a = 745.2 pm c = 432.8 pm		a = 739.4 pm c = 424.3 pm	a = 738.2 pm c = 421.4 pm	a = 726 pm c = 414 pm	a = 738.2 pm c = 412.7 pm	a = 738 pm c = 409 pm

*An – actinide
**Depending on the isotopes

Actinide fluorides^{[7][28][51][71][76]}

Compound	Color	Crystal symmetry, type	Lattice constants, Å			Density, g/cm3
			a	b	c
AcF3	White	Hexagonal, LaF3	4.27	-	7.53	7.88
PaF4	Dark brown	Monoclinic	12.7	10.7	8.42	–
PaF5	Black	Tetragonal, β-UF5	11.53	-	5.19	–
ThF4	Colorless	Monoclinic	13	10.99	8.58	5.71
UF3	Reddish-purple	Hexagonal	7.18	-	7.34	8.54
UF4	Green	Monoclinic	11.27	10.75	8.40	6.72
α-UF5	Bluish	Tetragonal	6.52	-	4.47	5.81
β-UF5	Bluish	Tetragonal	11.47	-	5.20	6.45
UF6	Yellowish	Orthorhombic	9.92	8.95	5.19	5.06
NpF3	Black or purple	Hexagonal	7.129	-	7.288	9.12
NpF4	Light green	Monoclinic	12.67	10.62	8.41	6.8
NpF6	Orange	Orthorhombic	9.91	8.97	5.21	5
PuF3	Violet-blue	Trigonal	7.09	-	7.25	9.32
PuF4	Pale brown	Monoclinic	12.59	10.57	8.28	6.96
PuF6	Red-brown	Orthorhombic	9.95	9.02	3.26	4.86
AmF3	Pink or light beige	[[Hexagonal crystal system	hexagonal]], LaF3	7.04 [59][77]	-	7.255	9.53
AmF4	Orange-red	Monoclinic	12.53	10.51	8.20	–
CmF3	From brown to white	Hexagonal	4.041	-	7.179	9.7
CmF4	Yellow	Monoclinic, UF4	12.51	10.51	8.20	–
BkF3	Yellow-green	Trigonal, LaF3 Orthorhombic, YF3	6.97 6.7	- 7.09	7.14 4.41	10.15 9.7
BkF4	-	Monoclinic, UF4	12.47	10.58	8.17	–
CfF3	- -	Trigonal, LaF3 Orthorhombic, YF3	6. 94 6.65	- 7.04	7.10 4.39	–
CfF4	- -	Monoclinic, UF4 Monoclinic, UF4	1.242 1.233	1.047 1.040	8.126 8.113	–

Einsteinium triiodide glowing in the dark

Actinides easily react with halogens forming salts with the formulas MX₃ and MX₄ (X = halogen). So the first berkelium compound, BkCl₃, was synthesized in 1962 with an amount of 3 nanogram. Like the halogens of rare earth elements, actinide chlorides, bromides, and iodides are water soluble, and fluorides are insoluble. Uranium easily yields a colorless hexafluoride, which sublimates at a temperature of 56.5 °C; because of its volatility, it is used in the separation of uranium isotopes with gas centrifuge or gaseous diffusion. Actinide hexafluorides have properties close to anhydrides. They are very sensitive to moisture and hydrolyze forming AnO₂F₂.^[78] Pentachloride and black hexachloride of uranium were synthesized, but they are both unstable.^[15]

Action of acids on actinides yields salts, and if the acids are non-oxidizing then the actinide in the salt is in low-valence state:

U + 2 H₂SO₄ → U (SO₄)₂ + 2 H₂

2 Pu + 6 HCl → 2 PuCl₃ + 3 H₂

However, in these reactions the regenerating hydrogen can react with the metal, forming the corresponding hydride. Uranium reacts with acids and water much easier than thorium.^[15]

Actinide salts can also be obtained by dissolving the corresponding hydroxides in acids. Nitrates, chlorides, sulfates and perchlorates of actinides are water soluble. When crystallizing from aqueous solutions, these salts forming a hydrates, such as Th(NO₃)₄·6H₂O, Th(SO₄)₂·9H₂O and Pu₂(SO₄)₃·7H₂O. Salts of high-valence actinides easily hydrolyze. So, colorless sulfate, chloride, perchlorate and nitrate of thorium transform into basic salts with formulas Th(OH)₂SOsub>4 and Th(OH)₃NO₃. The solubility and insolubility of trivalent and tetravalent actinides is like that of lanthanide salts. So phosphates, fluorides, oxalates, iodates and carbonates of actinides are weakly soluble in water; they precipitate as hydrates, such as ThF₄·3H₂O and Th(CrO₄)₂·3H₂O.^[15]

Actinides with oxidation state +6, except for the AnO₂²⁺-type cations, form [AnO₄]^2–, [An₂O₇]^2– and other complex anions. For example, uranium, neptunium and plutonium form salts of the Na₂UO₄ (uranate) and (NH₄)₂U₂O₇ (diuranate) types. In comparison with lanthanides, actinides easier form coordination compounds, and this ability increases with the actinide valence. Trivalent actinides do not form fluoride coordination compounds, whereas tetravalent thorium forms K₂ThF₆, KThF₅, and even K₅ThF₉ complexes. Thorium also forms the corresponding sulfates (for example Na₂SO₄·Th (SO₄)₂·5H₂O), nitrates and thiocyanates. Salts with the general formula An₂Th(NO₃)₆·nH₂O are of coordination nature, with the coordination number of thorium equal to 12. Even easier is to produce complex salts of pentavalent and hexavalent actinides. The most stable coordination compounds of actinides – tetravalent thorium and uranium – are obtained in reactions with diketones, e.g. acetylacetone.^[15]

[edit] Applications

Inside of a smoke detector containing americium-241.

While actinides have some established daily-life applications, such as in smoke detectors (americium)^[79][80] and gas mantles (thorium),^[61] they are mostly used in nuclear weapons and use as a fuel in nuclear reactors.^[61] The last two areas exploit the property of actinides to release enormous energy in nuclear reactions, which under certain conditions may become self-sustaining chain reaction.

Self-illumination of a nuclear reactor by the Cherenkov radiation.

The most important isotope for nuclear energy applications is uranium-235. It is used in the most popular thermal reactor, and its concentration in natural uranium does not exceed 0.72%. This isotope strongly absorbs thermal neutrons releasing much energy. One fission act of 1 gram of ²³⁵U converts into about 1 MW·day. Important is that ²³⁵U emits more neutrons than it absorbs.^[15] Upon reaching the critical mass, ²³⁵U enters into a self-sustaining chain reaction.^[56] Typically, uranium nucleus is divided into two fragments with the release of 2–3 neutrons, for example:

Other promising actinide isotopes for nuclear energy are thorium-232 and its fission product, formed uranium-233.

Nuclear reactor [56][81][82]

The core of any nuclear reactor contains a set of hollow metal rods, usually made of zirconium alloys, filled with nuclear fuel cells – mostly oxide, carbide, nitride or monosulfide of uranium, plutonium or thorium, or their mixture (the so-called MOX fuel). The most common fuel is oxide of uranium-235. Fast neutrons are slowed by moderators, which contain water, carbon, deuterium, or beryllium, as thermal neutrons to increase the efficiency of their interaction with uranium-235. The rate of nuclear reaction is controlled by introducing additional rods made of boron or cadmium or a liquid absorbent, usually boric acid. Reactors for plutonium production are called breeder reactor or breeders; they have a different design and use fast neutrons.

Emission of neutrons during the fission of uranium is important not only for maintaining the nuclear chain reaction, but also for the synthesis of the heavier actinides. Uranium-239 converts via β-decay into plutonium-239, which, like uranium-235, is capable of spontaneous fission. The world's first nuclear reactors were built not for energy, but for producing plutonium-239 for nuclear weapons.

About half of the produced thorium is used as the light-emitting material of gas mantles.^[61] Thorium is also added into multicomponent alloys of magnesium and zinc. So the Mg-Th alloys are light and strong, but also have high melting point and ductility and thus are widely used in the aviation industry and in the production of missiles. Thorium also has good electron emission properties, with long lifetime and low potential barrier for the emission.^[15] The relative content of thorium and uranium isotopes is widely used to estimate the age of various objects, including stars (see radiometric dating).^[83]

Plutonium-238 is potentially more efficient isotope for nuclear reactors, as it has smaller critical mass than uranium-235, but releases much more thermal energy (0.56 W/g).^[80][84] However, its application is limited by the high price (about 1000 USD/g). This isotope has been used in thermopiles and water distillation systems of some space satellites and stations. So Galileo and Apollo spacecrafts (e.g. Apollo 14^[85]) had heaters powered by kilogram quantities of plutonium-238 oxide; this heat is also transformed into electricity with thermopiles. The decay of plutonium-238 is produced relatively harmless alpha particles and is not accompanied by gamma-irradiation. Therefore and this isotope (~160 mg) is used as the energy source in heart pacemakers where it lasts about 5 times longer than conventional batteries.^[80]

Actinium-227 is used as a neutron source. Its high specific energy (14.5 W/g) and the possibility of obtaining significant quantities of thermally stable compounds are attractive for use in long-lasting thermoelectric generators for remote use. ²²⁸Ac is used as an indicator of radioactivity in chemical research, as it emits high-energy electrons (2.18 MeV) that can be easily detected. ²²⁸Ac-²²⁸Ra mixtures are widely used as an intense gamma-source in industry and medicine.^[22]

[edit] Toxicity

Schematic illustration of penetration of radiation through sheets of paper, aluminium and lead brick

Periodic table with elements colored according to the half-life of their most stable isotope.

  Stable elements;

  Radioactive elements with very long-lived isotopes. Their half-lives of over four million years confer them very small, if not negligible radioactivities;

  Radioactive elements that may present low health hazards. Their most stable isotopes have half-lives between 800 and 34,000 years. Because of this, they usually have some commercial applications;

  Radioactive elements that are known to pose high safety risks. Their most stable isotopes have half-lives between one day and 103 years. Their radioactivities confers them little potential for commercial uses;

  Highly radioactive elements. Their most stable isotopes have half-lives between one day and several minutes. They pose severe health risks. Few of them receive uses outside basic research;

  Extremely radioactive elements. Very little is known about these elements due to their extreme instability and radioactivity.

Radioactive substances can harm human health via (i) local skin contamination, (ii) internal exposure due to ingestion of radioactive isotopes, and (iii) external overexposure by β and γ-radiation. Together with radium and transuranium elements, actinium is one of the most dangerous radioactive poisons with high specific α-activity. The most important feature of actinium is its ability to accumulate and remain in the surface layer of skeletons. At the initial stage of poisoning, actinium accumulates in the liver. Another danger of actinium is that it undergoes radioactive decay faster than being excreted. Adsorption from the digestive tract is much smaller (~0.05%) for actinium than radium.^[22]

Protactinium in the body tends to accumulate in the kidneys and bones. The maximum safe dose of Pa in the human body is 0.03 µCi that corresponds to 0.5 micrograms of ²³¹Pa. This isotope, which might be present in the air as aerosol, is 2.5×10⁸ times more toxic than hydrocyanic acid.^[51]

Plutonium, when entering the body through air, food or blood (e.g. a wound), mostly settles in the lungs, liver and bones with only about 10% going to other organs, and remains there for decades. The long residence time of plutonium in the body is partly explained by its poor solubility in water. Some isotopes of plutonium emit ionizing α-radiation, which damages the surrounding cells. The median lethal dose (LD₅₀) for 30 days in dogs after intravenous injection of plutonium is 0.32 milligram per kg of body mass, and thus the lethal dose for humans is approximately 22 mg for a person weighing 70 kg; the amount for respiratory exposure should be approximately 4 times greater. Another estimate assumes that plutonium is 50 times less toxic than radium, and thus permissible content of plutonium in the body should be 5 µg or 0.3 µCi. Such amount is nearly invisible in under microscope. After trials on animals, this maximum permissible dose was reduced to 0.65 µg or 0.04 µCi. Studies on animals also revealed that the most dangerous Pu exposure route is through inhalation, after which 5–25% of inhaled substances is retained in the body. Depending on the particle size and solubility of the plutonium compounds, Pu is localized either in the lungs or in the lymphatic system, or is absorbed in the blood and then transported to the liver and bones. Contamination via food is the least likely way. In this case, only about 0.05% of soluble 0.01% insoluble compounds of plutonium absorbs into blood, and the rest is excreted. Exposure of damaged skin to plutonium would retain nearly 100% of it.^[69]

[edit] See also

• Actinides in the environment
• Lanthanides

[edit] References and notes

[edit] Bibliography

• Greenwood, Norman N.; Earnshaw, Alan. (1997), Chemistry of the Elements (2nd ed.), Oxford: Butterworth-Heinemann, ISBN 0080379419 

[edit] Further reading

• Tamer Andrea and Moris S. Eisen (2008). "Recent advances in organothorium and organouranium catalysis". Chem. Soc. Rev. 37: 550–567. doi:10.1039/b614969n. 
• Morss, Lester R.; Edelstein, Norman M.; Fuger, Jean, eds (2006). The Chemistry of the Actinide and Transactinide Elements (3rd ed.). Dordrecht, The Netherlands: Springer. ISBN 13978-1-4020-3555-5. 

[edit] External links

• Lawrence Berkeley Laboratory image of historic periodic table by Seaborg showing actinide series for the first time
• Lawrence Livermore National Laboratory, Uncovering the Secrets of the Actinides
• Los Alamos National Laboratory, Actinide Research Quarterly

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