Actinide
Part of a series on the |
Periodic table |
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The actinide (/ˈæktɪnaɪd/) or actinoid (/ˈæktɪnɔɪd/) series encompasses at least the 14 metallic chemical elements in the 5f series, with atomic numbers from 89 to 102, actinium through nobelium. (Number 103, lawrencium, is sometimes also included despite being part of the 6d transition series.) The actinide series derives its name from the first element in the series, actinium. The informal chemical symbol An is used in general discussions of actinide chemistry to refer to any actinide.[1][2][3]
The 1985
All the actinides are
All actinides are
Of the actinides,
In presentations of the periodic table, the f-block elements are customarily shown as two additional rows below the main body of the table.[1] This convention is entirely a matter of aesthetics and formatting practicality; a rarely used wide-formatted periodic table inserts the 4f and 5f series in their proper places, as parts of the table's sixth and seventh rows (periods).
Discovery, isolation and synthesis
Element | Year | Method |
---|---|---|
Neptunium | 1940 | Bombarding 238U with neutrons |
Plutonium | 1941 | Bombarding 238U with deuterons
|
Americium | 1944 | Bombarding 239Pu with neutrons |
Curium | 1944 | Bombarding 239Pu with α-particles |
Berkelium | 1949 | Bombarding 241Am with α-particles |
Californium | 1950 | Bombarding 242Cm with α-particles |
Einsteinium | 1952 | As a product of nuclear explosion |
Fermium | 1952 | As a product of nuclear explosion |
Mendelevium | 1955 | Bombarding 253Es with α-particles |
Nobelium | 1965 | Bombarding 243Am with 22Ne
|
Lawrencium | 1961 –1971 |
Bombarding 252Cf with 11B and of 243Am with 18O |
Like the lanthanides, the actinides form a family of elements with similar properties. Within the 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. Most do not occur in nature, and of those that do, only thorium and uranium do so in more than trace quantities. The most abundant or easily synthesized actinides are uranium and thorium, followed by plutonium, americium, actinium, protactinium, neptunium, and curium.[11]
The existence of transuranium elements was suggested in 1934 by
At present, there are two major methods of producing isotopes of transplutonium elements: (1) irradiation of the lighter elements with neutrons; (2) irradiation with accelerated charged particles. The first method is more important for applications, as only neutron irradiation using nuclear reactors allows the production of sizeable amounts of synthetic actinides; however, it is limited to relatively light elements. The advantage of the second method is that elements heavier than plutonium, as well as neutron-deficient isotopes, can be obtained, which are not formed during neutron irradiation.[16]
In 1962–1966, there were attempts in the United States to produce transplutonium isotopes using a series of six
From actinium to uranium
Neptunium and above
Neptunium (named for the planet
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:
This synthesis reaction was used by Fermi and his collaborators in their design of the reactors located at the Hanford Site, which produced significant amounts of plutonium-239 for the nuclear weapons of the Manhattan Project and the United States' post-war nuclear arsenal.[39]
Actinides with the highest mass numbers are synthesized by bombarding uranium, plutonium, curium and californium with
- .
The first isotopes of transplutonium elements,
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. The latter element was named after
Bombarding curium-242 with α-particles resulted in an isotope of californium
In 1945, B. B. Cunningham obtained the first bulk chemical compound of a transplutonium element, namely americium hydroxide.[44] Over the few years, milligram quantities of americium and microgram amounts of curium were accumulated that allowed production of isotopes of berkelium[45][46] and californium.[47][48][49] Sizeable amounts of these elements were produced in 1958,[50] and the first californium compound (0.3 μg of CfOCl) was obtained in 1960 by B. B. Cunningham and J. C. Wallmann.[51]
Einsteinium and fermium were identified in 1952–1953 in the fallout from the "
The first isotope of mendelevium,
There were several attempts to obtain isotopes of nobelium by Swedish (1957) and American (1958) groups, but the first reliable result was the synthesis of
In 1961, Ghiorso et al. obtained the first isotope of lawrencium by irradiating californium (mostly
Isotopes
Nuclear properties of isotopes of the most important transplutonium isotopes[57][58][59] | ||||||
---|---|---|---|---|---|---|
Isotope | Half-life | Probability of spontaneous fission in % |
Emission energy (MeV) (yield in %) |
Specific activity (Bq/kg)[notes 2] of | ||
α | γ | α, β-particles | fission | |||
241Am | 432.2(7) y | 4.3(18)×10−10 | 5.485 (84.8) 5.442 (13.1) 5.388 (1.66) |
0.059 (35.9) 0.026 (2.27) |
1.27×1014 | 546.1 |
243Am |
7.37(4)×103 y | 3.7(2)×10−9 | 5.275 (87.1) 5.233 (11.2) 5.181 (1.36) |
0.074 (67.2) 0.043 (5.9) |
7.39×1012 | 273.3 |
242Cm |
162.8(2) d | 6.2(3)×10−6 | 6.069 (25.92) 6.112 (74.08) |
0.044 (0.04) 0.102 (4×10−3) |
1.23×1017 | 7.6×109 |
244Cm |
18.10(2) y | 1.37(3)×10−4 | 5.762 (23.6) 5.804 (76.4) |
0.043 (0.02) 0.100 (1.5×10−3) |
2.96×1015 | 4.1×109 |
245Cm |
8.5(1)×103 y | 6.1(9)×10−7 | 5.529 (0.58) 5.488 (0.83) 5.361 (93.2) |
0.175 (9.88) 0.133 (2.83) |
6.35×1012 | 3.9×104 |
246Cm |
4.76(4)×103 y | 0.02615(7) | 5.343 (17.8) 5.386 (82.2) |
0.045 (19) | 1.13×1013 | 2.95×109 |
247Cm |
1.56(5)×107 y | — | 5.267 (13.8) 5.212 (5.7) 5.147 (1.2) |
0.402 (72) 0.278 (3.4) |
3.43×109 | — |
248Cm |
3.48(6)×105 y | 8.39(16) | 5.034 (16.52) 5.078 (75) |
— | 1.40×1011 | 1.29×1010 |
249Bk |
330(4) d | 4.7(2)×10−8 | 5.406 (1×10−3) 5.378 (2.6×10−4) |
0.32 (5.8×10−5) | 5.88×1016 | 2.76×107 |
249Cf |
351(2) y | 5.0(4)×10−7 | 6.193 (2.46) 6.139 (1.33) 5.946 (3.33) |
0.388 (66) 0.333 (14.6) |
1.51×1014 | 7.57×105 |
250Cf |
13.08(9) y | 0.077(3) | 5.988 (14.99) 6.030 (84.6) |
0.043 | 4.04×1015 | 3.11×1012 |
251Cf |
900(40) y | ? | 6.078 (2.6) 5.567 (0.9) 5.569 (0.9) |
0.177 (17.3) 0.227 (6.8) |
5.86×1013 | — |
252Cf |
2.645(8) y | 3.092(8) | 6.075 (15.2) 6.118 (81.6) |
0.042 (1.4×10−2) 0.100 (1.3×10−2) |
1.92×1016 | 6.14×1014 |
254Cf |
60.5(2) d | ≈100 | 5.834 (0.26) 5.792 (5.3×10−2) |
— | 9.75×1014 | 3.13×1017 |
253Es |
20.47(3) d | 8.7(3)×10−6 | 6.540 (0.85) 6.552 (0.71) 6.590 (6.6) |
0.387 (0.05) 0.429 (8×10−3) |
9.33×1017 | 8.12×1010 |
254Es |
275.7(5) d | < 3×10−6 | 6.347 (0.75) 6.358 (2.6) 6.415 (1.8) |
0.042 (100) 0.034 (30) |
6.9×1016 | — |
255Es |
39.8(12) d | 0.0041(2) | 6.267 (0.78) 6.401 (7) |
— | 4.38×1017(β) 3.81×1016(α) |
1.95×1013 |
255Fm |
20.07(7) h | 2.4(10)×10−5 | 7.022 (93.4) 6.963 (5.04) 6.892 (0.62) |
0.00057 (19.1) 0.081 (1) |
2.27×1019 | 5.44×1012 |
256Fm |
157.6(13) min | 91.9(3) | 6.872 (1.2) 6.917 (6.9) |
— | 1.58×1020 | 1.4×1019 |
257Fm |
100.5(2) d | 0.210(4) | 6.752 (0.58) 6.695 (3.39) 6.622 (0.6) |
0.241 (11) 0.179 (8.7) |
1.87×1017 | 3.93×1014 |
256Md |
77(2) min | — | 7.142 (1.84) 7.206 (5.9) |
— | 3.53×1020 | — |
257Md |
5.52(5) h | — | 7.074 (14) | 0.371 (11.7) 0.325 (2.5) |
8.17×1019 | — |
258Md |
51.5(3) d | — | 6.73 | — | 3.64×1017 | — |
255No |
3.1(2) min | — | 8.312 (1.16) 8.266 (2.6) 8.121 (27.8) |
0.187 (3.4) | 8.78×1021 | — |
259No |
58(5) min | — | 7.455 (9.8) 7.500 (29.3) 7.533 (17.3) |
— | 4.63×1020 | — |
256Lr |
27(3) s | < 0.03 | 8.319 (5.4) 8.390 (16) 8.430 (33) |
— | 5.96×1022 | — |
257Lr |
646(25) ms | — | 8.796 (18) 8.861 (82) |
— | 1.54×1024 | — |
33
There are 32 known isotopes of thorium ranging in mass number from 207 to 238.[57] Of these, the longest-lived is 232Th, whose half-life of 1.4×1010 years means that it still exists in nature as a primordial nuclide. The next longest-lived is 230Th, an intermediate decay product of 238U with a half-life of 75,400 years. Several other thorium isotopes have half-lives over a day; all of these are also transient in the decay chains of 232Th, 235U, and 238U.
28
There are 27 known isotopes of uranium, having mass numbers 215–242 (except 220).[58] 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 transformation of 232Th irradiated by slow neutrons. 233U has a much 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.[62]
There are 25 isotopes of neptunium with mass numbers 219–244 (except 221);[58] they are all highly radioactive. The most popular among scientists are long-lived 237Np (t1/2 = 2.20×106 years) and short-lived 239Np, 238Np (t1/2 ~ 2 days).[38]
There are 20 known isotopes of plutonium, having mass numbers 228–247.[58] The most stable isotope of plutonium is 244Pu with half-life of 8.13×107 years.[57]
Eighteen isotopes of americium are known with mass numbers from 229 to 247 (with the exception of 231).[58] 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.[63]
Among 19 isotopes of curium, ranging in mass number from 233 to 251,[58] 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 246Cm, and then 248Cm 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.
Seventeen
The 20 isotopes of californium with mass numbers 237–256 are formed in nuclear reactors;[58] 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.[64]
Parent isotope |
t1/2 | Daughter isotope |
t1/2 | Time to establish radioactive equilibrium |
---|---|---|---|---|
243Am | 7370 years | 239Np | 2.35 days | 47.3 days |
245Cm | 8265 years | 241Pu | 14 years | 129 years |
247Cm | 1.64×107 years | 243Pu | 4.95 hours | 7.2 days |
254Es | 270 days | 250Bk | 3.2 hours | 35.2 hours |
255Es | 39.8 days | 255Fm | 22 hours | 5 days |
257Fm | 79 days | 253Cf | 17.6 days | 49 days |
Among the 18 known isotopes of einsteinium with mass numbers from 240 to 257,[58] 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 (t1/2 = 275.5 days).[64]
Twenty
Among the 17 known isotopes of mendelevium (mass numbers from 244 to 260),[58] the most studied is 256Md, which mainly decays through electron capture (α-radiation is ≈10%) with a 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 therefore limits their availability.[57]
Long-lived isotopes of nobelium and isotopes of lawrencium (and of heavier elements) have relatively short half-lives. For nobelium, 13 isotopes are known, with mass numbers 249–260 and 262. The chemical properties of nobelium and lawrencium were studied with 255No (t1/2 = 3 min) and 256Lr (t1/2 = 35 s). The longest-lived nobelium isotope, 259No, has a half-life of approximately 1 hour.[57] Lawrencium has 14 known isotopes with mass numbers 251–262, 264, and 266. The most stable of them is 266Lr with a half life of 11 hours.
Among all of these, the only isotopes that occur in sufficient quantities in nature to be detected in anything more than traces and have a measurable contribution to the atomic weights of the actinides are the primordial 232Th, 235U, and 238U, and three long-lived decay products of natural uranium, 230Th, 231Pa, and 234U. Natural thorium consists of 0.02(2)% 230Th and 99.98(2)% 232Th; natural protactinium consists of 100% 231Pa; and natural uranium consists of 0.0054(5)% 234U, 0.7204(6)% 235U, and 99.2742(10)% 238U.[67]
Formation in nuclear reactors
The figure buildup of actinides is a table of nuclides with the number of neutrons on the horizontal axis (isotopes) and the number of protons on the vertical axis (elements). The red dot divides the nuclides in two groups, so the figure is more compact. Each nuclide is represented by a square with the mass number of the element and its half-life.[68] Naturally existing actinide isotopes (Th, U) are marked with a bold border, alpha emitters have a yellow colour, and beta emitters have a blue colour. Pink indicates electron capture (236Np), whereas white stands for a long-lasting metastable state (242Am).
The formation of actinide nuclides is primarily characterised by:[69]
- Neutron capture reactions (n,γ), which are represented in the figure by a short right arrow.
- The (n,2n) reactions and the less frequently occurring (γ,n) reactions are also taken into account, both of which are marked by a short left arrow.
- Even more rarely and only triggered by fast neutrons, the (n,3n) reaction occurs, which is represented in the figure with one example, marked by a long left arrow.
In addition to these neutron- or gamma-induced nuclear reactions, the radioactive conversion of actinide nuclides also affects the nuclide inventory in a reactor. These decay types are marked in the figure by diagonal arrows. The beta-minus decay, marked with an arrow pointing up-left, plays a major role for the balance of the particle densities of the nuclides. Nuclides decaying by positron emission (beta-plus decay) or electron capture (ϵ) do not occur in a nuclear reactor except as products of knockout reactions; their decays are marked with arrows pointing down-right. Due to the long half-lives of the given nuclides, alpha decay plays almost no role in the formation and decay of the actinides in a power reactor, as the residence time of the nuclear fuel in the reactor core is rather short (a few years). Exceptions are the two relatively short-lived nuclides 242Cm (T1/2 = 163 d) and 236Pu (T1/2 = 2.9 y). Only for these two cases, the α decay is marked on the nuclide map by a long arrow pointing down-left. A few long-lived actinide isotopes, such as 244Pu and 250Cm, cannot be produced in reactors because neutron capture does not happen quickly enough to bypass the short-lived beta-decaying nuclides 243Pu and 249Cm; they can however be generated in nuclear explosions, which have much higher neutron fluxes.
Distribution in nature
Thorium and uranium are the most abundant actinides in nature with the respective mass concentrations of 16 ppm and 4 ppm.[70] Uranium mostly occurs in the Earth's crust as a mixture of its oxides in the mineral 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.[71][72] 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%).[73]
Ore | Location | Uranium content, % |
Mass ratio 239Pu/ore |
Ratio 239Pu/U (×10−12) |
---|---|---|---|---|
Uraninite | Canada | 13.5 | 9.1×10−12 | 7.1 |
Uraninite | Congo | 38 | 4.8×10−12 | 12 |
Uraninite | Colorado, US | 50 | 3.8×10−12 | 7.7 |
Monazite | Brazil | 0.24 | 2.1×10−14 | 8.3 |
Monazite | North Carolina, US | 1.64 | 5.9×10−14 | 3.6 |
Fergusonite | - | 0.25 | <1×10−14 | <4 |
Carnotite | - | 10 | <4×10−14 | <0.4 |
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).[75]
The abundance of actinium in the Earth's crust is only about 5×10−15%.[61] 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.[30] Protactinium is more abundant (10−12%) in the Earth's crust than actinium. It was discovered in uranium ore in 1913 by Fajans and Göhring.[34] As actinium, the distribution of protactinium follows that of 235U.[61]
The half-life of the longest-lived isotope of neptunium,
Extraction
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:[76]
Among the actinides, thorium and uranium are the easiest to isolate. Thorium is extracted mostly from
In another extraction method, monazite is decomposed with a 45% aqueous solution of
- 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:[78]
- ThO2 + 2 Ca → 2 CaO + Th
Sometimes thorium is extracted by
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(NO3)2(TBP)2. The insoluble impurities are filtered and the uranium is extracted by reaction with hydroxides as (NH4)2U2O7 or with hydrogen peroxide as UO4·2H2O.[76]
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 CO2−
3 → 2 [UO2(CO3)3]4−
This equation suggests that the best solvent for the
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 hydrofluoric acid changes it to uranium tetrafluoride, which yields uranium metal upon reaction with magnesium metal:[78]
- 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.[76]
In another method, Pu4+ and UO2+
2 are first extracted with tributyl phosphate, then reacted with hydrazine washing out the recovered plutonium.[76]
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.[30]
Properties
Actinides have similar properties to lanthanides. Just as the 4f electron shells are filled in the lanthanides, the 5f electron shells are filled in the actinides. Because the 5f, 6d, 7s, and 7p shells are close in energy, many irregular configurations arise; thus, in gas-phase atoms, just as the first 4f electron only appears in cerium, so the first 5f electron appears even later, in protactinium. However, just as lanthanum is the first element to use the 4f shell in compounds,[80] so actinium is the first element to use the 5f shell in compounds.[81] The f-shells complete their filling together, at ytterbium and nobelium.[82] The first experimental evidence for the filling of the 5f shell in actinides was obtained by McMillan and Abelson in 1940.[83] As in lanthanides (see lanthanide contraction), the ionic radius of actinides monotonically decreases with atomic number (see also Aufbau principle).[84]
The shift of electron configurations in the gas phase does not always match the chemical behaviour. For example, the early-transition-metal-like prominence of the highest oxidation state, corresponding to removal of all valence electrons, extends up to uranium even though the 5f shells begin filling before that. On the other hand, electron configurations resembling the lanthanide congeners already begin at plutonium, even though lanthanide-like behaviour does not become dominant until the second half of the series begins at curium. The elements between uranium and curium form a transition between these two kinds of behaviour, where higher oxidation states continue to exist, but lose stability with respect to the +3 state.[82] The +2 state becomes more important near the end of the series, and is the most stable oxidation state for nobelium, the last 5f element.[82] Oxidation states rise again only after nobelium, showing that a new series of 6d transition metals has begun: lawrencium shows only the +3 oxidation state, and rutherfordium only the +4 state, making them congeners of lutetium and hafnium in the 5d row.[82]
Element | Ac | Th | Pa | U | Np | Pu | Am | Cm | Bk | Cf | Es | Fm | Md | No | Lr |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Core charge (Z) | 89 | 90 | 91 | 92 | 93 | 94 | 95 | 96 | 97 | 98 | 99 | 100 | 101 | 102 | 103 |
Atomic mass | [227] | 232.0377(4) | 231.03588(2) | 238.02891(3) | [237] | [244] | [243] | [247] | [247] | [251] | [252] | [257] | [258] | [259] | [266] |
Number of natural isotopes[86] | 3 | 8 | 3 | 8 | 3 | 4 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Natural isotopes[86][87] | 225, 227, 228 | 227–234 | 231, 233, 234 | 233–240 | 237, 239, 240 | 238–240, 244 | — | — | — | — | — | — | — | — | — |
Natural quantity isotopes | — | 230, 232 | 231 | 234, 235, 238 | — | — | — | — | — | — | — | — | — | — | — |
Longest-lived isotope | 227 | 232 | 231 | 238 | 237 | 244 | 243 | 247 | 247 | 251 | 252 | 257 | 258 | 259 | 266 |
Half-life of the longest-lived isotope | 21.8 years | 14 billion years | 32,500 years | 4.47 billion years | 2.14 million years | 80.8 million years | 7,370 years | 15.6 million years | 1,380 years | 900 years | 1.29 years | 100.5 days | 52 days | 58 min | 11 hours |
Most common isotope | 227 | 232 | 231 | 238 | 237 | 239 | 241 | 244 | 249 | 252 | 253 | 255 | 256 | 255 | 260 |
Half-life of the most common isotope | 21.8 years | 14 billion years | 32,500 years | 4.47 billion years | 2.14 million years | 24,100 years | 433 years | 18.1 years | 320 days | 2.64 years | 20.47 days | 20.07 hours | 78 min | 3.1 min | 2.7 min |
Electronic configuration in the ground state (gas phase) |
6d17s2 | 6d27s2 | 5f26d17s2 | 5f36d17s2 | 5f46d17s2 | 5f67s2 | 5f77s2 | 5f76d17s2 | 5f97s2 | 5f107s2 | 5f117s2 | 5f127s2 | 5f137s2 | 5f147s2 | 5f147s27p1 |
Oxidation states | 2, 3 | 2, 3, 4 | 2, 3, 4, 5 | 2, 3, 4, 5, 6 | 3, 4, 5, 6, 7 | 3, 4, 5, 6, 7 | 2, 3, 4, 5, 6, 7 | 2, 3, 4, 6 | 2, 3, 4 | 2, 3, 4 | 2, 3, 4 | 2, 3 | 2, 3 | 2, 3 | 3 |
Metallic radius (nm) | 0.203 | 0.180 | 0.162 | 0.153 | 0.150 | 0.162 | 0.173 | 0.174 | 0.170 | 0.186 | 0.186 | ? 0.198 | ? 0.194 | ? 0.197 | ? 0.171 |
Ionic radius (nm): An4+ An3+ |
— 0.126 |
0.114 — |
0.104 0.118 |
0.103 0.118 |
0.101 0.116 |
0.100 0.115 |
0.099 0.114 |
0.099 0.112 |
0.097 0.110 |
0.096 0.109 |
0.085 0.098 |
0.084 0.091 |
0.084 0.090 |
0.084 0.095 |
0.083 0.088 |
Temperature (°C): melting boiling |
1050 3198 |
1842 4788 |
1568 ? 4027 |
1132.2 4131 |
639 ? 4174 |
639.4 3228 |
1176 ? 2607 |
1340 3110 |
986 2627 |
900 ? 1470 |
860 ? 996 |
1530 — |
830 — |
830 — |
1630 — |
Density, g/cm3 | 10.07 | 11.78 | 15.37 | 19.06 | 20.45 | 19.84 | 11.7 | 13.51 | 14.78 | 15.1 | 8.84 | ? 9.7 | ? 10.3 | ? 9.9 | ? 14.4 |
Standard electrode potential (V): E° (An4+/An0) E° (An3+/An0) |
— −2.13 |
−1.83 — |
−1.47 — |
−1.38 −1.66 |
−1.30 −1.79 |
−1.25 −2.00 |
−0.90 −2.07 |
−0.75 −2.06 |
−0.55 −1.96 |
−0.59 −1.97 |
−0.36 −1.98 |
−0.29 −1.96 |
— −1.74 |
— −1.20 |
— −2.10 |
Color: [M(H2O)n]4+ [M(H2O)n]3+ |
— Colorless |
Colorless Blue |
Yellow Dark blue |
Green Purple |
Yellow-green Purple |
Brown Violet |
Red Rose |
Yellow Colorless |
Beige Yellow-green |
Green Green |
— Pink |
— — |
— — |
— — |
— — |
Approximate colors of actinide ions in aqueous solution Colors for the actinides 100–103 are unknown as sufficient quantities have not yet been synthesized. The colour of CmO2+2 was likewise not recorded. | |||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Actinide (Z) | 89 | 90 | 91 | 92 | 93 | 94 | 95 | 96 | 97 | 98 | 99 | 100 | 101 | 102 | 103 |
Oxidation state | |||||||||||||||
+2 | Fm2+ | Md2+ | No2+ | ||||||||||||
+3 | Ac3+ | Th3+ | Pa3+ | U3+ | Np3+ | Pu3+ | Am3+ | Cm3+ | Bk3+ | Cf3+ | Es3+ | Fm3+ | Md3+ | No3+ | Lr3+ |
+4 | Th4+ | Pa4+ | U4+ | Np4+ | Pu4+ | Am4+ | Cm4+ | Bk4+ | Cf4+ | ||||||
+5 | PaO+ 2 |
UO+ 2 |
NpO+ 2 |
PuO+ 2 |
AmO+ 2 |
||||||||||
+6 | UO2+ 2 |
NpO2+ 2 |
PuO2+ 2 |
AmO2+ 2 |
CmO2+ 2 |
||||||||||
+7 | NpO3+ 2 |
PuO3+ 2 |
AmO3− 5 |
Physical properties
Major crystal structures of some actinides vs. temperature |
Actinides are typical metals. All of them are soft and have a silvery color (but tarnish in air),
All actinides are
Lanthanides | Ln3+, Å | Actinides | An3+, Å | An4+, Å |
---|---|---|---|---|
Lanthanum | 1.061 | Actinium | 1.11 | – |
Cerium | 1.034 | Thorium | 1.08 | 0.99 |
Praseodymium | 1.013 | Protactinium | 1.05 | 0.93 |
Neodymium | 0.995 | Uranium | 1.03 | 0.93 |
Promethium | 0.979 | Neptunium | 1.01 | 0.92 |
Samarium | 0.964 | Plutonium | 1.00 | 0.90 |
Europium | 0.950 | Americium | 0.99 | 0.89 |
Gadolinium | 0.938 | Curium | 0.98 | 0.88 |
Terbium | 0.923 | Berkelium | – | – |
Dysprosium | 0.908 | Californium | – | – |
Holmium | 0.894 | Einsteinium | – | – |
Erbium | 0.881 | Fermium | – | – |
Thulium | 0.869 | Mendelevium | – | – |
Ytterbium | 0.858 | Nobelium | – | – |
Lutetium | 0.848 | Lawrencium | – | – |
Chemical properties
Like the lanthanides, all actinides are highly reactive with
Actinium is chemically similar to lanthanum, which is explained by their similar ionic radii and electronic structures. Like lanthanum, actinium almost always has an oxidation state of +3 in compounds, 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.[30][72]
Thorium is rather active chemically. Owing to lack of electrons on 6d and 5f orbitals, tetravalent thorium compounds are colorless. At pH < 3, 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 hydrolyse. The distinctive ability of thorium salts is their high solubility both in water and polar organic solvents.[72]
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 uranium(IV) and thorium(IV).
Uranium has a valence from 3 to 6, the last being most stable. In the hexavalent state, uranium is very similar to the
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
Plutonium also exhibits valence states between 3 and 7 inclusive, and thus is chemically similar to neptunium and uranium. It is highly reactive, and quickly forms an oxide film in air. Plutonium reacts with
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 erroneous. The most stable valence of americium is 3 in aqueous solution and 3 or 4 in solid compounds.[97]
Valence 3 is dominant in all subsequent elements up to lawrencium (with the exception of 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+.[98] Only valence 3 was observed for californium, einsteinium and fermium. The divalent 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.[97]
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.[93]
-
Uranyl nitrate (UO2(NO3)2)
-
Aqueous solutions of uranium III, IV, V, VI salts
-
Aqueous solutions of neptunium III, IV, V, VI, VII salts
-
Aqueous solutions of plutonium III, IV, V, VI, VII salts
Compounds
Oxides and hydroxides
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[101] - - |
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[102] | 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 |
- | - |
Oxidation state | 89 | 90 | 91 | 92 | 93 | 94 | 95 | 96 | 97 | 98 | 99 |
---|---|---|---|---|---|---|---|---|---|---|---|
+3 | Ac2O3 | Pu2O3 | Am2O3 | Cm2O3 | Bk2O3 | Cf2O3 | Es2O3 | ||||
+4 | ThO2 | PaO2 | UO2 | NpO2 | PuO2 | AmO2 | CmO2 | BkO2 | CfO2 | ||
+5 | Pa2O5 | U2O5 | Np2O5 | ||||||||
+5,+6 | U3O8 | ||||||||||
+6 | UO3 |
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 |
Molar mass | 264.04 | 263.035 | 270.03 | 269.047 | 276.063 | 275.06 | 270–284** | 279.069 | 283.078 |
Melting point[104] | 3390 °C | 2865 °C | 2547 °C | 2400 °C | 2175 °C | ||||
Crystal structure | An4+: __ / O2−: __ | ||||||||
Space group | Fm3m | ||||||||
Coordination number | An[8], O[4] |
- An – actinide
**Depending on the isotopes
Some actinides can exist in several oxide forms such as 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:[93]
- 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.[93] Np(OH)3 has not yet been synthesized, Pu(OH)3 has a blue color while Am(OH)3 is pink and Cm(OH)3 is colorless.[105] Bk(OH)3 and Cf(OH)3 are also known, as are tetravalent hydroxides for Np, Pu and Am and pentavalent for Np and Am.[105]
The strongest base is of actinium. All compounds of actinium are colorless, except for black
Thorium reacting with oxygen exclusively forms the dioxide:
Thorium dioxide is a refractory material with the highest melting point among any known oxide (3390 °C).
Two protactinium oxides have been 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.[93]
Decomposition of certain salts of uranium, for example UO2(NO3)·6H2O in air at 400 °C, yields orange or yellow UO3.[103] This oxide is amphoteric and forms several hydroxides, the most stable being uranyl hydroxide 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.[93]
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.[93]
Salts
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 |
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
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 , LaF3 |
7.04[74][108] | - | 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 | 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 |
– |
Actinides easily react with halogens forming salts with the formulas MX3 and MX4 (X =
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:
However, in these reactions the regenerating hydrogen can react with the metal, forming the corresponding hydride. Uranium reacts with acids and water much more easily than thorium.[93]
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 form 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)2SO4 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.[93]
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 (
Applications
While actinides have some established daily-life applications, such as in smoke detectors (americium)[110][111] and gas mantles (thorium),[78] they are mostly used in nuclear weapons and as fuel in nuclear reactors.[78] 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 reactions.
The most important isotope for
92U
emits more neutrons than it absorbs;[112] upon reaching the critical mass, 235
92U
enters into a self-sustaining chain reaction.[72]
- 1⟶ 115
0n
45Rh
+ 118
47Ag
+ 31
0n
Other promising actinide isotopes for nuclear power are thorium-232 and its product from the thorium fuel cycle, uranium-233.
Nuclear reactor[72][113][114] |
The core of most Generation II nuclear reactors contains a set of hollow metal rods, usually made of zirconium alloys, filled with solid nuclear fuel pellets – 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.
|
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.
About half of produced thorium is used as the light-emitting material of gas mantles.[78] Thorium is also added into multicomponent alloys of magnesium and zinc. 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.[112] The relative content of thorium and uranium isotopes is widely used to estimate the age of various objects, including stars (see radiometric dating).[115]
The major application of plutonium has been in
Plutonium-238 is potentially more efficient isotope for nuclear reactors, since it has smaller critical mass than uranium-235, but it continues to release much thermal energy (0.56 W/g)[111][119] by decay even when the fission chain reaction is stopped by control rods. Its application is limited by its high price (about US$1000/g). This isotope has been used in thermopiles and water distillation systems of some space satellites and stations. The Galileo and Apollo spacecraft (e.g. Apollo 14[120]) had heaters powered by kilogram quantities of plutonium-238 oxide; this heat is also transformed into electricity with thermopiles. The decay of plutonium-238 produces relatively harmless alpha particles and is not accompanied by gamma rays. Therefore, this isotope (~160 mg) is used as the energy source in heart pacemakers where it lasts about 5 times longer than conventional batteries.[111]
Development of self-glowing actinide-doped materials with durable crystalline matrices is a new area of actinide utilization as the addition of alpha-emitting radionuclides to some glasses and crystals may confer luminescence.[121]
Toxicity
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
Protactinium in the body tends to accumulate in the kidneys and bones. The maximum safe dose of protactinium in the human body is 0.03
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 four 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 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 plutonium 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, plutonium 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 and 0.01% of insoluble compounds of plutonium absorbs into blood, and the rest is excreted. Exposure of damaged skin to plutonium would retain nearly 100% of it.[95]
Using actinides in nuclear fuel, sealed radioactive sources or advanced materials such as self-glowing crystals has many potential benefits. However, a serious concern is the extremely high radiotoxicity of actinides and their migration in the environment.[122] Use of chemically unstable forms of actinides in MOX and sealed radioactive sources is not appropriate by modern safety standards. There is a challenge to develop stable and durable actinide-bearing materials, which provide safe storage, use and final disposal. A key need is application of actinide solid solutions in durable crystalline host phases.[121]
Nuclear properties
Nuclide | Half-life | Decay mode | Branching fraction | Source |
---|---|---|---|---|
206 81Tl |
4.202 ± 0.011 m | β− | 1.0 | LNHB |
208 81Tl |
3.060 ± 0.008 m | β− | 1.0 | BIPM-5 |
210 82Pb |
22.20 ± 0.22 y | β− | 1.0 | ENSDF |
α | ( 1.9 ± 0.4 ) x 10−8 | |||
211 82Pb |
36.1 ± 0.2 m | β− | 1.0 | ENSDF |
212 82Pb |
10.64 ± 0.01 h | β− | 1.0 | BIPM-5 |
214 82Pb |
26.8 ± 0.9 m | β− | 1.0 | ENSDF |
211 83Bi |
2.14 ± 0.02 m | β− | 0.00276 ± 0.00004 | ENSDF |
α | 0.99724 ± 0.00004 | |||
212 83Bi |
60.54 ± 0.06 m | α | 0.3593 ± 0.0007 | BIPM-5 |
β− | 0.6407 ± 0.0007 | |||
214 83Bi |
19.9 ± 0.4 m | α | 0.00021 ± 0.00001 | ENSDF |
β− | 0.99979 ± 0.00001 | |||
210 84Po |
138.376 ± 0.002 d | α | 1.0 | ENSDF |
219 86Rn |
3.96 ± 0.01 s | α | 1.0 | ENSDF |
220 86Rn |
55.8 ± 0.3 s | α | 1.0 | BIPM-5 |
221 87Fr |
4.9 ± 0.2 m | β− | 0.00005 ± 0.00003 | ENSDF |
α | 0.99995 ± 0.00003 | |||
223 88Ra |
11.43 ± 0.05 d | α | 1.0 | ENSDF |
14C | ( 8.9 ± 0.4 ) x 10−10 | |||
224 88Ra |
3.627 ± 0.007 d | α | 1.0 | BIPM-5 |
225 88Ra |
14.9 ± 0.2 d | β− | 1.0 | ENSDF |
226 88Ra |
( 1.600 ± 0.007 ) x 103 y | α | 1.0 | BIPM-5 |
228 88Ra |
5.75 ± 0.03 y | β− | 1.0 | ENSDF |
224 89Ac |
2.78 ± 0.17 h | α | 0.091 +0.020 -0.014 | ENSDF |
EC | 0.909 +0.014 -0.020 | |||
225 89Ac |
10.0 ± 0.1 d | α | 1.0 | ENSDF |
227 89Ac |
21.772 ± 0.003 y | α | 0.01380 ± 0.00004 | ENSDF |
β− | 0.98620 ± 0.00004 | |||
228 89Ac |
6.15 ± 0.02 h | β− | 1.0 | ENSDF |
227 90Th |
18.718 ± 0.005 d | α | 1.0 | BIPM-5 |
228 90Th |
698.60 ± 0.23 d | α | 1.0 | BIPM-5 |
229 90Th |
( 7.34 ± 0.16 ) x 103 y | α | 1.0 | ENSDF |
230 90Th |
( 7.538 ± 0.030 ) x 104 y | α | 1.0 | ENSDF |
SF | ≤ 4 x 10−13 | |||
231 90Th |
25.52 ± 0.01 h | β− | 1.0 | ENSDF |
α | ~ 4 x 10−13 | |||
232 90Th |
( 1.405 ± 0.006 ) x 1010 y | α | 1.0 | ENSDF |
SF | ( 1.1 ± 0.4 ) x 10−11 | |||
233 90Th |
22.15 ± 0.15 m | β− | 1.0 | LNHB |
234 90Th |
24.10 ± 0.03 d | β− | 1.0 | ENSDF |
231 91Pa |
( 3.276 ± 0.011 ) x 104 y | α | 1.0 | ENSDF |
SF | ≤ 3 x 10−12 | |||
232 91Pa |
1.32 ± 0.02 d | EC | 0.00003 ± 0.00001 | ENSDF |
β− | 0.99997 ± 0.00001 | |||
233 91Pa |
26.98 ± 0.02 d | β− | 1.0 | LNHB |
234 91Pa |
6.70 ± 0.05 h | β− | 1.0 | ENSDF |
234m 91Pa |
1.159 ± 0.016 m | IT | 0.0016 ± 0.0002 | IAEA-CRP-XG |
β− | 0.9984 ± 0.0002 | |||
232 92U |
68.9 ± 0.4 y | α | 1.0 | ENSDF |
SF | ||||
233 92U |
( 1.592 ± 0.002 ) x 105 y | α | 1.0 | ENSDF |
SF | ||||
234 92U |
( 2.455 ± 0.006 ) x 105 y | α | 1.0 | LNHB |
SF | ( 1.6 ± 0.2 ) x 10−11 | |||
235m 92U |
26 ± 1 m | IT | 1.0 | ENSDF |
235 92U |
( 7.038 ± 0.005 ) x 108 y | α | 1.0 | ENSDF |
SF | ( 7 ± 2 ) x 10−11 | |||
236 92U |
( 2.342 ± 0.004 ) x 107 y | α | 1.0 | ENSDF |
SF | ( 9.4 ± 0.4 ) x 10−10 | |||
237 92U |
6.749 ± 0.016 d | β− | 1.0 | LNHB |
238 92U |
( 4.468 ± 0.005 ) x 109 y | α | 1.0 | LNHB |
SF | ( 5.45 ± 0.04 ) x 10−7 | |||
239 92U |
23.45 ± 0.02 m | β− | 1.0 | ENSDF |
236 93Np |
( 1.55 ± 0.08 ) x 105 y | α | 0.0016 ± 0.0006 | LNHB |
β− | 0.120 ± 0.006 | |||
EC | 0.878 ± 0.006 | |||
236m 93Np |
22.5 ± 0.4 h | β− | 0.47 ± 0.01 | LNHB |
EC | 0.53 ± 0.01 | |||
237 93Np |
( 2.144 ± 0.007 ) x 106 y | α | 1.0 | ENSDF |
SF | ||||
238 93Np |
2.117 ± 0.002 d | β− | 1.0 | ENSDF |
239 93Np |
2.356 ± 0.003 d | β− | 1.0 | ENSDF |
236 94Pu |
2.858 ± 0.008 y | α | 1.0 | ENSDF |
LNHB | Laboratoire National Henri Becquerel, Recommended Data,
http://www.nucleide.org/DDEP_WG/DDEPdata.htm Archived 13 February 2021 at the Wayback Machine, 3 October 2006. |
BIPM-5 | M.-M. Bé, V. Chisté, C. Dulieu, E. Browne, V. Chechev, N. Kuzmenko, R. Helmer,
A. Nichols, E. Schönfeld, R. Dersch, Monographie BIPM-5, Table of Radionuclides, Vol. 2 – A = 151 to 242, 2004. |
ENSDF | "Evaluated Nuclear Structure Data File". Brookhaven National Laboratory. Retrieved 15 November 2006. |
IAEA-CRP-XG | M.-M. Bé, V. P. Chechev, R. Dersch, O. A. M. Helene, R. G. Helmer, M. Herman,
S. Hlavác, A. Marcinkowski, G. L. Molnár, A. L. Nichols, E. Schönfeld, V. R. Vanin, M. J. Woods, IAEA CRP "Update of X Ray and Gamma Ray Decay Data Standards for Detector Calibration and Other Applications", IAEA Scientific and Technical Information report STI/PUB/1287, May 2007, International Atomic Energy Agency, Vienna, Austria, ISBN 92-0-113606-4 .
|
See also
- Actinides in the environment
- Lanthanides
- Major actinides
- Minor actinides
- Transuranics
Notes
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Bibliography
- Golub, A. M. (1971). Общая и неорганическая химия (General and Inorganic Chemistry). Vol. 2.
- ISBN 978-0-08-037941-8.
- Myasoedov, B. (1972). ISBN 978-0-470-62715-0.
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