Actinides ( actinides ) are a family consisting of 15 radioactive chemical elements of Group III of the 7th period of the periodic system with atomic numbers 89-103.
Actinides | |
---|---|
Uranium metal | |
General information | |
Composition of the group | thorium , protactinium , uranium , neptunium , plutonium , americium , curium , berkeley , california , einsteinium , fermium , mendelevium , nobelium , lourencia |
Opening period | XVIII century (uranium) - XX century (lawrence) |
Being in nature | very small |
Chemical properties | |
Electronic configuration | List Thorium - [ Rn ] 6d 2 7s 2 Protaktinium - [ Rn ] 5f 2 6d 1 7s 2 Uranium - [ Rn ] 5f 3 6d 1 7s 2 Neptunium - [ Rn ] 5f 4 6d 1 7s 2 Plutonium - [ Rn ] 5f 6 7s 2 Americium - [ Rn ] 5f 7 7s 2 Curium - [ Rn ] 5f 7 6d 1 7s 2 Berkeley - [ Rn ] 5f 9 6d 0 7s 2 California - [ Rn ] 5f 10 7s 2 Einstein - [ Rn ] 5f 11 7s 2 Fermium - [ Rn ] 5f 12 7s 2 Mendelevius - [ Rn ] 5f 13 7s 2 Nobelium - [ Rn ] 5f 14 7s 2 Lawrence - [ Rn ] 5f 14 7s 2 7p 1 |
Finding a group in electronic blocks | f-block |
Toxicological data | |
Toxicity | highly radioactive elements |
This group consists of thorium , protactinium , uranium , neptunium , plutonium , americium , curium , berkelium , california , einsteinia , fermia , mendelevium , nobelia and lourencia . Actinium is often considered together with these elements for ease of comparison, but it does not apply to actinides [1] . The term “actinides” was proposed by Viktor Goldschmidt in 1937 [2] .
** | Ac | Th | Pa | U | Np | Pu | Am | Cm | Bk | Cf | Es | Fm | Md | No | Lr |
Content
Study and Synthesis
Like the lanthanides , actinides form a family of elements of similar properties. Two intersecting groups are distinguished from the actinides: “ transuranium elements ” - all the elements that follow in the Periodic Table for uranium and “transplutonium elements” - all that follow plutonium.
Both groups are not limited to these frames and, when specifying the prefix "trans-", may include elements following the lawrence — rutherford , etc. Compared with lanthanides, which (except for promethium ) are found in nature in appreciable quantities, actinoids are more difficult to synthesize. But there are exceptions, for example, it is easier to synthesize or find uranium and thorium in nature, followed by plutonium, protactinium, actinium, and only then super rare curium, americium, neptunium, berkeley, and California [3] .
At present, to obtain isotopes of transplutonium elements (TPE), two main methods are used: irradiation of lighter elements with neutrons or accelerated charged particles. The first method is practically the most important, since only in nuclear reactors, when the source material is irradiated with a large neutron flux, it is possible to obtain weight quantities of transplutonium elements. The advantage of the second method is that it allows to obtain the elements that follow the plutonium, and neutron-deficient isotopes that are not formed by neutron irradiation [3] .
In the years 1962-1966, an attempt was made to synthesize transplutonium isotopes in the United States by means of six underground nuclear explosions — Anachocia, Kennebec, Enchovi, Par, Barbel, and Cyclamen. To study the products of the explosion, small samples of rocks extracted from the explosion zone immediately after its use were used. It was not possible to detect heavy-element isotopes with a mass number greater than 257, although relatively large T ½ values for α-decay were predicted for them at that time. Perhaps, this happened because atoms with a high speed were spontaneously divided , or because of a different nature of the decay of intermediate isotopes ( emission of neutrons , fission ) [3] .
From actinium to neptunium
The first open actinides were uranium and thorium . Uranus was discovered by M. Klaproth in 1789 in uranium resin ore (the name of the element derives from the name of the planet Uranus ). M. Klaproth, restoring yellow uranium oxide with coal, produced a black substance, which he mistakenly took for metal. Only 60 years later, the French researcher Eugene Peligo studied it and realized that this substance is uranium dioxide . At the same time, the atomic mass of 120 was incorrectly calculated. Only DI Mendeleev in 1872, on the basis of the law he discovered, specified the atomic mass of uranium — 240. K. Zimmerman confirmed this value experimentally in 1882 [4] .
Thorium was discovered by F. Wohler [4] in a mineral that was found in Norway ( 1827 ). J. Berzelius studied this element in detail; he named it in honor of the Scandinavian god of thunder and lightning - Thor (1828).
Actinium was discovered in 1899 by Assistant M. Skłodowska-Curie A. Debiern in waste from the processing of uranium tar , from which radium and polonium were previously removed; it was identified in the fraction in which lanthanides are concentrated in the processing of ore. The element name "actinium" is derived from lat. actis - ray, shine. This metal was discovered not by its own radiation, but by the radiation of the daughter decay products [4] [5] .
Production of transuranic elements [1] [3] [6] | ||
---|---|---|
Element | Year of discovery | Method of obtaining |
Neptunium | 1940 | Bombardment of 238 U with neutrons |
Plutonium | 1941 | Bombing 238 U with deuterons |
Americium | 1944 | Bombardment of 239 Pu with neutrons |
Curium | 1944 | Bombardment of 239 Pu α-particles |
Berkelium | 1949 | Bombardment of 241 Am α-particles |
Californium | 1950 | Bombardment of 242 Cm α-particles |
Einsteinium | 1952 | Detected in thermonuclear explosion products |
Fermi | 1952 | Detected in thermonuclear explosion products |
Mendelevium | 1955 | Bombardment of 253 Es α-particles |
Nobelium | 1965 | Bombardment of 243 Am cores 15 N |
Lawrence | 1961-1971 | Bombardment of 252 Cf with 10 B cores and others. |
Due to the high similarity between actinia and lanthanum and the insignificant spread of actinium, it was not possible for a long time to isolate it in its pure form. Pure actinium was mined only in 1950 . At the moment, 31 isotopes with mass numbers of 206–236 and 8 excited isomeric states of some of its nuclides are known for the element . The most stable isotin isotope 227 Ac , which has a half-life of T ½ = 21.77 years [7] .
In 1917, O. Gan and L. Meitner discovered the long-lived isotope of the protactinium. The name “protactinium” means that an atom of this element is capable of forming actinium. At present, 29 protaktinium isotopes with mass numbers 212–240 and 3 excited isomeric states of some of its nuclides are known . The most stable nuclide is 231 Pa , whose half-life is 3.28⋅10 4 years [7] .
Most of the transuranium elements are already sufficiently studied, but it is not necessary to speak about the production quantities of these elements, excluding plutonium and americium .
The first suggested the existence of transuranium elements Enrico Fermi , which was the result of a number of his experiments in 1934 [8] [9] .
The synthesis of the neptunium isotope 239 Np , which was conducted in May 1940 by E. McMillan and F. Abelson , initiated the discovery of transuranic elements [10] . In the following years, nuclear synthesis of other neptunium isotopes was carried out [11] .
Actinides over the past decades have been thoroughly studied by G. Seaborg and his school. With the participation of Seaborg, most of the transuranic elements were synthesized.
From Plutonium
Transuranium elements in nature almost never occur. To obtain them using nuclear reactions that take place in nuclear reactors. So, for example, uranium-238 in a reactor under the action of neutrons is partially converted into plutonium-239 . When this happens the following reactions:
With further neutron absorption, 239 Pu turns into 241 Pu , which due to β-decay turns into 241 Am .
In this way, Enrico Fermi and his co-workers in the world's first reactor, the Chicago Polenitsa-1 , for the first time received significant quantities of plutonium-239, which were used to create nuclear weapons [12] .
Actinides with the highest atomic numbers were obtained by bombarding uranium, plutonium, curium, or californium nuclei with nitrogen, oxygen, carbon, neon, and boron ions in heavy ion accelerators. Thus, one of the first methods for the synthesis of nobelia is the bombardment of a target from uranium-238 by the nuclei of neon-22 in the reaction
- .
The first isotopes of TPE — americium-241 and curium-242 — were synthesized in 1944 by G. Seaborg, James, and A. Giorceau [13] . Curium isotopes were obtained by bombarding plutonium-239 nuclei with helium ions with an energy of 32 MeV:
- .
Also, the isotopes of americium-241 and curium-242 were isolated from plutonium irradiated with neutrons in the reactor , where they were formed as a result of nuclear transformations [3] .
When Curium-242 is bombarded with α particles, the California isotope 245 Cf is formed . Using a similar reaction from berium-244 from americium-241.
In 1945, Kenningham first isolated a solid compound of one of the TPE - americium hydroxide. Over the next 3–4 years, milligram quantities of americium and microgram amounts of curium were accumulated, which, as a result of exposure of americium and curium, allowed us to synthesize berkelium isotopes (Thomson, 1949) and California (Thomson, 1950). The weight quantities of these elements were singled out much later, in 1958 (Kenningham and Thomson), and the first California compound (CfOCl) was obtained only in 1960 (Kenningham and Walman).
Einstein and Fermi were isolated by a group of American scientists from the University of California , the Argonne National Laboratory and the Los Alamos Scientific Laboratory in 1952-1953 from the products of the Mike thermonuclear explosion on November 1, 1952 . As a result of the instantaneous irradiation of uranium-238 by a large neutron flux arising from a thermonuclear explosion, heavy isotopes of uranium were formed, including uranium-253 and uranium-255, with β-decay of which ultimately produced isotopes of einsteinium-253 and fermium-255 . Einstein was found by a group of American scientists led by A. Giorceau in 1952 and named after the great physicist A. Einstein . Fermium was first identified by the American scientist A. Giorceau in 1953 as the fermium-255 isotope mentioned above. Fermium is named after the physicist E. Fermi, who made a great contribution to the development of modern theoretical and experimental physics [13] . The first weighted (submicrogram) quantities of Einsteinia were singled out in 1961 by Kenningham and co-workers. Fermi and more TPEs with higher sequence numbers have not yet been obtained in weight amounts.
The first isotope of mendelevium 256 Md was synthesized in February 1955 (G. Seaborg and co-workers) under irradiation of Einsteinium-253 with helium ions. To synthesize the elements that follow Mendeleevy, it was necessary to use a new method — the irradiation of uranium nuclei and transuranium elements with heavy multiply charged ions. Due to the exceptionally low yield and short half-lives of the isotopes of transmendelian elements synthesized in these reactions, their identification turned out to be very difficult and not always reliable. As a rule, in the first works on the synthesis of elements with Z ⩾102, the obtained isotopes were identified by purely physical methods, by the nature of the radiation, and by the daughter decay products.
Attempts to obtain nobelium isotopes have been conducted since 1957 , but the first reliable result is the synthesis of the nobelium isotope 256 No , which was carried out by G. Flørov in 1963 . Neon-22 was used to obtain this isotope.
In 1961, A. Giorceau and co-workers obtained the first isotope of Lawrence by irradiating California (mainly California-252 ) with boron-10 and boron-11 ; the mass number of this isotope was not precisely determined (perhaps 258 or 259) at that time. The isotope 256 Lr isotope identified more reliably, synthesized in 1965 by G. Flerov using nuclides 243 Am and 18 O.
Isotopes
Nuclear properties of the most important isotopes of transplutonium elements | ||||||
---|---|---|---|---|---|---|
Isotope | Half-life [7] | The probability of spontaneous division ,% [7] | Radiation energy, MeV (output,%) [14] | Specific activity [15] | ||
α | γ | α, β-particles, Bq / kg | division, Bq / kg | |||
241 Am | 432.2 (7) years | 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⋅10 14 | 546.1 |
243 Am | 7.37 (4) ⋅10 3 years | 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⋅10 12 | 273.3 |
242 Cm | 162.8 (2) days | 6.2 (3) ⋅10 −6 | 6.069 (25.92) 6.112 (74.08) | 0.044 (0.04) 0.102 (4⋅10 −3 ) | 1.23⋅10 17 | 7.6⋅10 9 |
244 Cm | 18.10 (2) years | 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⋅10 15 | 4.1⋅10 9 |
245 Cm | 8.5 (1) ⋅10 3 years | 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⋅10 12 | 3.9⋅10 4 |
246 Cm | 4.76 (4) ⋅10 3 years | 0.02615 (7) | 5.343 (17.8) 5.386 (82.2) | 0.045 (19) | 1.13⋅10 13 | 2.95⋅10 9 |
247 Cm | 1.56 (5) ⋅10 7 years | - | 5.267 (13.8) 5.212 (5.7) 5.147 (1.2) | 0.402 (72) 0.278 (3.4) | 3.43⋅10 9 | - |
248 Cm | 3.48 (6) ⋅10 5 years | 8.39 (16) | 5,034 (16,52) 5.078 (75) | - | 1.40⋅10 11 | 1.29⋅10 10 |
249 Bk | 330 (4) days | 4.7 (2) ⋅10 −8 | 5.406 (1⋅10 −3 ) 5.378 (2.6⋅10 −4 ) | 0.32 (5.8⋅10 −5 ) | 5.88⋅10 16 | 2.76⋅10 7 |
249 Cf | 351 (2) year | 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⋅10 14 | 7.57⋅10 5 |
250 Cf | 13.08 (9) years | 0.077 (3) | 5.988 (14.99) 6.030 (84.6) | 0.043 | 4.04⋅10 15 | 3.11⋅10 12 |
251 Cf | 900 (40) years | ? | 6.078 (2.6) 5.567 (0.9) 5.569 (0.9) | 0.177 (17.3) 0,227 (6,8) | 5.86⋅10 13 | - |
252 Cf | 2.645 (8) years | 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⋅10 16 | 6.14⋅10 14 |
254 Cf | 60.5 (2) days | ≈100 | 5.834 (0.26) 5.792 (5.3⋅10 −2 ) | - | 9.75⋅10 14 | 3.13⋅10 17 |
253 Es | 20.47 (3) days | 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⋅10 17 | 8.12⋅10 10 |
254 Es | 275.7 (5) days | <3⋅10 −6 | 6.347 (0.75) 6.358 (2.6) 6,415 (1,8) | 0.042 (100) 0.034 (30) | 6.9⋅10 16 | - |
255 Es | 39.8 (12) days | 0,0041 (2) | 6.267 (0.78) 6,401 (7) | - | 4.38⋅10 17 (β) 3.81⋅10 16 (α) | 1.95⋅10 13 |
255 Fm | 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⋅10 19 | 5.44⋅10 12 |
256 Fm | 157.6 (13) min | 91.9 (3) | 6,872 (1,2) 6,917 (6,9) | - | 1.58⋅10 20 | 1,4⋅10 19 |
257 Fm | 100.5 (2) days | 0,210 (4) | 6.752 (0.58) 6,695 (3.39) 6,622 (0,6) | 0.241 (11) 0.179 (8.7) | 1.87⋅10 17 | 3.93⋅10 14 |
256 Md | 77 (2) min | - | 7.142 (1.84) 7.206 (5.9) | - | 3.53⋅10 20 | - |
257 Md | 5.52 (5) h | - | 7.074 (14) | 0.371 (11.7) 0.325 (2.5) | 8,17⋅10 19 | - |
258 Md | 51.5 (3) days | - | 6.73 | - | 3.64⋅10 17 | - |
255 No | 3.1 (2) min | - | 8.312 (1.16) 8.266 (2.6) 8.121 (27.8) | 0.187 (3.4) | 8.78⋅10 21 | - |
259 No | 58 (5) min | - | 7,455 (9.8) 7.500 (29.3) 7.533 (17.3) | - | 4.63⋅10 20 | - |
256 Lr | 27 (3) s | <0.03 | 8,319 (5,4) 8,390 (16) 8,430 (33) | - | 5.96⋅10 22 | - |
257 Lr | 646 (25) ms | - | 8,796 (18) 8,861 (82) | - | 1.54⋅10 24 | - |
By 1982, 24 actinium isotopes were known, 31 actinium isotopes and 8 more excited isomeric states of some of its nuclides are currently known [7] . In nature, three isotopes were found - 225 Ac , 227 Ac and 228 Ac , the rest are obtained by artificial means. In practice, three natural isotopes are used. Actinium-225 is a member of the radioactive neptunium series ; was first discovered in 1947 as a decay product of uranium-233 . If we sustain 1 g of uranium-233 during the year, then the activity of 225 Ac formed in the sample will be 1.8 · 10 6 disintegrations per minute. This nuclide is an α-emitter with a half-life of 10 days. Actinium-225 is less available than actinium-228, but in practical terms, as a radioactive indicator, it is more promising [5] .
Actinium-227 is a member of the uranium-actinium radioactive series . It is found in all uranium ores, but in small quantities. In radioactive equilibrium, 1 g of uranium accounts for only 2⋅10 −10 g of 227 Ac. The half-life of the 227 Ac isotope is 21.77 years [5] [7] .
Actinium-228 is a member of the radioactive thorium series ; O. Gan was discovered in 1906 . This isotope is formed during the decay of 228 Ra . 1 t of thorium contains 5⋅10 −8 g 228 Ac. An isotope is a β - emitter with a half-life of 6.15 h [5] .
Protaktinium isotopes contain 29 nuclides with mass numbers 212–240 [7] and 3 excited isomeric states of some of its nuclides . Of these, only two nuclides — 231 Pa and 234 Pa — are found in nature, the rest are synthesized. The life expectancy of all isotopes, with the exception of Protactinium-231, is small. From a practical point of view, the most important are the long-lived isotope 231 Pa and the artificial 233 Pa . Protactinium-233 is an intermediate product in the preparation of uranium-233 , it is also the most accessible among other artificial isotopes of protactinium. According to its physical properties (half-life, the energy of gamma radiation , etc.) is a convenient substance for chemical research. Thanks to this isotope, a lot of valuable chemical information on the chemistry of protactinium was obtained. The radiation activity of protactinium-233 is about 20,000 Ci . Protaktinium-233 is a β-emitter with a half-life of 26.97 days [7] [16] .
Uranium has 25 of its isotopes with mass numbers of 217–242 [14] . For uranium, the presence of 6 isomeric states of some of its nuclides is known. In nature, in considerable quantities uranium is in the form of three isotopes - 234 U , 235 U and 238 U. Of all the others, the most important is 233 U, which is obtained as the final product of transformations upon irradiation of 232 Th by slowed neutrons . The 233 U core has an effective fission cross section for thermal neutrons, compared with 235 U. Of the majority of uranium isotopes, 238 is considered the most convenient for studying chemical properties, since the half-life is 4.4⋅10 9 years [17] .
Nowadays, 19 neptunium isotopes are known with mass numbers from 225 to 244 [14] . Long-lived 237 Np (T ½ = 2.20⋅10 6 years) and short-lived 239 Np, 238 Np are usually used to work with isotopes. The most important of these is neptunium-237 . This isotope is most suitable for the study of physical and chemical properties. The spectrum of this isotope is very complex and consists of more than 20 monoenergy lines. The use of large quantities of 239 Np in the chemical laboratory is complicated by its high radioactivity [11] .
For most neptunium nuclides with a mass number from 231 to 241, the scatter in the half-life values ranges from 7.3 min ( 240m Np) to 2.2⋅10 6 years [11] .
For americium isotopes, 16 nuclides are currently known with mass numbers from 232 to 248 [14] . The most important of them are 241 Am and 243 Am, both are alpha emitters; have soft but intense γ-radiation; both can be obtained in isotopically pure form. The chemical properties of americium were studied mainly at 241 Am, however, further amounts of 243 Am were available, which is more convenient for chemical studies, since it is almost 20 times less active than americium-241. The disadvantage of the 243 Am isotope is the presence of the short-lived daughter isotope Neptunium-239, which has to be considered when determining from γ-activity [3] .
Currently, 19 isotopes of curium are known [14] . The most accessible of them - 242 Cm, 244 Cm are α-emitters , but have much shorter half-lives than those of americium isotopes. These isotopes have almost no γ-radiation , but spontaneous fission and the associated neutron emission are noticeable. The more long-lived isotopes of curium ( 245–248 Cm, all α-emitters) are formed as a mixture upon neutron irradiation of plutonium or americium. Curium-246 predominates in this mixture with not very long irradiation, and then curium-248 begins to accumulate. Both of these isotopes, especially 248 Cm, have longer half-lives and are much more convenient for chemical research than 242 Cm and 244 Cm; however, they also have a fairly high rate of spontaneous fission. The most living isotope of curium - 247 Cm - is not formed in large quantities due to strong fission on thermal neutrons.
For Berkelius, 14 of its isotopes with mass numbers of 238–252 are known [14] . The only available of these in large quantities - 249 Bk has a relatively short half-life (330 days) and emits mostly soft β-particles , which are inconvenient for registration. It also has weak alpha radiation (1.45⋅10 −3 % in relation to β-radiation), which is sometimes used to determine this isotope. The long-lived Berkelio-247 isotope with a half-life of 1380 years, having alpha radiation, is known, but so far it has not been obtained in weight amounts. The production of an isotope during neutron irradiation of plutonium does not occur due to the β-stability of curium isotopes with a mass number less than 248 [3] .
Californium isotopes with mass numbers of 237–256 are formed in a nuclear reactor [14] , like others. California-253 isotope is a β-emitter, and all others are α-emitters. In addition, isotopes with even mass numbers ( 250 Cf, 252 Cf and 254 Cf) are characterized by a high rate of spontaneous fission, especially the isotope of California-254, in which 99.7% of decays occur by spontaneous fission. It is worth noting the isotope California-249, which has a rather long half-life (352 years) and weak spontaneous division. This isotope also has strong γ-radiation, which can greatly facilitate its identification. The 249 Cf isotope is not obtained in large quantities in a nuclear reactor due to the slow β-decay of the parent 249 Bk isotope and a large cross section of interaction with neutrons, however it can be accumulated in an isotopically pure form as a product of the β-decay of the previously isolated 249 Bk. California, isolated from plutonium irradiated in a reactor, contains mainly 250 Cf and 252 Cf isotopes (with a large integral neutron flux, 252 Cf prevails), and it is difficult to work with it due to powerful neutron radiation [3] .
Characteristics of some equilibrium pairs of TPE isotopes [3] | ||||
---|---|---|---|---|
Parent isotope | T ½ | Child isotope | T ½ | WURR |
243 Am | 7370 years | 239 Np | 2.35 days | 47.3 days |
245 Cm | 8265 years | 241 Pu | 14 years old | 129 years |
247 Cm | 1.64⋅10 7 years | 243 Pu | 4.95 hours | 7.2 days |
254 Es | 270 days | 250 Bk | 3.2 hours | 35.2 hours |
255 Es | 39.8 days | 255 Fm | 22 hours | 5 days |
257 Fm | 79 days | 253 Cf | 17.6 days | 49 days |
16 isotopes of Einsteinium isotopes are known with mass numbers from 241 to 257 [14] . The most accessible of its isotopes is 253 Es, an α-emitter with a half-life of 20.47 days, having a relatively weak γ-radiation and a spontaneous fission rate, which is small compared to the isotopes of California. With longer irradiation, a long-lived Es is also formed in the reactor (T ½ = 275.5 days) [3] .
From fermium isotopes , 19 nuclides are known with mass numbers from 242–260. Isotopes 254 Fm, 255 Fm, 256 Fm are α-emitters with short half-lives (hours) and therefore cannot be isolated in weight quantities. But with longer and more powerful irradiation, one can apparently expect the accumulation of appreciable quantities of the long-lived fermium isotope-257 (T ½ = 100 days). All fermium isotopes, including 257 Fm, are characterized by very high spontaneous fission rates [3] [18] .
For Mendelevia, 15 nuclides are known with mass numbers from 245 to 260 [14] . All studies of the properties of mendelevium isotopes were carried out with 256 Md, which decays mainly by electron capture (α radiation ≈ 10%) with a half-life of 77 minutes. The long-lived isotope 258 Md (T ½ = 53 days) is known, it is also an alpha emitter. Both of these isotopes are derived from Einsteinium isotopes ( 253 Es and 255 Es, respectively), so the possibility of producing mendelevium isotopes is limited by the amount of Einsteinium available.
Long-lived nobelium isotopes have small half-lives; by analogy, all subsequent elements after actinides have less (in some places) half-lives. For this element, there are 11 known nuclides with mass numbers from 250 to 260, and 262. The study of the chemical properties of nobelia and lourencia was carried out with the isotopes 255 No (T ½ = 3 minutes) and 256 Lr (T ½ = 35 sec.). The most long-lived 259 No (Т ½ ≈1.5 hours) was synthesized in 1970 in the city of Oak Ridge , USA.
Spread in nature
Thorium and uranium have the highest prevalence among actinides; their atomic clarks are 3⋅10 −4 % and 2⋅10 −5 %, respectively. In the earth's crust, uranium is found in the form of the mineral form of uraninite - U 3 O 8 (pitch ore, uranium tar), and also carnotite - KUO 2 VO 4 · 3H 2 O, otenite - Ca (UO 2 ) 2 (PO 4 ) 2 · nH 2 O, etc. The last two minerals are yellow in color. Uranium is also found in almost all mineral forms of rare-earth minerals ( fergusonite , samarskite , evkenit , etc.).
Uranium in nature is found in the form of isotopes of 238 U (99.2739%), 235 U (0.7204%) and 234 U (0.0057%). Of these, 238 U has the highest half-life (T ½ = 4.51⋅10 9 years).
Leading uranium mining countries [19] :
- Canada ;
- Australia ;
- Kazakhstan ;
- Niger ;
- Russia
Uranus is one of the rare and scattered elements. The content of uranium in the earth's crust is approximately 2⋅10 −4 %. Total uranium reserves are estimated at millions of tons. About 200 minerals are known from uranium mineral forms, most of them belong to oxides of variable composition (see above: carnotite, otenite) [20] .
The most abundant thorium minerals are thorianite (ThO 2 ), thorite (ThSiO 4 ), monazite , sheralite (( Th , Ca , Ce ) (PO 4 , SiO 4 )), torogumite (Th (SiO 4 ) 1 − x (OH) 4x ). Thorium , as well as uranium, is accompanied with mineral forms of almost all rare-earth elements. Rich deposits of monazite sands are found in India, Brazil, Australia, Africa, Canada, the USA and Ceylon.
The distribution of actinium in the earth's crust is very small (atomic clarke 5⋅10 −15 %). It is estimated that the general distribution of actinia in the crust is 2,600 tons, while, for example, the content of radium is 40 million tons [16] . Actinium is found in such natural materials as sulfide, silicate, oxygen-containing minerals; in natural water - in even smaller quantities, compared with uranium ores. The content of actinium in most natural objects corresponds to the isotopic equilibrium of maternal isotopes of 235 U. Minerals such as molybdenite , chalcopyrite , cassiterite , quartz , pyrolusite , etc. have a high content of this element. with uranium [5] .
More common is protactinium , whose atomic clarke is 10 −12 %. Protaktinium was found in uranium ore in 1913 by K. Fayans and O. Goering [4] . The total content of protactinium in the earth's crust (lithosphere) in accordance with the uranium content (protactinium isotopes are formed during the decay of 235 U) is 4.4⋅10 7 tons. The content in rocks of volcanic origin is 0.8⋅10 −6 g / t, and in iron meteorites, 0.02⋅10 −6 g / t [16] .
The half-life of the longest-lived isotope 237 Np is negligible compared with the age of the Earth, so almost no natural mineral is found in neptunium. On Earth, its nuclides can be formed almost exclusively with the help of nuclear reactions . Neptunium is found in minerals as an intermediate decay product of other isotopes [11] .
Plutonium content in uranium and thorium ores [21] | ||||
---|---|---|---|---|
Ore | Location | Content uranium,% | Attitude 239 Pu / ore (by weight) | Attitude 239 Pu / U (⋅10 12 ) |
Uranite | Canada | 13.5 | 9.1⋅10 −12 | 7.1 |
Uranite | Belgian Congo | 38 | 4.8⋅10 −12 | 12 |
Uranite | Colorado | 50 | 3.8⋅10 −12 | 7.7 |
Uranite concentrate | Belgian Congo | 45.3 | 7⋅10 −12 | 15 |
Monazite | Brazil | 0.24 | 2,1⋅10 −14 | 8.3 |
Monazite | North Carolina | 1.64 | 5.9⋅10 −14 | 3.6 |
Fergusonit | - | 0.25 | <1⋅10 −14 | <4 |
Carnotite | - | ten | <4⋅10 −14 | <0.4 |
The presence of plutonium in small quantities in mineral forms of uranium was first established in 1942. The upper limit of the prevalence on Earth of 244 Pu, the longest-lived plutonium isotope, is 3⋅10–22 g / g. It is known that nasturan and carnotite , found in Canada and in the state of Colorado, contain a small amount of the α-emitting isotope of plutonium 239 Pu. The content of plutonium in a number of uranium ores was determined, followed by separation of plutonium from 239 Pu production wastes. None of these mineral forms (see table) identified any plutonium isotope other than plutonium-239 . Plutonium was not detected in lunar soil samples [21] .
However, the isolation of natural plutonium from even the most enriched uranium ores with this element is impractical and will not be able to displace the artificial production of this element. This is indicated by the fact that in order to extract microgram quantities of plutonium it will be necessary to process 100 tons of plutonium ore concentrate per each microgram of plutonium [21] .
Getting
In most cases, decomposition of the chemical compound of this element is used to obtain the pure substance of the elements, usually by reacting its oxide, fluoride, etc., with hydrogen . However, this method is not applicable to actinides, since they are very rare in nature, and therefore more complex methods of purification of compounds are used to isolate them, and then to obtain elements of this group.
Most often, fluorides are used to isolate pure actinide compounds, since they are poorly soluble in water and can be more easily removed by the exchange reaction . Actinide fluorides are reduced by calcium , magnesium or barium , as they are relatively more active compared to the third and subsequent subgroups. For example, metallic americium is produced by the action of barium vapor on its trifluoride [4] :
Similarly, they extract the rest. Plutonium is separated from its tetrafluoride (PuF 4 ), reducing it:
Metallic uranium is also extracted from tetrafluoride (UF 4 ), but magnesium is used as a reducing agent :
Among actinides, thorium and uranium are most easily mined. Thorium is mined mainly from monazite . At the same time, thorium di- phosphate (Th (PO 4 ) 2 ) with admixtures of rare-earth elements , which precipitate at elevated pH of the sulfate solution, is treated with nitric acid , and thorium nitrate is extracted with tributyl phosphate . Better still, from acidic solutions, thorium is separated from REE in the presence of rodanide ions.
During the processing of monazite by decomposition of a 45% sodium hydroxide solution (at 140 ° C), the hydroxides of mixed metals are first extracted, which are then filtered (at 80 ° C), washed with water and dissolved in concentrated hydrochloric acid . Next, the acidic solution is neutralized with hydroxides to pH = 5.8. At the same time, thorium hydroxide (Th (OH) 4 ) with admixtures of rare-earth hydroxides (3%) precipitates, most of which remain in solution [4] .
Thorium hydroxide is dissolved in inorganic acid and again purified from rare earth elements. The method of dissolving thorium hydroxide in nitric acid is considered more effective because the extracted solution can be purified by extraction with organic solvents:
But thorium concentrate does not completely dissolve in nitric acid. In hydrogen chloride, it dissolves better, forming thorium chloride and water.
Thorium can be separated from rare-earth elements (when their concentration is low) by precipitating thorium oxalate from acidic solutions. But the method of extraction of thorium salts with organic solvents that do not mix with water is considered the most promising [4] .
Metallic thorium is separated from anhydrous oxide, chloride or fluoride with calcium in an inert atmosphere :
- .
Sometimes thorium is extracted by electrolysis of heated fluoride in a mixture of sodium and potassium chlorides. Electrolysis is carried out at 700-800 ° C in a graphite crucible . Very pure thorium is extracted by decomposing its iodide using the method of Van Arkel and de Boer .
Uranium is mined from its ores in many ways. First, the ore is set on fire, then it is acted on with acids , so that the uranium goes into a dissolved state. When using sulfuric acid , which dissolves only hexavalent uranium compounds, it is also necessary to add oxides (MnO 2 , ferric salts, etc.) in order to convert tetravalent uranium to hexavalent. At the next stage, the uranium is separated from impurities. To do this, the solution is filtered, and sometimes uranium salts are extracted from the pulp directly with organic solvents ( diethyl ether , tributyl phosphate ). It is best to extract uranium from a nitrate solution in a kerosene TBP solution. In this case, the complex passes to the organic phase - UO 2 (NCS) 2 · 2TBP [4] .
When the solution, which consists of uranium salts, is filtered from an insoluble precipitate, uranium can be isolated by precipitation with hydroxides (in the form of (NH 4 ) 2 U 2 O 7 ) or hydrogen peroxide (in the form of UO 4 · 2H 2 O).
If uranium ore contains an admixture of minerals such as dolomite , magnesite , etc., and they neutralize a large amount of acid by the action of acid on uranium ore ( neutralization reaction ), it is better to use the carbonate method of decomposition of uranium ore. The main reagent for this is an aqueous solution of soda , which converts uranium into a soluble complex compound - [UO 2 (CO 3 ) 3 ] 4– . This compound is stable in aqueous solutions at low concentrations of hydroxide ions . The use of sodium carbonate has the advantage, because when it is used, except for uranium, almost all other metals remain in the form of sediment. The advantage of the carbonate method for the decomposition of uranium ores relatively acidic is the absence of corrosive characteristics of working solutions. The disadvantage of this method is that, in the presence of sodium carbonate, tetravalent uranium compounds do not dissolve. Therefore, for the complete purification of uranium, the ore is treated with soda during heating and a single supply of oxygen under pressure:
- .
From this equation it can be seen that the best solvent of uranium during carbonate processing is a mixture of carbonate with its bicarbonate. When an average carbonate is taken, due to the high pH of the solution, part of the uranium may precipitate as a diuranate. From carbonate solutions, diuranate is isolated, reducing it with hydrogen in the presence of nickel . This produces insoluble uranium tetracarbonate [4] .
Also promising is the method using high polymer resins as polyelectrolytes . Ions exchange occurs in the resins, resulting in the release of uranium. Using this method, uranium can be isolated from both acidic and basic (carbonate) solutions. Since, compared to other transuranic metals, uranium makes anionic complexes easier, for example [UO 2 (SO 4 ) 2 ] 2– , [UO 2 (CO 3 ) 3 ] 4– , it is better to use uranium during the ion exchange reaction. anion exchangers with quaternary ammonium groups R 4 N + A - .
From anion exchange resin, uranium is washed out with a solution of ammonium nitrate or nitric acid .
After separation, uranium is isolated in the form of uranyl nitrate - UO 2 (NO 3 ) 2 · 6H 2 O. When heated, it will produce uranium oxide (VI), which, when reduced by hydrogen, is converted into dioxide:
Under the action of hydrogen fluoride on uranium dioxide, uranium tetrafluoride is mined, which can then be reduced with magnesium to uranium metal:
To separate plutonium from the products of fission of radioactive materials, uranium irradiated with neutrons is dissolved in nitric acid. To the resulting solution add a reducing agent ( FeSO 4 , or H 2 O 2 ), which converts plutonium from an oxidation state of +6 to +4, and uranium remains as uranyl nitrate (UO 2 (NO 3 ) 2 ). After treatment with a reducing agent, the solution is neutralized with ammonium carbonate to pH = 8. At the same time, Pu 4+ goes to sediment [4] .
You can use another method. After the nitrate solution has been reduced with sulfur gas, hydrofluoric acid is added and lanthanum ions are precipitated, and at the same time plutonium and neptunium fluorides (M 4+ ) are precipitated. After filtration and washing, the fluoride precipitate is treated with potassium bromate to oxidize neptunium to which goes into solution. Then, using stronger oxidizers, plutonium is transferred to Pu 6+ and thus separated from the lanthanides .
Often, for the separation of plutonium and other actinides, starting with uranium, extraction with tributyl phosphate is used. First, nitrates are extracted with Pu 4+ and U 6+ , and then the extractant is brought into contact with hydrazine and the reduced plutonium is washed out [4] .
Preparations containing actinium are contaminated with rare earth elements. The difficulty of cleaning actinium is complicated by the similarity of actinium and lanthanum, which complicates the separation of actinium. Actinium can be obtained in several ways - by nuclear reactions or by methods of separation, precipitation, or ion exchange. In the first case, a nuclear reaction involving radium isotopes is used . In the second case, chemical methods are used to obtain actinium - ion exchange reactions, purification from impurities using reactions. There are, in addition to the above methods for separating actinium from impurities, and methods of chromatography, methods of extraction, electrochemistry, and other methods also applicable to other actinides [5] .
Properties
The properties of actinides are similar to lanthanides, but there are differences between them. The difference between the two groups is explained by the fact that the filling of the outer electron shells is interrupted in actinides — the sixth (group 6d) and seventh (after the appearance of the 7s 2 electron group), and the transition from each previous actinide to the next occurs (mainly, exclusively) the filling of f-electrons in the fifth electron shell. In actinides, by analogy with lanthanides, the f-layer in the fourth electron shell is filled [22] .
The first experimental proof of the filling of the fifth f-electron shell in the region of heavy elements close to uranium was obtained by E. McMillan and F. Abelson in 1940 [22] .
The radii of actinide ions , like lanthanide ions, monotonously decrease with increasing atomic numbers of elements. Actinide ions are paramagnetic , and the magnitude of the gram-ion magnetic ability for both types of cations varies equally depending on the number of f-electrons [4] .
Properties of actinides [20] [23] | |||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Property | Ac | Th | Pa | U | Np | Pu | Am | Cm | Bk | Cf | Es | Fm | Md | No | Lr |
Core charge | 89 | 90 | 91 | 92 | 93 | 94 | 95 | 96 | 97 | 98 | 99 | 100 | 101 | 102 | 103 |
Atomic mass | [227] | 232,038 | [231] | 238,029 | [237] | [244] | [243] | [247] | [247] | [251] | [252] | [257] | [258] | [259] | [262] |
The number of natural isotopes | 3 | one | 2 | 3 | - | - | - | - | - | - | - | - | - | - | - |
Longest isotope | 227 | 232 | 231 | 238 | 237 | 244 | 243 | 247 | 247 | 251 | 252 | 257 | 258 | 259 | 262 |
Half-life of the most long-lived isotope | 21.8 years | 14,000 Ma | 32500 years | 4470 million years | 2.14 Ma | 8.2 million years | 7370 years | 15.6 million years | 1400 years | 900 years | 1.29 years | 100.5 days | 52 days | 58 min | 261 min |
Electronic configuration in ground state | 6d 1 7s 2 | 6d 2 7s 2 | 5f 2 6d 1 7s 2 or 5f 1 6d 2 7s 2 | 5f 3 6d 1 7s 2 | 5f 4 6d 1 7s 2 or 5f 5 7s 2 | 5f 6 7s 2 | 5f 7 7s 2 | 5f 7 6d 1 7s 2 | 5f 9 7s 2 or 5f 8 6d 1 7s 2 | 5f 10 7s 2 | 5f 11 7s 2 | 5f 12 7s 2 | 5f 13 7s 2 | 5f 14 7s 2 | 5f 14 6d 1 7s 2 |
Oxidation state | 3 | 3, 4 | 3, 4, 5 | 3, 4, 5, 6 | 3, 4, 5, 6, 7 | 3, 4, 5, 6, 7 | 3, 4, 5, 6 | 3, 4 | 3, 4 | 2, 3 | 2, 3 | 2, 3 | 2, 3 | 2, 3 | 3 |
Metal radius, nm | 0.203 | 0.180 | 0.162 | 0.153 | 0.150 | 0.162 | 0.173 | 0.174 | 0.170 | 0.186 | 0.186 | - | - | - | - |
Ion radius, nm: M 4+ M 3+ | - 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 boil | 1050 3300 | 1750 4800 | 1572 4400 | 1130 3800 | 640 3900 | 640 3230 | 1176 2610 | 1340 - | 1050 - | 900 - | 860 - | 1530 - | 830 - | 830 - | 1630 - |
BOT , B: E ° (M 4+ / M 0 ) E ° (M 3+ / M 0 ) | - −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 (H 2 O) n ] 4+ [M (H 2 O) n ] 3+ | - Colorless | Colorless Blue | Yellow Dark blue | Green Purple | Yellow green Purple | Brown Purple | Red Pink | Yellow Colorless | Beige Yellow green | Green Green | - Pink | - - | - - | - - | - - |
Oxidation state | 89 | 90 | 91 | 92 | 93 | 94 | 95 | 96 | 97 | 98 | 99 |
+3 | Ac 3+ | Th 3+ | Pa 3+ | U 3+ | Np 3+ | Pu 3+ | Am 3+ | Cm 3+ | Bk 3+ | Cf 3+ | Es 3+ |
+4 | Th 4+ | Pa 4+ | U 4+ | Np 4+ | Pu 4+ | Am 4+ | Cm 4+ | Bk 4+ | Cf 4+ | ||
+5 | PaO 2 + | UO 2 + | NPO 2 + | PuO 2 + | AmO 2 + | ||||||
+6 | UO 2 2+ | NPO 2 2+ | PuO 2 2+ | AmO 2 2+ | |||||||
+7 | NPO 2 3+ | PuO 2 3+ | [AmO 6 ] 5− |
Physical Properties
From a physical point of view, actinides are typical metals . All of them are soft, have a silver color, rather high density and plasticity. Some of these metals can be cut with a knife. Thorium hardness is like mild steel . From the heated pure thorium, you can roll the sheets, pull the wire. Thorium is almost twice as light as uranium and plutonium, but harder than both of them. All actinides are to some extent radioactive . Of these, only thorium and uranium are found in nature in appreciable quantities.
Physical properties of some actinides [4] [21] [25] | |||||
---|---|---|---|---|---|
Metal name | Density, g / cm ³, at 25 ° C | Melting point, ° С | Colour | Cross section neutron capture barn | Atomic radius, Å |
Actinium | ten | 1050 | Silvery white | - | 1.88 |
Thorium | 11.7 | 1750 | Silvery white | 7.57 | 1,798 |
Protactinium | 15.4 | 1572 | Silvery white | - | 1,774 |
Uranus | 19.1 | 1135 | Silvery white | 7.68 (natural mixture) | 1,762 |
Neptunium | 20.2 | 644 | Silver | - | 1,759 |
Plutonium | 19.7 | 640 | Silvery white | - | 1.58 [26] |
Americium | 12 | 1176 | Silver | - | 1.82 |
Curium | 13.51 | 1345 | Silver | - | 1.74 |
Berkeley [27] | 13.25 | 986 | Silvery white | - | 1.70 |
Californium | 15.1 | 900 | Silvery white | - | - |
Einsteinium | - | 860 | Silver | - | - |
Fermi | - | 1527 | - | - | - |
Mendelevium | - | 827 | - | - | - |
Nobelium | - | 827 | - | - | - |
Lawrence | - | 1627 | - | - | - |
For all actinides, except for actinium, polymorphism is characteristic.
Actinide radii. Metal (dashed line) and ion (solid line) radii of actinium and 5f-elements: 1 - M 3+ , 2 - M 4+ , 3 - M 5+ .
Actinide phase diagram
Plutonium has seven polymorphic modifications, and uranium, neptunium, and californium have three. The crystal structures of protactinium, uranium, neptunium, and plutonium, by their complexity, have no analogs among lanthanides and are more similar to the structures of 3d transition metals. At the melting point, light actinides have a body-centered lattice, and, starting from plutonium, face-centered [20] .
The melting point of actinides changes with increasing number of f-electrons nonlinearly. With an increase in the number of these electrons, the melting point first (from protactinium to plutonium) decreases, and then (from americium to curium) increases. Plutonium's uniquely low melting point is explained by the hybridization of 5f and 6d orbitals and the formation of directional bonds in these metals. From curium to Einsteinia, the melting point decreases again and then rises to a maximum at fermium. A similar curve of melting temperatures is repeated from fermium to lourencia [20] .
For actinides from americium to Einsteinium, at any temperatures below the melting point, face-centered cubic and hexagonal closest packings are characteristic. For transuranium elements, the similarity with metallic lanthanides increases - at room temperature, the crystal structures of actinides from americium to californium and light lanthanides are similar.
Comparative characteristics of the radii of the ions of lanthanides and actinides [4] | ||||
---|---|---|---|---|
Lanthanides | The radii of the ions Ln 3+ , Å | Actinides | The radii of ions M 3+ , Å | The radii of the ions M 4+ , 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 | Uranus | 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 | Fermi | - | - |
Thulium | 0.869 | Mendelevium | - | - |
Ytterbium | 0.858 | Nobelium | - | - |
Lutetium | 0.848 | Lawrence | - | - |
Chemical Properties
All actinides are chemically active metals.
Like the lanthanides, 5f-elements have a high chemical activity with respect to oxygen, halogens, nitrogen and sulfur. Thus, thorium, uranium, and neptunium are already slowly oxidized in air at room temperature. Pure plutonium left in the air is pyrophoric .
The difference in the chemical properties of actinides and lanthanides is manifested in the fact that actinides react more easily and have different valence states. This is due to the smaller size of 5f orbitals compared to 4f orbitals, their screening by external electrons and therefore their ability to expand more easily beyond the 6s and 6p orbitals. Actinides are prone to hybridization . This is especially characteristic of those elements whose atoms have a small number of 5f electrons. This is explained by the fact that the energies of the 5f, 7s and 6d sublevels are very close [4] .
Most of the elements of this group can have different degrees of oxidation , and in the most stable compounds the following degrees of oxidation appear [4] :
- actinium - +3;
- thorium - +4;
- protaktinium - +5;
- uranium - +6;
- neptunium - +5;
- plutonium - +4;
- americium and other actinides - +3.
The chemical properties of actinium resembled lanthanum, which is explained, first of all, by their similar ionic radii. Like lanthanum, only degree of oxidation +3 is characteristic of actinium. Actinium, unlike lanthanum, exhibits weaker reactivity and more pronounced basic properties. Among the remaining triple charged ions, Ac 3+ is distinguished by the presence of the weakest acidic properties, that is, actinium in aqueous solutions is only slightly hydrolyzed [5] [20] .
Thorium is characterized by high chemical activity. For thorium, as for the elements of the fourth group, the oxidation state is +4. Due to the absence of electrons on the 6d and 5f orbitals, the tetravalent thorium compounds have no color. In solutions of thorium salts at pH <3, [Th (H 2 O) 8 ] 4+ cations predominate. The Th 4+ ion has an unusually large radius; depending on the coordination number, it can take values from 0.95 to 1.14 Å. The low ability of thorium salts to hydrolysis is associated with this characteristic feature. The distinctive ability of thorium salts is their high solubility not only in water , but also in polar organic solvents [20] .
Protaktinium has two valence states — 5 and 4. In contrast to the stable pentavalent state, tetravalent protaktinium in solutions is extremely easily oxidized to Pa 5+ with oxygen from the air. In this regard, tetravalent protaktinium in solutions is obtained by the action of strong reducing agents in a hydrogen atmosphere. By its chemical properties, quadrivalent protactinium is a close analogue of U IV and thorium. It is known that Pa IV forms many crystalline compounds, isostructural with compounds of U IV and thorium. Pa IV fluorides, phosphates, hypophosphates, iodates and phenylarsonates are insoluble in water and in sufficiently dilute acids . Protactinium forms soluble carbonates. By hydrolytic properties, pentavalent protactin is close to Ta V and Nb V. The complexity of the chemical behavior of protactinium is a consequence of the appearance of 5f orbits in atoms of a given element [16] .
For uranium , as well as for many d-elements, the presence of several degrees of oxidation is characteristic, in particular, uranium takes valence values from 3 to 6, the most stable degree of oxidation is +6. In the hexavalent state, uranium is a complete electronic analog of the elements of the sixth group, although the significant difference in the radii of the U 6+ and W 6+ ions makes the similarity between them only formal (however, they have the same compositions of higher oxides and some oxo anions , for example ). In the compounds of uranium IV and uranium VI there is a number of non-stoichiometric compounds , that is, oxides of variable composition. For example, the chemical formula of its dioxide, UO 2, is more correct to write UO 2 + x , where x has values from −0.4 to +0.32. Uranium VI compounds are not strong oxidizing agents . Uranium IV compounds exhibit reducing properties, for example, are easily oxidized by oxygen from the air. Uranium III compounds are very strong reducing agents. Uranium is prone to the formation of organometallic compounds . This property is explained by the presence of the d-orbital [20] .
For neptunium , valences of 3, 4, 5, 6 and 7 are possible. In solutions, it can be simultaneously in several of them. This is explained by the disproportionation of pentavalent neptunium in strongly acidic solutions due to the proximity of the redox potentials of the neptunium ion pairs. The most stable in solutions are Np V ions. In solid compounds, neptunium is stable and exhibits valence 4. Np III and Np IV ions , like other actinoids, exist in water as hydrated cations of the above neptunium ions. Np III is hydrolyzed in a weak alkaline medium. Neptunium metal is very reactive. The ions of this element are distinguished by a high propensity to form coordination compounds and hydrolysis [11] .
For plutonium , as well as for neptunium, valences from 3 to 7 are possible. The chemical behavior of plutonium is similar for uranium and neptunium. Chemically, plutonium is a very active element. It oxidizes in air, forming a film of PuO at 50 ° C. Plutonium reacts noticeably with hydrogen even at 25–50 ° C. Metallic plutonium rather actively interacts with halogens and hydrogen halides. This element has a strong potential for the formation of intermetallic compounds . The hydrolysis reactions of plutonium ions of different oxidation states are quite diverse. Depending on the conditions, Pu IV is characterized by polymerization reactions [28] [29] .
Americium is the most diverse, which reliably established the presence of oxidation states from +2 to +6. Divalent americium is obtained only in dry compounds and in non-aqueous solutions ( acetonitrile ). The oxidation states +3, +5, and +6 are characteristic of aqueous solutions of americium, although a large number of solid compounds corresponding to them are known. Quaternary americium forms stable solid compounds (dioxide, fluoride, americium hydroxide), in aqueous solution it exists in the form of various complex compounds . It was reported that in an alkaline solution, americium can be oxidized to the heptavalent state, however, these data turned out to be erroneous. The most stable valence of americium in aqueous solution is +3, in solid compounds, +3 and +4 [3] .
The valence of +3 is dominant in all subsequent elements, up to and including Lawrence (with the possible exception of Nobel). Curium exists in the tetravalent state in solid compounds (fluoride, curium dioxide), and in aqueous solution only in the form of an unstable fluoride complex compound . It was reported about the oxidation of curium in an aqueous solution to the hexavalent state, but other researchers could not reproduce this result.
Berkeley, along with valence +3, also exhibits a +4 valence, more stable than curium; it corresponds to a number of solid compounds (fluoride, berkelium dioxide), and in an aqueous solution, the stability of the Bk 4+ ion is close to the stability of the Ce 4+ ion. In California, Einsteinia and Fermium, the only valid valence is +3. Proved the presence of a divalent state in mendeleus and nobelia, and in nobelia it is more stable than the trivalent state. The valences of the last two transplutonium elements — Lawrence and Rutherford — are very scarce; It is known that lourencia, both in solution and in dry compounds, exhibits only valence +3; and rutherfordium in the form of chloride behaves like hafnium , that is, apparently, tetravalent [3] .
Due to the fact that thorium, protactinium and uranium have high stable oxidation states, they are sometimes placed as elements of the subgroups of the fourth, fifth and sixth groups. If such a tendency really existed, transuranic elements would have to be in the eighth and seventh groups, and they would be lighter than uranium, they would have had a high valence . But this is not observed, because from uranium to americium the ability to create compounds with a valence of +6 decreases. This can be seen by putting redox potentials obtained under standard conditions. [4] :
- uranium: −0.32 V,
- neptunium: +0.34 V,
- plutonium: +1.04 V,
- americium: +1.34 V.
Hence the conclusion that the reducing ability of the M 4+ ion increases from americium to uranium.
Like the lanthanides , all the actinide metals are easily combined with oxygen , halogens and chalcogens , carbon , hydrogen and sulfur. For americium it has been established that it is possible to obtain the hydride of this substance - AmH 3 . Thorium, protactinium and uranium are also combined with hydrogen at 250 ° C. Create hydrides and other actinides. Hydrides with the general formula MH 3 resemble salts in their properties. All connections are black [4] .
When reacting with carbon, the actinides preferentially create carbides with the general formula MC, MC 2 , and uranium U 2 C 3 . With sulfur, they produce sulfides with the general formula M 2 S 3 and MS 2 [4] .
Connections
Oxides and hydroxides
Several oxides are known for some actinides: M 2 O 3 , MO 2 , M 2 O 5 and MO 3 . For all metals, oxides M 2 O 3 , MO 2 and M 2 O 5 are basic , and MO 3 are amphoteric [4] . More pronounced basic properties of oxides. They easily combine with water , forming the bases :
- .
These bases are poorly soluble in water, and in their activity they are close to rare earth metal hydroxides. The strongest of these bases is hydroxide actinium . Actinium interacts relatively easily with water, displacing hydrogen . All actinium compounds, except for its black sulphide (Ac 2 S 3 ), are white [4] .
Oxides of tetravalent actinoids crystallize into a cubic crystal system, a fluorite- type crystal structure ( calcium fluoride ).
Dioxides of some actinides [30] | |||||||||
---|---|---|---|---|---|---|---|---|---|
Connection name | Thorium dioxide | Protaktinium dioxide | Uranium dioxide | Neptunium dioxide | Plutonium dioxide | Americium dioxide | Curium dioxide | Berkeley dioxide | California dioxide |
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 | |||||||
Chemical formula | ThO 2 | PaO 2 | UO 2 | NPO 2 | PuO 2 | AmO 2 | CmO 2 | BkO 2 | CFO 2 |
Molar mass | 264.04 g · mol −1 | 263.035 g · mol −1 | 270.03 g · mol −1 | 269.047 g · mol −1 | 276.063 g · mol −1 | 275.06 g · mol −1 | 270–284 g · mol −1 | 279.069 g · mol −1 | 283.078 g · mol −1 |
Melting temperature | 3390 ° C | 2878 ° C | 2600 ° C | 2400 ° C | 2050 ° C | ||||
Boiling temperature | 4400 ° C | 2800 ° C | |||||||
Structure | An 4+ : __ / O 2− : __ | ||||||||
Space group | |||||||||
Coordination number | An [8], O [4] |
- An - actinoid (s)
Thorium, combining with oxygen , forms only dioxide. It can be obtained by burning metallic thorium in oxygen at a temperature of 1000 ° C, or by heating some of its salts:
Thorium dioxide is a refractory substance (melting point 3220 ° C), very resistant to heat. Because of this property, thorium dioxide is sometimes used in the manufacture of refractory materials. The addition of 0.8–1% ThO 2 to pure tungsten stabilizes its structure; therefore, hairs of light bulbs have a better resistance to vibrations [4] .
Thorium dioxide is a basic oxide, but it will not work directly in the reaction of a metal with water. To dissolve ThO 2 in acids, it is first heated to a temperature of 500–600 ° C. Stronger heating (above 600 ° C) helps to obtain a ThO 2 structure that is highly resistant to acids and other reagents. A small addition of fluoride ions catalyzes the dissolution of thorium and its dioxide in acids .
Protaktinium produced two oxides: PaO 2 (black) and Pa 2 O 5 (white). The first one is isomorphic with ThO 2 . Easier to get Pa 2 O 5 . Both protaktinium oxides are basic. For pentavalent protactinium, Pa (OH) 5 - a weak poorly soluble base can be obtained [4] .
By decomposing some uranium salts, you can get orange or yellow UO 3 . This oxide is amphoteric; it is directly obtained by interaction with water and creates several hydroxides, of which the most stable is UO 2 (OH) 2 .
The reaction of uranium oxide (VI) with hydrogen produces uranium dioxide, which is similar in its properties to ThO 2 . This oxide is also essential. It corresponds to uranium tetrahydroxide (U (OH) 4 ) [4] .
Plutonium , neptunium and americium form two types of oxides: M 2 O 3 and MO 2 , which have basic properties. White Cm 2 O 3 and black CmO 2 were obtained from curium, and Cf 2 O 3 from California. The oxides of the remaining actinides are poorly understood. Neptunium trioxide is less resistant than uranium oxide, so it was not obtained in its pure form (only Np 3 O 8 ). At the same time, plutonium and neptunium oxides are well studied with the chemical formula MO 2 and M 2 O 3 [4] .
Oxides of new elements are often investigated first, which is associated with their great value, ease of preparation, and the fact that oxides usually serve as intermediates for the production of other substances.
Actinoid oxides [3] [5] [11] [16] [31] | |||||||
---|---|---|---|---|---|---|---|
Compound | Colour | Syngony and structural type | Cell parameters, Å | Density , g / cm ³ | Area of existence, ° C | ||
a | b | c | |||||
Ac 2 O 3 | White | Hexagonal, La 2 O 3 | 4.07 | - | 6.29 | 9,19 | - |
PaO 2 | - | Cubic, CaF 2 | 5,505 | - | - | - | - |
Pa 2 O 5 | White | Cubic, CaF 2 Quadratic 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 - |
ThO 2 | Colorless | Cubic | 5.59 | - | - | 9.87 | - |
UO 2 | Black brown | Cubic | 5.47 | - | - | 10.9 | - |
NPO 2 | Greenish brown | Cubic, CaF 2 | 5.424 | - | - | 11.1 | - |
Puo | The black | Cubic, NaCl | 4.96 | - | - | 13.9 | - |
PuO 2 | Olive Green | Cubic | 5.39 | - | - | 11.44 | - |
Am 2 O 3 | Reddish brown Reddish brown | Cubic, Mn 2 O 3 Hexagonal, La 2 O 3 | 11.03 3,817 | - | - 5.971 | 10.57 11.7 | - |
AmO 2 | The black | Cubic, CaF 2 | 5.376 | - | - | - | - |
Cm 2 O 3 | White [32] - - | Cubic, Mn 2 O 2 Hexagonal, LaCl 3 Monoclinic, Sm 2 O 3 | 11.01 3.80 14.28 | - - 3.65 | - 6 8.9 | 11.7 | - |
CmO 2 | The black | Cubic, CaF 2 | 5.37 | - | - | - | - |
Bk 2 O 3 | Light brown | Cubic, Mn 2 O 3 | 10,886 | - | - | - | - |
BkO 2 | Reddish brown | Cubic, CaF 2 | 5.33 | - | - | - | - |
Cf 2 O 3 [33] | Colorless Yellowish - | Cubic, Mn 2 O 3 Monoclinic, Sm 2 O 3 Hexagonal, La 2 O 3 | 10.79 14,12 3.72 | - 3.59 - | - 8.80 5.96 | - | - |
CFO 2 | The black | Cubic | 5.31 | - | - | - | - |
Es 2 O 3 | - | Cubic, Mn 2 O 3 Monoclinic Hexagonal, La 2 O 3 | 10.07 1.41 3.7 | - 3.59 - | - 8.80 6 | - | - |
Acid Salts
Actinide metals combine well with halogens, creating salts MHa 3 and MHa 4 (Ha - halogen ), so was obtained California chloride. In 1962, the first Berkelium compound was synthesized - BkCl 3 in the amount of 0.000003 mg [4] .
Like the halogens of rare-earth elements, chlorides , bromides and iodides of actinides dissolve in water, and fluorides are insoluble. Uranium is relatively easy to obtain colorless hexafluoride, which is able to sublimate at a temperature of 56.5 ° C. Due to the lightness of UF 6, it is used in the separation of uranium isotopes by the diffusion method.
Actinide hexafluorides are close in properties to anhydrides . In water, they hydrolyze, forming MO 2 F 2 . Pentachloride and black uranium hexachloride were also synthesized, but both of them are unstable [4] .
When exposed to acids on actinium, thorium, protactinium, uranium, neptunium, etc., salts are obtained. If they are acted on by non-oxidizing acids, as a rule, low-valence metals can be obtained:
However, in the course of these reactions, the reducing hydrogen can react with the metal itself to form the corresponding metal hydride. Uranium reacts much more easily with acids and water than thorium [4] .
Chlorides of trivalent actinides crystallize into a hexagonal syngony .
Trichlorides of some actinides [30] | |||||||||
---|---|---|---|---|---|---|---|---|---|
Connection name | Chloride actinium (III) | Uranium (III) chloride | Neptunium (III) chloride | Neptunium (III) chloride | America (III) chloride | Curium (III) chloride | Berkelium (III) chloride | California (III) chloride | |
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 | ||||||||
Chemical formula | AcCl 3 | UCl 3 | NpCl 3 | PuCl 3 | AmCl 3 | CmCl 3 | BkCl 3 | CFCl 3 | |
Molar mass | 333,386 g · mol −1 | 344.387 g · mol −1 | 343.406 g · mol −1 | 350.32 g · mol −1 | 349.42 g · mol −1 | 344–358 g · mol −1 | 353.428 g · mol −1 | 357.438 g · mol −1 | |
Melting temperature | 837 ° C | 800 ° C | 767 ° C | 715 ° C | 695 ° C | 603 ° C | 545 ° C | ||
Boiling temperature | 1657 ° C | 1767 ° C | 850 ° C | ||||||
Structure | An 3+ : __ / Cl - : __ | ||||||||
Space group | |||||||||
Coordination number | An * [9], Cl [3] | ||||||||
Lattice constant | 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 - actinoid (s)
Actinide fluorides [3] [11] [16] [21] [31] | ||||||
---|---|---|---|---|---|---|
Compound | Colour | Syngony , structural type | Cell parameters, Å | Density, g / cm ³ | ||
a | b | c | ||||
AcF 3 | White | Hexagonal, LaF 3 | 4.27 | - | 7.53 | 7.88 |
PaF 4 | Dark brown | Monoclinic | 12.7 | 10.7 | 8.42 | - |
PaF 5 | The black | Tetragonal , β-UF 5 | 11.53 | - | 5.19 | - |
ThF 4 | Colorless | Monoclinic | 13 | 10.99 | 8.58 | 5.71 |
UF 3 | Reddish purple | Hexagonal | 7.18 | - | 7.34 | 8.54 |
UF 4 | Green | Monoclinic | 11.27 | 10.75 | 8.40 | 6.72 |
α-UF 5 | Bluish | Tetragonal | 6.52 | - | 4.47 | 5.81 |
β-UF 5 | Bluish | Tetragonal | 11.47 | - | 5.20 | 6.45 |
UF 6 | Yellowish | Orthorhombic | 9.92 | 8.95 | 5.19 | 5.06 |
Npf 3 | Black or purple | Hexagonal | 7,129 | - | 7.288 | 9,12 |
Npf 4 | Light green | Monoclinic | 12.67 | 10.62 | 8.41 | 6.8 |
Npf 6 | Orange | Orthorhombic | 9.91 | 8.97 | 5.21 | five |
PuF 3 | Purple blue | Trigonal | 7.09 | - | 7.25 | 9.32 |
PuF 4 | Pale brown | Monoclinic | 12.59 | 10.57 | 8.28 | 6.96 |
PuF 6 | Reddish brown | Orthorhombic | 9.95 | 9.02 | 3.26 | 4.86 |
AmF 3 | Pink or light beige | Hexagonal , LaF 3 | 7.04 | - | 7.255 | 9.53 |
AmF 4 | Orange red | Monoclinic | 12.53 | 10.51 | 8.20 | - |
Cmf 3 | Chocolate brown to shiny white | Hexagonal | 4,041 | - | 7.179 | 9.7 |
Cmf 4 | Yellow | Monoclinic, UF 4 | 12.51 | 10.51 | 8.20 | - |
BkF 3 | Yellow green | Trigonal , LaF 3 Orthorhombic , YF 3 | 6.97 6.7 | - 7.09 | 7.14 4.41 | 10.15 9.7 |
BkF 4 | - | Monoclinic, UF 4 | 12.47 | 10.58 | 8.17 | - |
Cff 3 | - - | Trigonal, LaF 3 Orthorhombic, YF 3 | 6.94 6.65 | - 7.04 | 7.10 4.39 | - |
Cff 4 | - - | Monoclinic, UF 4 Monoclinic, UF 4 | 1,242 1.233 | 1,047 1,040 | 8,126 8,113 | - |
Salts of actinides are easily obtained by dissolving the corresponding hydroxides in acids. In turn, nitrates, chlorides, perchlorates and actinide sulfates can be dissolved in water. From aqueous solutions, these salts crystallize to form hydrates, for example:
- Th (NO 3 ) 4 · 6H 2 O,
- Th (SO 4 ) 2 · 9H 2 O,
- Pu 2 (SO 4 ) 3 · 7H 2 O.
Another property of these compounds is the ability of high-valence actinide salts to easily hydrolyze . Thus, the colorless average sulfate, chloride, perchlorate, thorium nitrate in solution quickly become basic salts with the chemical formulas Th (OH) 2 SO 4 , Th (OH) 3 NO 3 .
By their solubility, salts of trivalent and tetravalent actinoids are similar to salts of lanthanides. As for lanthanum and its analogues, phosphates , fluorides , oxalates , iodates , actinide carbonates are poorly soluble in water. In this case, almost all poorly soluble salts precipitate in solution as crystalline hydrates , for example, ThF 4 · 3H 2 O, Th (CrO 4 ) 2 · 3H 2 O [4] .
Actinides with an oxidation state of +6, except cationic complexes of the type , create anions [MO 4 ] 2– , [M 2 O 7 ] 2– and some more complex compounds. For example, uranium, neptunium and plutonium are known salts of the type of uranates (Na 2 UO 4 ) and dithiuranates ((NH 4 ) 2 U 2 O 7 ).
Compared with the lanthanides, actinides create coordination compounds better. The ability to form complex compounds in actinides increases with increasing metal valence. Trivalent actinides do not form fluoride coordination compounds, while tetravalent thorium forms salts like K 2 ThF 6 , KThF 5, and even K 5 ThF 9 . For a given metal, it is easy to obtain the corresponding sulfates , for example, Na 2 SO 4 · Th (SO 4 ) 2 · 5H 2 O, nitrates , and thiocyanates. Salts with the general formula M 2 Th (NO 3 ) 6 · n H 2 O have a coordination nature, in which the thorium has a coordination number of 12. Even more complex salts create pentavalent and hexavalent actinides. Sufficiently stable complexes form thorium and uranium with rhodanide ions. These complexes have a high resistance in non-aqueous solvents [4] .
It is also worth noting that the most stable coordination compounds of actinides, tetravalent thorium and uranium, are obtained by reaction with diketones, for example, with acetylacetone .
Application
Most of the actinides, up to americium inclusive, have found application in various fields of science and technology, for example, instrument engineering (smoke detectors), space technologies [4] . However, the use of actinoids to create nuclear weapons and use as fuel in nuclear reactors is the most widespread and significant. In both cases, the property of some actinides is used to release enormous energy during nuclear reaction - nuclear fission , which under certain conditions can be chained , that is, self-sustaining .
For nuclear energy, uranium is very important, especially its isotope, uranium-235 , which is used in the most common thermal neutron reactors , whose content in natural uranium does not exceed 0.72%. This isotope has a high cross section for capturing thermal neutrons , absorbing which 235 U is divided with the release of large amounts of energy. The energy converted into heat by one fission event (200 MeV ), in recalculation per 1 g reacted 235 U, gives approximately 1 MW · day. The maintenance of the fission of uranium-235 by the release of a larger number of neutrons is more valuable than is spent [4] . Upon reaching a critical mass of uranium-235 - 0.8 kg - a self - sustaining nuclear chain reaction occurs [20] . As a rule, the nucleus of uranium is divided into 2 fragments with the release of 2-3 neutrons, for example:
Also promising in nuclear power is the use of the nuclear cycle, based on the use of thorium-232 and the useful product resulting from its division - uranium-233 . Neutron emission in the case of forced fission of uranium is important not only for maintaining a nuclear chain reaction and obtaining a large amount of energy, but also for the synthesis of heavier actinides. Uranium-239 decays by β-decay and forms plutonium-239 , which, like uranium-235, is capable of spontaneous fission . The world's first nuclear reactors were not intended for peaceful uses of energy , but for producing plutonium-239, in order to use it to create nuclear weapons.
Nuclear reactor [20] [34] |
---|
The core of any nuclear reactor is the core composed of fuel assemblies , which in turn consist of fuel elements - metal rods, in which nuclear fuel is located inside the shell, usually made of zirconium alloys - most often in the form of uranium dioxide . Nuclear fuel can also be used in the form of uranium carbides, nitrides and monosulfides, as well as in the form of various compounds of plutonium, uranium and thorium (the so-called MOX-fuel ). To slow down fast neutrons in thermal-neutron reactors , moderators are used that contain carbon , deuterium , and beryllium . The simplest and most widely used moderator is water . Thermal neutrons obtained in this way interact with the nuclei of uranium-235 several orders of magnitude more often than with fast ones. To regulate the rate of nuclear fission, absorbers are introduced into the reactor — special rods made of boron , cadmium, and / or use a liquid absorber, most often in the form of a boric acid solution, the concentration of which regulates the reactivity of the reactor . Reactors for the production of plutonium are specially designed, they differ in the principle of operation (they work mainly on fast neutrons ) and are called breeder-reactors or breeders (from the English. Breed - to multiply). Their use allows the production of significant quantities of plutonium. |
Thorium is used as an alloying component of magnesium - zinc alloys . Magnesium multicomponent alloys with a mixture of thorium due to their lightness and strength, high melting temperature and ductility are widely used in the aviation industry and in the manufacture of projectiles . Metallic thorium has good electron emission capability. Lamps with thorium electrodes have a small initial potential and do not fail for a long time [4] . The relative content of thorium and uranium isotopes is often used to estimate the age of stars [35] .
In the future, plutonium-238 isotope is considered by researchers as an autonomous source of energy, since its nuclear transformations are accompanied by the release of large amounts of heat. In theory, its use can spread to the costumes of astronauts and divers . But due to its high price (1 g of isotope costs about $ 1,000), its use is limited. This isotope was used on some Earth satellites in thermopiles and for water distillation on spacecraft . On the American spacecraft Apollo-11 a small heater was placed, the source of energy of which was plutonium-238; it was activated when the darkened part of the moon was flown around [4] .
For the same purposes as for plutonium-238, curium-242 can be used. Also, some California isotopes have the ability to spontaneously divide. Since the critical mass of California is small, it is believed that in the future it will be possible to manufacture charges for atomic bullets from it .
The separation of plutonium from uranium, which occurs through chemical reactions, is much simpler than the separation of uranium isotopes, which makes it promising to use weapons-grade plutonium from warheads that have worked their life as a fuel mixed with thorium and uranium, the so-called MOX fuel.
Actinium-227 is used for the manufacture of neutron sources. High specific energy release - 14.5 W / g, the possibility of obtaining significant quantities of thermally stable actinium compounds - valuable properties, opening up good prospects for use in long-term thermoelectric generators , which are suitable for space purposes. 228 Ac is used as an indicator of radioactivity in chemical research, as it has high-energy β-radiation with an energy of 2.18 MeV , which is easily recorded. An equilibrium mixture of 228 Ac - 228 Ra isotopes is widely used as a source of intense γ-radiation in industry and medicine [5] .
Americium-241, being a source of soft γ-rays, is used in medical diagnostics and in instruments for controlling the thickness of steel tape and sheet glass. Based on curium-242, generators are used to power the onboard equipment of space stations, and Californium-252 is used in neutron radiography as an extremely powerful source of neutrons [36] .
Actinides, such as plutonium and uranium, have also found wide use in nuclear weapons. In the XX century, a large number of tests of nuclear bombs were conducted. By the end of the 20th century, mass testing of nuclear weapons ceased due to the improvement of the international situation and the massive reduction in the number of nuclear weapons in the world.
Toxicity
Radioactive substances have a harmful effect on the human body due to:
- local skin contamination that has been caused, for example, by spilling or scattering a radioactive substance;
- internal exposure due to radioactive isotopes;
- external excessive exposure to the strongest types - β- and γ-radiation.
Together with radium and transuranium elements, anemones are among the dangerous radioactive poisons with high specific α-activity . The most important feature of actinium is its ability to accumulate and retain in the skeleton as a surface layer. At the initial stage of actinium poisoning, it accumulates in the liver . Another danger of actinium is that it undergoes radioactive decay faster than it is eliminated from the body. The adsorption of actinium from the digestive tract compared with the adsorption of radium is insignificant (> 0.05%). The danger associated with skin contamination and ingestion is due to the fact that gaseous radioactive substances ( radon isotopes ) are formed in the process of actinium decay [5] .
When protaktiniya hit the body, it is prone to accumulation in the kidneys and bones. It was found that the maximum safe dose of protactinia when ingested into a human body is 0.03 µCi ; this dose corresponds to 0.5 µg 231 Pa. This isotope, which is contained in air in the form of aerosols , is 2.5⋅10 8 times more toxic than hydrocyanic acid (at the same concentrations) [16] .
Plutonium, when it enters the air, food, or into the bloodstream through a wound, is deposited in the lungs , liver, and bones . Only about 10% falls into other organs. Plutonium atoms linger in the body for decades. This is due to the biochemical properties of plutonium and the fact that plutonium isotopes have long half-lives. Part of the long-term elimination of plutonium from the body due to poor solubility in water. All plutonium isotopes have high radiotoxicity , in particular, due to the fact that part of the nuclei of plutonium emit ionizing α-radiation, which damages the surrounding cells. Radiotoxicity is inversely related to the half-life of the plutonium isotope. Animal studies have shown that the lethal dose of plutonium-244 (the least radiotoxic, the half-life of 80 million years) is a few milligrams per kilogram of tissue. LD 50 for 30 days for dogs after intravenous plutonium-244 is approximately 0.32 milligrams per kg of tissue. Based on these studies, an approximate assessment of the lethal dose for a person weighing 70 kg - 22 mg was obtained. Upon admission through the respiratory system, absorption should be about 4 times greater. This long-lived plutonium isotope exhibits mainly chemical toxicity, similar to non-radioactive heavy metals. Robert Stone, calculations were made of a safe dose of shorter-lived plutonium isotopes in the human body. Plutonium-239 (half-life of 24 thousand years) is 50 times less toxic than radium , and therefore the permissible content of plutonium-239 in the body, according to his calculations, should be 5 μg, or 0.3 μCi. It is noteworthy that this amount of plutonium is difficult to see even in a modern microscope. Soon, after testing such doses in animals, this dose was reduced 5-fold and began to be 1 µg, or 0.06 µCi. However, this dose was also reduced, and it began to be 0.65 μg, or 0.04 μCi [28] .
Studies have also been carried out on how plutonium enters the human body. In the course of these studies it was established the following [28] :
- Plutonium intake through the respiratory organs is the most likely (and therefore most dangerous) path. In this case, approximately 5 to 25% of the inhaled substance is retained in the body. Depending on the particle size and solubility of the absorbed plutonium compounds, the incoming plutonium is localized in the lungs or in the lymphatic system , or is absorbed into the blood and then transferred to the liver or bones;
- Plutonium intake through food is the least likely method. In this case, only about 0.05% of soluble plutonium compounds and only 0.01% of insoluble materials enter the blood. The rest goes further along the gastrointestinal tract and is eliminated from the body;
- if plutonium or its compounds get into cuts on the skin, up to 100% of the introduced substance will be retained in the body.
Gallery
Uranyl nitrate (UO 2 (NO 3 ) 2 ).
Aqueous solutions of uranium salts III, IV, V, VI.
Aqueous solutions of neptunium salts III, IV, V, VI, VII.
Aqueous solutions of plutonium salts III, V, VI, VII.
Ionic solutions of americium (III) salts on the left and americium (IV) on the right.
Uranium tetrachloride.
Uranium hexafluoride.
Concentrate U 3 O 8 .
See also
Notes
- ↑ 1 2 N. Greenwood, A. Earnsho. Chemistry of elements = Chemistry of the Elements / Trans. from English - M .: "Binom. Laboratory of Knowledge", 2008. - T. 2. - 670 p. - (The best foreign textbook). - ISBN 978-5-94774-374-6 .
- ↑ Reino W. Hakala. Letters (Eng.) // J. Chem. Educ. - 1952. - Iss. 29 (11) . - P. 581 . - DOI : 10.1021 / ed029p581.2 .
- ↑ 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 B. F. Myasoedov, L. I. Guseva, I. A. Lebedev, M. S. Milyukova, M. K. Chmutova. Analytical chemistry of transplutonium elements. - M .: Science, 1972. - 376 p. - (analytical chemistry of elements). - 1750 copies
- ↑ 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 28 30 31 32 33 34 AM Golub. General and Inorganic Chemistry = Zagaln and inorganic chemistry. - Vishcha school, 1971. - T. 2. - 416 p. - 6700 copies
- ↑ 1 2 3 4 5 6 7 8 9 10 Z. K. Karalova, B. F. Myasoedov. Actinium. - M .: "Science", 1982. - 144 p. - (Analytical chemistry of elements). - 1150 copies
- ↑ Nobelium and Lawrence were almost simultaneously discovered by Soviet and American scientists.
- 2 1 2 3 4 5 6 7 8 G. Audi, O. Bersillon, J. Blachot, AH Wapstra. The Nubase evaluation of nuclear and decay properties (English) // Nuclear Physics: journal. - 2003. - Vol. A 729 . - P. 3-128 .
- ↑ E. Fermi . On the possible finding of an element with an atomic number above 92 = Possible Production of Atomic Number Higher than 92 // UFN . - 1934 . - T. 14 , No. 7 . - p . 829-832 .
- П. P. Kudryavtsev, Fermi Experiments, // Course in the History of Physics . - 2nd ed., Corr. and add. - M .: Enlightenment, 1982. - p. 73.
- ↑ Seaborg GT The Transuranium Elements // Science. - 1946. - October 25 ( v. 104 , No. 2704 ). - p . 379-386 . - ISSN 0036-8075 . - DOI : 10.1126 / science.104.2704.379 .
- ↑ 1 2 3 4 5 6 7 Analytical chemistry of neptunium / Chapter. Ed .: V. A. Mikhailov. - M .: "Science", 1971. - 218 p. - (Analytical chemistry of elements). - 1700 copies
- ↑ E. Fermi. The Development of the First Chain Reaction Pile (Eng.) // Proceedings of the American Philosophy Society. - 1946. - Iss. 90 .
- ↑ 1 2 M.Ye. Dritz, P. B. Budberg, G. S. Brukhanov, A. M. Dritz, V. M. Panovko. Properties of elements. - M .: Metallurgy Publishing House, 1985. - 672 p. - 6500 copies
- ↑ 1 2 3 4 5 6 7 8 9 IAEA nuclides table (Eng.) . The appeal date was July 7, 2010. Archived February 6, 2011.
- ↑ The specific activity of nuclides was calculated using the half-lives and probabilities of spontaneous fission given in the table.
- ↑ 1 2 3 4 5 6 7 E. S. Palshin, B. F. Myasoedov, A. V. Davydov. Analytical chemistry of protactinium. - M .: "Science", 1968. - 241 p. - (Analytical chemistry of elements). - 2200 copies
- ↑ Ed. Col .: I. P. Alimarin, A. K. Babko, A. I. Busev, E. E. Weinstein et al. Analytical chemistry of uranium / Chap. Ed .: A. P. Vinogradov. - M .: Publishing House of the Academy of Sciences of the USSR, 1962. - 424 p. - (Analytical chemistry of elements). - 4000 copies
- ↑ Table of elements, their compounds, isotopes (Inaccessible link) . The appeal date was July 7, 2010. Archived February 6, 2011.
- ↑ A. Kornyshev. Uranium exporters waiting for the atomic boom (rus.) // Kommersant . - 2005. - Vol. 19 (3103) .
- ↑ 1 2 3 4 5 6 7 8 9 Inorganic chemistry in three volumes / Ed. Yu. D. Tretyakov. - M .: Publishing Center "Academy", 2007. - T. 3. - 400 p. - (Chemistry of transition elements). - 3000 copies - ISBN 5-7695-2533-9 .
- ↑ 1 2 3 4 5 F. Weigel, J. Katz, G. Seaborg, and others. Actinide Chemistry = The Chemistry of the Actinide Elements / Trans. from English by ed. J. Katz, G. Seaborg, L. Mors. - M .: "The World", 1997. - T. 2. - 664 p. - (Chemistry of actinides). - 500 copies - ISBN 5-03-001885-9 .
- ↑ 1 2 Chapters. ed. I. L. Knunyants et al. Brief Chemical Encyclopedia. - M .: State Scientific Publishing House "Soviet Encyclopedia", 1961. - T. 1. - 1263 p. - 70 000 copies
- ↑ In square brackets is the mass number of the most long-lived isotope
- ↑ Arnold F. Holleman, Nils Wiberg. = Lehrbuch der Anorganischen Chemie. - 102. - Berlin: de Gruyter, 2007. - T. 2. - p. 1956. - ISBN 978-3-11-017770-1 .
- ↑ CRC Handbook of Chemistry and Physics / Ed .: David R. Lide; William M. Haynes. - 90th ed. - London: CRC Press, 2009. - ISBN 9781420090840 , 1420090844. (unavailable link)
- ↑ For α-modification
- ↑ For β-form
- ↑ 1 2 3 Trans. from English language ed. B. A. Nadyktova and L. F. Timofeeva. Plutonium. - Sarov: RFNC-VNIIEF, 2003. - V. 1. - 292 p. - (Fundamental problems). - 500 copies - ISBN 5-9515-00-24-9 .
- ↑ M.S. Milyukova, N.I. Gusev, I.G. Sentyurin, I.S. Sklyarenko. Analytical chemistry of plutonium. - M .: "Science", 1965. - 447 p. - (Analytical chemistry of elements). - 3400 copies
- ↑ 1 2 Information from webelements.com (English) .
- ↑ 1 2 Table of inorganic and coordination chemical compounds . - The main characteristics of the compounds of various elements are shown. The appeal date is July 11, 2010. Archived August 24, 2011.
- ↑ According to other data, cubic curium single oxide has an olive color. See Curium Compounds on XuMuK.ru . The appeal date was July 11, 2010. Archived February 6, 2011.
- ↑ The influence of the atmosphere in which the formation of this compound occurs on the lattice parameters is noted. Changes in the lattice parameters and its type may reflect small deviations from stoichiometry as a result of oxidation or reduction of a part of trivalent California. Cubic California (III) oxide is considered to be the “main” compound.
- ↑ Bartolomey G. G., Baibakov V. D., Alkhutov M. S., Bat A. A. Fundamentals of the Theory and Methods of Calculation of Nuclear Power Reactors. - M .: Energoatomizdat, 1982. - 512 p.
- ↑ Sergey Popov, Alexander Sergeev. Ecumenical Alchemy (Rus.) // Around the World Magazine: article. - “Around the World”, 2008. - Vol. 2811 . - № 4 .
- ↑ Marina Chadeeva. The universe of their own hands: People like gods . Popular Mechanics (October 2004). The date of circulation is January 3, 2011. Archived February 6, 2011.
Literature
- Greenwood N.N., Ernsho A. Actinides and transactinide elements // Chemistry of elements = Chemistry of the elements / Trans. from English ed. count - Tutorial. - M .: Bean. Laboratory of Knowledge, 2008. - V. 2. - 607 p. - (The best foreign textbook. In 2 volumes). - 2000 copies - ISBN 978-5-94774-373-9 .
- Gregory R. Choppin, Jan-Olov Liljenzin, Jan Rydberg. Radiochemistry and Nuclear Chemistry . - 3rd ed. - Butterworth-Heinemann, 2002. - 709 p. - ISBN 0750674636 , 9780750674638.
For additional reading
- Griveau Jean-Christophe, Colineau Éric. Superconductivity in transuranium elements and compounds // Comptes Rendus Physique. - 2014. - Vol. 15. - P. 599-615. - ISSN 16310705 . - DOI : 10.1016 / j.crhy.2014.07.001 .