How is uranium written in the periodic table? Chemical element uranium: properties, characteristics, formula. Mining and use of uranium. Electronic structure of the uranium atom

A discovery on a planetary scale. This can be called the discovery of Uranus by scientists. The planet was discovered in 1781.

Its discovery became the reason for naming one of elements of the periodic table. Uranus metal was isolated from resin blende in 1789.

The hype around the new planet had not yet subsided, therefore, the idea of ​​​​naming the new substance lay on the surface.

At the end of the 18th century there was no concept of radioactivity. Meanwhile, this is the main property of terrestrial uranium.

Scientists who worked with him were exposed to radiation without knowing it. Who was the pioneer, and what other properties of the element are, we will tell further.

Properties of uranium

Uranium - element, discovered by Martin Klaproth. He fused resin with caustic. The fusion product was incompletely soluble.

Klaproth realized that the supposed , and are not present in the composition of the mineral. Then, the scientist dissolved the blende in .

Green hexagons fell out of the solution. The chemist exposed them to yellow blood, that is, potassium hexacyanoferrate.

A brown precipitate precipitated from the solution. Klaproth restored this oxide with linseed oil and calcined it. The result was a powder.

I had to calcinate it already by mixing it with brown. Grains of new metal were found in the sintered mass.

Later it turned out that it was not pure uranium, and its dioxide. The element was obtained separately only 60 years later, in 1841. And another 55 years later, Antoine Becquerel discovered the phenomenon of radioactivity.

Radioactivity of uranium due to the ability of the element’s nucleus to capture neutrons and fragment. At the same time, impressive energy is released.

It is determined by the kinetic data of radiation and fragments. It is possible to ensure continuous fission of nuclei.

The chain reaction is started when natural uranium is enriched with its 235th isotope. It’s not like it’s added to metal.

On the contrary, the low-radioactive and ineffective 238th nuclide, as well as the 234th, are removed from the ore.

Their mixture is called depleted, and the remaining uranium is called enriched. This is exactly what industrialists need. But we’ll talk about this in a separate chapter.

Uranus radiates, both alpha and beta with gamma rays. They were discovered by seeing the effect of metal on a photographic plate wrapped in black.

It became clear that the new element was emitting something. While the Curies were investigating what exactly, Maria received a dose of radiation that caused the chemist to develop blood cancer, from which the woman died in 1934.

Beta radiation can destroy not only the human body, but also the metal itself. What element is formed from uranium? Answer: - brevy.

Otherwise it is called protactinium. Discovered in 1913, just during the study of uranium.

The latter turns into brevium without external influences and reagents, only from beta decay.

Externally uranium – chemical element- colors with a metallic sheen.

This is what all actinides look like, to which substance 92 belongs. The group starts with number 90 and ends with number 103.

Standing at the top of the list radioactive element uranium, manifests itself as an oxidizing agent. Oxidation states can be 2nd, 3rd, 4th, 5th, 6th.

That is, the 92nd metal is chemically active. If you grind uranium into powder, it will spontaneously ignite in air.

In its usual form, the substance will oxidize upon contact with oxygen, becoming covered with an iridescent film.

If you bring the temperature to 1000 degrees Celsius, chem. uranium element connect with . A metal nitride is formed. This substance is yellow in color.

Throw it into water and it will dissolve, just like pure uranium. All acids also corrode it. The element displaces hydrogen from organic elements.

Uranium also pushes it out of salt solutions, , , , . If such a solution is shaken, particles of the 92nd metal will begin to glow.

Uranium salts unstable, disintegrate in light or in the presence of organic matter.

The element is perhaps only indifferent to alkalis. The metal does not react with them.

Discovery of uranium- this is detection above heavy element. Its mass makes it possible to isolate the metal, or more precisely, the minerals with it, from the ore.

It is enough to crush it and pour it into water. The uranium particles will settle first. This is where metal mining begins. Details in the next chapter.

Uranium mining

Having received a heavy sediment, industrialists leach the concentrate. The goal is to convert the uranium into solution. Sulfuric acid is used.

An exception is made for tar. This mineral is not soluble in acid, therefore alkalis are used. The secret of difficulties is in the 4-valent state of uranium.

Acid leaching also does not work with,. In these minerals, the 92nd metal is also 4-valent.

This is treated with hydroxide, known as caustic soda. In other cases, oxygen purge is good. There is no need to stock up on sulfuric acid separately.

It is enough to heat the ore with sulfide minerals to 150 degrees and direct an oxygen stream at it. This leads to the formation of acid, which washes away Uranus.

Chemical element and its application associated with pure forms of metal. To remove impurities, sorption is used.

It is carried out on ion exchange resins. Extraction with organic solvents is also suitable.

All that remains is to add alkali to the solution to precipitate ammonium uranates, dissolve them in nitric acid and subject them to.

The result will be oxides of the 92nd element. They are heated to 800 degrees and reduced with hydrogen.

The final oxide is converted to uranium fluoride, from which pure metal is obtained by calcium-thermal reduction. , as you can see, is not a simple one. Why try so hard?

Applications of uranium

The 92nd metal is the main fuel of nuclear reactors. A lean mixture is suitable for stationary ones, and for power plants an enriched element is used.

The 235th isotope is also the basis of nuclear weapons. Secondary nuclear fuel can also be obtained from metal 92.

Here it is worth asking the question, what element does uranium transform into?. From its 238th isotope, , is another radioactive, superheavy substance.

At the very 238th uranium great half life, lasts 4.5 billion years. Such long-term destruction leads to low energy intensity.

If we consider the use of uranium compounds, its oxides are useful. They are used in the glass industry.

Oxides act as dyes. Can be obtained from pale yellow to dark green. IN ultraviolet rays the material fluoresces.

This property is used not only in glasses, but also in uranium glazes for. Uranium oxides in them range from 0.3 to 6%.

As a result, the background is safe and does not exceed 30 microns per hour. Photo of uranium elements, or rather, products with his participation, are very colorful. The glow of glass and dishes attracts the eye.

Uranium price

For a kilogram of unenriched uranium oxide they give about 150 dollars. Peak values ​​were observed in 2007.

Then the cost reached 300 dollars per kilo. The development of uranium ores will remain profitable even at a price of 90-100 conventional units.

Who discovered the element uranium, did not know what its reserves were in the earth's crust. Now, they are counted.

Large deposits with a profitable production price will be depleted by 2030.

If new deposits are not discovered, or alternatives to the metal are not found, its cost will creep up.

Nuclear technologies are largely based on the use of radiochemistry methods, which in turn are based on the nuclear physical, physical, chemical and toxic properties of radioactive elements.

In this chapter we will limit ourselves brief description properties of the main fissile isotopes - uranium and plutonium.

Uranus

Uranus ( uranium) U - element of the actinide group, 7-0th period of the periodic system, Z=92, atomic mass 238.029; the heaviest found in nature.

There are 25 known isotopes of uranium, all of them radioactive. The easiest 217U (Tj/ 2 =26 ms), the heaviest 2 4 2 U (7 T J / 2 =i6.8 min). There are 6 nuclear isomers. Natural uranium contains three radioactive isotopes: 2 8 and (99, 2 739%, Ti/ 2 = 4.47109 l), 2 35U (0.7205%, G,/2 = 7.04-109 years) and 2 34U ( 0.0056%, Ti/ 2=2.48-yuz l). The specific radioactivity of natural uranium is 2.48104 Bq, divided almost in half between 2 34 U and 288 U; 2 35U makes a small contribution (the specific activity of the 2 zi isotope in natural uranium is 21 times less than the activity of 2 3 8 U). Thermal neutron capture cross-sections are 46, 98 and 2.7 barn for 2 zzi, 2 35U and 2 3 8 U, respectively; division section 527 and 584 barn for 2 zzi and 2 z 8 and, respectively; natural mixture of isotopes (0.7% 235U) 4.2 barn.

Table 1. Nuclear physical properties 2 z9 Ri and 2 35Ts.

Table 2. Neutron capture 2 35Ts and 2 z 8 C.

Six isotopes of uranium are capable of spontaneous fission: 282 U, 2 zzi, 234 U, 235 U, 2 z 6 i and 2 z 8 i. The natural isotopes 2 33 and 2 35 U fission under the influence of both thermal and fast neutrons, and 2 3 8 nuclei are capable of fission only when they capture neutrons with an energy of more than 1.1 MeV. When capturing neutrons with lower energy, the 288 U nuclei first transform into 2 -i9U nuclei, which then undergo p-decay and transform first into 2 -"*9Np, and then into 2 39Pu. The effective cross sections for the capture of thermal neutrons of 2 34U, 2 nuclei 35U and 2 з 8 and are equal to 98, 683 and 2.7-barn, respectively. The full division of 2 35U results in a “thermal energy equivalent” of 2-107 kWh/kg. nuclear fuel They use the isotopes 2 35U and 2 zi, which are capable of supporting a fission chain reaction.

Nuclear reactors produce n artificial isotopes of uranium with mass numbers 227-^240, of which the longest-lived is 233U (7 V 2 =i.62 *io 5 years); it is obtained by neutron irradiation of thorium. In the super-powerful neutron fluxes of a thermonuclear explosion, uranium isotopes with mass numbers of 239^257 are born.

Uran-232- technogenic nuclide, a-emitter, T x / 2=68.9 years, parent isotopes 2 h 6 Pu(a), 23 2 Np(p*) and 23 2 Ra(p), daughter nuclide 228 Th. The intensity of spontaneous fission is 0.47 divisions/s kg.

Uranium-232 is formed as a result of the following decays:

P + -decay of nuclide *3 a Np (Ti/ 2 =14.7 min):

In the nuclear industry 2 3 2 U is generated as by-product during the synthesis of the fissile (weapon-grade) nuclide 2 zzi in the thorium fuel cycle. When 2 3 2 Th is irradiated with neutrons, the main reaction occurs:

and a two-step side reaction:

The production of 232 U from thorium occurs only with fast neutrons (E„>6 MeV). If the starting substance contains 2 3°TH, then the formation of 2 3 2 U is complemented by the reaction: 2 3°TH + u-> 2 3'TH. This reaction occurs using thermal neutrons. Generation of 2 3 2 U is undesirable for a number of reasons. It is suppressed by using thorium with a minimum concentration of 2 3°TH.

The decay of 2 × 2 occurs in the following directions:

A decay in 228 Th (probability 10%, decay energy 5.414 MeV):

the energy of emitted alpha particles is 5.263 MeV (in 31.6% of cases) and 5.320 MeV (in 68.2% of cases).

• - spontaneous fission (probability less than ~ 12%);
• - cluster decay with the formation of nuclide 28 Mg (probability of decay less than 5*10" 12%):

Cluster decay with the formation of nuclide 2

Uranium-232 is the founder of a long decay chain, which includes nuclides - emitters of hard y-quanta:

^U-(3.64 days, a,y)-> 220 Rn-> (55.6 s, a)-> 21b Po->(0.155 s, a)-> 212 Pb->(10.64 hours , p, y) -> 212 Bi -> (60.6 m, p, y) -> 212 Po a, y) -> 208x1, 212 Po -> (3 "Yu' 7 s, a) -> 2o8 Pb (stab), 2o8 T1->(3.06 m, p, y-> 2o8 Pb.

The accumulation of 2 3 2 U is inevitable during the production of 2 zi in the thorium energy cycle. Intense y-radiation arising from the decay of 2 3 2 U hinders the development of thorium energy. What is unusual is that the even isotope 2 3 2 11 has a high fission cross section under the influence of neutrons (75 barns for thermal neutrons), as well as a high neutron capture cross section - 73 barns. 2 3 2 U is used in the radioactive tracer method in chemical research.

2 h 2 and is the founder of a long decay chain (according to the 2 h 2 T scheme), which includes nuclides emitters of hard y-quanta. The accumulation of 2 3 2 U is inevitable during the production of 2 zi in the thorium energy cycle. Intense y-radiation arising from the decay of 232 U hinders the development of thorium energy. What is unusual is that the even isotope 2 3 2 U has a high fission cross section under the influence of neutrons (75 barns for thermal neutrons), as well as a high neutron capture cross section - 73 barns. 2 3 2 U is often used in the radioactive tracer method in chemical and physical research.

Uran-233- man-made radionuclide, a-emitter (energy 4.824 (82.7%) and 4.783 MeV (14.9%)), Tvi= 1.585105 years, parent nuclides 2 37Pu(a)-? 2 33Np(p +)-> 2 ззРа(р), daughter nuclide 22 9Th. 2 zzi is obtained in nuclear reactors from thorium: 2 z 2 Th captures a neutron and turns into 2 zzT, which decays into 2 zzRa, and then into 2 zzi. The nuclei of 2 zi (odd isotope) are capable of both spontaneous fission and fission under the influence of neutrons of any energy, which makes it suitable for the production of both atomic weapons and reactor fuel. Effective fission cross section is 533 barn, capture cross section is 52 barn, neutron yield: per fission event - 2.54, per absorbed neutron - 2.31. The critical mass of 2 zzi is three times less than the critical mass of 2 35U (-16 kg). The intensity of spontaneous fission is 720 divisions/s kg.

Uranium-233 is formed as a result of the following decays:

- (3 + -decay of nuclide 2 33Np (7^=36.2 min):

On an industrial scale, 2 zi is obtained from 2 32Th by irradiation with neutrons:

When a neutron is absorbed, the 2 zzi nucleus usually splits, but occasionally captures a neutron, turning into 2 34U. Although 2 zzi usually divides after absorbing a neutron, it sometimes retains a neutron, turning into 2 34U. The production of 2 zirs is carried out in both fast and thermal reactors.

From a weapons point of view, 2 ZZI is comparable to 2 39Pu: its radioactivity is 1/7 that of 2 39Pu (Ti/ 2 = 159200 liters versus 24100 liters for Pu), the critical mass of 2 zi is 60% higher than that of ^Pu (16 kg versus 10 kg), and the rate of spontaneous fission is 20 times higher (bth - ' versus 310 10). The neutron flux from 2 zzi is three times higher than that of 2 39Pi. Creating a nuclear charge based on 2 zi requires more effort than on ^Pi. The main obstacle is the presence of 232 U impurity in 2ZZI, the y-radiation of decay projects of which makes it difficult to work with 2ZZI and makes it easy to detect finished weapons. In addition, the short half-life of 2 3 2 U makes it an active source of alpha particles. 2 zi with 1% 232 and has three times stronger a-activity than weapons-grade plutonium and, accordingly, greater radiotoxicity. This a-activity causes the creation of neutrons in the light elements of the weapon charge. To minimize this problem, the presence of elements such as Be, B, F, Li should be minimal. The presence of a neutron background does not affect the operation of implosion systems, but cannon circuits require a high level of purity for light elements. The content of 23 2 U in weapons-grade 2 zis should not exceed 5 parts per million (0.0005%). In the fuel of thermal power reactors, the presence of 2 This is not harmful, and even desirable, because it reduces the possibility of using uranium for weapons purposes. After reprocessing the spent fuel and reusing the fuel, the 232U content reaches about 1+0.2%.

The decay of 2 zi occurs in the following directions:

A decay in 22 9Th (probability 10%, decay energy 4.909 MeV):

the energy of emitted yahr particles is 4.729 MeV (in 1.61% of cases), 4.784 MeV (in 13.2% of cases) and 4.824 MeV (in 84.4% of cases).

• - spontaneous division (probability
• - cluster decay with the formation of nuclide 28 Mg (decay probability less than 1.3*10_13%):

Cluster decay with the formation of the nuclide 24 Ne (decay probability 7.3-10-“%):

The decay chain of 2 zzi belongs to the neptunium series.

The specific radioactivity of 2 zi is 3.57-8 Bq/g, which corresponds to a-activity (and radiotoxicity) of -15% of plutonium. Just 1% 2 3 2 U increases radioactivity to 212 mCi/g.

Uran-234(Uranus II, UII) part of natural uranium (0.0055%), 2.445105 years, a-emitter (energy of a-particles 4.777 (72%) and

4.723 (28%) MeV), parent radionuclides: 2 h 8 Pu(a), 234 Pa(P), 234 Np(p +),

daughter isotope in 2 z”th.

Typically, 234 U is in equilibrium with 2 h 8 u, decaying and forming at the same rate. Approximately half of the radioactivity of natural uranium is contributed by 234U. Typically, 234U is obtained by ion-exchange chromatography of old preparations of pure 2 × 8 Pu. During a-decay, *zRi gives way to 2 34U, so old preparations 2 h 8 Ru are good sources 2 34U. yuo g 238Pi contain after a year 776 mg 2 34U, after 3 years

2.2 g 2 34U. The concentration of 2 34U in highly enriched uranium is quite high due to preferential enrichment with light isotopes. Since 2 34u is a strong y-emitter, there are restrictions on its concentration in uranium intended for processing into fuel. Increased level 234 and is acceptable for reactors, but reprocessed spent fuel already contains unacceptable levels of this isotope.

Decay of 234i occurs in the following directions:

A-decay at 2 3°Т (probability 100%, decay energy 4.857 MeV):

the energy of emitted alpha particles is 4.722 MeV (in 28.4% of cases) and 4.775 MeV (in 71.4% of cases).

• - spontaneous division (probability 1.73-10-9%).
• - cluster decay with the formation of nuclide 28 Mg (probability of decay 1.4-10%, according to other data 3.9-10%):

• - cluster decay with the formation of nuclides 2 4Ne and 26 Ne (decay probability 9-10", 2%, according to other data 2,3-10_11%):

The only known isomer is 2 34ti (Tx/ 2 = 33.5 μs).

The absorption cross section of 2 34U thermal neutrons is 100 barn, and for the resonance integral averaged over various intermediate neutrons it is 700 barn. Therefore, in thermal neutron reactors it is converted to fissile 235U at a faster rate than the much larger amount of 238U (with a cross-section of 2.7 barn) is converted to 2 39Ru. As a result, spent fuel contains less 2 34U than fresh fuel.

Uran-235 belongs to the 4P+3 family, capable of producing a fission chain reaction. This is the first isotope in which the reaction of forced nuclear fission under the influence of neutrons was discovered. By absorbing a neutron, 235U becomes 2 zbi, which is divided into two parts, releasing energy and emitting several neutrons. Fissile by neutrons of any energy and capable of spontaneous fission, the isotope 2 35U is part of natural ufan (0.72%), an a-emitter (energies 4.397 (57%) and 4.367 (18%) MeV), Ti/j=7.038-8 years, mother nuclides 2 35Pa, 2 35Np and 2 39Pu, daughter - 23Th. Spontaneous fission rate 2 3su 0.16 fission/s kg. When one 2 35U nucleus fissions, 200 MeV of energy = 3.210 p J is released, i.e. 18 TJ/mol=77 TJ/kg. The cross section of fission by thermal neutrons is 545 barns, and by fast neutrons - 1.22 barns, neutron yield: per fission act - 2.5, per absorbed neutron - 2.08.

Comment. The cross section for slow neutron capture to produce the isotope 2 sii (oo barn), so that the total slow neutron absorption cross section is 645 barn.

• - spontaneous fission (probability 7*10~9%);
• - cluster decay with the formation of nuclides 2 °Ne, 2 5Ne and 28 Mg (the probabilities, respectively, are 8-io_10%, 8-kg 10%, 8*10",0%):

Rice. 1.

The only known isomer is 2 35n»u (7/ 2 = 2b min).

Specific activity 2 35C 7.77-4 Bq/g. The critical mass of weapons-grade uranium (93.5% 2 35U) for a ball with a reflector is 15-7-23 kg.

Fission 2 » 5U is used in atomic weapons, for energy production and for the synthesis of important actinides. The chain reaction is maintained by the excess of neutrons produced during the fission of 2 35C.

Uran-236 found naturally on Earth in trace quantities (there is more of it on the Moon), a-emitter (?

Rice. 2. Radioactive family 4/7+2 (including -з 8 и).

In an atomic reactor, 2 sz absorbs a thermal neutron, after which it fissions with a probability of 82%, and with a probability of 18% it emits a y-quantum and turns into 2 sb and (for 100 fissioned nuclei 2 35U there are 22 formed nuclei 2 3 6 U) . In small quantities it is part of fresh fuel; accumulates when uranium is irradiated with neutrons in a reactor, and is therefore used as a “signaling device” for spent nuclear fuel. 2 hb and is formed as a by-product during the separation of isotopes by gas diffusion during the regeneration of used nuclear fuel. 236 U is a neutron poison formed in a power reactor; its presence in nuclear fuel is compensated for by a high level of enrichment 2 35 U.

2 z b and is used as a tracer of mixing ocean waters.

Uranium-237,T&= 6.75 days, beta and gamma emitter, can be obtained from nuclear reactions:

Detection 287 and carried out along lines with Ey= o,ob MeV (36%), 0.114 MeV (0.06%), 0.165 MeV (2.0%), 0.208 MeV (23%)

237U is used in the radiotracer method in chemical research. Measuring the concentration (2-4°Am) in fallout from atomic weapons tests provides valuable information about the type of charge and the equipment used.

Uran-238- belongs to the 4P+2 family, is fissile by high-energy neutrons (more than 1.1 MeV), capable of spontaneous fission, forms the basis of natural uranium (99.27%), a-emitter, 7’; /2=4>468-109 years, directly decays into 2 34Th, forms a number of genetically related radionuclides, and after 18 products turns into 206 Рb. Pure 2 3 8 U has a specific radioactivity of 1.22-104 Bq. The half-life is very long - about 10 16 years, so the probability of fission in relation to the main process - the emission of an alpha particle - is only 10" 7. One kilogram of uranium gives only 10 spontaneous fissions per second, and during the same time alpha particles emit 20 million nuclei. Mother nuclides: 2 4 2 Pu(a), *38ra(p-) 234Th, daughter T,/ 2 = 2 :i 4 Th.

Uranium-238 is formed as a result of the following decays:

2 (V0 4) 2 ] 8H 2 0. Among the secondary minerals, hydrated calcium uranyl phosphate Ca(U0 2) 2 (P0 4) 2 -8H 2 0 is common. Often uranium in minerals is accompanied by other useful elements - titanium, tantalum, rare earths. Therefore, it is natural to strive for complex processing of uranium-containing ores.

Basic physical properties of uranium: atomic mass 238.0289 amu. (g/mol); atomic radius 138 pm (1 pm = 12 m); ionization energy (first electron 7.11 eV; electronic configuration -5f36d‘7s 2; oxidation states 6, 5, 4, 3; GP l = 113 2, 2 °; T t,1=3818°; density 19.05; specific heat capacity 0.115 JDKmol); tensile strength 450 MPa, heat of fusion 12.6 kJ/mol, heat of evaporation 417 kJ/mol, specific heat 0.115 J/(mol-K); molar volume 12.5 cm3/mol; characteristic Debye temperature © D =200K, temperature of transition to the superconducting state about.68K.

Uranium is a heavy, silvery-white, shiny metal. It is slightly softer than steel, malleable, flexible, has slight paramagnetic properties, and is pyrophoric in powder form. Uranium has three allotropic forms: alpha (orthorhombic, a-U, lattice parameters 0=285, b= 587, c=49b pm, stable up to 667.7°), beta (tetragonal, p-U, stable from 667.7 to 774.8°), gamma (with a cubic body-centered lattice, y-U, existing from 774.8° to melting points, frm=ii34 0), at which uranium is most malleable and convenient for processing.

At room temperature the orthorhombic a-phase is stable, the prismatic structure consists of wavy atomic layers parallel to the plane ABC, in an extremely asymmetrical prismatic lattice. Within layers, atoms are tightly connected, while the strength of bonds between atoms in adjacent layers is much weaker (Figure 4). This anisotropic structure makes it difficult to alloy uranium with other metals. Only molybdenum and niobium create solid-phase alloys with uranium. However, uranium metal can interact with many alloys, forming intermetallic compounds.

In the range 668^775° there is (3-uranium. The tetragonal type lattice has a layered structure with layers, parallel to the plane ab in positions 1/4С, 1/2 With and 3/4C of the unit cell. At temperatures above 775°, y-uranium with a body-centered cubic lattice is formed. The addition of molybdenum allows the y-phase to be present at room temperature. Molybdenum forms a wide range of solid solutions with y-uranium and stabilizes the y-phase at room temperature. y-Uranium is much softer and more malleable than the brittle a- and (3-phases.

Neutron irradiation has a significant impact on the physical and mechanical properties of uranium, causing an increase in the size of the sample, a change in shape, as well as a sharp deterioration in the mechanical properties (creep, embrittlement) of uranium blocks during the operation of a nuclear reactor. The increase in volume is due to the accumulation in uranium during fission of impurities of elements with a lower density (translation 1% uranium into fragmentation elements increases the volume by 3.4%).

Rice. 4. Some crystal structures of uranium: a - a-uranium, b - p-uranium.

The most common methods for obtaining uranium in the metallic state are the reduction of their fluorides with alkali or alkaline earth metals or the electrolysis of molten salts. Uranium can also be obtained by metallothermal reduction from carbides with tungsten or tantalum.

The ability to easily donate electrons determines restorative properties uranium and its great chemical activity. Uranium can interact with almost all elements except noble gases, acquiring oxidation states +2, +3, +4, +5, +6. In solution the main valence is 6+.

Rapidly oxidizing in air, metallic uranium is covered with an iridescent film of oxide. Fine uranium powder spontaneously ignites in air (at temperatures of 1504-175°), forming and;) Ov. At 1000°, uranium combines with nitrogen, forming yellow uranium nitride. Water can react with metal, slowly at low temperatures and quickly at high temperatures. Uranium reacts violently with boiling water and steam to release hydrogen, which forms a hydride with uranium

This reaction is more energetic than the combustion of uranium in oxygen. This chemical activity of uranium makes it necessary to protect uranium in nuclear reactors from contact with water.

Uranium dissolves in hydrochloric, nitric and other acids, forming U(IV) salts, but does not interact with alkalis. Uranium displaces hydrogen from inorganic acids and salt solutions of metals such as mercury, silver, copper, tin, platinum and gold. When shaken vigorously, the metal particles of uranium begin to glow.

Features of the structure of the electron shells of the uranium atom (presence of ^/-electrons) and some of its physicochemical characteristics serve as the basis for classifying uranium as an actinide. However, there is a chemical analogy between uranium and Cr, Mo and W. Uranium is highly reactive and reacts with all elements except noble gases. In the solid phase, examples of U(VI) are uranyl trioxide U0 3 and uranyl chloride U0 2 C1 2. Uranium tetrachloride UC1 4 and uranium dioxide U0 2

Examples of U(IV). Substances containing U(IV) are usually unstable and become hexavalent when exposed to air for a long time.

Six oxides are installed in the uranium-oxygen system: UO, U0 2, U 4 0 9, and 3 Ov, U0 3. They are characterized by a wide range of homogeneity. U0 2 is a basic oxide, while U0 3 is amphoteric. U0 3 - interacts with water to form a number of hydrates, the most important of which are diuranic acid H 2 U 2 0 7 and uranic acid H 2 1U 4. With alkalis, U0 3 forms salts of these acids - uranates. When U0 3 is dissolved in acids, salts of the doubly charged uranyl cation U0 2 a+ are formed.

Uranium dioxide, U0 2, of stoichiometric composition is brown. As the oxygen content in the oxide increases, the color changes from dark brown to black. Crystal structure of the CaF 2 type, A = 0.547 nm; density 10.96 g/cm"* (the highest density among uranium oxides). T , pl =2875 0 , Tk „ = 3450°, D#°298 = -1084.5 kJ/mol. Uranium dioxide is a semiconductor with hole conductivity and a strong paramagnetic. MPC = o.015 mg/m3. Insoluble in water. At a temperature of -200° it adds oxygen, reaching the composition U0 2>25.

Uranium (IV) oxide can be prepared by the following reactions:

Uranium dioxide exhibits only basic properties; it corresponds to the basic hydroxide U(OH) 4, which is then converted into hydrated hydroxide U0 2 H 2 0. Uranium dioxide slowly dissolves in strong non-oxidizing acids in the absence of atmospheric oxygen with the formation of III + ions:

U0 2 + 2H 2 S0 4 ->U(S0 4) 2 + 2H 2 0. (38)

It is soluble in concentrated acids, and the dissolution rate can be significantly increased by adding fluorine ion.

When dissolved in nitric acid, the formation of uranyl ion 1O 2 2+ occurs:

Triuran octaoxide U 3 0s (uranium oxide) is a powder whose color varies from black to dark green; when strongly crushed, it turns olive-green in color. Large black crystals leave green streaks on the porcelain. Three crystal modifications of U 3 0 are known h: a-U 3 C>8 - rhombic crystal structure (space group C222; 0 = 0.671 nm; 6 = 1.197 nm; c = o.83 nm; d =0.839 nm); p-U 3 0e - rhombic crystal structure (space group Stst; 0=0.705 nm; 6=1.172 nm; 0=0.829 nm. The beginning of decomposition is oooo° (transitions to 100 2), MPC = 0.075 mg/m3.

U 3 C>8 can be obtained by the reaction:

By calcination U0 2, U0 2 (N0 3) 2, U0 2 C 2 0 4 3H 2 0, U0 4 -2H 2 0 or (NH 4) 2 U 2 0 7 at 750 0 in air or in an oxygen atmosphere (p = 150+750 mmHg) obtain stoichiometrically pure U 3 08.

When U 3 0s is calcined at T>oooo°, it is reduced to 10 2 , but upon cooling in air it returns to U 3 0s. U 3 0e dissolves only in concentrated strong acids. In hydrochloric and sulfuric acids a mixture of U(IV) and U(VI) is formed, and in nitric acid - uranyl nitrate. Dilute sulfuric and hydrochloric acid react very weakly with U 3 Os even when heated; the addition of oxidizing agents (nitric acid, pyrolusite) sharply increases the dissolution rate. Concentrated H 2 S0 4 dissolves U 3 Os to form U(S0 4) 2 and U0 2 S0 4 . Nitric acid dissolves U 3 Oe to form uranyl nitrate.

Uranium trioxide, U0 3 - crystalline or amorphous substance bright yellow color. Reacts with water. MPC = 0.075 mg/m3.

It is obtained by calcining ammonium polyuranates, uranium peroxide, uranyl oxalate at 300-500° and uranyl nitrate hexahydrate. This produces an orange powder of an amorphous structure with a density

6.8 g/cmz. The crystalline form of IU 3 can be obtained by oxidation of U 3 0 8 at temperatures of 450°h-750° in a flow of oxygen. There are six crystalline modifications of U0 3 (a, (3, y> §> ?, n) - U0 3 is hygroscopic and in moist air turns into uranyl hydroxide. Its heating at 520°-^6oo° gives a compound of composition 1U 2>9, further heating to 6oo° allows one to obtain U 3 Os.

Hydrogen, ammonia, carbon, alkali and alkaline earth metals reduce U0 3 to U0 2. When passing a mixture of gases HF and NH 3, UF 4 is formed. In its highest valence, uranium exhibits amphoteric properties. When acids act on U0 3 or its hydrates, uranyl salts (U0 2 2+) are formed, colored yellow. green color:

Most uranyl salts are highly soluble in water.

When fused with alkalis, U0 3 forms uranic acid salts - MDKH uranates:

With alkaline solutions, uranium trioxide forms salts of polyuranic acids - polyuranates DHM 2 0y1U 3 pH^O.

Uranic acid salts are practically insoluble in water.

The acidic properties of U(VI) are less pronounced than the basic ones.

Uranium reacts with fluorine at room temperature. The stability of higher halides decreases from fluorides to iodides. Fluorides UF 3, U4F17, U2F9 and UF 4 are non-volatile, and UFe is volatile. The most important fluorides are UF 4 and UFe.

Ftppippiyanir okgilya t"yanya ppptrkart according to the practice:

The reaction in a fluidized bed is carried out according to the equation:

It is possible to use fluorinating agents: BrF 3, CC1 3 F (Freon-11) or CC1 2 F 2 (Freon-12):

Uranium fluoride (1U) UF 4 (“green salt”) is a bluish-greenish to emerald-colored powder. G 11L = yuz6°; Гк,«,.=-1730°. DN° 29 8= 1856 kJ/mol. The crystal structure is monoclinic (sp. gp. C2/s; 0=1.273 nm; 5=1.075 nm; 0=0.843 nm; d= 6.7 nm; p=12b°20"; density 6.72 g/cm3. UF 4 is a stable, inactive, non-volatile compound, poorly soluble in water. The best solvent for UF 4 is fuming perchloric acid HC10 4. Dissolves in oxidizing acids to form a uranyl salt ; quickly dissolves in a hot solution of Al(N0 3) 3 or AlC1 3, as well as in a solution of boric acid acidified with H 2 S0 4, HC10 4 or HC1. Complexing agents that bind fluoride ions, for example, Fe3 +, Al3 +. or boric acid, also contribute to the dissolution of UF 4. With fluorides of other metals it forms a number of poorly soluble double salts (MeUFe, Me 2 UF6, Me 3 UF 7, etc. NH 4 UF 5 is of industrial importance).

U(IV) fluoride is an intermediate product in the preparation

both UF6 and uranium metal.

UF 4 can be obtained by reactions:

or by electrolytic reduction of uranyl fluoride.

Uranium hexafluoride UFe - at room temperature, ivory-colored crystals with a high refractive index. Density

5.09 g/cmz, density of liquid UFe - 3.63 g/cmz. Volatile compound. Tvoag = 5^>5°> Gil=b4.5° (under pressure). Pressure saturated vapors reaches the atmosphere at 560°. Enthalpy of formation AH° 29 8 = -211b kJ/mol. The crystal structure is orthorhombic (space group. Rpt; 0=0.999 nm; fe= 0.8962 nm; c=o.5207 nm; d 5.060 nm (25 0). MPC - 0.015 mg/m3. From solid state UF6 can sublimate from the solid phase into a gas, bypassing the liquid phase over a wide range of pressures. Heat of sublimation at 50 0 50 kJ/mg. The molecule has no dipole moment, so UF6 does not associate. UFr vapor is an ideal gas.

It is obtained by the action of fluorine on its U compound:

In addition to gas-phase reactions, there are also liquid-phase reactions

producing UF6 using halofluorides, for example

There is a way to obtain UF6 without the use of fluorine - by oxidation of UF 4:

UFe does not react with dry air, oxygen, nitrogen and C0 2, but upon contact with water, even traces of it, it undergoes hydrolysis:

It interacts with most metals, forming their fluorides, which complicates the methods of its storage. Suitable vessel materials for working with UF6 are: when heated, Ni, Monel and Pt, in the cold - also Teflon, absolutely dry quartz and glass, copper and aluminum. At temperatures of 25°C 0 forms complex compounds with fluorides alkali metals and silver type 3NaFUFr>, 3KF2UF6.

It dissolves well in various organic liquids, inorganic acids and all halofluorides. Inert to dry 0 2, N 2, C0 2, C1 2, Br 2. UFr is characterized by reduction reactions with most pure metals. With hydrocarbons and others organic substances UF6 reacts vigorously, so closed containers containing UFe can explode. UF6 in the range of 25 -r100° forms complex salts with fluorides of alkali and other metals. This property is used in technology for selective extraction of UF

Uranium hydrides UH 2 and UH 3 occupy an intermediate position between salt-like hydrides and hydrides of the type solid solutions hydrogen in metal.

When uranium reacts with nitrogen, nitrides are formed. IN U-N system four phases are known: UN (uranium nitride), a-U 2 N 3 (sesquinitride), p- U 2 N 3 and UN If90. It is not possible to achieve the composition UN 2 (dinitride). Syntheses of uranium mononitride UN are reliable and well controlled, which are best carried out directly from the elements. Uranium nitrides are powdery substances, the color of which varies from dark gray to gray; look like metal. UN has a cubic face-centered crystal structure, like NaCl (0 = 4.8892 A); (/=14.324, 7^=2855°, stable in vacuum up to 1700 0. It is prepared by reacting U or U hydride with N 2 or NH 3 , decomposition of higher U nitrides at 1300° or their reduction with uranium metal. U 2 N 3 is known in two polymorphic modifications: cubic a and hexagonal p (0 = 0.3688 nm, 6 = 0.5839 nm), releases N 2 in a vacuum above 8oo°. It is obtained by reducing UN 2 with hydrogen. UN2 dinitride is synthesized by reacting U with N2 under high N2 pressure. Uranium nitrides are easily soluble in acids and alkali solutions, but are decomposed by molten alkalis.

Uranium nitride is obtained by two-stage carbothermic reduction of uranium oxide:

Heating in argon at 7M450 0 for 10*20 hours

Uranium nitride of a composition close to dinitride, UN 2, can be obtained by exposing UF 4 to ammonia at high temperature and pressure.

Uranium dinitride decomposes when heated:

Uranium nitride, enriched at 2 35 U, has a higher fission density, thermal conductivity and melting point than uranium oxides - the traditional fuel of modern power reactors. It also has good mechanical properties and stability superior to traditional fuels. Therefore, this compound is considered as a promising basis for nuclear fuel in fast neutron reactors (generation IV nuclear reactors).

Comment. It is very useful to enrich UN by ‘5N, because .4 N tends to capture neutrons, generating the radioactive isotope 14 C through the (n,p) reaction.

Uranium carbide UC 2 (?-phase) - light gray with a metallic sheen crystalline substance. IN U-C system(uranium carbides) there are UC 2 (?-phase), UC 2 (b 2-phase), U 2 C 3 (e-phase), UC (b 2-phase) - uranium carbides. Uranium dicarbide UC 2 can be obtained by the reactions:

U + 2C^UC 2 (54v)

Uranium carbides are used as fuel for nuclear reactors; they are promising as fuel for space rocket engines.

Uranyl nitrate, uranyl nitrate, U0 2 (N0 3) 2 -6H 2 0. The role of the metal in this salt is played by the uranyl 2+ cation. Yellow crystals with a greenish tint, easily soluble in water. An aqueous solution is acidic. Soluble in ethanol, acetone and ether, insoluble in benzene, toluene and chloroform. When heated, the crystals melt and release HN0 3 and H 2 0. Crystalline hydrate is easily evaporated in air. A characteristic reaction is that under the action of NH 3 a yellow precipitate of ammonium uranium is formed.

Uranium is capable of forming metal organic compounds. Examples are cyclopentadienyl derivatives of the composition U(C 5 H 5) 4 and their halogen-substituted u(C 5 H 5) 3 G or u(C 5 H 5) 2 G 2.

IN aqueous solutions uranium is most stable in the oxidation state of U(VI) in the form of the uranyl ion U0 2 2+. To a lesser extent, it is characterized by the U(IV) state, but it can even occur in the U(III) form. The oxidation state of U(V) can exist as the IO2+ ion, but this state is rarely observed due to its tendency to disproportionation and hydrolysis.

In neutral and acidic solutions, U(VI) exists in the form of U0 2 2+ - uranyl ion, colored yellow. Well-soluble uranyl salts include nitrate U0 2 (N0 3) 2, sulfate U0 2 S0 4, chloride U0 2 C1 2, fluoride U0 2 F 2, acetate U0 2 (CH 3 C00) 2. These salts are isolated from solutions in the form of crystalline hydrates with different number water molecules. Slightly soluble uranyl salts are: oxalate U0 2 C 2 0 4, phosphates U0 2 HP0., and UO2P2O4, ammonium uranyl phosphate UO2NH4PO4, sodium uranyl vanadate NaU0 2 V0 4, ferrocyanide (U0 2) 2. The uranyl ion is characterized by a tendency to form complex compounds. Thus, complexes with fluorine ions of the -, 4- type are known; nitrate complexes ‘ and 2 *; sulfuric acid complexes 2 " and 4-; carbonate complexes 4 " and 2 ", etc. When alkalis act on solutions of uranyl salts, sparingly soluble precipitates of diuranates of the type Me 2 U 2 0 7 are released (monouranates Me 2 U0 4 are not isolated from solutions, they are obtained by fusion uranium oxides with alkalis). Polyuranates Me 2 U n 0 3 n+i are known (for example, Na 2 U60i 9).

U(VI) is reduced in acidic solutions to U(IV) by iron, zinc, aluminum, sodium hydrosulfite, and sodium amalgam. The solutions are colored green. Alkalis precipitate from them hydroxide U0 2 (0H) 2, hydrofluoric acid - fluoride UF 4 -2.5H 2 0, oxalic acid - oxalate U(C 2 0 4) 2 -6H 2 0. The U 4+ ion has a tendency to form complexes less than that of uranyl ions.

Uranium (IV) in solution is in the form of U 4+ ions, which are highly hydrolyzed and hydrated:

In acidic solutions, hydrolysis is suppressed.

Uranium (VI) in solution forms the uranyl oxocation - U0 2 2+ Numerous uranyl compounds are known, examples of which are: U0 3, U0 2 (C 2 H 3 0 2) 2, U0 2 C0 3 -2(NH 4) 2 C0 3 U0 2 C0 3, U0 2 C1 2, U0 2 (0H) 2, U0 2 (N0 3) 2, UO0SO4, ZnU0 2 (CH 3 C00) 4, etc.

Upon hydrolysis of uranyl ion, a number of multinuclear complexes are formed:

With further hydrolysis, U 3 0s(0H) 2 and then U 3 0 8 (0H) 4 2 - appear.

For high-quality detection of uranium, chemical, luminescent, radiometric and spectral analyzes. Chemical methods are predominantly based on the formation of colored compounds (for example, red-brown color of a compound with ferrocyanide, yellow with hydrogen peroxide, blue with arsenazo reagent). The luminescent method is based on the ability of many uranium compounds to produce a yellowish-greenish glow when exposed to UV rays.

Quantitative determination of uranium is carried out various methods. The most important of them are: volumetric methods, consisting of the reduction of U(VI) to U(IV) followed by titration with solutions of oxidizing agents; gravimetric methods - precipitation of uranates, peroxide, U(IV) cupferranates, hydroxyquinolate, oxalate, etc. followed by calcination at 00° and weighing U 3 0s; polarographic methods in nitrate solution make it possible to determine 10*7-g10-9 g of uranium; numerous colorimetric methods (for example, with H 2 0 2 in an alkaline medium, with the arsenazo reagent in the presence of EDTA, with dibenzoylmethane, in the form of a thiocyanate complex, etc.); luminescent method, which makes it possible to determine when fused with NaF to Yu 11 g uranium.

235U belongs to radiation hazard group A, the minimum significant activity is MZA = 3.7-10 4 Bq, 2 3 8 and - to group D, MZA = 3.7-6 Bq (300 g).

Uranus(lat. uranium), u, radioactive chemical element of group III of the Mendeleev periodic system, belongs to the family actinides, atomic number 92, atomic mass 238.029; metal. Natural U. consists of a mixture of three isotopes: 238 u - 99.2739% with a half-life t 1 / 2 = 4.51 10 9 years, 235 u - 0.7024% (t 1 / 2 = 7.13 10 8 years) and 234 u – 0.0057% (t 1 / 2 = 2.48 10 5 years). Of 11 artificial radioactive isotopes with mass numbers from 227 to 240 long-lived – 233 u (t 1 / 2 = 1.62 10 5 years); it is obtained by neutron irradiation of thorium. 238 u and 235 u are the ancestors of two radioactive series.

Historical reference. U. opened in 1789. chemist M. G. Klaproth and named him in honor of the planet Uranus, discovered by V. Herschel in 1781. In the metallic state, U. was obtained in 1841 by the French. chemist E. Peligo during the reduction of ucl 4 with potassium metal. Initially, U. was attributed atomic mass 120, and only in 1871 D.I. Mendeleev I came to the conclusion that this value should be doubled.

Long time uranium was of interest only to a narrow circle of chemists and found limited use in the production of paints and glass. With the discovery of the phenomenon radioactivity U. in 1896 and radium in 1898, industrial processing of uranium ores began in order to extract and use radium in scientific research and medicine. Since 1942, after the discovery in 1939 of the phenomenon of nuclear fission , U. became the main nuclear fuel.

Distribution in nature. U. is a characteristic element for the granite layer and sedimentary shell of the earth's crust. The average content of uranium in the earth's crust (clarke) is 2.5 10 -4% by weight, in acidic igneous rocks 3.5 10 -4%, in clays and shales 3.2 10 -4%, in basic rocks 5 · 10 -5%, in ultrabasic rocks of the mantle 3 · 10 -7%. U. migrates vigorously in cold and hot, neutral and alkaline waters in the form of simple and complex ions, especially in the form of carbonate complexes. Redox reactions play an important role in the geochemistry of uranium, since uranium compounds, as a rule, are highly soluble in waters with an oxidizing environment and poorly soluble in waters with a reducing environment (for example, hydrogen sulfide).

About 100 uranium minerals are known; 12 of them are of industrial importance . During geological history the carbon content in the earth's crust decreased due to radioactive decay; This process is associated with the accumulation of Pb and He atoms in the earth's crust. Radioactive decay of carbon plays an important role in the energetics of the earth's crust, being a significant source of deep heat.

Physical properties. U. is similar in color to steel and is easy to process. It has three allotropic modifications - a, b and g with phase transformation temperatures: a ® b 668.8 ± 0.4 ° C, b® g 772.2 ± 0.4 ° C; a-shape has a rhombic lattice a= 2.8538 å, b= 5.8662 å, With= 4.9557 å), b-form – tetragonal lattice (at 720 °C A = 10,759 , b= 5.656 å), g-shape – body-centered cubic lattice (at 850°c a = 3.538 å). Density of U. in a-form (25°c) 19.05 ± 0.2 g/cm 3 ,t pl 1132 ± 1°С; t kip 3818 °C; thermal conductivity (100–200°c), 28.05 Tue/(m· TO) , (200–400 °c) 29.72 Tue/(m· TO) ; specific heat capacity (25°c) 27.67 kJ/(kg· TO) ; electrical resistivity at room temperature is about 3 10 -7 ohm· cm, at 600°c 5.5 10 -7 ohm· cm; has superconductivity at 0.68 ± 0.02K; weak paramagnetic, specific magnetic susceptibility at room temperature 1.72 · 10 -6.

Mechanical properties U. depend on its purity, on the modes of mechanical and thermal treatment. The average value of the elastic modulus for cast U. 20.5 10 -2 Mn/m 2 tensile strength at room temperature 372–470 Mn/m 2 , strength increases after hardening from b - and g -phases; average Brinell hardness 19.6–21.6 10 2 Mn/m 2 .

Irradiation by a neutron flux (which occurs in nuclear reactor) changes the physical and mechanical properties of uranium: creep develops and fragility increases, deformation of products is observed, which forces the use of uranium in nuclear reactors in the form of various uranium alloys.

U. – radioactive element. Nuclei 235 u and 233 u fission spontaneously, as well as upon capture of both slow (thermal) and fast neutrons with an effective fission cross section of 508 10 -24 cm 2 (508 barn) and 533 10 -24 cm 2 (533 barn) respectively. 238u nuclei fission upon capturing only fast neutrons with an energy of at least 1 Mev; upon capture of slow neutrons, 238 u turns into 239 pu , whose nuclear properties are close to 235 u. Critical the mass of U. (93.5% 235 u) in aqueous solutions is less than 1 kg, for an open ball - about 50 kg, for a ball with a reflector - 15 - 23 kg; critical mass 233 u – approximately 1/3 of the critical mass 235 u.

Chemical properties. Configuration of the outer electron shell of the atom U. 7 s 2 6 d 1 5 f 3 . U. is a reactive metal; in compounds it exhibits oxidation states + 3, + 4, + 5, + 6, sometimes + 2; the most stable compounds are u (iv) and u (vi). In air it slowly oxidizes with the formation of a film of dioxide on the surface, which does not protect the metal from further oxidation. In a powdered state, U. is pyrophoric and burns with a bright flame. With oxygen it forms dioxide uo 2, trioxide uo 3 and a large number of intermediate oxides, the most important of which is u 3 o 8. These intermediate oxides have properties close to uo 2 and uo 3. At high temperatures uo 2 has a wide range of homogeneity from uo 1.60 to uo 2.27. With fluorine at 500–600°c it forms tetrafluoride (green needle-shaped crystals, slightly soluble in water and acids) and hexafluoride uf 6 (a white crystalline substance that sublimes without melting at 56.4°c); with sulfur – a number of compounds, of which highest value has us (nuclear fuel). When uranium reacts with hydrogen at 220°C, the hydride uh 3 is obtained; with nitrogen at temperatures from 450 to 700 °C and atmospheric pressure– nitride u 4 n 7, at a higher nitrogen pressure and the same temperature you can get un, u 2 n 3 and un 2; with carbon at 750–800°c – uc monocarbide, uc 2 dicarbide, and also u 2 c 3; forms alloys of various types with metals . U. slowly reacts with boiling water to form uo 2 and h 2, with water vapor - in the temperature range 150–250 ° C; soluble in hydrochloric and nitric acids, slightly soluble in concentrated hydrofluoric acid. U (vi) is characterized by the formation of the uranyl ion uo 2 2 + ; uranyl salts are yellow in color and are highly soluble in water and mineral acids; salts u (iv) are green and less soluble; uranyl ion is extremely capable of complex formation in aqueous solutions with both inorganic and organic substances; The most important for technology are carbonate, sulfate, fluoride, phosphate and other complexes. A large number of uranates (salts of uranic acid not isolated in pure form) are known, the composition of which varies depending on the conditions of production; All uranates have low solubility in water.

U. and its compounds are radiation and chemically toxic. Maximum permissible dose (MAD) for occupational exposure 5 rem in year.

Receipt. U. is obtained from uranium ores containing 0.05–0.5% u. The ores are practically not enriched, with the exception of a limited method of radiometric sorting based on the radiation of radium, which always accompanies uranium. Basically, ores are leached with solutions of sulfuric, sometimes nitric acids or soda solutions with the transfer of uranium into an acidic solution in the form of uo 2 so 4 or complex anions 4-, and into a soda solution - in the form of 4-. To extract and concentrate uranium from solutions and pulps, as well as to purify it from impurities, sorption on ion-exchange resins and extraction with organic solvents (tributyl phosphate, alkylphosphoric acids, amines) are used. Next, ammonium or sodium uranates or u (oh) 4 hydroxide are precipitated from the solutions by adding alkali. To receive connections high degree purity, technical products are dissolved in nitric acid and subjected to refining purification operations, the final products of which are uo 3 or u 3 o 8; these oxides are reduced at 650–800°c by hydrogen or dissociated ammonia to uo 2, followed by its conversion to uf 4 by treatment with gaseous hydrogen fluoride at 500–600°c. uf 4 can also be obtained by precipitation of crystalline hydrate uf 4 · nh 2 o with hydrofluoric acid from solutions, followed by dehydration of the product at 450°C in a stream of hydrogen. In industry, the main method of obtaining uranium from uf 4 is its calcium-thermal or magnesium-thermal reduction with the yield of uranium in the form of ingots weighing up to 1.5 tons. The ingots are refined in vacuum furnaces.

A very important process in uranium technology is the enrichment of its 235 u isotope above the natural content in ores or the isolation of this isotope in its pure form , since it is 235 u that is the main nuclear fuel; This is done by gas thermal diffusion, centrifugal and other methods based on the difference in masses 235 u and 238 u; in separation processes, uranium is used in the form of volatile hexafluoride uf 6. When obtaining highly enriched carbon or isotopes, their critical masses are taken into account; the most convenient way in this case is the reduction of uranium oxides with calcium; The resulting slag, cao, is easily separated from the carbon by dissolution in acids.

Powder metallurgy methods are used to produce powdered carbon dioxide, carbides, nitrides, and other refractory compounds.

Application. Metal U. or its compounds are used mainly as nuclear fuel in nuclear reactors. A natural or low-enriched mixture of carbon isotopes is used in stationary reactors of nuclear power plants; a highly enriched product is used in nuclear power plants or in fast neutron reactors. 235 u is the source nuclear energy V nuclear weapons. 238 u serves as a source of secondary nuclear fuel - plutonium.

V. M. Kulifeev.

Uranium in the body. In trace quantities (10 -5 –10 -5%) it is found in the tissues of plants, animals and humans. In plant ash (with a U content in the soil of about · 10 -4), its concentration is 1.5 · 10 -5%. To the greatest extent, uranium is accumulated by some fungi and algae (the latter actively participate in the biogenic migration of uranium along the chain water - aquatic plants - fish - humans). U. enters the body of animals and humans with food and water into the gastrointestinal tract, with air into the respiratory tract, and also through the skin and mucous membranes. U. compounds are absorbed in the gastrointestinal tract - about 1% of the incoming amount of soluble compounds and no more than 0.1% of sparingly soluble ones; 50% and 20% are absorbed in the lungs, respectively. U. is distributed unevenly in the body. The main depots (places of deposition and accumulation) are the spleen, kidneys, skeleton, liver and, when inhaling poorly soluble compounds, the lungs and bronchopulmonary lymph nodes. U. (in the form of carbonates and complexes with proteins) does not circulate in the blood for a long time. The U content in organs and tissues of animals and humans does not exceed 10 -7 y/y. Thus, the blood of cattle contains 1 10 -8 g/ml, liver 8 10 -8 y/y, muscles 4 10 -8 y/y, spleen 9 10 -8 y/y. The U content in human organs is: in the liver 6 10 -9 y/y, in the lungs 6 10 -9 –9 10 -9 g/g, in the spleen 4.7 10 -9 y/y, in blood 4 10 -9 g/ml, in the kidneys 5.3 10 -9 (cortical layer) and 1.3 10 -9 y/y(medullary layer), in bones 1 10 -9 y/y, in bone marrow 1 10 -9 y/y, in hair 1.3 10 -7 y/y. U. contained in bone tissue causes its constant irradiation (the half-life of U. from the skeleton is about 300 days) . The lowest concentrations of U are in the brain and heart (10 -10 y/y). Daily intake of U. from food and liquids – 1.9 10 -6 g, s air – 7 10 -9 G. The daily excretion of U from the human body is: with urine 0.5 · 10 -7 –5 · 10 -7, with feces – 1.4 · 10 -6 –1.8 · 10 -6 g, s hair – 2 10 -8 g.

According to the International Commission on Radiation Protection, the average U content in the human body is 9·10 -8 g. This value may vary for different regions. It is believed that U is necessary for the normal life of animals and plants, but its physiological functions have not been clarified.

G. P. Galibin.

Toxic effect Uranium is due to its chemical properties and depends on solubility: uranyl and other soluble uranium compounds are more toxic. Poisoning with uranium and its compounds is possible at enterprises for the extraction and processing of uranium raw materials and other industrial facilities where it is used in the technological process. When it enters the body, it affects all organs and tissues, being a general cellular poison. Signs of poisoning are due primarily to kidney damage (the appearance of protein and sugar in the urine, subsequent oliguria) , the liver and gastrointestinal tract are also affected. There are acute and chronic poisonings; the latter are characterized by gradual development and less severe symptoms. With chronic intoxication, hematopoietic disorders are possible, nervous system and others. It is believed that the molecular mechanism of action of U. is associated with its ability to suppress the activity of enzymes.

Prevention of poisoning: continuity of technological processes, use of sealed equipment, prevention of air pollution, treatment of wastewater before discharging it into water bodies, honey. monitoring the health status of workers and compliance with hygienic standards for the permissible content of U and its compounds in the environment.

V. F. Kirillov.

Lit.: The doctrine of radioactivity. History and modernity, ed. B. M. Kedrova, M., 1973; Petrosyants A. M., From scientific research to the nuclear industry, M., 1970; Emelyanov V.S., Evstyukhin A.I., Metallurgy of nuclear fuel, M., 1964; Sokursky Yu. N., Sterlin Ya. M., Fedorchenko V. A., Uranium and its alloys, M., 1971; Evseeva L. S., Perelman A. I., Ivanov K. E., Geochemistry of uranium in the hypergenetic zone, 2nd ed., M., 1974; Pharmacology and toxicology of uranium compounds, [trans. from English], vol. 2, M., 1951; Guskova V.N., Uranus. Radiation-hygienic characteristics, M., 1972; Andreeva O. S., Occupational hygiene when working with uranium and its compounds, M., 1960; Novikov Yu. V., Hygienic issues of studying the uranium content in the external environment and its effect on the body, M., 1974.

The article talks about when the chemical element uranium was discovered and in what industries this substance is used in our time.

Uranium is a chemical element of the energy and military industries

At all times, people have tried to find highly efficient energy sources, and ideally, to create the so-called. Unfortunately, the impossibility of its existence was theoretically proven and justified back in the 19th century, but scientists still never lost hope of realizing the dream of some kind of device that would be capable of delivering large amounts of “clean” energy for a very long time.

This was partially realized with the discovery of such a substance as uranium. The chemical element with this name formed the basis for the development of nuclear reactors, which in our time provide energy to entire cities, submarines, polar ships, etc. True, their energy cannot be called “pure”, but last years Many companies are developing compact “atomic batteries” based on tritium for wide sale - they have no moving parts and are safe for health.

However, in this article we will examine in detail the history of the discovery of the chemical element called uranium and the fission reaction of its nuclei.

Definition

Uranium is a chemical element that has atomic number 92 on the periodic table. Its atomic mass is 238.029. It is designated by the symbol U. Under normal conditions, it is a dense, heavy metal with a silvery color. If we talk about its radioactivity, then uranium itself is an element with weak radioactivity. It also does not include completely stable isotopes. And the most stable of the existing isotopes is considered to be uranium-338.

We have figured out what this element is, and now we will look at the history of its discovery.

Story

A substance such as natural uranium oxide has been known to people since ancient times, and ancient craftsmen used it to make glaze, which was used to cover various ceramics to waterproof vessels and other products, as well as their decoration.

An important date in the history of the discovery of this chemical element was 1789. It was then that the chemist and German by birth Martin Klaproth was able to obtain the first metallic uranium. And the new element received its name in honor of the planet discovered eight years earlier.

For almost 50 years, the uranium obtained at that time was considered a pure metal, however, in 1840, the French chemist Eugene-Melchior Peligo was able to prove that the material obtained by Klaproth, despite suitable external signs, was not a metal at all, but uranium oxide. A little later, the same Peligo received real uranium - a very heavy gray metal. It was then that the atomic weight of such a substance as uranium was determined for the first time. The chemical element was placed in 1874 by Dmitri Mendeleev in his famous periodic table of elements, with Mendeleev doubling the atomic weight of the substance. And only 12 years later it was experimentally proven that he was not mistaken in his calculations.

Radioactivity

But the truly widespread interest in this element in scientific circles began in 1896, when Becquerel discovered the fact that uranium emits rays, which were named after the researcher - Becquerel's rays. Later, one of the most famous scientists in this field, Marie Curie, called this phenomenon radioactivity.

The next important date in the study of uranium is considered to be 1899: it was then that Rutherford discovered that the radiation of uranium is inhomogeneous and is divided into two types - alpha and beta rays. And a year later, Paul Villar (Villard) discovered the third, last type known to us today radioactive radiation- so-called gamma rays.

Seven years later, in 1906, Rutherford, based on his theory of radioactivity, conducted the first experiments, the purpose of which was to determine the age of various minerals. These studies laid the foundation, among other things, for the formation of theory and practice

Uranium nuclear fission

But, probably, the most important discovery, thanks to which the widespread mining and enrichment of uranium for both peaceful and military purposes began, is the process of fission of uranium nuclei. This happened in 1938, the discovery was carried out by German physicists Otto Hahn and Fritz Strassmann. Later, this theory received scientific confirmation in the works of several more German physicists.

The essence of the mechanism they discovered was as follows: if you irradiate the nucleus of the uranium-235 isotope with a neutron, then, capturing a free neutron, it begins to fission. And, as we all now know, this process is accompanied by the release of a colossal amount of energy. This happens mainly due to kinetic energy radiation itself and nuclear fragments. So now we know how uranium nuclei fission occurs.

The discovery of this mechanism and its results is the starting point for the use of uranium for both peaceful and military purposes.

If we talk about its use for military purposes, then for the first time the theory that it is possible to create conditions for such a process as the continuous reaction of fission of the uranium nucleus (since for detonation nuclear bomb enormous energy is required), the Soviet physicists Zeldovich and Khariton proved. But in order to create such a reaction, uranium must be enriched, since in its normal state it does not possess the necessary properties.

We have become familiar with the history of this element, now let’s figure out where it is used.

Applications and types of uranium isotopes

After the discovery of a process such as the chain fission reaction of uranium, physicists were faced with the question of where can it be used?

Currently, there are two main areas where uranium isotopes are used. These are the peaceful (or energy) industry and the military. Both the first and second use the reaction of the uranium-235 isotope, only the output power differs. Simply put, in a nuclear reactor there is no need to create and maintain this process with the same power as needed to explode a nuclear bomb.

So, the main industries that use the uranium fission reaction have been listed.

But obtaining the uranium-235 isotope is extremely difficult and expensive. technological problem, and not every state can afford to build enrichment factories. For example, to obtain twenty tons of uranium fuel, in which the content of the uranium 235 isotope will be from 3-5%, it will be necessary to enrich more than 153 tons of natural, “raw” uranium.

The uranium-238 isotope is mainly used in the design of nuclear weapons to increase their power. Also, when it captures a neutron with the subsequent process of beta decay, this isotope can eventually turn into plutonium-239, a common fuel for most modern nuclear reactors.

Despite all the disadvantages of such reactors (high cost, difficulty of maintenance, risk of accident), their operation pays off very quickly, and they produce incomparably more energy than classical thermal or hydroelectric power plants.

The reaction also made it possible to create nuclear weapons of mass destruction. It is distinguished by its enormous strength, relative compactness and the fact that it is capable of making large areas of land unsuitable for human habitation. True, modern atomic weapons use plutonium, not uranium.

Depleted uranium

There is also a type of uranium called depleted. It's very different low level radioactivity, which means it is not dangerous for people. It is again used in the military sphere, for example, it is added to the armor of the American Abrams tank to give it additional strength. In addition, in almost all high-tech armies you can find various ones. In addition to their high mass, they have another very interesting property - after the destruction of a projectile, its fragments and metal dust spontaneously ignite. And by the way, such a projectile was first used during World War II. As we see, uranium is an element that has found application in a wide variety of areas of human activity.

Conclusion

According to scientists' forecasts, around 2030 all large uranium deposits will be completely depleted, after which the development of its hard-to-reach layers will begin and the price will rise. By the way, it itself is absolutely harmless to people - some miners have been working on its extraction for entire generations. Now we understand the history of the discovery of this chemical element and how the fission reaction of its nuclei is used.

By the way, it is known interesting fact- uranium compounds were used for a long time as paints for porcelain and glass (so-called until the 1950s.

	U	92			Uranus
					t o kip. (o C)	4200	Step oxide	from +2 to +6
		238,0289			t o float(o C)	1134	Density	19040
	5f 3 6d 1 7s 2				OEO	1,22	in the ground bark	0,0003 %

It is difficult to say what name the German scientist Martin Klaproth would have given to the element discovered in 1789, if a few years earlier an event had not occurred that excited all circles of society: in 1781, the English astronomer William Herschel, observing the starry sky with a homemade telescope, discovered a luminous cloud, which he initially mistook for a comet, but later became convinced that he was seeing a new, hitherto unknown seventh planet solar system. In honor of the ancient Greek god of the sky, Herschel named it Uranus. Impressed by this event, Klaproth gave the newborn element the name of the new planet.

About half a century later, in 1841, the French chemist Eugene Peligo was able to obtain uranium metal for the first time. The industrial world remained indifferent to the heavy, relatively soft metal that uranium turned out to be. Its mechanical and chemical properties did not attract either metallurgists or machine builders. Only the glassblowers of Bohemia and the Saxon masters of porcelain and earthenware willingly used the oxide of this metal to give glasses a beautiful yellow-green color or decorate dishes with an intricate velvet-black pattern.

The ancient Romans knew about the “artistic abilities” of uranium compounds. During excavations carried out near Naples, a glass mosaic fresco of amazing beauty was found. Archaeologists were amazed: over two millennia the glass had hardly tarnished. When glass samples were subjected to chemical analysis, it turned out that they contained uranium oxide, to which the mosaic owed its longevity. But, if the oxides and salts of uranium were engaged in “socially useful work,” then the metal itself in its pure form was of almost no interest to anyone.

Even scientists were only very superficially familiar with this element. Information about him was scanty and sometimes completely incorrect. Thus, it was believed that its atomic weight was approximately 120. When D. I. Mendeleev created his Periodic Table, this value confused all his cards: uranium, due to its properties, did not want to fit into the cell of the table that was “reserved” for the element with this atomic weight. And then the scientist, contrary to the opinion of many of his colleagues, decided to accept a new value for the atomic weight of uranium - 240 and moved the element to the end of the table. Life has confirmed the rightness of the great chemist:

the atomic weight of uranium is 238.03.

But the genius of D.I. Mendeleev manifested itself not only in this. Back in 1872, when most scientists considered uranium, against the background of many valuable elements, as a kind of “ballast”, the creator of the Periodic Table was able to foresee its truly brilliant future: “Among all known chemical elements, uranium stands out in that it has the highest atomic weight... The highest, known, the concentration of mass of significant matter... existing in uranium... must entail outstanding features... Convinced that the study of uranium, starting from its natural sources, will lead to many more new discoveries, I boldly I recommend that those who are looking for subjects for new research should especially carefully study uranium compounds.”

The great scientist’s prediction came true less than a quarter of a century later: in 1896, the French physicist Henri Becquerel, conducting experiments with uranium salts, made a discovery that rightfully ranks among the greatest scientific discoveries ever made by man. Here's how it happened. Becquerel has long been interested in the phenomenon of phosphorescence (i.e., glow) inherent in certain substances. One day, a scientist decided to use one of the uranium salts for his experiments, which chemists call double sulfate of uranyl and potassium. On a photographic plate wrapped in black paper, he placed a patterned figure cut out of metal, covered with a layer of uranium salt, and exposed it to a bright light. sunlight so that the phosphorescence is as intense as possible. Four hours later, Becquerel developed the plate and saw a distinct silhouette of a metal figure on it. He repeated his experiments again and again - the result was the same. And so on February 24, 1896, at the meetings of the French Academy of Sciences, the scientist reported that such a phosphorescent substance as double sulfate of uranyl and potassium, exposed to light, exhibits invisible radiation that passes through black opaque paper and reduces silver salts on the photographic plate.

Two days later, Becquerel decided to continue the experiments, but as luck would have it, the weather was cloudy, and without the sun, what would phosphorescence be? Annoyed by the bad weather, the scientist hid the already prepared, but never illuminated, transparencies along with samples of uranium salts in his desk drawer, where they lay for several days. Finally, on the night of March 1, the wind cleared the Parisian sky of clouds and the sun's rays sparkled over the city in the morning. Becquerel, who had been impatiently awaiting this, hurried to his laboratory and took the transparencies out of his desk drawer to expose them to the sun. But, being a very pedantic experimenter, he last moment nevertheless, he decided to develop the transparencies, although logic seemed to dictate that nothing could have happened to him over the past days: after all, they were lying in a dark box, and without light not a single substance phosphoresces. At that moment, the scientist did not suspect that in a few hours ordinary photographic plates worth a few francs were destined to become priceless treasures, and the day of March 1, 1896 would forever go down in the history of world science.

What Becquerel saw on the developed plates literally amazed him: the black silhouettes of the samples appeared sharply and clearly on the photosensitive layer. This means phosphorescence has nothing to do with it. But then, what kind of rays does the uranium salt emit? The scientist again and again performed similar experiments with other uranium compounds, including those that did not have the ability to phosphorescent or had been lying in a dark place for years, and each time an image appeared on the plates.

Becquerel has the still not entirely clear idea that uranium represents “the first example of a metal exhibiting a property similar to invisible phosphorescence.”

At the same time, the French chemist Henri Moissan managed to develop a method for producing pure uranium metal. Becquerel asked Moissan for some uranium powder and found that the radiation of pure uranium was much more intense than its compounds, and this property of uranium remained unchanged at the most different conditions experiments, in particular with strong heating and cooling to low temperatures.

Becquerel was in no hurry to publish new data: he was waiting for Moissan to report on his very interesting research. obliged to this scientific ethics. And so on November 23, 1896, at a meeting of the Academy of Sciences, Moissan made a report on work to obtain pure uranium, and Becquerel spoke about a new property inherent in this element, which consisted in the spontaneous fission of the nuclei of its atoms. This property was called radioactivity.

Becquerel's discovery marked the beginning new era in physics - the era of transformation of elements. From now on, the atom could no longer be considered single and indivisible—a path opened up for science into the depths of this “brick” of the material world.

Naturally, uranium has now attracted the attention of scientists. At the same time, they were also interested in the following question: is radioactivity only inherent in uranium? Perhaps there are other elements in nature that have this property?

The answer to this question was given by the outstanding physicists Pierre Curie and Maria Skladovskaya-Curie. With the help of a device designed by her husband, Marie Curie examined a huge amount of metals, minerals, and salts. The work was carried out in incredibly difficult conditions. The laboratory was an abandoned wooden barn, which the couple found in one of the Parisian courtyards. “It was a barracks made of planks, with an asphalt floor and a glass roof that did not protect well from the rain, without any devices,” M. Curie later recalled. “It only had old wooden tables, a cast-iron stove that didn’t provide enough heat, and a blackboard that Pierre loved to use so much.” There were no fume hoods for experiments with harmful gases, so these operations had to be done in the yard when the weather permitted, or indoors with the windows open.” In P. Curie's diary there is an entry that sometimes work was carried out at a temperature of only six degrees above zero.

Many problems arose with obtaining the necessary materials. Uranium ore, for example, was very expensive, and the Curies could not buy enough of it with their modest funds. They decided to appeal to the Austrian government with a request to sell them at a low price the waste of this ore, from which uranium was extracted in Austria, used in the form of salts for coloring glass and porcelain. The scientists were supported by the Vienna Academy of Sciences, and several tons of waste were delivered to their Paris laboratory.

Marie Curie worked with extraordinary tenacity. The study of various materials confirmed the correctness of Becquerel, who believed that the radioactivity of pure uranium was greater than any of its compounds. This was confirmed by the results of hundreds of experiments. But Marie Curie researched more and more new substances. And suddenly... Surprise! Two uranium minerals - chalcolite and Bohemia resin ore - had a much more active effect on the device than uranium. The conclusion suggested itself: they contain some unknown element, characterized by an even higher capacity for radioactive decay. In honor of Poland, the birthplace of M. Curie, the couple named it polonium.

Back to work, again titanic work - and another victory: an element has been discovered that is hundreds of times more radioactive than uranium. Scientists named this element radium, which means “ray” in Latin.

The discovery of radium to some extent distracted the scientific community from uranium. For about forty years he did not really excite the minds of scientists, and engineering thought rarely indulged him with its attention. One volume of the technical encyclopedia, published in 1934, stated: “Elementary uranium practical application does not have." The reputable publication did not sin against the truth, but just a few years later life made significant adjustments to ideas about the possibilities of uranium.

At the beginning of 1939, two scientific reports appeared. The first, sent to the French Academy of Sciences by Frederic Joliot-Curie, was entitled “Experimental proof of the explosive fission of uranium and thorium nuclei under the influence of neutrons.” The second message—its authors were German physicists Otto Frisch and Lise Meitner—was published English magazine"Nature"; it was called: “Disintegration of uranium under the influence of neutrons: the new kind nuclear reaction." Both there and there they talked about a new, hitherto unknown phenomenon occurring with the nucleus of the heaviest element - uranium.

A few years earlier, the “boys” became seriously interested in uranium - this is the friendly name given to a group of young talented physicists who worked under the leadership of Enrico Fermi at the University of Rome. The hobby of these scientists was neutron physics, which contained a lot of new and unknown things.

It was discovered that when irradiated with neutrons, as a rule, the nuclei of one element transform into the nuclei of another, occupying the next cell in the Periodic Table. What if the last, 92nd element, uranium, is irradiated with neutrons? Then an element should be formed that is already in 93rd place—an element that even nature could not create!

The “boys” liked the idea. Of course, isn’t it tempting to find out what an artificial element is, what it looks like, how it behaves? So - uranium is irradiated. But what happened? Not just one radioactive element appeared in uranium, as expected, but at least a dozen. There was some mystery in the behavior of uranium. Enrico Fermi sends a message about this to one of the scientific journals. It is possible, he believes, that element 93 was formed, but there is no exact evidence of this. But, on the other hand, there is evidence that some other elements are present in irradiated uranium. But which ones?

An attempt to answer this question was made by Marie Curie's daughter, Irene Joliot-Curie. She repeated Fermi's experiments and carefully examined the chemical composition of uranium after irradiation with neutrons. The result was more than unexpected: the element lanthanum appeared in uranium, located approximately in the middle of the periodic table, i.e. very far from uranium.

When the same experiments were carried out by German scientists Otto Hahn and Friedrich Strassmann, they found not only lanthanum in uranium, but also barium. Riddle after riddle!

Hahn and Strassmann reported their experiments to their friend famous physicist Lise Meitner. Now several leading scientists are trying to solve the uranium problem at once. And so, first Frederic Joliot-Curie, and after some time Lise Meitner came to the same conclusion: when hit by a neutron, the uranium nucleus seems to fall apart. This explains the unexpected appearance of lanthanum and barium, elements with an atomic weight approximately half that of uranium.

American physicist Luis Alvarez, later laureate Nobel Prize, this news caught me one January morning in 1939 in the hairdresser’s chair. He was calmly looking through the newspaper when suddenly a modest headline caught his eye: “The uranium atom is divided into two halves.”

A moment later, to the amazement of the barber and the customers waiting in line, the strange client ran out of the barber shop, half-cut, with a napkin tied tightly around his neck and flapping in the wind. Ignoring the surprised passersby, the physicist rushed to the University of California laboratory where he worked to report the stunning news to his colleagues. At first they were stunned by the very original appearance of Alvarez waving a newspaper, but when they heard about the sensational discovery, they immediately forgot about his unusual hairstyle.

Yes, it was a real sensation in science. But Joliot-Curie also established another important fact: the disintegration of the uranium nucleus has the character of an explosion, in which the resulting fragments fly apart at enormous speed. While it was possible to split only individual nuclei, the energy of the fragments only heated a piece of uranium. If the number of fissions is large, then a huge amount of energy will be released.

But where can one get enough neutrons to simultaneously bombard a large number of uranium nuclei with them? After all, the sources of neutrons known to scientists produced many billions of times less than required. Nature itself came to the rescue. Joliot-Curie discovered that when a uranium nucleus fissions, several neutrons are emitted from it. Having got into the nuclei of neighboring atoms, they should lead to a new decay - the so-called chain reaction. And since these processes last millionths of a second, colossal energy is immediately released—an explosion is inevitable. It would seem that everything is clear. But pieces of uranium have been irradiated with neutrons more than once, but they did not explode, i.e., a chain reaction did not occur. Apparently, some other conditions are needed. Which ones? Frederic Joliot-Curie could not yet answer this question.

And yet the answer was found. It was found in the same 1939 by young Soviet scientists Ya. B. Zeldovich and Yu. B. Khariton. In their work, they established that there are two ways to develop a nuclear chain reaction. First, it is necessary to increase the size of a piece of uranium, since when a small piece is irradiated, many newly released neutrons can fly out of it without encountering a single nucleus on their way. As the mass of uranium increases, the probability of a neutron hitting a target naturally increases.

There is another way: enriching uranium with the isotope 235. The fact is that natural uranium has two main isotopes, the atomic weights of which are 238 and 235. In the nucleus of the first of them, which accounts for 140 times more atoms, there are three more neutrons more. Uranium-235, “poor” in neutrons, greedily absorbs them - much more strongly than its “prosperous” brother, which does not even divide into parts, but turns into another element. Scientists later used this property of the isotope to obtain artificial transuranium elements. For a chain reaction, the indifference of uranium-238 to neutrons turns out to be disastrous: the process languishes before it has time to gain strength. But the more neutron-hungry isotope 235 atoms in uranium, the more energetic the reaction will be.

But for the process to begin, the first neutron is also needed—that “match” that should cause an atomic “fire.” Of course, for this purpose you can use conventional neutron sources, which scientists have previously used in their research - not very convenient, but possible. Isn't there a more suitable "match"?

Eat. It was found by other Soviet scientists K. A. Petrzhak and G. N. Flerov. Studying the behavior of uranium in 1939-1940, they came to the conclusion that the nuclei of this element are capable of decaying spontaneously. This was confirmed by the results of experiments conducted by them in one of the Leningrad laboratories. But perhaps the uranium did not decay on its own, but, for example, under the influence of cosmic rays: after all, the Earth is constantly under their fire. This means that the experiments need to be repeated deep underground, where these space guests do not penetrate. After consulting with the largest Soviet atomic scientist I.V. Kurchatov, the young researchers decided to conduct experiments at some Moscow metro station. This did not encounter any obstacles at the People's Commissariat of Railways, and soon equipment that weighed about three tons was delivered to the office of the head of the Dynamo metro station, located at a depth of 50 meters, on the shoulders of scientists.

As always, blue trains passed by, thousands of passengers went down and up the escalator, and none of them imagined that experiments were being carried out somewhere very nearby, the importance of which is difficult to overestimate. And finally, results similar to those observed in Leningrad were obtained. There was no doubt: spontaneous decay is inherent in uranium nuclei. To notice it, you had to show extraordinary experimental skill: in 1 hour out of every

Out of 60,000,000,000,000 uranium atoms, only one decays. Truly a drop in the bucket!

K. A. Petrzhak and G. N. Flerov wrote the final page in that part of the biography of uranium that preceded the world's first chain reaction. It was carried out on December 2, 1942 by Enrico Fermi.

At the end of the 30s, Fermi, like many other prominent scientists, was forced to emigrate to America to escape the Nazi plague. Here he intended to continue his most important experiments. But this required a lot of money. It was necessary to convince the American government that Fermi's experiments would produce powerful atomic weapons that could be used to fight fascism. This mission was undertaken by the world-famous scientist Albert Einstein. He writes a letter to US President Franklin Roosevelt, which begins with the words: “Sir! The latest work of E. Fermi and L. Szilard, which I have read in the manuscript, allows me to hope that the element uranium in the near future can be turned into a new important source of energy...” In the letter, the scientist called on the government to start funding uranium research. Given Einstein's enormous authority and the seriousness of the international situation, Roosevelt gave his consent.

At the end of 1941, Chicago residents could notice an unusual excitement reigning in the territory of one of the stadiums, which had nothing to do with sports. Cars with cargo drove up to its gate every now and then. Numerous security guards did not allow outsiders to even approach the stadium fence. Here, on the tennis courts located under the western stand, Enrico Fermi prepared his most dangerous experiment - the implementation of a controlled chain reaction of fission of uranium nuclei. Work on the construction of the world's first nuclear reactor was carried out day and night for a year.

The morning came on December 2, 1942. All night the scientists did not close their eyes, checking their calculations again and again. It’s no joke: the stadium is located in the very center of a multimillion-dollar city, and although calculations convinced that the reaction in a nuclear boiler would be slow, i.e., would not be explosive, no one had the right to risk the lives of hundreds of thousands of people. The day had already begun long ago, it was time to have breakfast, but everyone forgot about it - they couldn’t wait to begin the assault on the atom as soon as possible. However, Fermi is in no hurry: we need to give tired people a rest, they need a release, so that they can then carefully weigh and think about everything again. Caution and caution again. And so, when everyone was waiting for the command to start the experiment, Fermi uttered his famous phrase, which went down in the history of the conquest of the atom - just two words: “Let’s go have breakfast!”

Breakfast is over, everything is back in its place - the experience begins. The scientists' gaze is focused on the instruments. The minutes of waiting are agonizing. And finally, the neutron counters clicked like machine guns. They seemed to be choking on a huge number of neutrons, not having time to count them! The chain reaction has begun! This happened at 15:25 Chicago time. The atomic fire was allowed to burn for 28 minutes, and then, at Fermi's command, the chain reaction was stopped.

One of the participants in the experiment answered the phone and, using a pre-agreed encrypted phrase, told his superiors: “The Italian navigator has reached the New World!” This meant that the eminent Italian scientist Enrico Fermi had released energy atomic nucleus and proved that man can control and use it at will.

But will differs from will. In those years when the events described took place, the chain reaction was considered primarily as a stage on the way to the creation atomic bomb. It was in this direction that the work of atomic scientists in America was continued.

The situation in scientific circles associated with these works was extremely tense. But even here there were some oddities.

In the fall of 1943, it was decided to try to take the leading physicist Niels Bohr from German-occupied Denmark to America in order to use his enormous knowledge and talent. On a dark night, on a fishing boat, secretly guarded by English submarines, the scientist, disguised as a fisherman, was taken to Sweden, from where he was to be transported by plane to England, and then to the USA.

Bohr's entire luggage consisted of one bottle. This ordinary green bottle of Danish beer, in which he secretly kept the priceless heavy water, the physicist was as close as the apple of his eye: according to many atomic scientists, it was heavy water that could serve as a neutron moderator for a nuclear reaction.

Bohr endured the tiring flight very hard and, as soon as he came to his senses, the first thing he did was check whether the bottle of heavy water was intact. And then, to his great chagrin, the scientist discovered that he had become a victim of his own absent-mindedness: in his hands was a bottle of real Danish beer, and the vessel with heavy water remained in the refrigerator at home.

When the first small piece of uranium-235 intended for the atomic bomb was produced at the giant Oak Ridge plants in Tennessee, it was sent by special courier to Los Alamos, hidden among the canyons of New Mexico, where this deadly weapon was created. The courier, who had to drive the car himself, was not told what was in the box given to him, but he heard more than once creepy stories about the mysterious "death rays" born in Oak Ridge. The further he drove, the more excitement he became. In the end, he decided, at the first suspicious sign in the behavior of the box hidden behind him, to run as fast as he could from the car.

Driving through long bridge, the driver suddenly heard a loud shot from behind. As if catapulted, he jumped out of the car and ran as fast as he had ever run in his life. But after running a considerable distance, he stopped in exhaustion, became convinced that he was safe and sound, and even dared to look back. Meanwhile, a long tail of impatiently honking cars had already grown behind his car. I had to go back and continue on my way.

But as soon as he got behind the wheel, a loud shot was heard again, and the instinct of self-preservation again literally threw the poor fellow out of the car and made him rush away from the ill-fated box. Only after an angry policeman caught up with him on a motorcycle and saw government documents did the frightened driver learn that the shots were coming from a nearby training ground, where new artillery shells were being tested at that time.

Work at Los Alamos was carried out in the strictest secrecy. All major scientists were here under fictitious names. Thus, Niels Bohr, for example, was known in Los Alamos as Nicolae Baker, Enrico Fermi was Henry Farmer, Eugene Wigner was Eugene Wagner.

One day, when Fermi and Wigner were leaving the territory of a secret plant, they were stopped by a sentry. Fermi presented his ID in the name of Farmer, and Wigner could not find his documents. The guard had a list of those who were allowed to enter and leave the plant. “What is your last name?” he asked. The absent-minded professor first muttered “Wigner” out of habit, but immediately caught himself and corrected himself: “Wagner.” This aroused suspicion among the guard. Wagner was on the list, but Wigner was not. He turned to Fermi, whom he already knew well by sight, and asked: “Is this man’s name Wagner?” “His name is Wagner. This is as true as the fact that I am Farmer,” Fermi solemnly assured the sentry, hiding a smile, and he let the scientists through.

Around mid-1945, work on the creation of the atomic bomb, on which two billion dollars had been spent, was completed, and on August 6, a giant fire mushroom appeared over the Japanese city of Hiroshima, claiming tens of thousands of lives. This date became a dark day in the history of civilization. The greatest achievement of science has given rise to the greatest tragedy of mankind.

Scientists and the whole world were faced with the question: what next? Continue to improve nuclear weapons, create even more terrible means of exterminating people?

No! From now on, the colossal energy contained in the nuclei of atoms must serve man. The first step on this path was taken by Soviet scientists under the leadership of Academician I.V. Kurchatov. On June 27, 1954, Moscow radio broadcast a message of exceptional importance: “At present, in the Soviet Union, through the efforts of Soviet scientists and engineers, work on the design and construction of the first industrial nuclear power plant with a useful capacity of 5000 kilowatts has been successfully completed.” For the first time, a current flowed through the wires that carried energy born in the depths of the uranium atom.

“This historical event,” the Daily Worker wrote in those days, “has immeasurably greater international significance than the dropping of the first atomic bomb on Hiroshima...”

The launch of the first nuclear power plant marked the beginning of the development of a new branch of technology - nuclear energy. Uranium became the peaceful fuel of the 20th century.

Another five years passed, and the world's first nuclear-powered icebreaker, Lenin, rolled off the slipways of Soviet shipyards. To make its engines work at full power (44 thousand horsepower!), you need to “burn” only a few tens of grams of uranium. A small piece of this nuclear fuel can replace thousands of tons of fuel oil or coal, which are forced to literally drag behind them ordinary ships traveling, for example, on a London-New York flight. And the nuclear-powered icebreaker "Lenin", with a reserve of several tens of kilograms of uranium fuel, can crush the ice of the Arctic for three years without entering the port for "refueling".

In 1974, an even more powerful nuclear icebreaker, the Arktika, “began to fulfill its duties.”

Every year the share of nuclear fuel in the global balance of energy resources becomes more and more noticeable. Nowadays, every fourth light bulb in Russia shines because of nuclear power plants. The advantages of this type of fuel are undeniable. But don't forget about the dangers of radiation. Millions of people suffered. Among them, more than 100,000 were killed due to the terrible accident at the Chernobol nuclear power plant in 1986. And even now the territory near the Chernobyl nuclear power plant is contaminated and unsuitable for living. It will be at least another hundred years before a person can return and live there. But even without accidents, everything is not so smooth. After all, the use of uranium fuel is associated with many difficulties, of which perhaps the most important is the destruction of the resulting radioactive waste. Should we lower them in special containers to the bottom of the seas and oceans? Bury them deep in the ground? It is unlikely that such methods will completely solve the problem: after all, in the end, deadly substances remain on our planet. Shouldn't we try to send them somewhere far away - to other celestial bodies? This is exactly the idea put forward by one of the US scientists. He proposed loading waste from nuclear power plants onto “cargo” spaceships traveling along the Earth-Sun route. Of course, today such “parcels” would be quite expensive for senders, but, according to some optimistic experts, in 10 years these transport operations will become completely justified.

Nowadays, it is no longer necessary to have a rich imagination to predict the great future of uranium. Uranus tomorrow is space rockets, directed into the depths of the Universe, and giant underwater cities, provided with energy for decades, this is the creation of artificial islands and watering of deserts, this is penetration into the very depths of the Earth and the transformation of the climate of our planet.

Uranium, perhaps the most amazing metal of nature, opens up fabulous prospects for man!