Plutonium (Latin Plutonium, denoted by the symbol Pu) is a radioactive chemical element with atomic number 94 and atomic weight 244.064. Plutonium is an element of group III of the periodic system of Dmitry Ivanovich Mendeleev, belongs to the family of actinides. Plutonium is a heavy (density under normal conditions 19.84 g/cm³), brittle, silver-white radioactive metal.

Plutonium has no stable isotopes. Of the hundred possible isotopes of plutonium, twenty-five have been synthesized. Fifteen of them have been studied for nuclear properties (mass numbers 232-246). Four have found practical applications. The longest-lived isotopes - 244Pu (half-life 8.26.107 years), 242Pu (half-life 3.76 105 years), 239Pu (half-life 2.41 104 years), 238Pu (half-life 87.74 years) - α-emitters and 241Pu (half-life 14 years) - β-emitter. In nature, plutonium occurs in trace amounts in uranium ores (239Pu); it is formed from uranium under the action of neutrons, the sources of which are reactions occurring during the interaction of α-particles with light elements (which are part of ores), spontaneous fission of uranium nuclei and cosmic radiation.

The ninety-fourth element was discovered by a group of American scientists - Glenn Seaborg, Kennedy, Edwin McMillan and Arthur Wahl in 1940 at Berkeley (at the University of California) while bombing a target of uranium oxide ( U3O8) by highly accelerated deuterium nuclei (deuterons) from a sixty-inch cyclotron. In May 1940, the properties of plutonium were predicted by Louis Turner.

In December 1940, the plutonium isotope Pu-238 was discovered, with a half-life of ~90 years, a year later - the more important Pu-239 with a half-life of ~24,000 years.

Edwin Macmillan in 1948 suggested that the chemical element be named plutonium in honor of the discovery of the new planet Pluto and by analogy with neptunium, which was named after the discovery of Neptune.

Metallic plutonium (isotope 239Pu) is used in nuclear weapons and serves as nuclear fuel for power reactors operating on thermal and especially fast neutrons. The critical mass for 239Pu in the form of metal is 5.6 kg. Among other things, the 239Pu isotope is the starting material for the production of transplutonium elements in nuclear reactors. The 238Pu isotope is used in small-sized nuclear sources of electric current used in space research, as well as in stimulators of human cardiac activity.

Plutonium-242 is important as a "raw material" for the relatively rapid accumulation of higher transuranium elements in nuclear reactors. δ-stabilized plutonium alloys are used in the manufacture of fuel cells, as they have better metallurgical properties compared to pure plutonium, which undergoes phase transitions when heated. Plutonium oxides are used as an energy source for space technology and are used in fuel rods.

All plutonium compounds are poisonous, which is a consequence of α-radiation. Alpha particles pose a serious danger if their source is in the body of an infected person, they damage the body tissues surrounding the element. Plutonium gamma radiation is not harmful to the body. It is worth considering that different isotopes of plutonium have different toxicity, for example, typical reactor-grade plutonium is 8-10 times more toxic than pure 239Pu, since it is dominated by 240Pu nuclides, which is a powerful source of alpha radiation. Plutonium is the most radiotoxic element of all actinides, however, it is considered far from being the most dangerous element, since radium is almost a thousand times more dangerous than the most poisonous isotope of plutonium - 239Pu.

Biological properties

Plutonium is concentrated by marine organisms: the accumulation coefficient of this radioactive metal (the ratio of concentrations in the body and in the external environment) for algae is 1000-9000, for plankton - approximately 2300, for starfish - about 1000, for mollusks - up to 380, for muscles, bones , liver and stomach of fish - 5, 570, 200 and 1060, respectively. Terrestrial plants assimilate plutonium mainly through the root system and accumulate it up to 0.01% of their mass. In the human body, the ninety-fourth element is retained mainly in the skeleton and liver, from where it is almost not excreted (especially from the bones).

Plutonium is highly toxic, and its chemical hazard (like any other heavy metal) is much weaker (from a chemical point of view, it is also poisonous like lead.) In comparison with its radioactive toxicity, which is a consequence of alpha radiation. Moreover, α-particles have a relatively low penetrating power: for 239Pu, the range of α-particles in air is 3.7 cm, and in soft biological tissue 43 microns. Therefore, α-particles pose a serious danger if their source is in the body of the infected. In doing so, they damage the surrounding tissues of the body.

At the same time, γ-rays and neutrons, which plutonium also emits and which are able to penetrate the body from the outside, are not very dangerous, because their level is too low to cause harm to health. Plutonium belongs to the group of elements with especially high radiotoxicity. At the same time, different isotopes of plutonium have different toxicity, for example, typical reactor-grade plutonium is 8-10 times more toxic than pure 239Pu, since it is dominated by 240Pu nuclides, which is a powerful source of alpha radiation.

When taken in water and food, plutonium is less toxic than substances such as caffeine, certain vitamins, pseudoephedrine, and many plants and fungi. This is due to the fact that this element is poorly absorbed by the gastrointestinal tract, even when taken in the form of a soluble salt, this very salt is bound by the contents of the stomach and intestines. However, ingestion of 0.5 grams of finely divided or dissolved plutonium can lead to death from acute digestive irradiation in days or weeks (for cyanide, this value is 0.1 grams).

From the point of view of inhalation, plutonium is an ordinary toxin (approximately corresponds to mercury vapor). When inhaled, plutonium is carcinogenic and can cause lung cancer. So, when one hundred milligrams of plutonium is inhaled in the form of particles of an optimal size for retention in the lungs (1-3 microns), it leads to death from pulmonary edema in 1-10 days. A dose of twenty milligrams leads to death from fibrosis in about a month. Smaller doses lead to chronic carcinogenic poisoning. The risk of inhalation of plutonium into the body is increased due to the fact that plutonium tends to form aerosols.

Despite being a metal, it is highly volatile. A short stay of the metal in the room significantly increases its concentration in the air. Once in the lungs, plutonium partially settles on the surface of the lungs, partially passes into the blood, and then into the lymph and bone marrow. Most (about 60%) goes to the bone tissue, 30% to the liver and only 10% is excreted naturally. The amount of plutonium ingested depends on the size of the aerosol particles and the solubility in the blood.

Plutonium entering the human body in one way or another is similar in properties to ferric iron, therefore, when it enters the circulatory system, plutonium begins to concentrate in tissues containing iron: bone marrow, liver, spleen. The body perceives plutonium as iron, therefore, the transferrin protein takes plutonium instead of iron, which stops the transfer of oxygen in the body. Microphages disperse plutonium through the lymph nodes. The plutonium that has entered the body is removed from it for a very long time - over 50 years, only 80% will be removed from the body. The elimination half-life from the liver is 40 years. For bone tissue, the half-life of plutonium is 80-100 years, in fact, the concentration of the ninety-fourth element in the bones is constant.

Throughout World War II and after it, scientists working in the Manhattan Project, as well as scientists from the Third Reich and other research organizations, conducted experiments using plutonium on animals and humans. Animal studies have shown that a few milligrams of plutonium per kilogram of tissue is a lethal dose. The use of plutonium in humans consisted in the fact that chronically ill patients were usually injected intramuscularly with 5 micrograms of plutonium. In the end, it was found that the lethal dose for a patient is one microgram of plutonium, and that plutonium is more dangerous than radium and prone to accumulating in bones.

As you know, plutonium is an element that is practically absent in nature. However, about five tons of it was released into the atmosphere as a result of nuclear tests in the period 1945-1963. The total amount of plutonium released into the atmosphere due to nuclear testing before the 1980s is estimated at 10 tons. According to some estimates, the soil in the United States of America contains an average of 2 millicuries (28 mg) of plutonium per km2 from fallout, and the presence of plutonium in the Pacific Ocean is increased compared to the total distribution of nuclear materials on earth.

The latter phenomenon is associated with the conduct of US nuclear tests on the territory of the Marshall Islands in the Pacific test site in the mid-1950s. The residence time of plutonium in the surface waters of the ocean is from 6 to 21 years, however, even after this period, plutonium falls to the bottom along with biogenic particles, from which it is restored to soluble forms as a result of microbial decomposition.

World pollution by the ninety-fourth element is associated not only with nuclear tests, but also with accidents in production and equipment interacting with this element. So in January 1968, a US Air Force B-52 carrying four nuclear warheads crashed in Greenland. As a result of the explosion, the charges were destroyed and plutonium leaked into the ocean.

Another case of radioactive contamination of the environment as a result of an accident occurred with the Soviet spacecraft Kosmos-954 on January 24, 1978. As a result of an uncontrolled de-orbit, a satellite with a nuclear power source on board fell into Canadian territory. The accident released more than a kilogram of plutonium-238 into the environment, spreading over an area of ​​about 124,000 m².

The most terrible example of an accidental release of radioactive substances into the environment is the accident at the Chernobyl nuclear power plant, which occurred on April 26, 1986. As a result of the destruction of the fourth power unit, 190 tons of radioactive substances (including plutonium isotopes) were released into the environment over an area of ​​about 2200 km².

The release of plutonium into the environment is associated not only with man-made accidents. Cases of plutonium leakage are known, both from laboratory and factory conditions. More than twenty accidental leaks from 235U and 239Pu laboratories are known. During 1953-1978. emergency cases led to a loss of 0.81 (Mayak, March 15, 1953) to 10.1 kg (Tomsk, December 13, 1978) 239Pu. Accidents at industrial enterprises resulted in the total death of two people in the city of Los Alamos (August 21, 1945 and May 21, 1946) due to two accidents and the loss of 6.2 kg of plutonium. In the city of Sarov in 1953 and 1963. approximately 8 and 17.35 kg fell outside the nuclear reactor. One of them led to the destruction of a nuclear reactor in 1953.

The fission of the 238Pu nucleus by neutrons releases energy in the amount of 200 MeV, which is 50 million times more than during the most famous exothermic reaction: C + O2 → CO2. "Burning" in a nuclear reactor, one gram of plutonium gives 2,107 kcal - this is the energy contained in 4 tons of coal. A thimble of plutonium fuel in terms of energy can be equated to forty wagonloads of good firewood!

The "natural isotope" of plutonium (244Pu) is believed to be the longest-lived isotope of all the transuranium elements. Its half-life is 8.26∙107 years. Scientists have been trying for a long time to obtain an isotope of a transuranium element that would exist longer than 244Pu - high hopes in this regard were pinned on 247Cm. However, after its synthesis, it turned out that the half-life of this element is only 14 million years.

Story

In 1934, a group of scientists led by Enrico Fermi made a statement that in the course of scientific work at the University of Rome, they discovered a chemical element with serial number 94. At the insistence of Fermi, the element was named hesperium, the scientist was convinced that he had discovered a new element, which is now called plutonium, thus making an assumption about the existence of transuranium elements and becoming their theoretical discoverer. Fermi defended this hypothesis in his Nobel lecture in 1938. Only after the discovery of nuclear fission by the German scientists Otto Frisch and Fritz Strassmann, Fermi was forced to make a note in the printed version, published in Stockholm in 1939, indicating the need to revise "the whole problem of transuranium elements." The fact is that the work of Frisch and Strassmann showed that the activity discovered by Fermi in his experiments was due precisely to fission, and not to the discovery of transuranium elements, as he had previously believed.

The new one, the ninety-fourth element, was discovered at the end of 1940. It happened in Berkeley at the University of California. When bombarding uranium oxide (U3O8) with heavy hydrogen nuclei (deuterons), a group of American radiochemists led by Glenn T. Seaborg discovered a previously unknown alpha particle emitter with a half-life of 90 years. This emitter turned out to be an isotope of element No. 94 with a mass number of 238. Thus, on December 14, 1940, the first microgram quantities of plutonium were obtained, along with an admixture of other elements and their compounds.

In the course of an experiment conducted in 1940, it was found that during the ongoing nuclear reaction, the short-lived isotope neptunium-238 (half-life 2.117 days) is first obtained, and plutonium-238 is already obtained from it:

23392U (d,2n) → 23893Np → (β−) 23894Pu

Long and laborious chemical experiments to separate a new element from impurities lasted two months. The existence of a new chemical element was confirmed on the night of February 23-24, 1941 by G.T. Seaborg, E.M. at least two oxidation states. A little after the end of the experiments, it was found that this isotope is non-fissile, and, therefore, uninteresting for further study. Soon (March 1941) Kennedy, Seaborg, Segré and Wahl synthesized the more important isotope plutonium-239 by irradiating uranium with highly accelerated neutrons in a cyclotron. This isotope is produced by the decay of neptunium-239, emits alpha rays, and has a half-life of 24,000 years. The first pure compound of the element was obtained in 1942, and the first plutonium metal by weight was obtained in 1943.

The name of the new element 94 was proposed in 1948 by Macmillan, who, a few months before the discovery of plutonium, together with F. Aibelson, received the first element heavier than uranium - element No. 93, which was named neptunium in honor of the planet Neptune - the first behind Uranus. By analogy, element No. 94 was called plutonium, since the planet Pluto is the second planet behind Uranus. In turn, Seaborg suggested calling the new element "plutonium", but then he realized that the name does not sound very good compared to "plutonium". In addition, he put forward other names for the new element: ultimium, extermium, due to the erroneous judgment at the time that plutonium would be the last chemical element in the periodic table. As a result, the element was named "plutonium" in honor of the discovery of the last planet in the solar system.

Being in nature

The half-life of the longest-lived isotope of plutonium is 75 million years. The figure is very impressive, however, the age of the Galaxy is measured in billions of years. From this it follows that the primary isotopes of the ninety-fourth element, formed during the great synthesis of the elements of the Universe, had no chance of surviving to this day. And yet, this does not mean that there is no plutonium in the Earth at all. It is constantly formed in uranium ores. By capturing cosmic radiation neutrons and neutrons produced by spontaneous (spontaneous) fission of 238U nuclei, some - very few - atoms of this isotope turn into 239U atoms. The nuclei of this element are very unstable, they emit electrons and thereby increase their charge, the formation of neptunium, the first transuranium element, occurs. 239Np is also unstable, its nuclei also emit electrons, so in just 56 hours half of 239Np turns into 239Pu.

The half-life of this isotope is already quite long, at 24,000 years. On average, the content of 239Pu is about 400,000 times less than that of radium. Therefore, not only to extract - even to detect "terrestrial" plutonium is extremely difficult. Small amounts of 239Pu - a trillionth - and decay products can be found in uranium ores, for example, in a natural nuclear reactor in Oklo, Gabon (West Africa). The so-called "natural nuclear reactor" is considered the only one in the world in which the formation of actinides and their fission products in the geosphere is currently taking place. According to modern estimates, a self-sustaining reaction with the release of heat took place in this region several million years ago, which lasted more than half a million years.

So, we already know that in uranium ores, as a result of the capture of neutrons by uranium nuclei, neptunium (239Np) is formed, the product of β-decay of which is natural plutonium-239. Thanks to special instruments - mass spectrometers, the presence of plutonium-244 (244Pu), which has the longest half-life - about 80 million years, was detected in Precambrian bastnaesite (in cerium ore). In nature, 244Pu occurs mainly in the form of dioxide (PuO2), which is even less soluble in water than sand (quartz). Since the relatively long-lived isotope plutonium-240 (240Pu) is in the decay chain of plutonium-244, its decay takes place, but this happens very rarely (1 in 10,000). Very small amounts of plutonium-238 (238Pu) refer to the very rare double beta decay of the parent isotope, uranium-238, which has been found in uranium ores.

Traces of the isotopes 247Pu and 255Pu have been found in the dust collected after the explosions of thermonuclear bombs.

Minimal amounts of plutonium can hypothetically be found in the human body, given that a huge number of nuclear tests have been carried out in one way or another related to plutonium. Plutonium accumulates mainly in the skeleton and liver, from where it is practically not excreted. In addition, the ninety-fourth element is accumulated by marine organisms; terrestrial plants absorb plutonium mainly through the root system.

It turns out that artificially synthesized plutonium still exists in nature, so why is it not mined, but obtained artificially? The fact is that the concentration of this element is too low. They say about another radioactive metal - radium: "in a gram of production - in a year of work", and radium in nature is 400,000 times more than plutonium! For this reason, not only to extract - even to detect "terrestrial" plutonium is extremely difficult. This was done only after the physical and chemical properties of plutonium obtained in nuclear reactors were studied.

Application

The 239Pu isotope (along with U) is used as nuclear fuel in power reactors operating on thermal and fast neutrons (mainly), as well as in the manufacture of nuclear weapons.

About 500 nuclear power plants around the world generate approximately 370 GW of electricity (or 15% of the world's total electricity generation). Plutonium-236 is used in the manufacture of atomic electric batteries, the service life of which reaches five years or more, they are used in current generators that stimulate the heart (pacemakers). 238Pu is used in small nuclear power sources used in space research. So plutonium-238 is the power source for the New Horizons, Galileo and Cassini probes, the Curiosity rover and other spacecraft.

In nuclear weapons, plutonium-239 is used, since this isotope is the only suitable nuclide for use in a nuclear bomb. In addition, the more frequent use of plutonium-239 in nuclear bombs is due to the fact that plutonium occupies a smaller volume in the sphere (where the bomb core is located), therefore, one can gain in the explosive power of the bomb due to this property.

The scheme by which a nuclear explosion occurs involving plutonium lies in the design of the bomb itself, the core of which consists of a sphere filled with 239Pu. At the moment of impact with the ground, the sphere is compressed to a million atmospheres due to the structure and due to the explosive surrounding this sphere. After the impact, the nucleus expands in volume and density in the shortest time - ten microseconds, the assembly slips through the critical state on thermal neutrons and goes into the supercritical state on fast neutrons - a nuclear chain reaction begins with the participation of neutrons and nuclei of the element. In the final explosion of a nuclear bomb, a temperature of the order of tens of millions of degrees is released.

Isotopes of plutonium have found their application in the synthesis of transplutonium (following plutonium) elements. For example, in the Oak Ridge National Laboratory, long-term neutron irradiation with 239Pu produces 24496Cm, 24296Cm, 24997Bk, 25298Cf, 25399Es, and 257100Fm. Americium 24195Am was obtained in the same way in 1944 for the first time. In 2010, plutonium-242 oxide bombarded with calcium-48 ions served as a source of ununquadium.

δ-stabilized plutonium alloys are used in the manufacture of fuel rods, because they have significantly better metallurgical properties compared to pure plutonium, which undergoes phase transitions when heated and is a very brittle and unreliable material. Alloys of plutonium with other elements (intermetallic compounds) are usually obtained by direct interaction of the elements in the required ratios, mainly arc melting is used, sometimes unstable alloys are obtained by spray deposition or cooling of melts.

The main industrial alloying elements for plutonium are gallium, aluminum and iron, although plutonium is able to form alloys and intermediate compounds with most metals with rare exceptions (potassium, sodium, lithium, rubidium, magnesium, calcium, strontium, barium, europium and ytterbium). Refractory metals: molybdenum, niobium, chromium, tantalum and tungsten are soluble in liquid plutonium, but almost insoluble or slightly soluble in solid plutonium. Indium, silicon, zinc, and zirconium are capable of forming metastable δ-plutonium (δ"-phase) upon rapid cooling. Gallium, aluminium, americium, scandium, and cerium can stabilize δ-plutonium at room temperature.

Large amounts of holmium, hafnium and thallium make it possible to keep some δ-plutonium at room temperature. Neptunium is the only element that can stabilize α-plutonium at high temperatures. Titanium, hafnium and zirconium stabilize the structure of β-plutonium at room temperature upon rapid cooling. The use of such alloys is quite diverse. For example, a plutonium-gallium alloy is used to stabilize the δ phase of plutonium, which avoids the α-δ phase transition. The plutonium-gallium-cobalt ternary alloy (PuGaCo5) is a superconducting alloy at 18.5 K. There are a number of alloys (plutonium-zirconium, plutonium-cerium and plutonium-cerium-cobalt) that are used as nuclear fuel.

Production

Commercial plutonium is obtained in two ways. This is either the irradiation of 238U nuclei contained in nuclear reactors, or the separation by radiochemical methods (coprecipitation, extraction, ion exchange, etc.) of plutonium from uranium, transuranium elements and fission products contained in spent fuel.

In the first case, the 239Pu isotope most significant in practice (in a mixture with a small admixture of 240Pu) is produced in nuclear reactors with the participation of uranium and neutron nuclei using β-decay and with the participation of neptunium isotopes as an intermediate fission product:

23892U + 21D → 23893Np + 210n;

23893Np → 23894Pu

β--decay

In this process, a deuteron enters uranium-238, resulting in the formation of neptunium-238 and two neutrons. Next, neptunium-238 spontaneously fissions, emitting beta-minus particles, which form plutonium-238.

Usually the content of 239Pu in the mixture is 90-95%, 240Pu-1-7%, the content of other isotopes does not exceed tenths of a percent. Isotopes with long half-lives - 242Pu and 244Pu are obtained by prolonged irradiation with 239Pu neutrons. Moreover, the 242Pu yield is several tens of percent, and 244Pu is a fraction of a percent of the 242Pu content. Small amounts of isotopically pure plutonium-238 are formed when neptunium-237 is irradiated with neutrons. Light isotopes of plutonium with mass numbers 232-237 are usually obtained in a cyclotron by irradiating uranium isotopes with α-particles.

The second method for the industrial production of 239Pu uses the Purex process based on extraction with tributyl phosphate in a light diluent. In the first cycle, Pu and U are jointly purified from fission products, and then they are separated. In the second and third cycles, plutonium is subjected to further purification and concentration. The scheme of such a process is based on the difference in the properties of tetra- and hexavalent compounds of the elements to be separated.

Initially, spent fuel rods are dismantled and the cladding containing spent plutonium and uranium is removed by physical and chemical means. Next, the extracted nuclear fuel is dissolved in nitric acid. After all, it is a strong oxidizing agent when dissolved, and uranium, plutonium, and impurities are oxidized. Zero-valence plutonium atoms are converted to Pu + 6, and both plutonium and uranium are dissolved. From this solution, the ninety-fourth element is reduced to the trivalent state with sulfur dioxide, and then precipitated with lanthanum fluoride (LaF3).

However, the precipitate, in addition to plutonium, contains neptunium and rare earth elements, but the bulk (uranium) remains in solution. Next, the plutonium is re-oxidized to Pu + 6 and lanthanum fluoride is added again. Now rare-earth elements pass into the precipitate, and plutonium remains in solution. Next, neptunium is oxidized to a tetravalent state with potassium bromate, since this reagent does not act on plutonium, then during the secondary precipitation with the same lanthanum fluoride, trivalent plutonium precipitates, and neptunium remains in solution. The end products of such operations are plutonium-containing compounds - PuO2 dioxide or fluorides (PuF3 or PuF4), from which (by reduction with barium, calcium or lithium vapor) metallic plutonium is obtained.

More pure plutonium can be achieved by electrolytic refining of pyrochemically produced metal, which is carried out in electrolysis cells at a temperature of 700 ° C with an electrolyte of potassium, sodium and plutonium chloride using a tungsten or tantalum cathode. The plutonium thus obtained has a purity of 99.99%.

To obtain large quantities of plutonium, breeder reactors are being built, the so-called "breeders" (from the English verb to breed - to multiply). These reactors got their name due to their ability to obtain fissile material in an amount exceeding the cost of this material for obtaining. The difference between reactors of this type from the rest is that the neutrons in them are not slowed down (there is no moderator, for example, graphite) in order to react as much as possible with 238U.

After the reaction, 239U atoms are formed, which later form 239Pu. The core of such a reactor, containing PuO2 in depleted uranium dioxide (UO2), is surrounded by a shell of even more depleted uranium-238 dioxide (238UO2), in which 239Pu is formed. The joint use of 238U and 235U allows "bredders" to produce energy from natural uranium 50-60 times more than other reactors. However, these reactors have a big drawback - fuel rods must be cooled by a medium other than water, which reduces their energy. Therefore, it was decided to use liquid sodium as a coolant.

The construction of such reactors in the United States of America began after the end of the Second World War, the USSR and Great Britain started their creation only in the 1950s.

Physical properties

Plutonium is a very heavy (density at n.a. 19.84 g / cm³) silvery metal, very similar to nickel in the purified state, however, plutonium quickly oxidizes in air, tarnishes, forming an iridescent film, first light yellow, then turning into dark purple. With strong oxidation, an olive-green oxide powder (PuO2) appears on the metal surface.

Plutonium is a very electronegative and reactive metal, many times more than even uranium. It has seven allotropic modifications (α, β, γ, δ, δ", ε and ζ), which change in a certain temperature range and at a certain pressure range. At room temperature, plutonium is in the α-form - this is the most common allotropic modification for plutonium In the alpha phase, pure plutonium is brittle and quite hard - this structure is about as hard as gray cast iron unless it is alloyed with other metals to make the alloy ductile and soft. (Only osmium, iridium, platinum, rhenium, and neptunium are heavier than it.) Further allotropic transformations of plutonium are accompanied by abrupt changes in density. and delta-prim). When melted (transition from the epsilon phase to the liquid phase), plutonium also contracts, allowing unmelted plutonium to float.

Plutonium is distinguished by a large number of unusual properties: it has the lowest thermal conductivity of all metals - at 300 K it is 6.7 W / (m K); plutonium has the lowest electrical conductivity; in its liquid phase, plutonium is the most viscous metal. The resistivity of the ninety-fourth element at room temperature is very high for a metal, and this feature will increase with decreasing temperature, which is not typical for metals. Such an "anomaly" can be traced up to a temperature of 100 K - below this mark, the electrical resistance will decrease. However, from the mark of 20 K, the resistance again begins to increase due to the radiation activity of the metal.

Plutonium has the highest electrical resistivity of any actinide studied (so far), which is 150 µΩ cm (at 22°C). This metal has a low melting point (640°C) and an unusually high boiling point (3227°C). Closer to the melting point, liquid plutonium has a very high viscosity and surface tension compared to other metals.

Due to its radioactivity, plutonium is warm to the touch. A large piece of plutonium in a thermal jacket is heated to a temperature exceeding the boiling point of water! In addition, due to its radioactivity, plutonium undergoes changes in its crystal lattice over time - a kind of annealing occurs due to self-irradiation due to an increase in temperature above 100 K.

The presence of a large number of allotropic modifications in plutonium makes it a difficult metal to process and roll out due to phase transitions. We already know that in the alpha form the ninety-fourth element is similar in properties to cast iron, however, it has the property of changing and turning into a ductile material, and forming a malleable β-form at higher temperature ranges. Plutonium in the δ form is usually stable at temperatures between 310°C and 452°C, but can exist at room temperature if doped with low percentages of aluminium, cerium, or gallium. Being alloyed with these metals, plutonium can be used in welding. In general, the delta form has more pronounced metal characteristics - it is close to aluminum in terms of strength and forging ability.

Chemical properties

The chemical properties of the ninety-fourth element are in many ways similar to the properties of its predecessors in the periodic system - uranium and neptunium. Plutonium is a rather active metal; it forms compounds with oxidation states from +2 to +7. In aqueous solutions, the element exhibits the following oxidation states: Pu (III), as Pu3+ (exists in acidic aqueous solutions, has a light purple color); Pu (IV), as Pu4+ (chocolate shade); Pu (V), as PuO2+ (clear solution); Pu(VI) as PuO22+ (light orange solution) and Pu(VII) as PuO53- (green solution).

Moreover, these ions (except PuO53-) can be in solution simultaneously in equilibrium, which is explained by the presence of 5f-electrons, which are located in the localized and delocalized zone of the electron orbital. At pH 5-8, Pu (IV) dominates, which is the most stable among the other valences (oxidation states). Plutonium ions of all oxidation states are prone to hydrolysis and complex formation. The ability to form such compounds increases in the series Pu5+

Compact plutonium slowly oxidizes in air, becoming covered with an iridescent oily film of oxide. The following plutonium oxides are known: PuO, Pu2O3, PuO2 and the phase of variable composition Pu2O3 - Pu4O7 (berthollides). In the presence of a small amount of moisture, the rate of oxidation and corrosion increases significantly. If the metal is exposed to small amounts of humid air for a long enough time, plutonium dioxide (PuO2) forms on its surface. With a lack of oxygen, its dihydride (PuH2) can also be formed. Surprisingly, plutonium rusts much faster in an inert gas (eg, argon) with water vapor than in dry air or pure oxygen. In fact, this fact is easy to explain - the direct action of oxygen forms an oxide layer on the plutonium surface, which prevents further oxidation, the presence of moisture produces a loose mixture of oxide and hydride. By the way, thanks to just such a coating, the metal becomes pyrophoric, that is, it is capable of spontaneous combustion, for this reason, metallic plutonium, as a rule, is processed in an inert atmosphere of argon or nitrogen. At the same time, oxygen is a protective substance and prevents moisture from affecting the metal.

The ninety-fourth element reacts with acids, oxygen and their vapors, but not with alkalis. Plutonium is highly soluble only in very acidic media (for example, hydrochloric acid HCl), and also dissolves in hydrogen chloride, hydrogen iodide, hydrogen bromide, 72% perchloric acid, 85% phosphoric acid H3PO4, concentrated CCl3COOH, sulfamic acid and boiling concentrated nitric acid. Plutonium does not noticeably dissolve in alkali solutions.

When alkalis act on solutions containing tetravalent plutonium, a precipitate of plutonium hydroxide Pu(OH)4 xH2O, which has basic properties, precipitates. When alkalis act on solutions of salts containing PuO2+, amphoteric hydroxide PuO2OH precipitates. Salts correspond to it - plutonites, for example, Na2Pu2O6.

Plutonium salts readily hydrolyze on contact with neutral or alkaline solutions, creating insoluble plutonium hydroxide. Concentrated plutonium solutions are unstable due to radiolytic decomposition leading to precipitation.

Plutonium
atomic number	94
Appearance of a simple substance
Atom properties
Atomic mass (molar mass)	244.0642 a. e. m. (/mol)
Atom radius	151 pm
Ionization energy (first electron)	491.9(5.10) kJ/mol (eV)
Electronic configuration	5f 6 7s 2
Chemical properties
covalent radius	n/a pm
Ion radius	(+4e) 93 (+3e) 108 pm
Electronegativity (according to Pauling)	1,28
Electrode potential	Pu ← Pu 4+ -1.25V Pu←Pu 3+ -2.0V Pu ← Pu 2+ -1.2V
Oxidation states	6, 5, 4, 3
Thermodynamic properties of a simple substance
Density	19.84 /cm³
Molar heat capacity	32.77 J /( mol)
Thermal conductivity	(6.7) W /( )
Melting temperature	914
Melting heat	2.8 kJ/mol
Boiling temperature	3505
Heat of evaporation	343.5 kJ / mol
Molar volume	12.12 cm³/mol
The crystal lattice of a simple substance
Lattice structure	monoclinic
Lattice parameters	a=6.183 b=4.822 c=10.963 β=101.8
c/a ratio	—
Debye temperature	162

Plutonium- a radioactive chemical element of the actinide group, widely used in the production nuclear weapons(the so-called "weapon-grade plutonium"), as well as (experimentally) as a nuclear fuel for nuclear reactors for civil and research purposes. The first artificial element obtained in quantities available for weighing (1942).

The table on the right shows the main properties of α-Pu, the main allotropic modification of plutonium at room temperature and normal pressure.

History of plutonium

The plutonium isotope 238 Pu was first artificially obtained on February 23, 1941 by a group of American scientists led by Glenn Seaborg by irradiating nuclei uranium deuterons. It is noteworthy that plutonium was discovered in nature only after artificial production: negligible amounts of 239 Pu are usually found in uranium ores as a product of the radioactive transformation of uranium.

Finding plutonium in nature

In uranium ores, as a result of the capture of neutrons (for example, neutrons from cosmic radiation) by uranium nuclei, neptunium(239 Np), whose β-decay product is natural plutonium-239. However, plutonium is formed in such microscopic quantities (0.4-15 parts of Pu per 10 12 parts of U) that its extraction from uranium ores is out of the question.

origin of name plutonium

In 1930, the astronomical world was excited by the remarkable news: a new planet had been discovered, the existence of which Percival Lovell, an astronomer, mathematician and author of fantastic essays on life on Mars, had long talked about. Based on long-term observations of movements uranium and Neptune Lovell came to the conclusion that beyond Neptune in the solar system there must be another, the ninth planet, forty times further from the Sun than the Earth.

This planet, the elements of the orbit of which Lovell calculated back in 1915, was discovered on photographic images taken on January 21, 23 and 29, 1930 by astronomer K. Tombo at the Flagstaff Observatory ( USA) . The planet was named Pluto. By the name of this planet, located in the solar system beyond Neptune, the 94th element was named plutonium, artificially obtained at the end of 1940 from the nuclei atoms uranium a group of American scientists led by G. Seaborg.

Physical properties plutonium

There are 15 isotopes of plutonium - In the largest quantities, isotopes with mass numbers from 238 to 242 are obtained:

238 Pu -> (half-life 86 years, alpha decay) -> 234 U,

This isotope is used almost exclusively in space RTGs, for example, on all devices that flew beyond the orbit of Mars.

239 Pu -> (half-life 24,360 years, alpha decay) -> 235 U,

This isotope is most suitable for the design of nuclear weapons and fast neutron nuclear reactors.

240 Pu -> (half-life 6580 years, alpha decay) -> 236 U, 241 Pu -> (half-life 14.0 years, beta decay) -> 241 Am, 242 Pu -> (half-life 370,000 years, alpha -decay) -> 238 U

These three isotopes are not of serious industrial importance, but they are obtained as by-products when energy is obtained in nuclear reactors on uranium, by successive capture of several neutrons by uranium-238 nuclei. The isotope 242 is most similar in nuclear properties to uranium-238. Americium-241, produced by the decay of the 241 isotope, was used in smoke detectors.

Plutonium is interesting in that it undergoes six phase transitions from solidification temperature to room temperature, more than any other chemical element. With the latter, the density increases abruptly by 11%, as a result, plutonium castings crack. The alpha phase is stable at room temperature, the characteristics of which are given in the table. For application, the delta phase, which has a lower density, and a cubic body-centered lattice are more convenient. Plutonium in the delta phase is very ductile, while the alpha phase is brittle. To stabilize plutonium in the delta phase, alloying with trivalent metals is used (gallium was used in the first nuclear charges).

Use of plutonium

The first plutonium-based nuclear charge was detonated on July 16, 1945 at the Alamogordo test site (test code-named "Trinity").

The biological role of plutonium

Plutonium is highly toxic; MPC for 239 Pu in open water bodies and in the air of working premises is 81.4 and 3.3*10 −5 Bq/l, respectively. Most plutonium isotopes have a high ionization density and a short particle path, so its toxicity is due not so much to its chemical properties (probably, in this respect, plutonium is no more toxic than other heavy metals), but to the ionizing effect on the surrounding tissues of the body. Plutonium belongs to the group of elements with especially high radiotoxicity. In the body, plutonium produces large irreversible changes in the skeleton, liver, spleen, kidneys, and causes cancer. The maximum allowable content of plutonium in the body should not exceed tenths of a microgram.

Artistic works related to the theme plutonium

- Plutonium was used for the De Lorean DMC-12 machine in the movie Back to the Future as a fuel for the flow accumulator to travel to the future or the past.

- Plutonium was the charge of the atomic bomb exploded by terrorists in Denver, USA, in the work of Tom Clancy's "All the fears of the world"

- Kenzaburo Oe "Pinchrunner's Notes"

- In 2006, the company "Beacon Pictures" released the film "Plutonium-239" ( "Pu-239")

Chemistry

Plutonium Pu - element No. 94 is associated with very high hopes and very high fears of mankind. Today it is one of the most important, strategically important, elements. This is the most expensive of the technically important metals - it is much more expensive than silver, gold and platinum. He is truly precious.

Background and history

In the beginning there were protons - galactic hydrogen. As a result of its compression and subsequent nuclear reactions, the most incredible "ingots" of nucleons were formed. Among them, these "ingots", were, apparently, containing 94 protons each. Estimates by theoreticians suggest that about 100 nucleon formations, which include 94 protons and from 107 to 206 neutrons, are so stable that they can be considered isotope nuclei of element No. 94.
But all these isotopes - hypothetical and real - are not so stable as to be preserved to this day from the moment the elements of the solar system were formed. The half-life of the longest-lived isotope of element No. 94 is 81 million years. The age of the galaxy is measured in billions of years. Consequently, the "original" plutonium had no chance to survive to this day. If it was formed during the great synthesis of the elements of the Universe, then those ancient atoms of it “died out” long ago, just as dinosaurs and mammoths died out.
In the XX century. new era, AD, this element was recreated. Out of 100 possible isotopes of plutonium, 25 have been synthesized. 15 of them have been studied for their nuclear properties. Four have found practical applications. And it was only recently opened. In December 1940, while irradiating uranium with heavy hydrogen nuclei, a group of American radiochemists led by Glenn T. Seaborg discovered a hitherto unknown alpha particle emitter with a half-life of 90 years. This emitter turned out to be an isotope of element No. 94 with a mass number of 238. In the same year, but several months earlier, E.M. Macmillan and F. Abelson received the first element heavier than uranium - element No. 93. This element was called neptunium, and the 94th - plutonium. The historian will definitely say that these names originate in Roman mythology, but in essence the origin of these names is rather not mythological, but astronomical.
Elements No. 92 and 93 are named after the distant planets of the solar system - Uranus and Neptune, but Neptune is not the last in the solar system, the orbit of Pluto lies even further - a planet about which almost nothing is known so far ... A similar construction we also observe on the “left flank” of the periodic table: uranium - neptunium - plutonium, however, humanity knows much more about plutonium than about Pluto. By the way, astronomers discovered Pluto just ten years before the synthesis of plutonium - almost the same period of time separated the discoveries of Uranus - the planet and uranium - the element.

Riddles for ransomware

The first isotope of element No. 94, plutonium-238, has now found practical application. But in the early 1940s, they didn't even think about it. It is possible to obtain plutonium-238 in quantities of practical interest only by relying on a powerful nuclear industry. At the time, she was just getting started. But it was already clear that by releasing the energy contained in the nuclei of heavy radioactive elements, it was possible to obtain weapons of unprecedented power. The Manhattan Project appeared, having nothing but a name in common with the well-known area of ​​New York. This was the general name for all the work related to the creation of the first atomic bombs in the United States. The head of the Manhattan Project was not a scientist, but a military man - General Groves, who "affectionately" called his highly educated wards "broken pots".
The leaders of the "project" were not interested in plutonium-238. Its nuclei, as, indeed, the nuclei of all plutonium isotopes with even mass numbers, do not fission with low-energy neutrons, so it could not serve as a nuclear explosive. Nevertheless, the first not very intelligible reports about elements Nos. 93 and 94 only appeared in print in the spring of 1942.
How can this be explained? Physicists understood: the synthesis of plutonium isotopes with odd mass numbers is a matter of time, and not far off. The odd isotopes were expected to, like uranium-235, be able to sustain a nuclear chain reaction. In them, not yet received, some people saw a potential nuclear explosive. And these hopes plutonium, unfortunately, justified.
In the ciphers of that time, element No. 94 was called nothing more than ... copper. And when the need arose for copper itself (as a structural material for some parts), then in encryption, along with “copper”, “genuine copper” appeared.

"Tree of the Knowledge of Good and Evil"

In 1941, the most important isotope of plutonium, an isotope with a mass number of 239, was discovered. And almost immediately the prediction of theorists was confirmed: the nuclei of plutonium-239 fissioned with thermal neutrons. Moreover, in the process of their fission, no less number of neutrons were born than in the fission of uranium-235. Ways of obtaining this isotope in large quantities were immediately outlined ...
Years have passed. Now it is no secret to anyone that the nuclear bombs stored in the arsenals are stuffed with plutonium-239 and that these bombs are enough to cause irreparable damage to all life on Earth.
It is widely believed that with the discovery of a nuclear chain reaction (the inevitable consequence of which was the creation of a nuclear bomb), humanity was clearly in a hurry. You can think differently or pretend to think differently - it's more pleasant to be an optimist. But even optimists inevitably face the question of the responsibility of scientists. We remember the triumphant day in June 1954, the day when the first nuclear power plant in Obninsk gave electricity. But we cannot forget the August morning of 1945 - "Hiroshima morning", "Albert Einstein's rainy day"... We remember the first post-war years and unbridled atomic blackmail - the basis of American policy of those years. But did humanity endure few anxieties in subsequent years? Moreover, these worries were multiplied by the realization that if a new world war breaks out, nuclear weapons will be used.
Here you can try to prove that the discovery of plutonium did not add to the fears of mankind, that, on the contrary, it was only useful.
Suppose it happened that for some reason, or, as they would say in the old days, by the will of God, plutonium was not available to scientists. Would our fears and fears then decrease? Nothing happened. Nuclear bombs would be made from uranium-235 (and in no less quantity than from plutonium), and these bombs would "eat up" even larger parts of the budgets than they do now.
But without plutonium, there would be no prospects for the peaceful use of nuclear energy on a large scale. For a "peaceful atom" there simply would not be enough uranium-235. The evil inflicted on mankind by the discovery of nuclear energy would not be balanced, even if only partially, by the achievements of the "good atom".

How to measure, with what to compare

When a plutonium-239 nucleus is split by neutrons into two fragments of approximately equal mass, about 200 MeV of energy is released. This is 50 million times more energy released in the most famous exothermic reaction С + O 2 = СO 2 . "Burning" in a nuclear reactor, a gram of plutonium gives 2,107 kcal. In order not to violate traditions (and in popular articles, the energy of nuclear fuel is usually measured in off-system units - tons of coal, gasoline, trinitrotoluene, etc.), we also note: this is the energy contained in 4 tons of coal. And in an ordinary thimble is placed the amount of plutonium, energetically equivalent to forty carloads of good birch firewood.
The same energy is released during the fission of uranium-235 nuclei by neutrons. But the bulk of natural uranium (99.3%!) is the isotope 238 U, which can only be used by converting uranium into plutonium ...

Stone Energy

Let us evaluate the energy resources contained in the natural reserves of uranium.
Uranium is a scattered element, and it is practically everywhere. Anyone who has visited, for example, Karelia, surely remembered the granite boulders and coastal rocks. But few people know that there is up to 25 g of uranium in a ton of granite. Granites make up almost 20% of the weight of the earth's crust. If we count only uranium-235, then 3.5-105 kcal of energy is contained in a ton of granite. It's a lot, but...
The processing of granite and the extraction of uranium from it requires an even greater amount of energy - about 106-107 kcal/t. Now, if it were possible to use not only uranium-235, but also uranium-238 as an energy source, then granite could be considered at least as a potential energy raw material. Then the energy obtained from a ton of stone would already be from 8-107 to 5-108 kcal. This is equivalent to 16-100 tons of coal. And in this case, granite could give people almost a million times more energy than all the chemical fuel reserves on Earth.
But uranium-238 nuclei do not fission by neutrons. For nuclear energy, this isotope is useless. More precisely, it would be useless if it could not be turned into plutonium-239. And what is especially important: there is practically no need to spend energy on this nuclear transformation - on the contrary, energy is produced in this process!
Let's try to figure out how this happens, but first a few words about natural plutonium.

400 thousand times smaller than radium

It has already been said that plutonium isotopes have not been preserved since the synthesis of elements during the formation of our planet. But this does not mean that there is no plutonium in the Earth.
It is formed all the time in uranium ores. Capturing cosmic radiation neutrons and neutrons produced by spontaneous (spontaneous) fission of uranium-238 nuclei, some - very few - atoms of this isotope turn into uranium-239 atoms. These nuclei are very unstable, they emit electrons and thereby increase their charge. Neptunium is formed - the first transuranium element. Neptunium-239 is also very unstable, and its nuclei emit electrons. In just 56 hours, half of neptunium-239 turns into plutonium-239, the half-life of which is already quite long - 24 thousand years.
Why isn't plutonium mined from uranium ores?? Small, too low concentration. “Production per gram is labor per year” - this is about radium, and plutonium in ores is 400 thousand times less than radium. Therefore, not only to extract - even to detect "terrestrial" plutonium is extremely difficult. This was done only after the physical and chemical properties of plutonium obtained in nuclear reactors were studied.
Plutonium is accumulated in nuclear reactors. In powerful neutron fluxes, the same reaction occurs as in uranium ores, but the rate of formation and accumulation of plutonium in the reactor is much higher - a billion billion times. For the reaction of converting ballast uranium-238 into power-grade plutonium-239, optimal (within acceptable) conditions are created.
If the reactor operates on thermal neutrons (recall that their speed is about 2000 m per second, and the energy is fractions of an electron volt), then an amount of plutonium is obtained from a natural mixture of uranium isotopes, slightly less than the amount of “burnt out” uranium-235. Not much, but less, plus the inevitable losses of plutonium during its chemical separation from irradiated uranium. In addition, a nuclear chain reaction continues in a natural mixture of uranium isotopes only until a small fraction of uranium-235 is used up. Hence the conclusion is logical: a "thermal" reactor on natural uranium - the main type of currently operating reactors - cannot ensure the expanded reproduction of nuclear fuel. But then what is the future? To answer this question, let's compare the course of a nuclear chain reaction in uranium-235 and plutonium-239 and introduce one more physical concept into our reasoning.
The most important characteristic of any nuclear fuel is the average number of neutrons emitted after the nucleus has captured one neutron. Physicists call it the eta number and denote it with the Greek letter c. In "thermal" uranium reactors, the following pattern is observed: each neutron generates an average of 2.08 neutrons (η=2.08). The plutonium placed in such a reactor under the action of thermal neutrons gives η=2.03. But there are also reactors operating on fast neutrons. It is useless to load a natural mixture of uranium isotopes into such a reactor: the chain reaction will not start. But if the "raw materials" are enriched with uranium-235, it will be able to develop in a "fast" reactor. In this case, c will already be equal to 2.23. And plutonium, placed under fire with fast neutrons, will give n equal to 2.70. We will have "an extra full neutron" at our disposal. And this is not enough.

Let's see what the received neutrons are spent on. In any reactor, one neutron is needed to maintain a nuclear chain reaction. 0.1 neutron is absorbed by the structural materials of the facility. The "excess" goes to the accumulation of plutonium-239. In one case, the "excess" is 1.13, in the other - 1.60. After the "burning" of a kilogram of plutonium in the "fast" reactor, colossal energy is released and 1.6 kg of plutonium is accumulated. And uranium in a "fast" reactor will give the same energy and 1.1 kg of new nuclear fuel. In both cases, expanded reproduction is evident. But we must not forget about the economy.
Due to a number of technical reasons, the plutonium breeding cycle takes several years. Let's say five years. This means that the amount of plutonium will increase only by 2% per year if η=2.23, and by 12% if η=2.7! Nuclear fuel is capital, and any capital must yield, say, 5% per annum. In the first case, there are big losses, and in the second - big profits. This primitive example illustrates the "weight" of every tenth number in nuclear power.
Another thing is also important. Nuclear power must keep up with the growth in energy demand. Calculations show that his condition is feasible in the future only when η approaches three. If the development of nuclear energy sources lags behind the needs of society for energy, then there will be two ways: either “slow down progress”, or take energy from some other sources. They are known: thermonuclear fusion, the energy of annihilation of matter and antimatter, but are not yet technically available. And it is not known when they will be real sources of energy for mankind. And the energy of heavy nuclei has long become a reality for us, and today plutonium, as the main "supplier" of atomic energy, has no serious competitors, except, perhaps, uranium-233.

The sum of many technologies

When the required amount of plutonium accumulates in uranium as a result of nuclear reactions, it must be separated not only from the uranium itself, but also from fission fragments - both uranium and plutonium, burned out in a nuclear chain reaction. In addition, there is a certain amount of neptunium in the uranium-plutonium mass. The most difficult thing is to separate plutonium from neptunium and rare earth elements (lanthanides). Plutonium as a chemical element is somewhat unlucky. From the point of view of a chemist, the main element of nuclear energy is just one of fourteen actinides. Like rare earth elements, all elements of the actinium series are very close to each other in chemical properties, the structure of the outer electron shells of atoms of all elements from actinium to 103 is the same. It is even more unpleasant that the chemical properties of actinides are similar to those of rare earth elements, and among the fission fragments of uranium and plutonium there are more than enough lanthanides. But on the other hand, the 94th element can be in five valence states, and this "sweets the pill" - it helps to separate plutonium from both uranium and fission fragments.
The valency of plutonium varies from three to seven. Compounds of tetravalent plutonium are chemically the most stable (and, consequently, the most common and most studied).
The separation of chemically similar actinides - uranium, neptunium and plutonium - can be based on the difference in the properties of their tetra- and hexavalent compounds.

There is no need to describe in detail all the stages of the chemical separation of plutonium and uranium. Usually, their separation begins with the dissolution of uranium bars in nitric acid, after which the uranium, neptunium, plutonium and fragment elements contained in the solution are “separated”, using traditional radiochemical methods for this - precipitation, extraction, ion exchange and others. The final plutonium-containing products of this multi-stage technology are its dioxide PuO 2 or fluorides - PuF 3 or PuF 4 . They are reduced to metal with barium, calcium, or lithium vapors. However, the plutonium obtained in these processes is not suitable for the role of a structural material - it is impossible to make fuel elements of nuclear power reactors from it, it is impossible to cast a charge of an atomic bomb. Why? The melting point of plutonium - only 640 ° C - is quite achievable.
No matter what “ultra-sparing” conditions are used to cast parts from pure plutonium, cracks will always appear in the castings during solidification. At 640°C, solidifying plutonium forms a cubic crystal lattice. As the temperature decreases, the density of the metal gradually increases. But then the temperature reached 480 ° C, and then suddenly the density of plutonium drops sharply. The reasons for this anomaly were dug up quite quickly: at this temperature, plutonium atoms are rearranged in the crystal lattice. It becomes tetragonal and very "loose". Such plutonium can float in its own melt, like ice on water.
The temperature continues to fall, now it has reached 451 ° C, and the atoms again formed a cubic lattice, but located at a greater distance from each other than in the first case. With further cooling, the lattice becomes first orthorhombic, then monoclinic. In total, plutonium forms six different crystal forms! Two of them have a remarkable property - a negative coefficient of thermal expansion: with increasing temperature, the metal does not expand, but contracts.
When the temperature reaches 122°C and the plutonium atoms rearrange their rows for the sixth time, the density changes especially strongly - from 17.77 to 19.82 g/cm 3 . More than 10%!
Accordingly, the volume of the ingot decreases. If the metal could still withstand the stresses that arose at other transitions, then at this moment destruction is inevitable.
How, then, to make parts from this amazing metal? Metallurgists alloy plutonium (add small amounts of the necessary elements to it) and get castings without a single crack. They are used to make plutonium charges for nuclear bombs. The weight of the charge (it is determined primarily by the critical mass of the isotope) is 5-6 kg. It would easily fit in a cube with a rib size of 10 cm.

Heavy isotopes of plutonium

Plutonium-239 also contains a small amount of higher isotopes of this element - with mass numbers 240 and 241. The 240 Pu isotope is practically useless - it is ballast in plutonium. From the 241st, americium is obtained - element No. 95. In its pure form, without admixture of other isotopes, plutonium-240 and plutonium-241 can be obtained by electromagnetic separation of plutonium accumulated in the reactor. Before this, plutonium is additionally irradiated with neutron fluxes with strictly defined characteristics. Of course, all this is very complicated, especially since plutonium is not only radioactive, but also very toxic. Working with it requires extreme caution.
One of the most interesting isotopes of plutonium, 242 Pu, can be obtained by irradiating 239 Pu for a long time in neutron fluxes. 242 Pu very rarely captures neutrons and therefore "burns out" in the reactor more slowly than other isotopes; it persists even after the remaining isotopes of plutonium have almost completely passed into fragments or turned into plutonium-242.
Plutonium-242 is important as a "raw material" for the relatively rapid accumulation of higher transuranium elements in nuclear reactors. If plutonium-239 is irradiated in a conventional reactor, then it will take about 20 years to accumulate microgram amounts of plutonium from grams, for example, californium-252.
It is possible to reduce the accumulation time of higher isotopes by increasing the intensity of the neutron flux in the reactor. They do so, but then it is impossible to irradiate a large amount of plutonium-239. After all, this isotope is divided by neutrons, and too much energy is released in intense flows. There are additional difficulties with the cooling of the reactor. To avoid these complications, the amount of irradiated plutonium would have to be reduced. Consequently, the output of California would again be miserable. Vicious circle!
Plutonium-242 is not fissile by thermal neutrons, and it can be irradiated in large quantities in intense neutron fluxes ... Therefore, in reactors, all elements from americium to fermium are “made” from this isotope and accumulate in weight quantities.
Whenever scientists succeeded in obtaining a new isotope of plutonium, they measured the half-life of its nuclei. The half-lives of isotopes of heavy radioactive nuclei with even mass numbers change regularly. (The same cannot be said for odd isotopes.)
As the mass increases, so does the "lifetime" of the isotope. A few years ago, plutonium-242 was the highest point on this graph. And then how will this curve go - with a further increase in the mass number? To point 1, which corresponds to a lifetime of 30 million years, or to point 2, which already corresponds to 300 million years? The answer to this question was very important for the geosciences. In the first case, if 5 billion years ago the Earth consisted entirely of 244 Pu, now only one atom of plutonium-244 would remain in the entire mass of the Earth. If the second assumption is correct, then plutonium-244 may be in the Earth in concentrations that could already be detected. If we were lucky enough to find this isotope in the Earth, science would receive the most valuable information about the processes that took place during the formation of our planet.

Half-lives of some isotopes of plutonium

A few years ago, scientists faced the question: is it worth trying to find heavy plutonium in the Earth? To answer it, it was necessary first of all to determine the half-life of plutonium-244. Theorists could not calculate this value with the required accuracy. All hope was only for the experiment.
Plutonium-244 accumulated in a nuclear reactor. Element No. 95, americium (isotope 243 Am), was irradiated. Having captured a neutron, this isotope passed into americium-244; americium-244 in one of 10 thousand cases passed into plutonium-244.
A plutonium-244 preparation was isolated from a mixture of americium and curium. The sample weighed only a few millionths of a gram. But they were enough to determine the half-life of this most interesting isotope. It turned out to be equal to 75 million years. Later, other researchers specified the half-life of plutonium-244, but not by much - 81 million years. In 1971, traces of this isotope were found in the rare earth mineral bastnäsite.
Scientists have made many attempts to find an isotope of a transuranium element that lives longer than 244 Pu. But all attempts were in vain. At one time, hopes were placed on curium-247, but after this isotope was accumulated in a reactor, it turned out that its half-life was only 16 million years. It was not possible to beat the record for plutonium-244 - it is the longest-lived of all isotopes of transuranium elements.
Even heavier isotopes of plutonium are subject to beta decay, and their lifetimes range from a few days to a few tenths of a second. We know for certain that all isotopes of plutonium, up to 257 Pu, are formed in thermonuclear explosions. But their lifetime is tenths of a second, and many short-lived isotopes of plutonium have not yet been studied.

Possibilities of the first plutonium isotope

And finally - about plutonium-238 - the very first of the "man-made" isotopes of plutonium, an isotope that at first seemed unpromising. It's actually a very interesting isotope. It is subject to alpha decay, i.e., its nuclei spontaneously emit alpha particles - helium nuclei. Alpha particles generated by the nuclei of plutonium-238 carry a lot of energy; dissipated in matter, this energy is converted into heat. How big is this energy? Six million electron volts are released when one atomic nucleus of plutonium-238 decays. In a chemical reaction, the same energy is released when several million atoms are oxidized. A source of electricity containing one kilogram of plutonium-238 develops a thermal power of 560 watts. The maximum power of a chemical current source of the same mass is 5 watts.
There are many emitters with similar energy characteristics, but one feature of plutonium-238 makes this isotope indispensable. Usually alpha decay is accompanied by strong gamma radiation penetrating through large thicknesses of matter. 238 Pu is an exception. The energy of gamma quanta accompanying the decay of its nuclei is low, and it is not difficult to defend against it: the radiation is absorbed by a thin-walled container. The probability of spontaneous nuclear fission of this isotope is also small. Therefore, it has found application not only in current sources, but also in medicine. Batteries with plutonium-238 serve as an energy source in special cardiac stimulators.
But 238 Pu is not the lightest of the known isotopes of element No. 94; plutonium isotopes with mass numbers from 232 to 237 have been obtained. The half-life of the lightest isotope is 36 minutes.

Plutonium is a big topic. Here is the most important of the most important. After all, it has already become a standard phrase that the chemistry of plutonium has been studied much better than the chemistry of such "old" elements as iron. Entire books have been written about the nuclear properties of plutonium. Plutonium metallurgy is another amazing section of human knowledge... Therefore, you should not think that after reading this story, you really learned plutonium - the most important metal of the 20th century.

• HOW THE PLUTONIUM IS CARRIED OUT. Radioactive and toxic plutonium requires special care during transportation. A container was designed specifically for its transportation - a container that does not collapse even during aviation accidents. It is made quite simply: it is a thick-walled stainless steel vessel surrounded by a mahogany shell. Obviously plutonium is worth it, but imagine how thick the walls must be if you know that a container for transporting only two kilograms of plutonium weighs 225 kg!
• POISON AND ANTIDOTE. On October 20, 1977, the Agence France-Presse reported that a chemical compound had been found that could remove plutonium from the human body. A few years later, quite a lot became known about this compound. This complex compound is a linear carboxylase catechinamide, a substance of the chelate class (from the Greek - "hela" - a claw). It is into this chemical claw that the atom of plutonium, free or bound, is captured. In laboratory mice, up to 70% of the absorbed plutonium was removed from the body with the help of this substance. It is believed that in the future this compound will help to extract plutonium from both industrial waste and nuclear fuel.

Plutonium was discovered at the end of 1940 at the University of California. It was synthesized by McMillan, Kennedy and Wahl by bombarding uranium oxide (U 3 O 8) with deuterium nuclei (deuterons) strongly accelerated in a cyclotron. Later it was found that this nuclear reaction first produces the short-lived isotope neptunium-238, and from it already plutonium-238 with a half-life of about 50 years. A year later, Kennedy, Seaborg, Segre, and Wahl synthesized the more important isotope, plutonium-239, by irradiating uranium with highly accelerated neutrons in a cyclotron. Plutonium-239 is formed from the decay of neptunium-239; it emits alpha rays and has a half-life of 24,000 years. A pure plutonium compound was first obtained in 1942. Then it became known that there is natural plutonium found in uranium ores, in particular in ores, deposits in the Congo.

The name of the element was proposed in 1948: McMillan called the first transuranic element neptunium due to the fact that the planet Neptune is the first one beyond Uranus. By analogy, they decided to call element 94 plutonium, since the planet Pluto is the second planet after Uranus. Pluto, discovered in 1930, got its name from the name of the god Pluto, the ruler of the underworld in Greek mythology. At the beginning of the XIX century. Clark proposed to name the element barium plutonium, deriving this name directly from the name of the god Pluto, but his proposal was not accepted.

Enrico Fermi, along with his collaborators at the University of Rome, reported that they had discovered a chemical element with atomic number 94 in 1934. Fermi named this element hesperium, believing that he discovered the element now called plutonium, thus making the assumption about the existence of transuranium elements and becoming their theoretical discoverer. He adhered to this position in his Nobel lecture in 1938, however, having learned about the discovery of nuclear fission by Otto Frisch and Fritz Strassmann, he was forced to make a note in the printed version, published in Stockholm in 1939, indicating the need to revise "the entire problem of transuranic elements." The work of German scientists showed that the activity detected by Fermi in his experiments was due precisely to fission, and not to the discovery of transuranium elements, as he had previously believed.

Cyclotron at Berkeley, used to produce neptunium and plutonium.

The discovery of plutonium by a group of employees of the University of California at Berkeley, led by G. T. Seaborg, was made using a 60-inch cyclotron, which was at the disposal of the university. The first bombardment of triuranium-238 octoxide with deuterons accelerated in a cyclotron to 14-22 MeV and passing through 0.002 inch thick aluminum foil was made on December 14, 1940. Comparing samples obtained and aged for 2.3 days with the isolated fraction of pure neptunium, scientists found a significant difference in their alpha activities and suggested that its increase after 2 days is due to the influence of a new element that is a child of neptunium. Further physical and chemical studies continued for 2 months. On the night of February 23-24, 1941, a decisive experiment was carried out on the oxidation of the proposed element using peroxide disulfate ions and silver ions as a catalyst, which showed that neptunium-238, after two days, undergoes beta-minus decay, and forms a chemical element number 94 in the following reaction:

23892U → 23893Np → 23894Pu

Glenn Theodore Seaborg, along with collaborators at Berkeley, synthesized plutonium for the first time. He was the leader or key member of teams that received eight more elements: Am, Cm, Bk, Cf, Es, Fm, Md, No. The element seaborgium is named after him. Edwin Macmillan and Glenn Seaborg were awarded the Nobel Prize in 1951 for "the study of the chemistry of the transuranium elements".

Thus, the existence of a new chemical element was confirmed by G. T. Seaborg, E. M. Macmillan, J. W. Kennedy, and A. C. Wall through the study of its first chemical properties - the ability to have at least two oxidation states.

A little later, it was found that this isotope is non-fissile, and therefore uninteresting for further research for military purposes, since threshold nuclei cannot serve as the basis for a fission chain reaction. Realizing this, US nuclear physicists directed their efforts to obtaining the fissile isotope-239. In March 1941, 1.2 kg of the purest uranium salt, immured in a large block of paraffin, was bombarded with neutrons in a cyclotron. The bombardment of uranium nuclei lasted for two days, as a result of which approximately 0.5 micrograms of plutonium-239 were obtained. The appearance of a new element, as predicted by the theory, was accompanied by a stream of alpha particles.

On March 28, 1941, the experiments carried out showed that Pu is capable of fission under the action of slow neutrons, with a cross section very significantly exceeding the cross section for U, and the neutrons obtained in the fission process are suitable for obtaining the following acts of nuclear fission, that is, they allow one to rely on the implementation of a chain nuclear reaction. From that moment, experiments began on the creation of a plutonium nuclear bomb and the construction of reactors for its development. The first pure compound of the element was obtained in 1942, and the first plutonium metal by weight in 1943.

A paper submitted for publication in the journal Physical Review in March 1941 described a method for obtaining and studying the element. However, the publication of this document was stopped after data were received that the new element could be used in a nuclear bomb. The publication of the work took place a year after the Second World War for security reasons and with some adjustments.

In the Third Reich, atomic researchers also did not remain inactive. In the laboratory of Manfred von Arden, methods were developed to obtain the 94th element. In August 1941, physicist Fritz Houtermans completed his secret report "On the Question of Unleashing Nuclear Chain Reactions." In it, he pointed out the theoretical possibilities for the manufacture of a new explosive from natural uranium in a uranium "boiler".

origin of name

With the help of this astrograph, the first pictures of Pluto were obtained.

In 1930, a new planet was discovered, the existence of which had long been talked about by Percival Lovell, an astronomer, mathematician and author of fantastic essays on life on Mars. On the basis of many years of observations of the movements of Uranus and Neptune, he came to the conclusion that behind Neptune in the solar system there must be another, ninth planet, located forty times farther from the Sun than the Earth. The elements of the orbit of the new planet were calculated by him in 1915. Pluto was discovered in photographs taken on January 21, 23 and 29, 1930 by astronomer Clyde Tombaugh at the Lowell Observatory in Flagstaff. The planet was discovered on February 18, 1930. The name of the planet was given by an eleven-year-old schoolgirl from Oxford, Venetia Burney. In Greek mythology, Hades is the god of the underworld.

The first printed mention of the term plutonium dates from March 21, 1942. The name of the 94th chemical element was proposed by Arthur Wahl and Glenn Seaborg. In 1948, Edwin Macmillan suggested that the 93rd chemical element be named neptunium, since Neptune is the first planet beyond Uranus. By analogy, plutonium was named after the second planet beyond Uranus, Pluto. The discovery of plutonium occurred 10 years after the discovery of the dwarf planet.

Initially, Seaborg suggested calling the new element "plutium", but later decided that the name "plutonium" sounded better. To designate the element, he jokingly gave two letters "Pu" - this designation seemed to him the most acceptable in the periodic table. Seaborg also suggested some other variants of names, for example, ultimium, extermia. However, due to the misconception at the time that plutonium would be the last chemical element on the periodic table, the element was named "plutonium" after the discovery of the last planet in the solar system.

First studies

After several months of initial research, the chemistry of plutonium began to be considered similar to that of uranium. Further research was continued at the secret metallurgical laboratory at the University of Chicago. Thanks to Cunningham and Werner, on August 18, 1942, the first microgram of pure plutonium compound was isolated from 90 kg of uranyl nitrate irradiated with neutrons in a cyclotron. On September 10, 1942 - a month later, during which scientists increased the amount of the compound - a weighing took place. This historical sample weighed 2.77 micrograms and consisted of plutonium dioxide; currently stored in Lawrence Hall, Berkeley. By the end of 1942, 500 micrograms of the salt of the element had been accumulated. For a more detailed study of the new element in the United States, several groups were formed:

• a group of scientists who were supposed to isolate pure plutonium by chemical methods,
• a group that studied the behavior of plutonium in solutions, including the study of its oxidation states, ionization potentials, and reaction kinetics,
• a group that studied the chemistry of complex formation of plutonium ions; and other groups.

Research has shown that plutonium can be found in oxidation states between 3 and 6, and that the lower oxidation states tend to be more stable than neptunium. At the same time, the similarity of the chemical properties of plutonium and neptunium was established. In 1942, Stan Thomson, a member of Glenn Seaborg's group, discovered that tetravalent plutonium was obtained in large quantities when placed in an acidic solution in the presence of bismuth phosphate. Subsequently, this led to the study and application of the bismuth-phosphate method for the extraction of plutonium. In November 1943, some amounts of plutonium fluoride were separated to obtain a pure sample of the element in the form of a few micrograms of fine powder. Subsequently, samples were obtained that could be seen with the naked eye.

The first cyclotron in the USSR used to produce plutonium.

In the USSR, the first experiments on obtaining Pu were started in 1943-1944. under the guidance of academicians I. V. Kurchatov and V. G. Khlopin. In a short time, extensive studies of the properties of plutonium were carried out in the USSR. At the beginning of 1945, at the first cyclotron in Europe, built in 1937 at the Radium Institute, the first Soviet sample of plutonium was obtained by neutron irradiation of uranium nuclei. In the city of Ozyorsk, since 1945, the construction of the first industrial nuclear reactor for the production of plutonium began, the first object of the Mayak Production Association, which was launched on June 19, 1948.

Production in the Manhattan Project

The most important locations for the Manhattan Project.

The Manhattan Project originates from Einstein's letter to Roosevelt. The letter drew the president's attention to the fact that Nazi Germany was conducting active research, as a result of which it could soon acquire an atomic bomb. In August 1939, Leo Sillard asked his friend Albert Einstein to sign a letter. As a result of Franklin Roosevelt's positive response, the Manhattan Project was subsequently formed in the United States.

During World War II, the goal of the project was to create a nuclear bomb. The draft atomic program, from which the Manhattan Project was formed, was approved and simultaneously created by decree of the President of the United States on October 9, 1941. The Manhattan Project began its activities on August 12, 1942. Its three main goals were:

• Plutonium production at the Hanford complex
• Uranium enrichment at Oak Ridge, Tennessee
• Research in the field of nuclear weapons and the structure of the atomic bomb at the Los Alamos National Laboratory

A commemorative photograph of the scientists who took part in the Chicago Woodpile-1. Front row, second from right: Leo Sillard; first from left: Enrico Fermi.

The first nuclear reactor to produce large quantities of the element compared to cyclotrons was the Chicago Woodpile-1. It entered service on 2 December 1942 thanks to Enrico Fermi and Leo Sillard; On this day, the first self-sustaining nuclear chain reaction took place. Uranium-238 and uranium-235 were used to produce plutonium-239. The reactor was built under the stands at Stagg Field at the University of Chicago. It consisted of 6 tons of uranium metal, 34 tons of uranium oxide, and 400 tons of "black bricks" of graphite. The only thing that could stop a nuclear chain reaction was cadmium rods, which capture thermal neutrons well and, as a result, can prevent a possible incident. Due to the lack of radiation protection and cooling, its usual power was only 0.5 ... 200 watts.

Workers at the X-10 Graphite Reactor.

The second reactor that made it possible to produce plutonium-239 was the X-10 Graphite Reactor. It was put into operation on November 4, 1943 in the city of Oak Ridge, it is currently located on the territory of the Oak Ridge National Laboratory. This reactor was the second in the world after the Chicago Woodpile-1 and the first reactor to be created in the continuation of the Manhattan Project. The reactor was the first step towards the creation of more powerful nuclear reactors, that is, it was experimental. The end of his work came in 1963; open to the public since the 1980s and is one of the oldest nuclear reactors in the world.

On April 5, 1944, Emilio Segre received the first samples of plutonium produced in the X-10 reactor. Within 10 days, he discovered that the concentration of plutonium-240 in the reactor was very high compared to cyclotrons. This isotope has a very high ability to spontaneous fission, as a result of which the general background of neutron irradiation increases. On this basis, it was concluded that the use of high-purity plutonium in a cannon-type nuclear bomb, in particular in the Khudoy bomb, could lead to premature detonation. Due to the fact that the technology of development of nuclear bombs has improved more and more, it was found that for a nuclear charge it is best to use nuclear matter in the form of spheres.

Construction of Reactor B, the first nuclear reactor capable of producing plutonium on an industrial scale.

The first commercial Pu production nuclear reactor is Reactor B, located in the USA. Construction began in June 1943 and ended in September 1944. The reactor power was 250 MW. For the first time, water was used as a coolant in this reactor. Reactor B produced plutonium-239, which was first used in the Trinity test. Nuclear materials obtained from this reactor were used in the bomb dropped on Nagasaki on August 9, 1945. The constructed reactor was closed in February 1968 and is located in the desert region of Washington State, near the city of Richland.

Hanford Complex. Reactors B, D, F, etc. are located along the river in the upper part of the scheme.

During the Manhattan Project, many areas were created at the Hanford complex for the receipt, storage, processing and use of nuclear materials. These burial sites contain about 205 kg of plutonium isotopes. Multiple areas were formed to store the nine nuclear reactors that produced the chemical element, the numerous ancillary buildings that polluted the environment. Others of these areas were created with the aim of separating plutonium and uranium from impurities by chemical means. After the closure of this complex, more than 20 tons of plutonium in safe forms were disposed of.

In 2004, as a result of excavations, burials were discovered on the territory of the Hanford complex. Among them was found weapons-grade plutonium, which was in a glass vessel. This sample of weapons-grade plutonium proved to be the longest-lived and was examined by the Pacific National Laboratory. The results showed that this sample was created on the X-10 graphite reactor in 1944.

One of the participants in the project was involved in the secret transfer of drawings on the principles of the construction of uranium and plutonium bombs, as well as samples of uranium-235 and plutonium-239.

Trinity and the Fat Man

The first nuclear test, called Trinity, on July 16, 1945, near Alamogordo, New Mexico, used plutonium as the nuclear charge. The Thing used conventional lenses to compress plutonium to a critical mass. This device was created to test a new type of nuclear bomb "Fat Man" based on plutonium. At the same time, neutrons began to flow from the Hedgehog for a nuclear reaction. The device was made from polonium and beryllium; this source was used in the first generation of nuclear bombs, since at that time this composition was considered the only source of neutrons. All this composition made it possible to achieve a powerful nuclear explosion. The total mass of the bomb used in the Trinity nuclear test was 6 tons, although the bomb core contained only 6.2 kg of plutonium, and the estimated altitude for the explosion over the city was 225-500 m. Approximately 20% of the plutonium used in this bomb was 20,000 tons in TNT equivalent.

The Fat Man bomb was dropped on Nagasaki on August 9, 1945. As a result of the explosion, 70 thousand people were instantly killed and another 100 thousand were injured. It had a similar mechanism: a core made of plutonium was placed in a spherical aluminum shell, which was surrounded by chemical explosives. During the detonation of the shell, the plutonium charge was compressed from all sides and its density outgrew the critical one, after which a nuclear chain reaction began. The Malysh, dropped on Hiroshima three days earlier, used uranium-235 but not plutonium. Japan signed a surrender agreement on August 15. After these cases, a message was published in the media about the use of a new chemical radioactive element - plutonium.

cold war

Large quantities of plutonium were produced during the Cold War by the US and the USSR. The US reactors at the Savannah River Site and Hanford produced 103 tons of plutonium during the war, while the USSR produced 170 tons of weapons-grade plutonium. Today, about 20 tons of plutonium is produced in nuclear power as a by-product of nuclear reactions. For every 1,000 tons of plutonium in storage, there are 200 tons of plutonium recovered from nuclear reactors. For 2007, the SIIM estimated the world's plutonium at 500 tons, which is roughly equally divided into weapons and energy needs.

The proposed layout of the nuclear waste storage tunnel at the Yucca Mountain Repository.

Immediately after the end of the Cold War, all nuclear stockpiles became a proliferation problem. For example, in the United States, two-ton blocks were fused from plutonium extracted from nuclear weapons, in which the element is in the form of inert plutonium oxide. These blocks are glazed with borosilicate glass with an admixture of zirconium and gadolinium. Then these blocks were covered with stainless steel and buried in the ground to a depth of 4 km. The US local and state authorities did not allow nuclear waste to be stored in Yucca Mountain. In March 2010, the US authorities decided to revoke the license for the right to store nuclear waste. Barack Obama proposed to review the policy of waste storage and provide recommendations for the development of new effective methods for the management of spent fuel and waste.

medical experiments

Throughout the Second World War and after it, scientists conducted experiments on animals and humans, injecting doses of plutonium intravenously. Animal studies have shown that a few milligrams of plutonium per kilogram of tissue is a lethal dose. The "standard" dose was 5 micrograms of plutonium, and in 1945 this figure was reduced to 1 microgram due to the fact that plutonium tends to accumulate in bones and is therefore more dangerous than radium.

Eighteen human tests of plutonium were carried out without prior consent, in order to find out where and how plutonium is concentrated in the human body, and to develop standards for the safe handling of it. The first places where experiments were carried out as part of the Manhattan Project were: Hanford, Berkeley, Los Alamos, Chicago, Oak Ridge, Rochester.