Description of plutonium

Plutonium(Plutonium) is a silvery heavy chemical element, a radioactive metal with atomic number 94, which is represented in the periodic table by the symbol Pu.

This electronegative active chemical element belongs to the group of actinides with an atomic mass of 244.0642, and, like neptunium, which received its name in honor of the planet of the same name, this chemical owes its name to the planet Pluto, since the predecessors of the radioactive element in Mendeleev’s periodic table of chemical elements are and neptunium, which were also named after distant cosmic planets in our Galaxy.

Origin of plutonium

Element plutonium was first discovered in 1940 at the University of California by a group of radiologist and scientific researchers G. Seaborg, E. McMillan, Kennedy, A. Walch when bombarding a uranium target from a cyclotron with deuterons - heavy hydrogen nuclei.

In December of the same year, scientists discovered plutonium isotope– Pu-238, the half-life of which is more than 90 years, and it was found that under the influence of complex nuclear chemical reactions the isotope neptunium-238 is initially produced, after which the isotope is already formed plutonium-238.

In early 1941, scientists discovered plutonium 239 with a decay period of 25,000 years. Isotopes of plutonium can have different neutron contents in the nucleus.

A pure compound of the element was only obtained at the end of 1942. Every time radiological scientists discovered a new isotope, they always measured the half-lives of the isotopes.

At the moment, plutonium isotopes, of which there are 15 in total, differ in time duration half-life. It is with this element that great hopes and prospects are associated, but at the same time, serious fears of humanity.

Plutonium has significantly greater activity than, for example, uranium and is one of the most expensive technically important and significant substances of a chemical nature.

For example, the cost of a gram of plutonium is several times more than one gram, , or other equally valuable metals.

The production and extraction of plutonium is considered costly, and the cost of one gram of metal in our time confidently remains at around 4,000 US dollars.

How is plutonium obtained? Plutonium production

The production of the chemical element occurs in nuclear reactors, inside which uranium is split under the influence of complex chemical and technological interrelated processes.

Uranium and plutonium are the main, main components in the production of atomic (nuclear) fuel.

If it is necessary to obtain a large amount of a radioactive element, the method of irradiation of transuranic elements, which can be obtained from spent nuclear fuel and irradiation of uranium, is used. Complex chemical reactions allow the metal to be separated from uranium.

To obtain isotopes, namely plutonium-238 and weapons-grade plutonium-239, which are intermediate decay products, irradiation of neptunium-237 with neutrons is used.

A tiny fraction of plutonium-244, which is the longest-lived isotope due to its long half-life, was discovered in cerium ore, which is likely preserved from the formation of our planet Earth. This radioactive element does not occur naturally in nature.

Basic physical properties and characteristics of plutonium

Plutonium is a fairly heavy radioactive chemical element with a silvery color that only shines when purified. Nuclear mass of metal plutonium equal to 244 a. eat.

Due to its high radioactivity, this element is warm to the touch and can heat up to a temperature that exceeds the boiling temperature of water.

Plutonium, under the influence of oxygen atoms, quickly darkens and becomes covered with an iridescent thin film of initially light yellow, and then a rich or brown hue.

With strong oxidation, the formation of PuO2 powder occurs on the surface of the element. This type of chemical metal is subject to strong oxidation processes and corrosion even at low levels of humidity.

To prevent corrosion and oxidation of the metal surface, a drying facility is necessary. Photo of plutonium can be viewed below.

Plutonium is a tetravalent chemical metal; it dissolves well and quickly in hydroiodic substances and acidic environments, for example, in chloric acid.

Metal salts are quickly neutralized in environments with a neutral reaction, alkaline solutions, while forming insoluble plutonium hydroxide.

The temperature at which plutonium melts is 641 degrees Celsius, the boiling point is 3230 degrees.

Under the influence of high temperatures, unnatural changes in the density of the metal occur. In its form, plutonium has various phases and has six crystal structures.

During the transition between phases, significant changes in the volume of the element occur. The element acquires its most dense form in the sixth alpha phase (the last stage of the transition), while the only things heavier than the metal in this state are neptunium and radium.

When melted, the element undergoes strong compression, so the metal can float on the surface of water and other non-aggressive liquid media.

Despite the fact that this radioactive element belongs to the group of chemical metals, the element is quite volatile, and when it is in a closed space over a short period of time, its concentration in the air increases several times.

The main physical properties of the metal include: low degree, level of thermal conductivity of all existing and known chemical elements, low level of electrical conductivity; in the liquid state, plutonium is one of the most viscous metals.

It is worth noting that any plutonium compounds are toxic, poisonous and pose a serious danger of radiation to the human body, which occurs due to active alpha radiation, therefore all work must be performed with the utmost care and only in special suits with chemical protection.

You can read more about the properties and theories of the origin of a unique metal in the book Obruchev "Plutonia"" Author V.A. Obruchev invites readers to plunge into the amazing and unique world of the fantastic country of Plutonia, which is located deep in the bowels of the Earth.

Applications of plutonium

The industrial chemical element is usually classified into weapons-grade and reactor-grade (“energy-grade”) plutonium.

Thus, for the production of nuclear weapons, of all existing isotopes, it is permissible to use only plutonium 239, which should not contain more than 4.5% plutonium 240, since it is subject to spontaneous fission, which significantly complicates the production of military projectiles.

Plutonium-238 is used for the operation of small-sized radioisotope sources of electrical energy, for example, as an energy source for space technology.

Several decades ago, plutonium was used in medicine in pacemakers (devices for maintaining heart rhythm).

The first atomic bomb created in the world had a plutonium charge. Nuclear plutonium(Pu 239) is in demand as nuclear fuel to ensure the functioning of power reactors. This isotope also serves as a source for producing transplutonium elements in reactors.

If we compare nuclear plutonium with pure metal, the isotope has higher metallic parameters and does not have transition phases, so it is widely used in the process of obtaining fuel elements.

Oxides of the Plutonium 242 isotope are also in demand as a power source for space lethal units, equipment, and fuel rods.

Weapons-grade plutonium is an element that is presented in the form of a compact metal that contains at least 93% of the Pu239 isotope.

This type of radioactive metal is used in the production of various types of nuclear weapons.

Weapons-grade plutonium is produced in specialized industrial nuclear reactors that operate on natural or low-enriched uranium as a result of the capture of neutrons.

There are 15 known isotopes of plutonium. The most important of these is Pu-239 with a half-life of 24,360 years. The specific gravity of plutonium is 19.84 at a temperature of 25°C. The metal begins to melt at a temperature of 641°C and boils at 3232°C. Its valency is 3, 4, 5 or 6.

The metal has a silvery tint and turns yellow when exposed to oxygen. Plutonium is a chemical reactive metal and easily dissolves in concentrated hydrochloric acid, perchloric acid, and hydroiodic acid. During decay, the metal releases heat energy.

Plutonium is the second transuranic actinide discovered. In nature, this metal can be found in small quantities in uranium ores.

Plutonium is poisonous and requires careful handling. The most fissionable isotope of plutonium has been used as a nuclear weapon. In particular, it was used in a bomb that was dropped on the Japanese city of Nagasaki.

This is a radioactive poison that accumulates in the bone marrow. Several accidents, some fatal, occurred while experimenting on people to study plutonium. It is important that the plutonium does not reach critical mass. In solution, plutonium forms a critical mass faster than in the solid state.

Atomic number 94 means that all plutonium atoms are 94. In air, plutonium oxide forms on the surface of the metal. This oxide is pyrophoric, so smoldering plutonium will flicker like ash.

There are six allotropic forms of plutonium. The seventh form appears at high temperatures.

In an aqueous solution, plutonium changes color. Various shades appear on the surface of the metal as it oxidizes. The oxidation process is unstable and the color of plutonium can change suddenly.

Unlike most substances, plutonium becomes denser when melted. In the molten state, this element is more viscous than other metals.

The metal is used in radioactive isotopes in thermoelectric generators that power spacecraft. In medicine, it is used in the production of electronic cardiac stimulators.

Inhaling plutonium vapor is hazardous to health. In some cases, this can cause lung cancer. Inhaled plutonium has a metallic taste.

Plutonium (Latin Plutonium, symbol Pu) is a radioactive chemical element with atomic number 94 and atomic weight 244.064. Plutonium is an element of Group III of Dmitry Ivanovich Mendeleev’s periodic table and belongs to the actinide family. Plutonium is a heavy (density under normal conditions 19.84 g/cm³) brittle radioactive metal of a silvery-white color.

Plutonium has no stable isotopes. Of the hundred possible isotopes of plutonium, twenty-five have been synthesized. The nuclear properties of fifteen of them were studied (mass numbers 232-246). Four have found practical application. The longest-lived isotopes are 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 negligible quantities in uranium ores (239Pu); it is formed from uranium under the influence of neutrons, the sources of which are reactions occurring during the interaction of α-particles with light elements (included in 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) when 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 Lewis Turner.

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

Edwin MacMillan in 1948 proposed to name the chemical element 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 (239Pu isotope) is used in nuclear weapons and serves as nuclear fuel in power reactors operating on thermal and especially fast neutrons. The critical mass for 239Pu as 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 power sources used in space research, as well as in human cardiac stimulants.

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, since 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 find their application 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 surrounding tissue of the body. Gamma radiation from plutonium is not dangerous to the body. It is worth considering that different isotopes of plutonium have different toxicities, for example, typical reactor 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 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. Land plants absorb plutonium mainly through the root system and accumulate it 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 danger (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 ability: for 239Pu, the range of α-particles in air is 3.7 cm, and in soft biological tissue 43 μm. Therefore, alpha particles pose a serious danger if their source is in the body of an infected person. At the same time, they damage the tissues of the body surrounding the element.

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 a group of elements with particularly high radiotoxicity. At the same time, different isotopes of plutonium have different toxicity, for example, typical reactor 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 ingested through water and food, plutonium is less toxic than substances such as caffeine, some vitamins, pseudoephedrine, and many plants and fungi. This is explained by the fact that this element is poorly absorbed by the gastrointestinal tract, even when supplied in the form of a soluble salt, this same salt is bound by the contents of the stomach and intestines. However, ingestion of 0.5 grams of finely divided or dissolved plutonium can result in death from acute digestive irradiation within days or weeks (for cyanide this value is 0.1 grams).

From an inhalation point of view, plutonium is an ordinary toxin (roughly equivalent to mercury vapor). When inhaled, plutonium is carcinogenic and can cause lung cancer. So, when inhaled, one hundred milligrams of plutonium in the form of particles of an optimal size for retention in the lungs (1-3 microns) 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 danger of inhalation of plutonium into the body increases due to the fact that plutonium is prone to the formation of aerosols.

Even though it is a metal, it is quite volatile. A short stay of metal in a room significantly increases its concentration in the air. Plutonium that enters the lungs partially settles on the surface of the lungs, partially passes into the blood, and then into the lymph and bone marrow. Most (approximately 60%) ends up in bone tissue, 30% in the liver and only 10% is excreted naturally. The amount of plutonium that enters the body depends on the size of aerosol particles and solubility in the blood.

Plutonium entering the human body in one way or another is similar in properties to ferric iron, therefore, penetrating into 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, as a result of which the transfer of oxygen in the body stops. Microphages carry plutonium to the lymph nodes. Plutonium that enters the body takes a very long time to be removed from the body - within 50 years, only 80% will be removed from the body. The 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 element ninety-four in bones is constant.

Throughout World War II and after its end, scientists working in the Manhattan Project, as well as scientists of 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 of usually 5 mcg of plutonium being injected intramuscularly into chronically ill patients. It was eventually determined that the lethal dose to a patient was one microgram of plutonium, and that plutonium was more dangerous than radium and tended to accumulate in bones.

As is known, plutonium is an element practically absent in nature. However, about five tons of it were 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 tests before the 1980s is estimated at 10 tons. By some estimates, soil in the United States contains an average of 2 millicuries (28 mg) of plutonium per km2 of fallout, and the occurrence of plutonium in the Pacific Ocean is elevated relative to the overall distribution of nuclear materials on earth.

The latest phenomenon is associated with US nuclear testing in the Marshall Islands at the Pacific Test Site in the mid-1950s. The residence time of plutonium in surface ocean waters ranges from 6 to 21 years, however, even after this period, plutonium falls to the bottom along with biogenic particles, from which it is reduced to soluble forms as a result of microbial decomposition.

Global pollution with 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 deorbit, a satellite with a nuclear power source on board fell into Canadian territory. As a result of the accident, more than a kilogram of plutonium-238 was released into the environment, spreading over an area of ​​about 124,000 m².

The most terrible example of an emergency leak 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 not only associated with man-made incidents. There are known cases of plutonium leakage, both from laboratory and factory conditions. More than twenty accidental leaks from the 235U and 239Pu laboratories are known. During 1953-1978. accidents led to a loss of 0.81 (Mayak, March 15, 1953) to 10.1 kg (Tomsk, December 13, 1978) 239Pu. Industrial incidents resulted in a total of two deaths at 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.

When a 238Pu nucleus fissions with neutrons, 200 MeV of energy is released, which is 50 million times more than the most famous exothermic reaction: C + O2 → CO2. “Burning” in a nuclear reactor, one gram of plutonium produces 2,107 kcal - this is the energy contained in 4 tons of coal. A thimble of plutonium fuel in energy equivalent can be equivalent to forty wagons of good firewood!

The “natural isotope” of plutonium (244Pu) is believed to be the longest-lived isotope of all 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 - great 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 during scientific work at the University of Rome they had discovered a chemical element with serial number 94. At Fermi’s insistence, the element was named hesperium, the scientist was convinced that he had discovered a new element, which is now called plutonium, thus suggesting the existence of transuranium elements and becoming their theoretical discoverer. Fermi defended this hypothesis in his Nobel lecture in 1938. It was only after the discovery of nuclear fission by the German scientists Otto Frisch and Fritz Strassmann that Fermi was forced to make a note in the printed version published in Stockholm in 1939 indicating the need to reconsider “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.

A new element, the ninety-fourth, was discovered at the end of 1940. It happened in Berkeley at the University of California. By 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 the 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.

During an experiment conducted in 1940, it was found that during a nuclear reaction, the short-lived isotope neptunium-238 is first produced (half-life 2.117 days), and from it plutonium-238:

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

Long and laborious chemical experiments to separate the 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. Macmillan, J. W. Kennedy and A. C. Wall through the study of its first chemical properties - the ability to possess at least at least two oxidation states. A little later than the end of the experiments, it was established that this isotope is non-fissile, and, therefore, uninteresting for further study. Soon (March 1941), Kennedy, Seaborg, Segre and Wahl synthesized a more important isotope, plutonium-239, by irradiating uranium with highly accelerated neutrons in a cyclotron. This isotope is formed 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 weight quantities of metallic plutonium were 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. Eibelson, obtained the first element heavier than uranium - element No. 93, which was named neptunium in honor of the planet Neptune - the first beyond Uranus. By analogy, they decided to call element No. 94 plutonium, since the planet Pluto is second after Uranus. In turn, Seaborg proposed calling the new element “plutium,” but then realized that the name did 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 that time that plutonium would become 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. It follows from this 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 neutrons from cosmic radiation and neutrons produced by the 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, and 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 very long and amounts to 24,000 years. On average, the content of 239Pu is about 400,000 times less than that of radium. Therefore, it is extremely difficult not only to mine, but even to detect “terrestrial” plutonium. Small quantities of 239Pu - parts per trillion - and decay products can be found in uranium ores, for example in the natural nuclear reactor at Oklo, Gabon (West Africa). The so-called “natural nuclear reactor” is considered to be the only one in the world in which actinides and their fission products are currently being formed in the geosphere. 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 β-decay product of which is natural plutonium-239. Thanks to special instruments - mass spectrometers - the presence of plutonium-244 (244Pu), which has the longest half-life - approximately 80 million years, was discovered in Precambrian bastnaesite (cerium ore). In nature, 244Pu is found predominantly 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 does occur, but this occurs very rarely (1 case in 10,000). Very small amounts of plutonium-238 (238Pu) are due to the very rare double beta decay of the parent isotope, uranium-238, which was found in uranium ores.

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

Minimal amounts of plutonium could hypothetically be present in the human body, given that a huge number of nuclear tests have been conducted 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, element ninety-four is accumulated by marine organisms; Land 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. About another radioactive metal - radium they say: “a gram of production - a year of work,” and radium in nature is 400,000 times more abundant than plutonium! For this reason, it is extremely difficult not only to mine, but even to detect “terrestrial” plutonium. This was done only after the physical and chemical properties of plutonium produced 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 half a thousand nuclear power plants around the world generate approximately 370 GW of electricity (or 15% of the world's total electricity production). 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-sized nuclear power sources used in space research. Thus, plutonium-238 is the power source for the New Horizons, Galileo and Cassini probes, the Curiosity rover and other spacecraft.

Nuclear weapons use plutonium-239 because 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 less volume in the sphere (where the bomb core is located), therefore, the explosive power of the bomb can be gained due to this property.

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

Plutonium isotopes have found their use in the synthesis of transplutonium (next to plutonium) elements. For example, at the Oak Ridge National Laboratory, with long-term neutron irradiation of 239Pu, 24496Cm, 24296Cm, 24997Bk, 25298Cf, 25399Es and 257100Fm are obtained. In the same way, americium 24195Am was first obtained in 1944. In 2010, plutonium-242 oxide bombarded with calcium-48 ions served as a source for 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 elements in the required proportions, while arc melting is mainly 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 capable of forming alloys and intermediates 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) when rapidly cooled. Gallium, aluminum, americium, scandium and cerium can stabilize δ-plutonium at room temperature.

Large quantities of holmium, hafnium and thallium allow some δ-plutonium to be stored 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 when rapidly cooled. The applications of such alloys are quite diverse. For example, a plutonium-gallium alloy is used to stabilize the δ phase of plutonium, which avoids the α-δ phase transition. 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

Industrial plutonium is produced in two ways. This is either irradiation of 238U nuclei contained in nuclear reactors, or separation by radiochemical methods (co-precipitation, extraction, ion exchange, etc.) of plutonium from uranium, transuranic elements and fission products contained in spent fuel.

In the first case, the most practical isotope 239Pu (mixed with a small admixture of 240Pu) is produced in nuclear reactors with the participation of uranium nuclei and neutrons 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. Neptunium-238 then spontaneously fissions, emitting beta-minus particles that form plutonium-238.

Typically, the content of 239Pu in the mixture is 90-95%, 240Pu is 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 yield of 242Pu 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 of 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 separated. In the second and third cycles, the plutonium is further purified and concentrated. The scheme of such a process is based on the difference in the properties of tetra- and hexavalent compounds of the elements being 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. Plutonium atoms with zero valence are converted into Pu+6, and both plutonium and uranium are dissolved. From such a solution, the ninety-fourth element is reduced to the trivalent state with sulfur dioxide and then precipitated with lanthanum fluoride (LaF3).

However, in addition to plutonium, the sediment contains neptunium and rare earth elements, but the bulk (uranium) remains in solution. Next, the plutonium is again oxidized to Pu+6 and lanthanum fluoride is added again. Now the rare earth elements precipitate, and the plutonium remains in solution. Next, neptunium is oxidized to a tetravalent state with potassium bromate, since this reagent has no effect on plutonium, then during secondary precipitation with the same lanthanum fluoride, trivalent plutonium passes into a precipitate, and neptunium remains in solution. The end products of such operations are plutonium-containing compounds - PuO2 dioxide or fluorides (PuF3 or PuF4), from which metallic plutonium is obtained (by reduction with barium, calcium or lithium vapor).

Purer plutonium can be achieved by electrolytic refining of the pyrochemically produced metal, which is done in electrolysis cells at 700° C with an electrolyte of potassium, sodium and plutonium chloride using a tungsten or tantalum cathode. The plutonium obtained in this way has a purity of 99.99%.

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

After the reaction, 239U atoms are formed, which subsequently 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 dioxide-238 (238UO2), in which 239Pu is formed. The combined use of 238U and 235U allows “breeders” to produce 50-60 times more energy from natural uranium 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 World War II; the USSR and Great Britain began their construction only in the 1950s.

Physical properties

Plutonium is a very heavy (density at normal level 19.84 g/cm³) silvery metal, in a purified state very similar to nickel, but in air plutonium quickly oxidizes, fades, forming an iridescent film, first light yellow, then turning into dark purple. When severe oxidation occurs, an olive green oxide powder (PuO2) appears on the metal surface.

Plutonium is a highly electronegative and reactive metal, many times more so even than 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, which will give the alloy ductility and softness. In addition, in this highest density form, plutonium is the sixth densest element (Only osmium, iridium, platinum, rhenium and neptunium are heavier. Further allotropic transformations of plutonium are accompanied by abrupt changes in density. For example, when heated from 310 to 480 ° C, it does not expand, like other metals, but contracts (delta phases " and "delta prime") When melted (transition from the epsilon phase to the liquid phase), the plutonium also contracts, allowing unmelted plutonium to float.

Plutonium has 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. This “anomaly” can be traced up to a temperature of 100 K - below this mark the electrical resistance will decrease. However, from 20 K the resistance begins to increase again due to the radiation activity of the metal.

Plutonium has the highest electrical resistivity of all the actinides 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 (3,227 °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 shell 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 temperature increases 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 tends to change and turn into a ductile material, and form 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 aluminum, cerium or gallium. When alloyed with these metals, plutonium can be used in welding. In general, the delta form has more pronounced characteristics of a metal - it is close to aluminum in strength and forgeability.

Chemical properties

The chemical properties of the ninety-fourth element are in many ways similar to the properties of its predecessors in the periodic table - uranium and neptunium. Plutonium is a fairly 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+ (light solution); Pu (VI), as PuO22+ (light orange solution) and Pu(VII), as PuO53- (green solution).

Moreover, these ions (except for PuO53-) can be simultaneously in equilibrium in the solution, 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 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 Pu5+ series

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 a phase of variable composition Pu2O3 - Pu4O7 (Berthollides). In the presence of small amounts of moisture, the rate of oxidation and corrosion increases significantly. If a metal is exposed to small amounts of moist air for long enough, plutonium dioxide (PuO2) forms on its surface. With a lack of oxygen, its dihydride (PuH2) can also form. Surprisingly, plutonium rusts much faster in an atmosphere of an inert gas (such as 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 a layer of oxide on the surface of plutonium, which prevents further oxidation; the presence of moisture produces a loose mixture of oxide and hydride. By the way, thanks to this coating, the metal becomes pyrophoric, that is, it is capable of spontaneous combustion; for this reason, metallic plutonium is usually 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 is also soluble in hydrogen chloride, hydrogen iodide, hydrogen bromide, 72% perchloric acid, 85% orthophosphoric acid H3PO4, concentrated CCl3COOH, sulfamic acid and boiling concentrated nitric acid. Plutonium does not dissolve noticeably in alkali solutions.

When solutions containing tetravalent plutonium are exposed to alkalis, a precipitate of plutonium hydroxide Pu(OH)4 xH2O, which has basic properties, precipitates. When solutions of salts containing PuO2+ are exposed to alkalis, amphoteric hydroxide PuO2OH precipitates. It is answered by salts - plutonites, for example, Na2Pu2O6.

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

This metal is called precious, but not for its beauty, but for its irreplaceability. In the periodic table of Mendeleev, this element occupies cell number 94. It is with it that scientists pin their greatest hopes, and it is plutonium that they call the most dangerous metal for humanity.

Plutonium: description

In appearance it is a silvery-white metal. It is radioactive and can be represented in the form of 15 isotopes with different half-lives, for example:

• Pu-238 – about 90 years
• Pu-239 – about 24 thousand years
• Pu-240 – 6580 years
• Pu-241 – 14 years
• Pu-242 – 370 thousand years
• Pu-244 – about 80 million years

This metal cannot be extracted from ore, since it is a product of the radioactive transformation of uranium.

How is plutonium obtained?

The production of plutonium requires the fission of uranium, which can only be done in nuclear reactors. If we talk about the presence of the element Pu in the earth's crust, then for 4 million tons of uranium ore there will be only 1 gram of pure plutonium. And this gram is formed by the natural capture of neutrons by uranium nuclei. Thus, in order to obtain this nuclear fuel (usually the isotope 239-Pu) in an amount of several kilograms, it is necessary to carry out a complex technological process in a nuclear reactor.

Properties of plutonium

The radioactive metal plutonium has the following physical properties:

• density 19.8 g/cm 3
• melting point – 641°C
• boiling point – 3232°C
• thermal conductivity (at 300 K) – 6.74 W/(m K)

Plutonium is radioactive, which is why it is warm to the touch. Moreover, this metal is characterized by the lowest thermal and electrical conductivity. Liquid plutonium is the most viscous of all existing metals.

The slightest change in the temperature of plutonium leads to an instant change in the density of the substance. In general, the mass of plutonium is constantly changing, since the nuclei of this metal are in a state of constant fission into smaller nuclei and neutrons. The critical mass of plutonium is the name given to the minimum mass of a fissile substance at which fission (a nuclear chain reaction) remains possible. For example, the critical mass of weapons-grade plutonium is 11 kg (for comparison, the critical mass of highly enriched uranium is 52 kg).

Uranium and plutonium are the main nuclear fuels. To obtain plutonium in large quantities, two technologies are used:

• uranium irradiation
• irradiation of transuranium elements obtained from spent fuel

Both methods involve the separation of plutonium and uranium as a result of a chemical reaction.

To obtain pure plutonium-238, neutron irradiation of neptunium-237 is used. The same isotope is involved in the creation of weapons-grade plutonium-239; in particular, it is an intermediate decay product. $1 million is the price for 1 kg of plutonium-238.

The plutonium isotope 238 Pu was first artificially obtained on February 23, 1941 by a group of American scientists led by G. Seaborg by irradiating uranium nuclei with deuterons. Only then was plutonium discovered in nature: 239 Pu is usually found in negligible quantities in uranium ores as a product of the radioactive transformation of uranium. Plutonium is the first artificial element obtained in quantities available for weighing (1942) and the first whose production began on an industrial scale.
The element's name continues the astronomical theme: it is named after Pluto, the second planet after Uranus.

Being in nature, receiving:

In uranium ores, as a result of the capture of neutrons (for example, neutrons from cosmic radiation) by uranium nuclei, neptunium (239 Np) is formed, the product b- the decay of which is natural plutonium-239. However, plutonium is formed in such microscopic quantities (0.4-15 parts Pu per 10 12 parts U) that its extraction from uranium ores is out of the question.
Plutonium is produced in nuclear reactors. In powerful neutron streams, 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 energy-grade plutonium-239, optimal (within acceptable) conditions are created.
Plutonium-244 also accumulated in a nuclear reactor. Isotope of element No. 95 - americium, 243 Am, having captured a neutron, turned into americium-244; americium-244 transformed into curium, but in one out of 10 thousand cases a transition occurred into plutonium-244. A plutonium-244 preparation weighing only a few millionths of a gram was isolated from a mixture of americium and curium. But they were enough to determine the half-life of this interesting isotope - 75 million years. Later it was refined and turned out to be equal to 82.8 million years. In 1971, traces of this isotope were found in the rare earth mineral bastnäsite. 244 Pu is the longest-lived of all isotopes of transuranium elements.

Physical properties:

Silvery-white metal, has 6 allotropic modifications. Melting point 637°C, boiling point - 3235°C. Density: 19.82 g/cm3.

Chemical properties:

Plutonium is capable of reacting with oxygen to form oxide(IV), which, like all the first seven actinides, has a weak basic character.
Pu + O 2 = PuO 2
Reacts with dilute sulfuric, hydrochloric, perchloric acids.
Pu + 2HCl(p) = PuCl 2 + H 2 ; Pu + 2H 2 SO 4 = Pu(SO 4) 2 + 2H 2
Does not react with nitric and concentrated sulfuric acids. The valency of plutonium varies from three to seven. Chemically, the most stable (and therefore the most common and most studied) compounds are tetravalent plutonium. The separation of actinides with similar chemical properties - uranium, neptunium and plutonium - can be based on the difference in the properties of their tetra- and hexavalent compounds.

The most important connections:

Plutonium(IV) oxide, PuO 2 , has a weak basic character.
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Application:

Plutonium was widely used in the production of nuclear weapons (so-called “weapons-grade plutonium”). The first plutonium-based nuclear device was detonated on July 16, 1945 at the Alamogordo test site (test codenamed Trinity).
It is used (experimentally) as nuclear fuel for nuclear reactors for civil and research purposes.
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, for example, California-251 from grams of plutonium. Plutonium-242 is not fissile by thermal neutrons, and even in large quantities it can be irradiated in intense neutron fluxes. Therefore, in reactors, all elements from californium to einsteinium are “made” from this isotope and accumulated in weight quantities.

Kovalenko O.A.
HF Tyumen State University

Sources:
"Harmful chemicals: Radioactive substances" Directory L. 1990 p. 197
Rabinovich V.A., Khavin Z.Ya. "A short chemical reference book" L.: Chemistry, 1977 p. 90, 306-307.
I.N. Beckman. Plutonium. (textbook, 2009)