Polonium-210 has a very clear association with radiation. And this is not in vain, because it is extremely dangerous.
Discovery history
Its existence was predicted back in 1889 by Mendeleev, when he created his famous periodic table. In practice, this element, number 84, was obtained nine years later by the efforts of the Curies, who studied the phenomenon of radiation. tried to find out the reason for the strong radiation emanating from certain minerals, and therefore began to work with several rock samples, processing them in all ways available to her, dividing into fractions and discarding the unnecessary. As a result, she received a new substance, which became an analogue of bismuth and the third discovered radioactive element after uranium and thorium.
Despite the successful results of the experiment, Maria was in no hurry to talk about her find. conducted by a colleague of the Curie spouses, also did not give grounds to talk about the discovery of a new element. Nevertheless, in a report at a meeting of the Paris Academy of Sciences in July 1898, the couple reported on the alleged receipt of a substance that exhibits the properties of a metal and proposed to name it polonium in honor of Poland, Mary's homeland. This was the first and only case in history when an element that has not yet been reliably identified has already received a name. Well, the first sample appeared only in 1910.
Physical and chemical properties
Polonium is a relatively soft, silvery-white metal. It is so radioactive that it glows in the dark and heats up constantly. At the same time, its melting point is slightly higher than that of tin - only 254 degrees Celsius. The metal oxidizes very quickly in air. At low temperatures, it forms a monatomic simple cubic crystal lattice.
By their own chemical properties Polonium is very close to its counterpart - tellurium. In addition, the nature of its compounds is greatly influenced by high level radiation. So reactions involving polonium can be quite spectacular and interesting, albeit quite dangerous in terms of health benefits.
isotopes
Total science on this moment 27 (according to other sources - 33) forms of polonium are known. None of them is stable and they are all radioactive. The heaviest of the isotopes (with ordinal numbers from 210 to 218) are found in nature in small quantities, the rest can only be obtained artificially.
Radioactive polonium-210 is the longest-lived natural forms. It is found in small amounts in radium-uranium ores and is formed by a chain of reactions starting with U-238 and lasting about 4.5 billion years in terms of half-life.
Receipt
1 ton contains the isotope polonium-210 in an amount equal to approximately 100 micrograms. They can be isolated during the processing of production waste, however, to obtain a more or less significant volume of the element, a huge amount of material would have to be processed. Much simpler and effective ways is the synthesis by neutron irradiation of natural bismuth in nuclear reactors.
As a result, after some more procedures, polonium-210 is obtained. Isotopes 208 and 209 can also be obtained by irradiating bismuth or lead with accelerated beams of alpha particles, protons, or deuterons.
Radioactivity
Polonium-210, like other isotopes, is an alpha emitter. The heavier group also emits gamma rays. Despite the fact that the 210 isotope is a source of only alpha particles, it is quite dangerous, it cannot be taken by hand and even approached at close range, because, when heated, it passes into an aerosol state. It is also extremely dangerous to get polonium inside with breath or food. That is why work with this substance takes place in special sealed boxes. It is curious that this element was found in tobacco leaves about half a century ago. The decay period of polonium-210 compared to other isotopes is quite large, and therefore it can accumulate in the plant and subsequently harm the health of the smoker even more. However, any attempts to extract this substance from tobacco have been unsuccessful.
Danger
Since polonium-210 emits only alpha particles, taking certain precautions, you should not be afraid to work with it. These waves rarely travel more than a dozen centimeters, and they usually cannot penetrate the skin.
However, once inside the body, they cause him great harm. When it enters the blood, it quickly spreads to all tissues - after a few minutes, its presence can be seen in all organs. It is primarily present in the kidneys and liver, but in general it is distributed fairly evenly, which can explain its high overall damaging effect.
The toxicity of polonium is so great that even small doses cause chronic radiation sickness and death after 6-11 months. The main routes of excretion from the body are through the kidneys and gastrointestinal tract. There is a dependence on the method of entry. The half-life is 30 to 50 days.
Accidental poisoning with polonium is completely impossible. To obtain a sufficient amount of the substance, it is necessary to have access to a nuclear reactor and deliberately put an isotope on the victim. The complexity of diagnosis also lies in the fact that only a few cases are known throughout history. The first victim is the daughter of the discoverers of polonium, Irene Joliot-Curie, who, during research, broke the capsule with the substance in the laboratory and died 10 years later. Two more cases occur in the 21st century. The first of them is the sensational case of Litvinenko, who died in 2006, and the second is the death of Yasser Arafat, in whose things traces of a radioactive isotope were found. However, a definitive diagnosis has not yet been confirmed.
Decay
One of the longest-lived isotopes, along with 208 and 209, is polonium-210. (that is, the time during which the number of radioactive particles is halved) for the first two is 2.9 and 102 years, respectively, and for the last 138 days and 9 hours. As for the rest of the isotopes, their lifetime is calculated mainly in minutes and hours.
The combination of various properties of polonium-210 makes it the most convenient of the range for use in various areas of life. Being in a special metal shell, he can no longer harm his health, but is able to give his energy for the benefit of mankind. So what is polonium-210 used for today?
Modern application
According to some reports, about 95% of polonium production is concentrated in Russia, and about 100 grams of the substance is synthesized per year, and almost all of it is exported to the United States.
There are several areas where polonium-210 is used. First of all, these are spacecraft. With its compact size, it is indispensable as an excellent source of energy and heat. Although its effectiveness is halved about every 5 months, heavier isotopes are much more expensive to produce.
In addition, polonium is absolutely indispensable in nuclear physics. It is widely used in the study of the effect of alpha radiation on other substances.
Finally, another area of application is the production of devices for removing static electricity for both industry and home use. It is even surprising how such a dangerous element can become almost a kitchen utensil, being enclosed in a reliable shell.
Element No. 84 - polonium - the first element inscribed in the periodic table after the discovery of radioactivity. He is the first (in order of atomic numbers) and the lightest of the elements that do not have stable isotopes. He is one of the first radioactive elements used in space research.
At the same time, element #84 is perhaps one of the least known, least popular radioactive elements. At first he remained in the shadows, relegated to the background by the glory of radium. Later, it was not advertised too much, like almost all materials of atomic and space research.
opening, name
The history of the discovery of element No. 84 is fairly well known. It was discovered by Pierre Curie and Marie Skłodowska-Curie. In the laboratory journal of the Curies, the symbol "Po" (inscribed by Pierre's hand) first appears on July 13, 1898.
A few years after the death of Pierre Curie, his wife and co-author of two of his most striking discoveries wrote the book Pierre Curie. Thanks to this book, we will learn "first hand" the history of the discovery of polonium and radium, get acquainted with the features and principles of the work of two outstanding scientists. Here is an excerpt from this book: “... The ore we chose was tar blende, uranium ore, which in its pure form is approximately four times more active than uranium oxide ... The method used by us is new method chemical analysis based on radioactivity. It consists in separating by the usual means of chemical analysis and in measuring, under appropriate conditions, the radioactivity of all isolated products. In this way, one can get an idea of the chemical properties of the desired radioactive element; the latter is concentrated in those fractions whose radioactivity becomes more and more as the separation proceeds. Soon we were able to determine that the radioactivity was predominantly concentrated in two different chemical fractions, and we came to the conclusion that at least two new radioelements were present in the tar blende: polonium and radium. We reported the existence of the element polonium in July 1898 and of radium in December of that year...”
The first report of polonium is dated 18 July. It is written in the highest degree restrained and correct. There is a phrase there: "If the existence of this new metal is confirmed, we propose to call it polonium, after the name of the homeland of one of us."
Polonia is Latin for Poland.
"Polonium" is not the first "geographical" name for the element. By that time, germanium, ruthenium, gallium, and scandium had already been discovered. Nevertheless, this name is special, it can be regarded as a protest name: an independent Polish state did not exist at that time. Poland was fragmented, divided between the Austrian, German and Russian empires...
In the well-known book “Marie Curie”, written by the youngest daughter of the Curies, Eva, the following conclusion was made: “The choice of this name shows that Marie, having become a French physicist, did not renounce her homeland. This is also evidenced by the fact that before the note “On a new radioactive substance in the composition of uraninite” * appeared in the “Reports of the Academy of Sciences”, Marie sent the manuscript to her homeland, to Joseph Bogussky, head of that laboratory of the Museum of Industry and Agriculture where her first scientific experiments began. The message was published in Swialto, a monthly illustrated review, almost simultaneously with the publication in Paris.
* Uranium mineral, its composition is UO 2 . The Curies explored various uranium-bearing minerals.
Why radium and not polonium?
Indeed, why did radium, and not polonium, bring the Curie spouses worldwide fame? After all, the first element discovered by them was element number 84.
After a year of work, they had no doubt that two new elements were present in the uranium pitch. But these elements made themselves known only by radioactivity, and in order to convince everyone, and above all chemists, that the discoveries had really taken place, it was necessary to isolate these activities, to obtain new elements, at least in the form of individual compounds.
All radioactive elements and isotopes, as is known, are now combined into families: when decaying, the nucleus of a radioactive atom turns into the atomic nucleus of another, child element. All elements of radioactive families are in a certain balance with each other. It has been measured that in uranium ores the equilibrium ratio of uranium to polonium is 1.9·10 10 , and 0.2 mg of polonium is in equilibrium with a gram of radium. This means that in uranium minerals there is almost 20 billion times less radium than uranium, and 5000 times less polonium.
The Curies, of course, did not know these exact figures. Nevertheless, having understood what a titanic work to isolate new elements, they made the only right decision. In the book about Pierre Curie we have already quoted, it is said: “The results obtained after a year of work clearly showed that radium is easier to isolate than polonium; therefore efforts were concentrated on radium.”
artificial polonium
Here the question is quite appropriate: if polonium is really an ultra-rare and super-hard-to-reach element, then what does the extraction of polonium cost in our time?
We do not have exact figures, but today element No. 84 is no less accessible than radium. It is really difficult to get it from ore, but there is another way - nuclear fusion.
Today, polonium is obtained in two ways, with bismuth-209 serving as the feedstock in both cases. IN nuclear reactors it is irradiated with streams of neutrons, and then, through a relatively simple chain of nuclear transformations, the most important isotope of element No. 84 today, polonium-210, is formed:
And if the same isotope of bismuth is placed in another most important nuclear fusion machine - the cyclotron and fired there with proton streams, then according to the reaction
the longest-lived isotope of element 84 is formed.
The first reaction is more important: polonium-210 is a much more interesting isotope for technology than polonium-209. (More about the reasons below.) In addition, the second reaction produces lead-209 simultaneously with polonium, one of the most difficult to remove impurities in polonium.
In general, the purification of polonium and its isolation from a mixture with other metals for modern technology don't represent much difficult task. There are different ways to isolate polonium, in particular electrochemical, when metallic polonium is isolated on a platinum or gold cathode and then separated by sublimation.
Polonium is a fusible and relatively low-boiling metal; its melting and boiling points are 254 and 962°C, respectively.
Fundamentals of Chemistry
It is quite obvious that the currently existing perfect methods for obtaining and isolating polonium became possible only after a thorough study of this rare radioactive metal. And his connections, of course.
The foundations of the chemistry of polonium were laid down by its discoverers. In one of the laboratory notebooks of the Curie spouses there is an entry made in 1898: “After the first treatment of resin blende with sulfuric acid, polonium is not completely precipitated and can be partially extracted by washing with dilute SO 4 H 2 (here and below, the chemical indexing of the original is preserved). In contrast, two treatments of the resin blend residue and one treatment of the German [ore] residue with carbonates give carbonates, and from the carbonate dissolved in acetic acid, SO 4 H 2 completely precipitates the active substance.
Later, much more was learned about this element. We learned, in particular, that elemental polonium, a silvery-white metal, exists in two allotropic modifications. The crystals of one of them - low-temperature - have a cubic lattice, and the other - high-temperature - rhombic.
The phase transition from one form to another occurs at 36°C, but at room temperature polonium is in the high temperature form. It is heated by its own radioactive radiation.
By appearance Polonium is like any ordinary metal. In terms of fusibility - for lead and bismuth. By electrochemical properties - to noble metals. According to the optical and X-ray spectra - only on itself. And according to the behavior in solutions - to all other radioactive elements: due to ionizing radiation in solutions containing polonium, ozone and hydrogen peroxide are constantly formed and decomposed.
By chemical properties, polonium is a direct analogue of sulfur, selenium and tellurium. It exhibits valencies 2–, 2+, 4+ and 6+, which is natural for an element of this group. Numerous polonium compounds are known and fairly well studied, ranging from the simple oxide PoO 2 , soluble in water, to complex complex compounds.
The latter should not be surprising. The tendency to complex formation is the fate of most heavy metals, and polonium is one of them. By the way, its density - 9.4 g / cm 3 - is slightly less than that of lead.
A very important study of the properties of polonium for radiochemistry as a whole was carried out in 1925-1928. at the Leningrad Radium Institute. It was fundamentally important to find out whether radioactive elements found in solutions in vanishingly small quantities can form their own colloidal compounds. The answer to this question - the answer is positive - was given in the work "On the question of colloid properties polonium." Its author was I.E. An old man, later a well-known radiochemist, corresponding member of the USSR Academy of Sciences.
Polonium on Earth and in space
People far from radiochemistry and nuclear physics, the following statement will seem strange: today polonium is a much more important element than radium. The historical merits of the latter are indisputable, but this is the past. Polonium is an element of today and tomorrow. First of all, this applies to the polonium-210 isotope.
In total, 27 isotopes of polonium are known with mass numbers from 192 to 218. This is one of the most polyisotopic, so to speak, elements. The half-life of the longest-lived isotope, polonium-209, is 103 years. Therefore, naturally, in earth's crust there is only radiogenic polonium, and there is extremely little of it - 2·10 -14%. Several naturally occurring isotopes of polonium have proper names and symbols that determine the place of these isotopes in the radioactive series. So, polonium-210 is also called radium F (RaF), 211 Po - AcC " , 212Po-ThC " , 214 Po–PaC " , 215 Po - AcA, 216 Po - ThA and 218 Po - RaA.
Each of these names has its own history; all of them are associated with the "parent" isotopes of one or another atomic variety of polonium, so it would be more correct to call them not "names", but "patronymics". With the advent modern system Isotope designations The listed old names gradually almost fell into disuse.
The most important isotope of polonium-210 is a pure alpha emitter. The particles emitted by it are decelerated in the metal and, running in it only a few micrometers, waste their energy in the process. nuclear energy, by the way. But energy does not appear and does not disappear. The energy of polonium's alpha particles turns into heat, which can be used, say, for heating, and which is not so difficult to turn into electricity.
This energy is already being used both on Earth and in space. The 210 Po isotope is used in the power plants of some artificial satellites. In particular, he flew beyond the Earth on the Soviet satellites Cosmos-84 and Cosmos-90.
Pure alpha emitters, and polonium-210 in the first place, have several obvious advantages over other radiation sources. First, the alpha particle is quite massive and therefore carries a lot of energy. Secondly, such emitters practically do not require special protection measures: the penetrating power and the path length of alpha particles are minimal. There are third, and fourth, and fifth, but these two advantages are the main ones.
Basically, to work on space stations acceptable energy sources are plutonium-238, dolonium-210, strontium-90, cerium-144 and curium-244. But polonium-210 has an important advantage over other competing isotopes - the highest specific power, 1210 W/cm 3 . It releases so much thermal energy that this heat is capable of melting the sample. To prevent this from happening, the polonium is placed in a lead matrix. The resulting alloy of polonium and lead has a melting point of about 600°C, much higher than either of the constituent metals. The power, however, decreases in this case, but it remains quite large - about 150 W / cm 3.
W. Corliss and D. Harvey, authors of the book "Power Sources on Radioactive Isotopes" (in Russian, this book was published in 1967), write: "As they show latest research, 210 Po can be used in manned spaceships". As another advantage of polonium-210, they mention the availability of this isotope. The same book says that bismuth and polonium obtained from it are easily separated by ion exchange. So the space service of polonium, apparently, is just beginning.
And a good start has been made. The radioactive isotope polonium-210 served as fuel for the "stove" installed on Lunokhod-2.
The nights on the moon are very long and cold. For 14.5 Earth days, the lunar rover was at temperatures below –130°C. But in the instrument container all this time it was necessary to maintain a temperature acceptable for complex scientific equipment.
The polonium heat source was placed outside the instrument container. Polonium radiated heat continuously; but only when the temperature in the instrument compartment dropped below the required limit, the coolant gas, heated by polonium, began to flow into the container. The rest of the time, excess heat was dissipated into outer space.
The nuclear stove of Lunokhod-2 was distinguished by complete autonomy and absolute reliability.
True, polonium-210 has a limitation. Its relatively short half-life of only 138 days places a natural limit on the service life of polonium radioisotope sources.
Similar devices are used on Earth. In addition to them, polonium-beryllium and polonium-boron neutron sources are important. These are hermetically sealed metal ampoules containing a polonium-210-coated boron carbide or beryllium carbide ceramic pellet. A stream of neutrons from the nucleus of an atom of boron or beryllium gives rise to alpha particles emitted by polonium.
Such neutron sources are light and portable, completely safe in operation, and very reliable. A brass ampoule with a diameter of 2 cm and a height of 4 cm - the Soviet polonium-beryllium source of neutrons - produces up to 90 million neutrons every second.
Among other mundane matters of element #84, perhaps mention should be made of its use in standard electrode alloys. These alloys are needed for glow plugs of internal combustion engines. The alpha particles emitted by the polonium-210 lower the voltage required to generate a spark and therefore make it easier to start the engine.
Safety
Special care must be taken when working with polonium. Perhaps this is one of the most dangerous radio elements. Its activity is so great that, although it emits only alpha particles, it is impossible to take it with your hands, the result will be radiation damage to the skin and, possibly, to the whole organism: polonium penetrates quite easily through the skin. Element No. 84 is also dangerous at a distance exceeding the length of the path of alpha particles. It is able to quickly turn into an aerosol state and infect the air. Therefore, work with polonium only in sealed boxes, and the fact that it is not difficult to protect yourself from polonium radiation is extremely favorable for everyone who deals with this element.
The attentive reader has probably already noticed that in this article, wherever it is said about practical application polonium, only one isotope appears - with a mass number of 210. Indeed, other isotopes of element No. 84, including the longest-lived polonium-209, have not yet gone beyond the laboratories.
True, many scientists believe that polonium-208, also a pure alpha emitter, is also promising for space energy sources. Its half-life is much longer than that of polonium-210 - 2.9 years. But so far this isotope is almost inaccessible. How much time to walk him only in promising, the future will show.
Polonium is a radioactive chemical element of Group VI of the Periodic Table of Elements. Atomic number 84. Atomic mass 209. Denoted by the symbol Po (lat. Polonium).
The element was discovered in 1898 by the spouses Pierre Curie and Maria Skłodowska-Curie in resin blende, uranium ore. In this case, element 84 was concentrated in the bismuth fraction. The first sample of polonium containing 0.1 mg of this element was isolated in 1910. The element is named after the homeland of Maria Skłodowska-Curie—Poland (lat. Polonia). M. Curie suggested that the increased radioactivity of some samples of uranium resin ore is due to the presence of other, still unknown radioactive substances in the ore. This was confirmed, and from uranium ore was first isolated new element, concentrating in bismuth compounds - polonium, and then an element similar to barium - radium.
Polonium is always present in uranium and thorium minerals. The equilibrium content of polonium in the earth's crust is 2·10 −14% by mass. In uranium ores, the equilibrium ratio of uranium to polonium is 1.9x10 10 . This means that in uranium minerals there is almost twenty billion times less polonium than uranium (0.2 mg of polonium is in equilibrium with 1 g of radium).
The content of polonium in the earth's crust is 2-10 -15%. There are seven isotopes of polonium, which are formed in all three naturally radioactive families in the process of decay of emanation (radon, thoron, actinon) or their decay products. In the process of decay, they turn into stable or radioactive isotopes of lead. 210 Rho's main source environment is 222 Rn released from the soil.
Polonium (Po)
Atomic number 84
Appearance silver gray metal
Atomic mass (molar mass) 208.9824 amu (g/mol)
Atom radius 176 pm
Thermodynamic properties
Density 9.32 g/cm³
Specific heat capacity 0.125 J/(K mol)
Melting point 527 K
Heat of fusion (10) kJ/mol
Boiling point 1.235 K
Heat of vaporization (102.9) kJ/mol
Molar volume 22.7 cm³/mol
Isotopes of polonium
At the beginning of 2006, 33 isotopes of polonium are known in the range of mass numbers from 188 to 220. (Polonium is one of the most polyisotopic elements). In addition, 10 metastable excited states of polonium isotopes are known. The longest lived isotope 209 Po (obtained artificially), has a half-life of 102 years.
The most long-lived of the natural isotopes of polonium-210 (a natural radionuclide) is an almost pure alpha emitter (T = 138.401 days), which is formed in the radioactive series of uranium-238. It is one of the products of the long-lived active radon sediment.
In the vast majority of cases, 210 Po decays into the ground state of 206 Pb with the emission of alpha particles with an energy of 5.3 MeV, and only an insignificant fraction (0.00122%) of 210 Po nuclei decays into an excited (803 keV) state of 206 Pb, which decays with the emission of gamma rays. quants. It is possible to detect gamma radiation accompanying such alpha decay only in a precision experiment. The 210 Po isotope is not only the longest-lived among the natural ones, i.e. existing on Earth, and not obtained artificially, polonium isotopes, but also the most common. It is constantly formed due to a chain of isotope decays that starts with 238 U and ends with 206 Pb.
Thus, active radon sediment accumulated in old radon ampoules can serve as a source of obtaining polonium-210.
1 ton of uranium ore contains 100 micrograms of polonium. Basically it is 210 Po. All other natural isotopes of polonium are even smaller (and by many). Polonium can be isolated from uranium ores during the processing of waste from uranium production. However, in order to obtain a noticeable amount of polonium, an unthinkable amount of such waste would have to be processed.
In addition to 210 Po, two more artificial radioactive isotopes of polonium have relatively long half-lives - these are 208 Po (T=2.898 years) and 209 Po (T=102 years). These isotopes can be obtained by bombarding lead or bismuth targets with accelerated beams of alpha particles, protons, or deuterons in a cyclotron. All other polonium isotopes have half-lives ranging from 8.8 days (206 Po) to fractions of a microsecond
Physical and chemical properties
Polonium is a silvery metal that glows in the dark, fusible and relatively low-boiling; its melting and boiling points are 254 and 962 °C, respectively.
Comparison of the properties of polonium with sulfur properties, selenium and tellurium, on the one hand, and bismuth, lead and thallium, on the other, shows that metallic polonium in its physical properties more closely resembles elements neighboring in period (Bi) than in group (Te).
Pure polonium has two allotropic modifications: a low-temperature α-form with a cubic lattice, and a high-temperature β-form with a rhombic lattice. The phase transition from one form to another occurs at 36°C. Interestingly, freshly prepared polonium is in its high-temperature form at room temperature. It is heated by its own radiation - heat is released in the sample itself when α-particles are emitted by polonium. In appearance, polonium is similar to any most ordinary metal. In terms of fusibility - for lead and bismuth. By electrochemical properties - to noble metals. According to the optical and X-ray spectra - only on itself. And according to the behavior in solutions - to all other radioactive elements: due to ionizing radiation in solutions containing polonium, ozone and hydrogen peroxide are constantly formed and decomposed. The most applicable methods for obtaining metallic polonium are the thermal decomposition of polonium sulfide in a vacuum at 500-700°C or vacuum sublimation from the surface of noble metal electrodes, onto which polonium is released by electrolysis.
The atomic diameter of polonium is 3.38A, the density is 9.392 g/cm3 (slightly less than that of lead), m.p. 254°C, b.p. 962°С, heat of vaporization 24.597 kcal/mol. Thermal coefficient of linear expansion 2,35*10 -5. The electrical resistivity for the α- and β-forms at 0°C is 42 and 44 (µOhm.cm), respectively. In terms of chemical properties, polonium is a direct analog of sulfur, selenium, and tellurium. It exhibits valencies 2-, 2+, 4+, 6+, which is natural for an element of this group. The most stable of them is Po4+.
Polonium is well adsorbed on various materials, especially on metals. It has amphoteric properties. Forms colloidal hydroxides or basic salts in alkaline, neutral or slightly acidic solutions.
Elemental polonium oxidizes in air. Polonium dioxide (PoO 2)x and polonium monoxide PoO are known. Polonium reacts rapidly with oxygen when heated, forming PoO 2 dioxide at 250°C. Acid polonium trioxide PoO3 and salts of polonium acid that do not exist in the free state, K 2 PoO 4 polonates, were obtained in indicator amounts. With halogens, when heated, polonium gives tetrahalides RoH 4 . It does not interact with hydrogen and nitrogen. When metallic polonium is heated with metals, polonides are formed that are isomorphic with the corresponding tellurides. Polonium metal dissolves in nitric and hydrochloric acids.
Polonium metal readily dissolves in concentrated (but not dilute) nitric acid, releasing nitrogen oxides.
Receipt
The 210 Rho isotope can be isolated from uranium ores as a by-product of radium mining. Typically, 210 Rho is obtained from the long-lived radioactive lead isotope 210 Pb (T=23.3 years).
Polonium is isolated from radium salts and old radon ampoules by extraction, ion exchange, chromatography or sublimation. First, RaD is removed, which is kept for the accumulation of polonium. Often, for the purposes of extraction isolation of polonium, the good solubility of chelate complexes of this element in organic solvents (for example, compounds with TTA, dithizone) is used.
To separate RaD and Po, either anodic separation of polonium on platinum is carried out, or precipitation of PbS with hydrogen sulfide, as well as crystallization of bromides from concentrated HBr solutions. Extraction can be carried out by extraction from the hydrochloric acid medium with organic solvents (acetylacetone, tributyl phosphate, etc.). Often, for the purposes of extraction isolation of polonium, the good solubility of chelate complexes of this element in organic solvents (for example, compounds with TTA, dithizone) is used.
Metallic Po is obtained by thermal decomposition in vacuum of PoS sulfide or dioxide (PoO 2)x at 500 C. Vacuum sublimation is used to isolate polonium from large amounts of irradiated bismuth, as well as methods based on extraction or co-precipitation of polonium with carriers from molten bismuth. The process of extraction of polonium from molten bismuth at 400-500°C with sodium hydroxide in an inert atmosphere is a technological method for extracting it from irradiated bismuth. For two successive extractions, this method can extract 99.5% of polonium.
In practice, polonium nuclide 210 Po is artificially synthesized in gram quantities by irradiating natural 209Bi with neutrons in nuclear reactors. The resulting 210 Bi is converted into 210 Po by β-decay.
Application
Radioactive sources of 210 Po are used both in scientific research and in technology. While working on the Manhattan Atomic Bomb Project (USA), polonium-
the beryllium neutron source was supposed to be used as the fuse of the atomic bomb. Neutrons in such a source are obtained as a result of the interaction of alpha particles from the decay of 210 Po with beryllium, the reaction 9 Be (, n). However, this decision was later abandoned.
Polonium is used to manufacture compact and very powerful neutron sources that do not have γ-radiation. To do this, it is alloyed with an element having isotopes with a high (α,n)-reaction cross section, for example, with beryllium or boron. These are hermetically sealed metal ampoules containing a polonium-210-coated boron carbide or beryllium carbide ceramic pellet. Such neutron sources are light and portable, completely safe in operation and very reliable. For example, a brass ampoule with a diameter of two and a height of four centimeters produces up to 90 million neutrons every second. Polonium-beryllium neutron generators are used as energy sources in space research. Isotopic power generators for 210 Ro were successfully used on the communications satellites Kosmos-84 and Kosmos-85.
The specific energy release of polonium is high - 140 W/g. Capsule containing 0.5 g of polonium,heated up to 500° C. (1 cm 3 210 Ro emits 1320 watts of heat). This power is very high, it easily brings polonium into a molten state, so it is alloyed, for example, with lead. And although these alloys have a noticeably lower energy density (150 W/cm 3 ), nevertheless more convenient to use and safer.
Such alloys are used to create in thermoelectric sources, which are used in particular in spacecraft. For example, the Soviet lunar rover had a polonium heater to heat the instrument compartment.
Polonium is also used in devices for removing static electricity. Some devices of this kind may contain polonium with an activity of up to 500 μCi (about 0.1 micrograms). This amount is theoretically enough to kill 5,000 people. Polonium-210 can serve as an alloy with lithium-6, a substance that can significantly reduce the critical mass of a nuclear charge and serve as a kind of nuclear detonator. Therefore, polonium is a strategic metal, it must be very strictly taken into account, and its storage must be under the control of the state in view of the threat of nuclear terrorism.
Polonium is also used in the electrode alloys of automotive spark plugs forto reduce the spark initiation voltage, as well as for α-activation analysis. Small amounts of polonium are used to study radiation-chemical processes in liquids under the action of α-radiation on living organisms.
Sanitary aspects
When working with polonium, you have to be especially careful - this is one of the most dangerous radioelements. Although polonium-210 emits only alpha particles, it cannot be handled by hand, the result will be radiation damage to the skin and, possibly, to the whole body: polonium penetrates through the skin quite easily. Element No. 84 is also dangerous at a distance exceeding the length of the path of alpha particles. Its compounds self-heat, pass into an aerosol state and infect the air. Therefore, work with polonium only in sealed boxes.
With the same weight, 210 Po is 2.5 * 10 11 times more toxic than hydrocyanic acid. Once in the human body, polonium is distributed through the bloodstream through the tissues. Polonium is excreted from the body mainly with feces and urine. Most of it is excreted in the first few days. In 50 days, about half of the polonium that has entered the body is excreted. The presence of polonium in people infected with it is identified by the weak gamma radiation of secretions. Ingestion of one hundred thousandth of a milligram of polonium into the human body in 50% of cases leads to death. Polonium is a very volatile metal, in air for 45 hours 50% of it evaporates at a temperature of 55 ° C.
Named after Poland. Polonia is the name of the country in Latin and one of the elements. The metal was discovered in 1898 and was the first to be added to the list after the discovery of radioactivity. Polonium Introduced to the world by Pierre and Marie Curie.
The woman was even given for the discovery Nobel Prize. Living in France, Maria remembered her homeland - Poland, and therefore named the new element in her honor, without reflecting the main one in the name - who discovered polonium.
Chemical and physical properties polonium
Polonium belongs to the chalcogens. The concept is formed on the basis of 2 Greek words "chalkos" - "" and "genos" - "born". So, polonium and other elements of the 16th group of the periodic table are substances that make up copper ores. In addition to the 84th metal, oxygen, , and are found in them.
In its group, the 84th metal occupies the last position. It means that polonium nucleus and the entire atom is larger than the atoms of other chalcogens. At the same time, the ionization energy and electronegativity of a radioactive element are minimal.
Under normal conditions mass of polonium has a metallic, silver-white color. During the day it resembles lead, but in the dark it glows slightly. Blue radiation - a consequence polonium radioactivity. The 84th metal can also be determined by its ability to self-heat.
So much thermal energy is released that the sample melts before our eyes. It turns out that polonium independently reaches 250 degrees - the change temperature state of aggregation. The metal boils at 962 on the Celsius scale.
It is not by chance that the metal resembles lead. Polonium decay ends with the transition of the element to it. It turns out a stable, that is, not radioactive, isotope number 206. It is safe, unless, of course, you inhale it, smear it on your skin every day, or eat it in its pure form, and not in products.
Polonium 210, from which lead is obtained, on the contrary, is dangerous even in small doses. The lethal limit is 2 milligrams. Those who inhale, get poisoned with food, or through wounds on the skin are at risk.
Otherwise, you can protect yourself from polonium. Unlike many radioactive elements, the 84th emits rays of only one spectrum - alpha. The mask and gloves will protect.
Rumor has it that Alexander Litvinenko and Boris Berezovsky poisoned with polonium, namely the 210th isotope. In total, there are 27 metal isotopes in nature. Everyone is radioactive, but the decay period of the 210th is the shortest - about 139 days.
polonium poisoning FSB officer Litvinenko or businessman Berezovsky narrows the circle of suspects. The 210th isotope is produced exclusively in nuclear reactors, on particle accelerators. Units have access to the element.
chemical reactions polonium typical for metal. The element actively interacts with halogens, that is, substances from the 17th group of the periodic system.
When it meets hydrogen, a hydride is formed. He is flying. Polonium nitrate gives fusion with nitric acid. Reactions with acids are accompanied by the evolution of hydrogen.
The use of polonium
Polonium decay, its radioactivity, limit the scope of the element to atomic technologies. In particular, the 84th element goes to batteries spacecraft. Due to the presence of a radioactive metal, they have the highest specific power - 1210 W / cm 3.
An example of a battery that runs on polonium fuel is Lunokhod-2. In it, the 84th element maintains the required temperature in the fuel compartment.
Use of polonium as a heat source is complicated by the same power of the substance. Emitting about 1300 watts, the metal melts. The liquid state complicates the work with the element.
Therefore, polonium is often alloyed with lead. Thus, the solid state of the carrier is preserved, but the energy density decreases. Technologists make concessions for the sake of convenience in work.
Buy Polonium, to highlight it, experts in the nuclear industry are also striving for neutron emitters. Models from the 84th metal with beryllium emit almost no y-particles, only alpha. Outwardly, the emitters look like sealed ampoules.
Inside is a tablet of boron carbide. It is coated with 210th polonium. The design is lightweight, easy to carry, safe. The body is usually brass. For a second, the installation produces about 90,000,000 neutrons.
Alloy 210th polonium c reduces the critical mass of the nuclear charge. The indicator changes significantly. It turns out that the duet of the light isotope of lithium and the 84th element serves as a detonator. This is the root cause of the recognition of polonium as a strategically important material controlled by the state.
On federal level the substance is being monitored due to the threat of nuclear terrorism. For Russia, this is especially true, because it is one of the main miners of radioactive metal in the world.
Polonium mining
half life of polonium small in nature. Therefore, the isotopes present in uranium ores do not accumulate. Mining has to be carried out in a short time and get a small "exhaust". First, radium is extracted from the ore. The remains of the rock are dissolved by pouring hydrochloric acid.
It is to be precipitated, hydrogen sulfide and, in fact, polonium. They need to be divided. Bismuth is removed by fractional crystallization. This method relies on the different solubility of substances. You can also use chromatography. The necessary elements are absorbed based on color. Sometimes, an electrochemical method is used.
Most of the polonium is not extracted from uranium ores, but based on bismuth. It is placed in nuclear installations and bombarded with protons. This is how the 209th metal isotope is obtained. The 210th is "born" as a result of the processing of the same bismuth by neutrons.
In nature, small doses of polonium are formed during the decay of radon. A radioactive element is also released in the process of smoking tobacco. Condition - it must be grown using phosphate fertilizers. The amount of polonium produced is not hazardous to health.
To harm a person, as already mentioned, you need to take about 2 milligrams of the substance at a time. Ironically, the daughter of the discoverer of polonium, Irene Julio-Curie, received about the same dose.
The girl followed in the footsteps of her mother, became a chemist, worked day and night in the laboratory. It was there that once an ampoule with the 84th element broke. The woman fell ill with cancer and died in 1956.
Polonium price
Polonium price, as well as its production, sale, is a secret under 7 locks. While investigating the case of the poisoning of Alexander Litvinenko, law enforcement officers reported that the dose received by the officer was worth approximately 29 million euros.
At the same time, there is evidence that 0,000,000,000,001 grams of an element costs about 60 euros. Approximately this is the price tag exhibited by the "Avant-garde". This is a Russian enterprise trading in the 210th isotope.
Experts assure that all enterprises in the country export no more than 10 grams of polonium per month. So, in particular, says Sergei Kiriyenko. The man holds the position of head of Rosatom. The main sales market is the United States of America.
Previously, deliveries were made to the UK. However, this channel has been closed since 2002. The bulk of the radioactive metal remains inside the country, providing Russia's nuclear power industry.
Polonium (lat. Polonium; denoted by the symbol Po) is a chemical element with atomic number 84 in the periodic system, a radioactive semimetal of silver-white color. It has no stable isotopes.
History and origin of the name
The element was discovered in 1898 by the spouses Pierre Curie and Marie Sklodowska-Curie in resin blende. The element was named after the homeland of Maria Sklodowska-Curie - Poland (lat. Polonia).
In 1902, the German scientist Wilhelm Markwald discovered a new element. He named it radiotellurium. Curie, after reading a note about the discovery, reported that this was the element of polonium, discovered by them four years earlier. Markwald disagreed with this assessment, stating that polonium and radiotellurium are different elements. After a series of experiments with the element, the Curies proved that polonium and radiotellurium have the same half-life. Markwald was forced to retreat.
The first sample of polonium containing 0.1 mg of this element was isolated in 1910.
Properties
Polonium is a soft, silvery-white radioactive metal.
Polonium metal oxidizes rapidly in air. Polonium dioxide (PoO 2) x and polonium monoxide PoO are known. Forms tetrahalides with halogens. Under the action of acids, it goes into solution with the formation of pink Po 2+ cations:
Ro + 2HCl → PoCl 2 + H 2.
When polonium is dissolved in hydrochloric acid in the presence of magnesium, hydrogen polonide is formed:
Ro + Mg + 2HCl → MgCl 2 + H 2 Po,
Which is liquid at room temperature (-36.1 to 35.3 °C)
Acid polonium trioxide PoO 3 and salts of polonium acid that do not exist in the free state, K 2 PoO 4 polonates, were obtained in indicator amounts. Polonium dioxide PoO 2 is also known. Forms halides of composition PoX 2 , PoX 4 and PoX 6 . Like tellurium, polonium is capable of forming chemical compounds - polonides - with a number of metals.
Polonium is the only chemical element that forms a monatomic simple cubic crystal lattice at low temperatures.
Receipt
In practice, 210 Po polonium nuclide in gram quantities is artificially synthesized by irradiating metallic 209 Bi with neutrons in nuclear reactors. The resulting 210 Bi is converted into 210 Po by β-decay. When the same isotope of bismuth is irradiated with protons according to the reaction
209 Bi + p → 209 Po + n
209 Po is the longest-lived isotope of polonium.
Microquantities of polonium are extracted from uranium ore processing waste. Isolate polonium by extraction, ion exchange, chromatography and sublimation.
Metallic Po is obtained by thermal decomposition in vacuum of PoS sulfide or dioxide (PoO 2) x at 500 °C.
98% of the world's polonium production is in Russia.
