The radioactive isotope of polonium has a half-life of 0.16. Polonium: the history of the discovery of the element. Biological impact and radiation safety

In 1898, while studying uranium pitch from Bohemia, containing up to 75% uranium, Curie-Sklodowska noticed that the pitch had a significantly higher radioactivity than pure uranium preparations isolated from the same pitch. This suggested that the mineral contains one or more new elements of high radioactivity. In July of the same year, Curie-Sklodowska made a complete analysis of uranium pitch, carefully monitoring the radioactivity of each product isolated from it. The analysis turned out to be very difficult, since the mineral contained several elements. Two fractions had increased radioactivity; one of them contained bismuth salts, the other - barium salts. A product was isolated from the bismuth fraction, the activity of which was 400 times higher than that of uranium. Curie-Sklodowska came to the natural conclusion that such a high activity is due to the presence of salts of some hitherto unknown metal. She named it polonium in honor of her homeland Paul (lat. Polonia - Poland). However, for several years after this discovery, the existence of polonium was considered controversial. In 1902, Markwald checked the analysis of uranium resin on a large amount of the mineral (about 2 tons). He isolated the bismuth fraction, discovered a "new" element in it, and named it radiotellurium (Radiotellurium), since, being highly radioactive, the metal was similar to tellurium in other properties. As Markwald determined, the radiotellurium salt he isolated was a million times more active than uranium and 1000 times more active than polonium. The element has an atomic weight of 212 and a density of 9.3. Mendeleev at one time predicted the existence of an element with such properties and, based on its supposed position in the periodic system, called the element dwi-tellurium. In addition, Markwald's findings have been confirmed by several researchers. However, Rutherford soon established that radiotellurium is one of the radioactive decay products of the uranium series, and named the element Ra-F (Radium-F). Only a few years later it became obvious that polonium, radiotellurium and radium-F are one and the same element with alpha and gamma radiation and a half-life of about 140 days. As a result, it was recognized that the priority of the discovery of a new element belongs to the Polish scientist, and the name proposed by her was left.

Using radioactive isotopes as poison, you need to know what to prepare for

Events recent months showed that even such a rare and expensive substance as polonium can end up in the hands of people who do not know how to handle it. And when other people are nearby who did not even suspect of its existence, it's time to issue a manual "for dummies" on the use of polonium.

Where did it come from, this polonium?

As a detonator material, 210 Po is not perfect, as a heat source it is suitable only in exotic cases, because it is expensive. To create a reactor with a capacity of one kilowatt, 20 grams of polonium is needed. To get them, 270 kilograms of chemically pure bismuth is loaded into the reactor. Then the irradiated bismuth is distilled in vacuum, in three stages, at temperatures from 300 to 750°C. All this in compliance with the rules of radiation safety, which raises the cost to the third power. It is simply amazing how, at such an expense, someone came up with the idea of ​​using polonium as a poison to poison a single person.

In terms of cost, this poisoning can be compared with the murder of Pope Clement VII (Clement VII, 1478-1534). He died as a result of chronic poisoning with finely ground diamonds. For several months, the enemies fed the pope 14 spoons of this powder, spending 40,000 ducats. With such money it was possible to equip the expedition of Columbus.

What to do if you encounter polonium?

During the investigation of the murder, another remarkable property of this metal was revealed - the ability to adsorb on any surface. Polonium just sticks into metal, porcelain, glass - into any material on which it is placed. Nanograms of poison were placed in a cup, and it remained on the cup in a detectable amount. The cup was taken out of the room and placed in the dishwasher - polonium remains on the details of this machine. He is on the clothes of the performer, and on the plane. It seems that this poison was specially chosen to mark the entire path of the one who applied it.

Once in the human body, polonium exhibits the same surface-active properties. It shows an amazing affinity for proteins, with which it immediately reacts and remains in protein molecules (where it is discovered by forensic experts). If you just touch polonium, then 6% of the molecules from the surface of the metal are absorbed into the skin. In this case, the skin must be immediately decontaminated: at least washed with laundry soap - 3 times for 2 minutes. Washing powder mixed with thiourea is even better.

Anyone who has swallowed polonium should immediately take an emetic. In such circumstances, emetics are not given in tablets - you can’t wait - apomorphine is injected subcutaneously. Then, of course, a laxative: bitter salt (magnesium sulfate) or Glauber's salt (sodium sulfate) and cleansing enemas.

In the event that polonium has managed to stick to the proteins of a poisoned organism, complex compounds are used. They are created using unithiol or oxathiol, which exchange polonium from proteins, take it in tongs and transfer it to a solution. Just pills here, too, will not get off. I have to lie in the hospital, where unithiol is administered by dropper for 30 minutes twice a day. Getting rid of polonium in such cases occurs in a week.

What to do with polonium, which happened to be in your possession quite by accident?

Luckily, densely packed polonium can't do any harm. It can even be mailed and carried in your pocket. However, polonium emits such powerful radiation that glass and quartz containers with its solutions crack. So it's best to split a large number of polonium (if you are so rich) into smaller parts, isolate each in a plastic bag, and put the bag in a plastic or metal box - like Kashcheev's death. And lock it in a safe. And do not get out of there until 2008. And then you can throw it away.

The scientific aspects of the Litvinenko case were analyzed by Dr. chem. sciences, head. Laboratory of the Radioisotope Complex of the Institute for Nuclear Research of the Russian Academy of Sciences.

Is it possible to determine the origin of polonium technical way? Theoretically it is possible, but practically it is very difficult. Each nuclear reactor (in a certain irradiation channel) is characterized by its own neutron spectrum. The presence of fast neutrons leads to the formation, along with polonium-210 (half-life - 138.4 days), of small amounts of polonium-209 (half-life - 102 years, alpha particle energy - 4.9 MeV) according to nuclear reaction(n, 2n) from the accumulated polonium-210, as well as in even smaller amounts of polonium-208 (2.9 years).

Thus, according to such a "nuclear clock", in principle, it is possible to determine the place and date of production of polonium. However, this is not easy, and in certain cases impossible. It depends on how much polonium was found and where: the ratio between stable lead-206 formed from polonium-210 and background lead, the content of which in the natural mixture of isotopes is 24.1%, is important. You will need a special mass separator to separate polonium isotopes (or a long exposure to decay polonium-210), as well as calibration samples of polonium from the reactor, made in the same irradiation mode.

Russian polonium is produced at VNII experimental physics in the city of Sarov. Irradiation of bismuth at the reactor is carried out, apparently, in another place - P / O "Mayak" in the city of Ozersk, Chelyabinsk region. The method for producing polonium-210 is not secret, so it can be produced at any other reactors where there is a special channel for irradiating targets in order to obtain isotopes. Such reactors are located in several countries of the world. Power reactors are generally not suitable for this, although some of them have a channel for irradiating targets. More than 95% of the polonium-210 was reported to be produced in Russia.

There are also other methods for obtaining polonium, but they are practically not used now, since they are much less productive and more expensive. One of these methods, used by Marie Curie, is chemical isolation from uranium ores (polonium-210 is found in the decay chain of uranium-238). Actually, polonium was discovered in 1898. Polonium-210 can also be obtained at charged particle accelerators by nuclear reactions 208 Pb (A, 2 n) or 209 Bi (d, n). At the same time, far from any accelerator is suitable for obtaining polonium-210. This requires an alpha particle or deuteron accelerator. There are not many such accelerators in the world. They exist in Russia and the UK. However, as far as I know, in Britain, the Amersham accelerator has long been tuned out for alpha particles and is constantly working exclusively on the production of medical isotopes for diagnostics. In a number of places I visited abroad, colleagues told me that their plants were inspected to see if they were producing polonium.

At one time, JSC Techsnabexport sold polonium-210 to the UK (to Reviss). But this was five years before the unfortunate events, and, as colleagues told me, the company was very carefully checked after that. Products containing polonium are not officially supplied to the UK from the USA and Russia. Polonium-210 was previously obtained at the Oak Ridge National Laboratory (USA), but now it is not produced there in significant quantities, but, on the contrary, some is received from Russia.

The work of both reactors and accelerators is strictly controlled. If someone still decides to produce polonium illegally, with existing system control is easy to uncover.

Nuclear physical properties

As already mentioned, the half-life of polonium is 138.4 days. This means that every 138 days its activity decreases by 2 times, and in two years - by about 40 times. Such a half-life is very convenient for the use of a radionuclide as a poison.

Polonium-210, when decaying, emits alpha particles with an energy of 5.3 MeV, which have a short range in solids. For example, aluminum foil tens of microns thick completely absorbs such alpha particles. The gamma radiation that could be detected by Geiger counters is extremely weak: gamma rays with an energy of 803 keV are emitted with a yield of only 0.001% per decay. Polonium-210 has the lowest gamma constant of all common alpha active radionuclides. So, for americium-241 (widely used, for example, in smoke detectors), the gamma constant is 0.12, and Po is 5 10 -5 Rxcm 2 / hxmCi. In this case, the dose coefficient and, consequently, radiotoxicity are quite comparable.

Thus, even without a protective shell, it is extremely difficult to remotely detect the amount of polonium-210 sufficient for poisoning using a conventional counter, since the radiation level is comparable to the natural background (see Fig. 2). Thus, polonium-210 is very convenient for clandestine transportation, and there is no need even to use lead containers. However, special care must be taken during transport to avoid depressurization of the container (see below).
Rice. 2. Gamma radiation (dose rate) of polonium-210 depending on its activity and distance to the detector (1 mCi - 3.7 × 10 7 Bq) It is not at all advisable to use polonium-210 for provocations, since it can only be detected with the help of special equipment, which is not normally used.

The 803 keV gamma line can only be detected by long measurements using a good gamma spectrometer, and the semiconductor detector should be located very close to the source. There is evidence that this is how the increased radioactivity was found in Litvinenko at first, but at first the radiation was erroneously attributed to radioactive thallium (thallium-206), which is obtained by the decay of bismuth-210m (see the diagram in Fig. 1).

This was reported on the Internet even before polonium was identified. But then this version was recognized as erroneous, since this isotope of bismuth has too long a half-life, and they began to consider the possibility of having other alpha emitters. After that, urine was analyzed for the presence of alpha-active radionuclides and polonium was found, moreover, in huge quantities. The assumption that some provocateurs “told” the British experts about polonium-210 seems to me taken from the ceiling. British scientists did everything consistently and quite logically.

On the surface, the alpha activity of polonium-210 can be detected using an alpha counter, which is usually used only for special purposes, and not for routine checks for radioactive contamination. However, to determine that the radiation refers specifically to polonium-210, more complex equipment, usually stationary, is required - an alpha spectrometer. Activity on the order of 1 Bq (decay per second) on the surface can be easily registered. If alpha activity is detected, then sample preparation is already performed (for example, using chemical isolation) and a line in the 5.3 MeV alpha spectrum is detected on the alpha spectrometer, which characterizes this particular alpha-active radionuclide.

Chemical properties

Polonium can exist in different chemical forms, but in this case it is most likely to be in the form soluble compounds(for example, nitrates, chlorides, sulfates), while in a significant part in solution it can also be in colloidal form. It is important that polonium is largely sorbed from neutral and slightly acidic solutions on various surfaces, in particular, on metal and glass (maximum sorption is at pH ~ 5). It is difficult to completely wash it with conventional methods. Therefore, it is not at all surprising that a teapot and a cup from which polonium was consumed were discovered.
Rice. 3. 3d-graphic of the Metropolitan Police of London, characterizing the contamination in the kettle, from which Litvinenko was poisoned. From green (low) to purple (high). From the site www.litvinenkoinquiry.org Actually, polonium in microquantities begins to sublimate only at temperatures of about 300 ° C. But it can turn into environment also together with the water vapor in which it is contained, and in the process with recoil nuclei.

Polonium diffuses fairly easily into plastics and other organic matter, sources based on it are made with a multilayer coating. And if the ampoule was depressurized, then even the smallest traces of it can be detected with the help of an alpha counter.

Polonium is a polyvalent element that is prone to the formation of various complexes and can form various chemical

forms. In this regard, part of it is quite easily distributed in the natural environment. Therefore, it is quite understandable that traces of polonium have spread, and they can trace the source of polonium contamination.

Biological impact and radiation safety

Biological studies of the effects of polonium on animals were carried out in our country mainly in the 60s at the Institute of Biophysics in the laboratory of Professor Yu.I. Moskalev, there are several publications.

It has long been known that polonium-210 is one of the most dangerous radionuclides. The levels of human exposure to polonium-210 are shown in the table (data on experiments with animals are recalculated by us for the mass of a person).

The absorption of this substance through the gastrointestinal tract is estimated from 5 to 20%. Through the lungs is more effective, but such an introduction is extremely inconvenient for latent poisoning, since this can greatly pollute those around you and the performers. Only about 2% per day is absorbed through the skin, and this use of polonium for poisoning is also ineffective.

Polonium is distributed in the body to all organs, but, of course, not quite evenly. And it is excreted from the body with any biological substances: feces, urine, sweat ... The half-life, according to various sources, is from 50 to 100 days. One industrial accident was reported in our country, which led to the death of a person 13 days after the ingestion of 530 MBq (14 mCi) of polonium.

According to indirect data (according to the impact), the amount of polonium introduced into Litvinenko could be (0.2−4)x10 9 Bq (becquerels), that is, disintegrations per second), by mass it is 1−25 μg, practically invisible amount.

If polonium was contained in a cup of tea, for example, ~10 9 Bq per 100 g, then up to 0.01-0.10 ml, that is, up to 10 5 -10 6 Bq. This does not pose a serious danger to human life, although it exceeds the permissible pollution standards. Such an amount can be easily detected, and an activity of the order of 1 Bq is also detected.

In the Litvinenko story, according to the Health Protection Agency, the following happened:

• 120 people were likely exposed to polonium but received doses below 6 mSv (millisieverts), which poses no health risk;
• 17 people received a dose above 6 mSv, but not so significant as to cause any disease in the near future, the increase in the risk of disease in the distant future is probably very small. However, the highest dose

not life-threatening, received, of course, the wife of Alexander Litvinenko Marina, with whom he had the most contact.

The allowable dose for professionals working with radioactivity in Russia is 20 mSv/yr. not elevated. Only exposure to an effective dose of more than 200 mSv during the year is considered potentially hazardous. Thus, claims that the use of polonium created a great danger to others is an exaggeration.

The question was raised in the press whether polonium-210 had been used as a poisonous substance before and whether this could be established. In particular, the poisons that may have poisoned Y. Shchekochikhin and tried to poison A. Politkovskaya remained unknown. If polonium-210 was present in these cases, then over the past time it has decayed to a level below the background level. However, exhumation may reveal polonium-209, which could be present as an impurity (see above).

The hypothesis that Yasser Arafat was poisoned with polonium-210 was practically not confirmed. Some excess of polonium-210 can be explained by natural causes - inhalation of radon-222 during the long stay of the Palestinian leader in the bunker. Polonium-210 is a decay product of radon. A corresponding amount of lead-210, which is also a decay product of radon, was found in Arafat's body.

Application

So far, polonium-210 has been used for the following purposes.

1. To create autonomous sources of energy generated as a result of alpha decay. The Soviet Lunokhod and some satellites of the Kosmos series were equipped with such devices.
2. As a source of neutrons, in particular, for the initiators of a nuclear explosion in atomic bombs. Neutrons are produced when beryllium is irradiated with alpha particles and initiate nuclear explosion when the mass of uranium-235 or plutonium-239 becomes critical. Also, such sources were used for neutron activation analysis of natural samples and materials.
3. As a source of alpha particles in the form of applicators for the treatment of certain skin diseases. Now it is practically not used for such purposes, since there are much more suitable radionuclides.
4. As an air ionizer in antistatic devices such as the Staticmaster manufactured by Calumet in the USA. These materials are not exported to the UK, and to extract the polonium-210 needed for poisoning, many such devices would have to be processed, which requires a radiochemical laboratory.

The photo was taken two days before Litvinenko's death (November 23, 2006). From www.litvinenkoinquiry.org Findings related to Litvinenko's death

Conclusions of a technical nature that may be essential for solving a crime can be divided into two groups: quite certain and those that are very likely, but for an unambiguous statement, an investigation is required not only in the UK, but also in Russia.

well defined

1. Polonium-210 is a covert poison. Its main difference from other radioactive substances is the difficulty of initial detection. Accordingly, it is pointless to use it for provocation, there are much more accessible and suitable radionuclides for this.
2. Polonium-210 is a substance that can be conveniently surreptitiously transported in quantities sufficient to cause poisoning. It is also easy to discreetly introduce it into a person’s drink. Other methods of administration (for example, airborne spraying or skin injection) are less effective, unreliable, difficult, and very dangerous for the poisoner.
3. Accidental contamination with polonium-210 by negligence is almost unbelievable, since such a degree of contamination requires a huge amount that can only exist in places of mass production of polonium in a plant, and this can be easily determined by the distribution of polonium on the human body.
4. None of the published allegations by the UK investigating authorities contain technical contradictions.

Very likely, but needs to be confirmed

1. It is most likely that the polonium-210 was produced in Russia. It could have been brought to the UK from Russia or the USA, where this substance is officially supplied. Other sources are not excluded in principle, but it would be practically impossible to hide such production. Polonium-210 has long been discontinued in the UK.
2. Extraction from antistatic devices in the US requires a special radiochemistry lab, which is extremely difficult to conceal under the current US control system. In other countries, such antistatic devices are practically not used.
3. It is possible to determine the origin of polonium by analysis only under certain circumstances (sufficient quantities and concentration, absence of background lead, sufficient exposure before analysis, availability of a special mass separator and samples for comparison). Under favorable conditions, it is also possible to establish in which production cycle it was obtained.
4. The substance was not stolen. This is extremely difficult to organize under the existing control system. Previously, several facts of the loss of polonium were recorded, but all of them were disclosed, since it is not a big problem to reveal them.

Shortly after the discovery of radioactivity, Paul Curie and Marie Skłodowska-Curie, studying uranium resin ore, found that it had a much higher radioactivity than pure uranium. It has been suggested that the ore contains other chemical elements more radioactive than uranium. The processing of many tons of uranium ore made it possible in 1898 to isolate two more new chemical elements from it: radium and element No. 84, which was named Polonium in honor of Poland.

Receipt:

In nature, polonium isotopes are included in the natural radioactive series 238 U and are always present in uranium ores, but due to the short half-life they do not accumulate in it in significant quantities. Content in uranium ore of the most stable isotope 210 Po (half-life 138.3 days) 2*10 -10 . To isolate polonium from the ore, radium is first extracted, then the residues are dissolved in hydrochloric acid and precipitate polonium together with bismuth hydrogen sulfide. Polonium is separated from bismuth by fractional crystallization of compounds with different solubility, chromatography, electrochemical methods. At present, 210 Po is received mainly in nuclear reactors, irradiating bismuth with neutrons:
209 Bi(n, g) 210 Bi; 210Bi(-, b) 210 Po
The longest-lived isotope of polonium (half-life 103 years) is obtained by bombarding bismuth with protons:
209 Bi (p, n) 209 Po.

Physical properties:

A silvery white metal reminiscent of bismuth and lead. Due to the high radioactivity in the dark, a light blue glow can be seen, and self-heating is also observed. The polonium releases so much thermal energy that the heat is capable of melting the sample. The melting point of Po is 254°C; boiling point 962°C, density 9.4 g/cm 3 .
Polonius undergoes a- decay, turning into a stable isotope of lead: 210 Po (-, a) 206Pb

Chemical properties:

According to its properties, polonium is a typical metal; it oxidizes in air, interacts with halogens, and forms a volatile hydride with hydrogen. Polonium's position electrochemical series stress is contradictory: according to some data, it reacts with acids with the release of hydrogen, according to others - it is located between Cu and Ag, according to the third - it is displaced by silver from solutions ..
Polonium is oxidized with nitric acid to form Po(IV) nitrate:
Po + 8HNO 3 \u003d Po (NO 3) 4 + 4NO 2 + 4H 2 O
In compounds, it exhibits oxidation states -2, +2 and +4 (+6 is not typical).

The most important connections:

Oxidation state -2. Polonium hydride PoH 2 is similar in properties to hydrogen telluride, but even less stable. Traces of PoH 2 are formed by dissolving polonium in hydrochloric acid in the presence of magnesium. Polonides- compounds of polonium with more active metals, such as Na 2 Po
+2 oxidation state. Polonium halides (PoCl 2 - red, PoBr 2) are similar in properties to salts. Black sulfide PoS and red sulfite PoSO 3 are also known.
+4 oxidation state, the most characteristic.
Polonium(IV) oxide, PoO 2 (red) - amphoteric oxide with a predominance of basic properties, interacts with alkalis only when fused, forming polonites M 2 PoO 3 . It reacts with acids as a basic oxide:
PoO 2 + 2H 2 SO 4 \u003d Po (SO 4) 2 + 2H 2 O
Polonium(IV) salts Po(SO 4) 2 *nH 2 O, Po(NO 3) 4, colorless. crystals, in solution are strongly hydrolyzed, forming colloidal solutions of PoO(OH) 2 (light yellow). This hydroxide is also amphoteric, it can be considered full acid.
Polonium(IV) halides PoCl 4 (yellow), PoBr 4 (red), PoI 4 black), insoluble in water, interact with alkali metal halides to form K 2 type compounds

Application:

The main area of ​​application of polonium-210 is the manufacture of atomic batteries used in spacecraft. Compared to other sources, polonium-210 has the highest specific power, 1210 W/cm3. The radioactive isotope polonium-210 served, for example, as fuel for the "stove" installed on Lunokhod-2, maintaining an acceptable temperature in the instrument compartment of this apparatus.
It is also used as a source a-particles, and in a mixture with beryllium or boron - as an ampoule neutron source. a-particles emitted by polonium generate a stream of neutrons from the nuclei of an atom of boron or beryllium.
The high toxicity of polonium is due mainly to its radioactivity. emitted by him a-radiation, on the one hand, is most easily absorbed even by a sheet of paper. The penetrating power and path length of the alpha particle are minimal. On the other hand, this radiation has the most destructive effect when the source enters the body. Since polonium is able to quickly become aerosolized and contaminate the air, it is also dangerous at a distance greater than the range of alpha particles. See also:
Trifonov D.N. M. Sklodowska-Curie: knowledge of radioactivity. / Chemistry at school, 1997, No. 7.

The content of the article

POLONIUM- radioactive chemical element Group VI of the periodic system, an analogue of tellurium. Atomic number 84. Has no stable isotopes. There are 27 known radioactive isotopes of polonium with mass numbers from 192 to 218, of which seven (with mass numbers from 210 to 218) are found in nature in very small quantities as members of the radioactive series of uranium, thorium and actinium, the remaining isotopes were obtained artificially. The longest-lived isotopes of polonium are artificially produced 209 Po ( t 1/2 = 102 years) and 208 Rho ( t 1/2 \u003d 2.9 years), as well as 210 Rho contained in radium-uranium ores ( t 1/2 = 138.4 days). Content in earth's crust 210 Rho is only 2 10 -14%; 1 ton of natural uranium contains 0.34 g of radium and fractions of a milligram of polonium-210. The shortest-lived known isotope of polonium is 213 Po ( t 1/2 = 3 10 -7 s). The lightest isotopes of polonium are pure alpha emitters, while the heavier isotopes simultaneously emit alpha and gamma rays. Some isotopes decay by electron capture, and the heaviest ones also exhibit very weak beta activity ( cm. RADIOACTIVITY). Different isotopes of polonium have historical names adopted as early as the beginning of the 20th century, when they were obtained as a result of a chain of decays from the "parent element": RaF (210 Po), AcC "(211 Po), ThC" (212 Po), RaC " (214 Po), AcA (215 Po), ThA (216 Po), RaA (218 Po).

The discovery of polonium.

The existence of an element with serial number 84 was predicted by D.I. Mendeleev in 1889 - he called it ditellurium (in Sanskrit - the “second” tellurium) and suggested that it atomic mass will be close to 212. Of course, Mendeleev could not foresee that this element would turn out to be unstable. Polonium is the first radioactive element, discovered in 1898 by the Curies in search of a source of strong radioactivity in certain minerals ( cm. RADIUM). When it turned out that uranium resin ore radiates more strongly than pure uranium, Marie Curie decided to chemically isolate a new radioactive chemical element from this compound. Before that, only two weakly radioactive chemical elements were known - uranium and thorium. Curie started with the traditional quality chemical analysis mineral according to the standard scheme, which was proposed by the German analytical chemist K. R. Fresenius (1818–1897) back in 1841 and according to which many generations of students for almost a century and a half determined cations by the so-called “hydrogen sulfide method”. At the beginning she had about 100 g of the mineral; then American geologists gave Pierre Curie another 500 g. Carrying out a systematic analysis, M. Curie each time checked individual fractions (precipitates and solutions) for radioactivity using a sensitive electrometer invented by her husband. Inactive fractions were discarded, active ones were analyzed further. She was assisted by one of the leaders of the chemical workshop at the School of Physics and Industrial Chemistry, Gustav Bemon.

First of all, Curie dissolved the mineral in nitric acid, evaporated the solution to dryness, dissolved the residue in water, and passed a stream of hydrogen sulfide through the solution. At the same time, a precipitate of metal sulfides precipitated; according to the Fresenius method, this precipitate could contain insoluble sulfides of lead, bismuth, copper, arsenic, antimony, and a number of other metals. The precipitate was radioactive, despite the fact that the uranium and thorium remained in solution. She treated the black precipitate with ammonium sulfide to separate the arsenic and antimony - under these conditions they form soluble thiosalts, for example, (NH 4) 3 AsS 4 and (NH 4) 3 SbS 3 . The solution did not detect radioactivity and was discarded. Lead, bismuth and copper sulfides remained in the sediment.

The part of the Curie precipitate that did not dissolve in ammonium sulfide was again dissolved in nitric acid, added to the solution sulfuric acid and evaporated it on a burner flame until thick white fumes of SO 3 appeared. Under these conditions, flying Nitric acid completely removed, and metal nitrates are converted to sulfates. After cooling the mixture and adding cold water, insoluble lead sulfate PbSO 4 turned out to be in the precipitate - there was no activity in it. She discarded the precipitate, and added a strong solution of ammonia to the filtered solution. At the same time, a precipitate fell out again, this time - white color; it contained a mixture of basic bismuth sulfate (BiO) 2 SO 4 and bismuth hydroxide Bi(OH) 3 . The complex copper ammonia SO 4 of bright blue color remained in the solution. The white precipitate, unlike the solution, turned out to be highly radioactive. Since the lead and copper had already been separated, the white precipitate contained bismuth and an admixture of the new element.

Curie again converted the white precipitate into dark brown Bi 2 S 3 sulfide, dried it, and heated it in an evacuated ampoule. Bismuth sulfide did not change at the same time (it is resistant to heat and melts only at 685 ° C), however, some vapors were released from the precipitate, which settled in the form of a black film on the cold part of the ampoule. The film was radioactive and apparently contained a new chemical element - an analogue of bismuth in the periodic table. It was polonium - the first discovered radioactive element after uranium and thorium, inscribed in the periodic table (in the same 1898, radium was discovered, as well as a group of noble gases - neon, krypton and xenon). As it turned out later, polonium easily sublimates when heated - its volatility is about the same as that of zinc.

The Curies were in no hurry to call the black coating on the glass a new element. One radioactivity was not enough. A colleague and friend of Curie, French chemist Eugene Anatole Demarce (1852–1903), a specialist in the field of spectral analysis (he discovered europium in 1901), studied the emission spectrum of black plaque and found no new lines in it that could indicate the presence of a new element. Spectral analysis- one of the most sensitive methods that allows you to detect many substances in microscopic quantities invisible to the eye. Nevertheless, in an article published on July 18, 1898, the Curies wrote: “We think that the substance we isolated from uranium resin contains a metal that is not yet known, which is analogous to bismuth in analytical properties. If the existence of a new metal is confirmed, we propose to call it polonium, after the birthplace of one of us” (Polonia in Latin - Poland). This is the only case when a new chemical element, not yet identified, has already received a name. However, it was not possible to obtain weight amounts of polonium - there was too little of it in uranium ore (later polonium was obtained artificially). And it was not this element that glorified the Curie spouses, but radium

properties of polonium.

Tellurium already partially exhibits metallic properties, while polonium is a soft silvery-white metal. Due to the strong radioactivity, it glows in the dark and gets very hot, so continuous heat removal is needed. The melting point of polonium is 254 ° C (slightly higher than that of tin), the boiling point is 962 ° C, therefore, even with a slight heating, polonium sublimates. The density of polonium is almost the same as that of copper - 9.4 g/cm 3 . In chemical research, only polonium-210 is used; longer-lived isotopes are practically not used due to the difficulty of obtaining them with the same chemical properties.

The chemical properties of metallic polonium are close to those of its closest analogue, tellurium; it exhibits oxidation states of –2, +2, +4, +6. In air, polonium slowly oxidizes (quickly when heated to 250 ° C) with the formation of red dioxide PoO 2 (when cooled, it becomes yellow as a result of rearrangement of the crystal lattice). Hydrogen sulfide from solutions of polonium salts precipitates black sulfide PoS.

The strong radioactivity of polonium is reflected in the properties of its compounds. So, in dilute hydrochloric acid, polonium slowly dissolves with the formation of pink solutions (the color of Po 2+ ions): Po + 2HCl ® PoCl 2 + H 2, however, under the influence of its own radiation, the dichloride turns into yellow PoCl 4 . Dilute nitric acid passivates polonium, while concentrated nitric acid quickly dissolves it. With non-metals of group VI, polonium is related by the reaction with hydrogen to form the volatile hydride PoH 2 (m.p. -35 ° C, b.p. +35 ° C, easily decomposes), the reaction with metals (when heated) to form solid black polonides colors (Na 2 Po, MgPo, CaPo, ZnPo, HgPo, PtPo, etc.) and reaction with molten alkalis to form polonides: 3Po + 6NaOH ® 2Na 2 Po + Na 2 PoO 3 + H 2 O. Polonium reacts with chlorine at heating with the formation of bright yellow crystals of PoCl 4 , with bromine, red crystals of PoBr 4 are obtained, with iodine, already at 40 ° C, polonium reacts to form black volatile iodide PoI 4 . White polonium tetrafluoride PoF 4 is also known. When heated, the tetrahalides decompose to form more stable dihalides, for example, PoCl 4 ® PoCl 2 + Cl 2 . In solutions, polonium exists in the form of cations Po 2+ , Po 4+ , ​​anions PoO 3 2– , PoO 4 2– , and various complex ions, for example, PoCl 6 2– .

Obtaining polonium.

Polonium-210 is synthesized by neutron irradiation of natural bismuth (it contains only 208 Bi) in nuclear reactors (the beta-active isotope of bismuth-210 is formed intermediately): 208 Bi + n ® 210 Bi ® 210 Po + e. When bismuth is irradiated with accelerated protons, polonium-208 is formed, it is separated from bismuth by sublimation in a vacuum - as M. Curie did. In our country, the method for isolating polonium was developed by Zinaida Vasilievna Ershova (1905–1995). In 1937 she was sent to Paris to the Institute of Radium in the laboratory of M.Curie (headed at that time by Irene Joliot-Curie). As a result of this business trip, colleagues began to call her "Russian Madame Curie." Under the scientific guidance of Z.V. Ershova, a permanent, environmentally friendly production of polonium was created in the country, which made it possible to implement the domestic program for launching lunar rovers, in which polonium was used as a heat source.

Long-lived isotopes of polonium have not yet received a noticeable practical application due to the complexity of their synthesis. To obtain them, one can use the nuclear reactions 207 Pb + 4 He ® 208 Po + 3n, 208 Bi + 1 H ® 208 Po + 2n, 208 Bi + 2 D ® 208 Po + 3n, 208 Bi + 2 D ® 208 Po + 2n , where 4 He are alpha particles, 1 H are accelerated protons, 2 D are accelerated deuterons (deuterium nuclei).

The use of polonium

Polonium-210 emits alpha rays with an energy of 5.3 MeV, which are decelerated in solid matter, passing only thousandths of a millimeter and giving up their energy in the process. Its lifetime allows the use of polonium as an energy source in atomic batteries. spaceships: to obtain a power of 1 kW, only 7.5 g of polonium is enough. In this respect, it is superior to other compact "atomic" energy sources. Such an energy source worked, for example, on Lunokhod-2, heating the equipment during a long moonlit night. Of course, the power of polonium energy sources decreases over time - by half every 4.5 months, but longer-lived polonium isotopes are too expensive. Polonium is also conveniently used to study the effects of alpha radiation on various substances. As an alpha emitter, polonium mixed with beryllium is used to make compact neutron sources: 9 Be + 4 He ® 12 C + n. Boron can be used instead of beryllium in such sources. In 2004, inspectors from the International Atomic Energy Agency (IAEA) were reported to have discovered a polonium production program in Iran. This led to the suspicion that it could be used in a beryllium source to "start" with the help of neutrons a nuclear chain reaction in uranium, leading to a nuclear explosion.

Polonium, when it enters the body, can be considered one of the most toxic substances: for 210 Rho, the maximum permissible content in the air is only 40 billionths of a microgram per 1 m 3 of air, i.e. Polonium is 4 trillion times more toxic than hydrocyanic acid. The alpha particles emitted by the polonium (and to a lesser extent also the gamma rays) cause damage, which destroy tissues and cause malignant tumors. Polonium atoms can be formed in human lungs as a result of the decay of radon gas in them. In addition, metallic polonium is able to easily form the smallest aerosol particles. Therefore, all work with polonium is carried out remotely in sealed boxes.

Ilya Leenson