Why was polonium needed? Polonium: the history of the discovery of the element Polonium application
London- Polonium first received widespread attention in 2006, when it was used to assassinate Kremlin critic and former KGB agent Alexander Litvinenko in London.
Yasser Arafat's widow this week called for the Palestinian leader's body to be exhumed after Swiss scientists found traces of radioactive polonium-210 on clothing he was believed to have worn before his death in 2004.
So what is polonium, and how dangerous is it?
What is polonium?
Polonium-210 is one of the rarest elements, and it was discovered in 1898 by the spouses Pierre Curie and Maria Skłodowska-Curie and named after Maria's homeland, Poland. The element accumulates naturally in extremely small quantities in the earth's crust, and is also produced artificially in nuclear reactors. It is used in small quantities for legitimate industrial purposes, mainly to relieve static electricity.
Is he dangerous?
Very. If it enters the body, it is fatal even in negligible doses. Less than one gram of silver powder is enough to kill someone. In a 2007 study, UK Department of Health scientists showed that once polonium enters the bloodstream, its powerful effects are almost impossible to stop. The poisoned victim experiences gradual organ failure as alpha particles attack the liver, kidneys and bone marrow. Litvinenko's symptoms are also typical - nausea, hair loss, swollen throat and paleness.
Who can get polonium?
The good news is that few people do. The element can be a byproduct of chemical processing of uranium, but it is most often produced by nuclear reactors or particle accelerators. These nuclear facilities are tightly controlled and operate under strict international agreements.
Retired British radiation expert John Croft, who worked with Litvinenko, believes that a sufficient dose of polonium to kill would likely be obtained from a government with civilian or military nuclear capabilities. Russia, which produces polonium and is suspected of killing Litvinenko, fits this description, as does Arafat's enemy Israel. But there are also a dozen other countries, including the United States.
Why might he be of interest to killers?
Polonium is a good weapon. Its large radioactive alpha particles do not penetrate the skin or be detected by radiation detectors, making it relatively easy to smuggle across borders. Polonium can enter the body through a wound or inhalation, but the most reliable way is to consume polonium through food or drink. Litvinenko drank tea laced with polonium during a meeting at a luxury hotel in London.
Who did they kill?
Polonium poisoning is so rare that it took doctors several weeks to identify Litvinenko's illness, and security experts had difficulty remembering a previous case of poisoning. Five years have passed since Litvinenko's murder, but no one has been detained. British investigators have named former KGB agent Andrei Lugovoy as the main suspect, but Russia is refusing to extradite him.
Some believe that Curie's daughter Irene, who died of leukemia, fell ill after accidentally receiving a dose of polonium in the laboratory.
Israeli author Michal Karpin stated that the deaths of several Israeli scientists due to cancer were the result of a leak at the Weizmann Institute of Science in 1957. Israeli authorities have never recognized the relationship.
Can scientists prove that Arafat was poisoned with polonium?
Scientists have warned that traces of polonium on Arafat's clothing are not enough to prove poisoning. Exhuming the body for testing is a much more reliable method. University College London radiology specialist Derek Hill said that eight years after Arafat's death, polonium should have already decayed and is much less radioactive than it was in 2004. But he said the level would still be many times higher than normal, and an autopsy should show "with a reasonable degree of certainty" whether polonium was present in Arafat's body at the time of death.
The poisoning of Alexander Litvinenko would have required, according to British experts, the use of significant technical knowledge and skills.
Litvinenko died on November 23 due to a lethal dose of radiation from the polonium-210 isotope found in his body.
Since then, traces of this isotope have been found in five places in London, including a sushi bar and a hotel where the ex-FSB officer visited.
However, polonium-210 belongs to a class of radioactive substances whose detection and production poses significant difficulties.
This isotope occurs naturally in nature and in the human body in extremely low concentrations. In order to obtain quantities of this substance sufficient for criminal use, sophisticated technology and special knowledge are required.
Professor Nick Priest, one of the few British physicists who has direct experience with polonium-210, told the BBC that just one milligram of this isotope would be enough to kill Litvinenko.
Polonium-210 emits a powerful stream of alpha particles. Unlike gamma radiation, alpha particles penetrate a relatively short distance, to the depth of only a few cells in biological tissues.
However, alpha particles initially have high energy, giving which they are capable of causing great destruction to cellular structures.
"If you put this substance in a test tube or flask, it cannot be recognized by external signs," says Dr Frank Barnaby, a nuclear physicist at the University of Oxford. "That is what makes it an almost perfect poison."
But if such a test tube is opened, then polonium-210 very easily spreads through the air with water vapor and pollutes the environment.
At least three methods for obtaining this isotope are known. Polonium-210 can be extracted from uranium ore, from uranium enriched in a reactor, or from another isotope, radium-226.
The fruit of Marie Curie's efforts
Polonium was discovered by Marie Curie in 1897 by chemical extraction from the mineral uranium oxide. The researcher gave the element its name in honor of her homeland - Poland.
According to physicist Nick Priest, this method is not able to produce enough of the isotope necessary to kill an adult.
To obtain the required quantity, the use of a nuclear reactor is required, he believes.
According to him, the most realistic way to obtain polonium-210 is to irradiate the element bismuth with neutrons in such a reactor, resulting in the isotope bismuth-210.
This isotope has a short half-life, after which it decays into polonium-210 and thallium-206.
As Nick Priest points out, there have been reports of the presence of small amounts of radioactive thallium in Litvinenko’s body, which may serve as an indirect sign of polonium being produced in the reactor.
Thallium-206 has a very short half-life, so there should be traces of bismuth-210 in polonium, which in turn gives us thallium.
This can happen if bismuth is not completely separated from polonium at the final stage of the process.
Obtaining polonium from the radium-226 isotope is considered a complex process because this radium isotope produces hard, penetrating radiation.
Lunar rovers walked on it
According to experts, there are only 40-50 reactors in the world capable of producing polonium-210. All available data points to sources outside the UK.
Among them are several nuclear facilities in the former Soviet Union, as well as in Australia and Germany.
“There is only one reactor in Britain that could produce this isotope, and I am sure that the physicists working on it did not do such things,” says Nick Priest.
Polonium is used in various measuring devices, but it is not easy to extract from them.
In the past, polonium, like beryllium, was used as a nuclear reaction initiator in atomic bombs produced in the USA, Great Britain and the USSR. In addition, Soviet lunar rovers in the 70s were equipped with isotope batteries based on polonium-210.
The culprits are harder to find
The Litvinenko case again forces us to turn to the topic of illegal trade in Russian radioactive substances. Since 1995, the IAEA has maintained a database of recorded episodes of the spread of nuclear waste and radioactive materials. According to data for last year, a total of 827 such episodes were registered.
The IAEA has no information about the presence of the polonium-210 isotope on the black market, but there have been unconfirmed reports in this regard.
On Tuesday, Sergei Kiriyenko, the head of Rosatom, rejected suggestions that the polonium-210 that caused Litvinenko's death could have been illegally exported from Russia. According to him, Russia exports only 8 grams of polonium-210 per month, and all this amount is sent to the United States. Exports to the UK ceased five years ago.
In theory, investigators leading the Litvinenko case could trace the origins of polonium-210, but to do so would require first finding residual traces of other isotopes.
But even if such data were obtained, it would not necessarily lead to the discovery of the culprit, especially in the case of theft of such materials. According to many physicists, polonium-210 was chosen as a murder weapon precisely because of its high toxicity and difficulty of detection.
Radioactive element of group VI of the periodic system of Mendeleev. Polonium was discovered in 1898 by Marie Sklodowska-Curie and Pierre Curie. The name was given in honor of Poland.
M. Curie found that some samples of uranium resin ore are more radioactive than uranium itself. Therefore, this ore must have contained substances more radioactive than uranium. These substances (elements) were isolated. First polonium and then radium.
The longest-lived of the natural isotopes is 210 Po. The half-life of 210 Po is 138.376 days, i.e. During this time, the initial amount of 210 Po is halved. After this time, half of the 210 Po nuclei turn into nuclei of the stable lead isotope 206 Pb. The transformation of 210 Po into 206 Pb occurs as a result of α decay
210 Po → 206 Pb + α.
Rice. 1. Scheme of the decay of 210 Po. |
Those. In addition to lead nuclei (206 Pb), the decay of 210 Po also produces helium nuclei 4 He, which are usually called α (alpha) particles. Moreover, 210 Po is an almost pure α-emitter. Alpha decay, if it occurs not to the ground state or not only to the ground state of the final nucleus, is accompanied by gamma radiation. In the overwhelming 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 a tiny fraction (0.00122%) of 210 Po nuclei decays into the excited (803 keV) state of 206 Pb, which decays with the emission of gamma-ray particles. quanta The gamma radiation accompanying such alpha decay can be detected only in a precision experiment.
The 210Po isotope is not only the longest-lived among natural ones, i.e. existing on Earth, and not artificially obtained, isotopes of polonium, but also the most common. It is constantly formed due to a chain of isotope decays that begins with 238 U and ends with 206 Pb.
238 U → 234 Th → 234 Pa → 234 U → 230 Th → 228 Ra → 222 Rn → 218 Po → 214 Pb → 214 Bi → 214 Po → 210 Pb → 210 Bi → 210 Po → 206 Pb.
Half-life (T 1/2) of 238 U is 4.5 billion years. In the natural uranium mixture, 238 U is more than 99%. For the number of nuclei (N) isotopes of uranium (238 U) and polonium (210 Po) in a natural mixture and their half-lives (T 1/2), the following relation is true:
N(238 U)/N(210 Po) = T 1/2 (238 U)/T 1/2 (210 Po).
Similar relationships are valid for all isotopes in a chain of successive decays, since they are in the so-called secular equilibrium , when the number of decays per unit time is the same for all isotopes. As many isotope nuclei are formed as a result of previous decay per unit time, the same number of them decay. Thus, 1 ton of uranium ore contains only about 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 uranium production waste. However, in order to obtain a noticeable amount of polonium, an incredible amount of such waste would have to be processed. 210 Po is produced in nuclear reactors by irradiating bismuth with neutrons as a result of the reaction
209 Bi(n,γ ) 210 Bi.
210 Bi undergoes beta decay and turns into 210 Po. The half-life of 210 Bi is 5.013 days.
In addition to 210 Po, two more artificially radioactive isotopes of polonium have relatively long half-lives - 208 Po (T 1/2 = 2.898 g) and 209 Po (T 1/2 = 102 g). These isotopes can be produced by bombarding lead or bismuth targets with cyclotron-accelerated beams of alpha particles, protons or deuterons. 209 Po can be purchased from Oak Ridge National Laboratory with permission from the Atomic Energy Commission (A.E.C.) of the United States for approximately $3,200 per µCi (microcurie)*. In such a source there will be 6 ·
10 -8 g 209 Po. All other polonium isotopes have half-lives from 8.8 days (206 Po) to fractions of a microsecond ( ).
Different types of ionizing radiation (α,β,γ) have markedly different penetrating abilities. Alpha particles from radioactive isotopes flying through matter easily pick up electrons and turn into helium atoms. So, in order to turn into helium, it is enough for alpha particles of 210 Po to fly less than 4 cm in air, less than 50 microns in biological tissue, and less than 30 microns in aluminum. Thus, alpha radiation from radioactive sources cannot be detected by conventional dosimeters that use Geiger counters. Alpha particles of such energies will not pass through the meter body, even if its surface is smeared with an alpha radioactive isotope. It is enough to place a pure α-emitter in a sealed package with walls no thicker than a sheet of paper (the main thing is that the radioactive drug does not “spill out” from it); more sensitive devices, such as, for example, semiconductor or scintillation detectors, will not be able to detect its radiation . The latter can help detect alpha radiation if they are in close proximity to an “open” source of radioactive contamination.
In Fig. 2 shows the characteristics of the scintillation pollution detector LB 124 SCINT, manufactured by BERTHOLD TECHNOLOGIES GmbH & Co.
Radioactive sources of 210 Po are used in both scientific research and technology. During work on the Manhattan Project, the polonium-beryllium neutron source was intended to be used as a fuse for an 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(α,n). However, this decision was later abandoned. The specific energy release of polonium is high - 140 Watt/g. A capsule containing 0.5 g of polonium is heated to 500 o C. This property is used to create thermoelectric sources based on it, which are, in particular, used in spacecraft. Polonium is also used in static electricity removal devices. Some devices of this kind may contain polonium with an activity of up to 500 µCi (about 0.1 microgram). This amount is theoretically enough to kill 5,000 people. However, this polonium is securely packaged, and extracting it for malicious purposes requires sophisticated technology and in-depth knowledge. As a rule, the activity of sources offered on the market is low. So you can purchase a 210 Po source with an activity of 0.1 µCi (microcuries) for $69. A source with such activity emits 3,700 particles per second. The mass of 210 Po in such a source is about 2 ·
10 -11
Alpha radiation from radioactive sources cannot penetrate the skin. However, alpha-emitting nuclides pose a great danger when entering the body through the respiratory and digestive organs, open wounds and burn surfaces, and not only due to ionizing radiation, but also simply as toxic substances. The maximum permissible dose load on the body when 210 Po is ingested is only 0.03 µCi (6.8 - 10 -12 g). With the same weight 210 Po is approximately 2.5. 10 11 times more toxic than hydrocyanic acid. Once in the human body, polonium spreads throughout the tissues through the bloodstream. Polonium is excreted from the body mainly through feces and urine. Most of it is excreted in the first few days. In 50 days, about half of the polonium that enters the body is eliminated. The presence of polonium in people infected with it is identified by the weak gamma radiation of the secretions. Ingestion of one hundred thousandth of a milligram of polonium into the human body is fatal in 50% of cases. Polonium is a very volatile metal; in air, in 45 hours, 50% of it evaporates at a temperature of 55 o C.
* Units of activity - 1 Ci (Curie) = 3.7. 10 10 decays per second, 1 Ci = 10 3 mCi = 10 6 μCi. 1 Bq = 1 decay per second.
| Isotopes of polonium | |||
|---|---|---|---|
| A | T 1/2 | Decay mode | Radioactive series |
| 190 | 2.53 ms | α , EZ 0.1% | |
| 191 | 22 ms | α | |
| 192 | 33.2 ms | α 99.5%, EZ0.5% | |
| 194 | 0.392 s | α | |
| 195 | 4.64 s | α 75%, EZ 25% | |
| 196 | 5.8 s | α 98%, EZ2% | |
| 197 | 1.4 m | EZ 56%, α 44% | |
| 198 | 1.87 m | α 57%, EZ 43% | |
| 199 | 4.58 m | EZ 92.5%, α 7.5% | |
| 200 | 10.9 m | EZ 88.9%, α 11.1% | |
| 201 | 15.3 m | EZ 98.4%, α 1.6% | |
| 202 | 44.7 m | EZ 98.08%, α 1.92% | |
| 203 | 36.7 m | EZ 99.89%, α 0.11% | |
| 204 | 3.53 h | EZ 99.34%, α 0.66% | |
| 205 | 1.66 h | EZ 99.96%, α 0.04% | |
| 206 | 8.8 d | EZ 94.55%, α 5.45% | |
| 207 | 5.80 h | EZ 99.98%, α 0.02% | |
| 208 | 2.898 g | α, EZ | |
| 209 | 102 g | α 99.52%, EZ 0.48% | |
| 210 | 138.376 d | α | 238U |
| 211 | 0.516 s | α | 235 U |
| 212 | 0.299 µs | α | 236U |
| 213 | 3.65 µs | α | 237 Np |
| 214 | 164.3 µs | α | 238U |
| 215 | 1.781 ms | α,β - 0.00023% | 235 U |
| 216 | 0.145 s | α | 236U |
| 217 | 1.47 s | α >95%,β -<5% | 237 Np |
| 218 | 3.10 m | α 99.98%,β - 0.02% | 238U |
| 219 | 2 m | α ?,β - ? | |
The scientific aspects of the Litvinenko case were analyzed for TRV-Nauka by Dr. chem. sciences, head Laboratory of the Radioisotope Complex of the Institute of Nuclear Research of the Russian Academy of Sciences
Passions surrounding the mysterious death of Alexander Litvinenko do not subside. Finally, public hearings on his case began in London. And relatively recently, interest in this topic was fueled by the assumption that Palestinian leader Yasser Arafat was killed in a similar way. Thanks to this, the general public learned at least something about radioactive isotopes and their possible applications, however, in a very one-sided way.
At one time, I had to comment on this case in many Russian and foreign publications, radio and television programs. But the mass media is not the most suitable platform for discussing the scientific aspects of this interesting problem: the issue is too politicized. People put forward the most fantastic versions, without bothering themselves with any evidence at all. At the same time, there are a number of scientific publications that discuss various, primarily medical, aspects. This question was also raised at a number of scientific conferences on the production and use of isotopes, in which I took part.
Here I will briefly outline the following aspect: the production and properties of polonium-210, which may be associated with the poisoning of A. Litvinenko. A number of Russian "experts" expressed surprise at why this particular substance was used, and many were unclear as to how it was used. In particular, Lev Fedorov, Dr. chem. Sciences, President of the Union for Chemical Safety, said on Ekho Moskvy: “How can you poison with polonium-210? I can’t imagine this... If I were thinking about how to poison a person, then the last thing I would say is polonium... Naturally, the person who would carry it across the borders would have to carry it in a lead container ».
A number of other experts tried to justify their conclusions based on general considerations. Thus, the famous banker Alexander Lebedev, himself a former KGB employee, stated in our public discussion with him on the NTV channel (“Sunday Evening with Vladimir Solovyov,” December 3, 2006): “I assure you that today there is not the slightest possibility of allowing our special services to do such things... Because this will certainly be followed by criminal punishment.”
Let's put aside the political aspects, who benefited or did not benefit from this. Let's figure out why polonium was used?
Obtaining polonium-210
The main method for producing polonium-210 is irradiating bismuth with slow neutrons in a nuclear reactor (see Fig. 1). Polonium must then be chemically isolated from the irradiated bismuth. This can be done by sublimation (since polonium has relatively high volatility at elevated temperatures), electrochemical or other methods. Polonium-210 produced in this way is very cheap. Talk about its high cost is not true. Another thing is its availability.
There is also a third stage in the technology, this is the preparation of the radiation source for final use. Sources can be of different types. In this particular case, the polonium must be placed in a capsule, preferably with a multi-layer shell (to avoid polonium penetration). To poison, you must either open this capsule so that the contents get into the drink, or, which is much more convenient, make a miniature ampoule with a soluble shell; this is not difficult.
For the first time, pure polonium in the Soviet Union was obtained at NII-9 (now the A. A. Bochvar High-Tech Research Institute of Inorganic Materials), which was a leader in the study of this element. The work was carried out under the guidance of our outstanding scientist Zinaida Vasilievna Ershova.
Is it possible to determine the origin of polonium using a technical method? Theoretically this is possible, but practically it is very difficult. Each nuclear reactor (in a specific 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 the nuclear reaction (n, 2n) from accumulated polonium-210, as well as even smaller quantities of polonium-208 (2.9 years).
Thus, using such a “nuclear clock” it is, in principle, possible to determine the place and date of polonium production. However, this is not easy to do, and in certain cases it is impossible. This depends on how much polonium was found and where: what is important is the ratio between the stable lead-206 formed from polonium-210 and the background lead, the content of which in the natural mixture of isotopes is 24.1%. A special mass separator will be required to separate polonium isotopes (or a long exposure time for the decay of polonium-210), as well as calibration samples of polonium from the reactor, prepared in the same irradiation mode.
Russian polonium is produced at the All-Russian Research Institute of Experimental Physics in Sarov. Bismuth irradiation at the reactor is apparently carried out in another place - P/O Mayak in the city of Ozyorsk, Chelyabinsk region. The method for producing polonium-210 is not secret, so it can be produced in any other reactors where there is a special channel for irradiating targets in order to obtain isotopes. Such reactors are located in several countries around the world. Energy reactors, as a rule, are not suitable for this, although some of them have a channel for irradiating targets. It has been reported that more than 95% of polonium-210 is produced in Russia.
There are also other methods for producing polonium, but they are now practically not used, since they are much less productive and more expensive. One of these methods, used by Marie Curie, is chemical separation from uranium ores (polonium-210 is contained in the decay chain of uranium-238). Actually, polonium was discovered in 1898. Polonium-210 can also be obtained in charged particle accelerators using the nuclear reactions 208 Pb(A, 2n) or 209 Bi(d, n). At the same time, not just any accelerator is suitable for producing polonium-210. This requires an alpha particle or deuteron accelerator. There are not many such accelerators in the world. They exist in both Russia and Great Britain. However, as far as I know, in Britain the Amersham accelerator has not been configured for alpha particles for a long time 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 installations were inspected to see if they were producing polonium.
At one time, Techsnabexport JSC sold polonium-210 to the UK (to Reviss). But this was five years before the sad events, and, as my colleagues told me, the company was checked very carefully 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 in significant quantities there, but, on the contrary, a certain amount is obtained from Russia.
The operation of both reactors and accelerators is strictly controlled. If someone does decide to produce polonium illegally, with the existing control system this can easily be discovered.
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. This half-life is very convenient for using 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 decay yield of only 0.001%. Polonium-210 has the lowest gamma constant of all common alpha-active radionuclides. Thus, for americium-241 (widely used, for example, in smoke detectors), the gamma constant is 0.12, and for Po - 5·10 –5 R×cm 2 /h×mCi (where R is a roentgen, mCi is a millicurie ). In this case, the dose coefficient and, therefore, radiotoxicity are quite comparable.
Thus, even without a protective shell, it is extremely difficult to detect a sufficient amount of polonium-210 for poisoning remotely using a conventional counter, since the radiation level is comparable to the natural background (see Fig. 2). Thus, polonium-210 is very convenient for secret transportation, and there is no need to even use lead containers. However, during transportation, special care must be taken to avoid depressurization of the container (see below).
Polonium-210 is not at all advisable to use for provocations, since it can only be detected using special equipment, which is not used in ordinary cases.
The 803 keV gamma line can only be detected through long-term measurements using a good gamma spectrometer, and the semiconductor detector must be located very close to the source. There is evidence that this is how increased radioactivity was initially found in Litvinenko, but at first the radiation was mistakenly attributed to radioactive thallium (thallium-206), which is obtained from the decay of bismuth-210m (see 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 the presence of other alpha emitters. After this, the urine was analyzed for the presence of alpha-active radionuclides and polonium was found, and in huge quantities. The assumption that British experts were “tipped off” about polonium-210 by certain provocateurs seems to me to have been taken out of thin air. British scientists did everything consistently and quite logically.
On the surface, alpha activity of polonium-210 can be detected using an alpha counter, which is usually used only for special purposes and not for routine testing for radioactive contamination. However, to determine that the radiation relates specifically to polonium-210, more complex equipment, usually stationary, is required - an alpha spectrometer. Activity on the order of 1 Bq (disintegrations per second) at the surface can be easily detected. If alpha activity is detected, then sample preparation is carried out (for example, using chemical isolation) and a line in the alpha spectrum of 5.3 MeV is detected on an alpha spectrometer, characterizing this particular alpha-active radionuclide.
Chemical properties
Polonium can exist in different chemical forms, but in this case it is most likely to be found in the form of soluble compounds (for example, nitrates, chlorides, sulfates), while a significant part of the solution can also be in colloidal form. It is important that from neutral and slightly acidic solutions, polonium is largely sorbed on various surfaces, in particular on metal and glass (maximum sorption is at pH ~ 5). It is difficult to wash it completely using conventional methods. It is therefore not at all surprising that a teapot and cup from which polonium was consumed were discovered.
Polonium itself, in microquantities, begins to sublimate only at temperatures of about 300°C. But it can also pass into the environment together with the vapor of the water in which it is contained, and in the process with recoil nuclei.
Polonium diffuses quite easily in plastic and other organic substances; 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 using an alpha counter.
Polonium is a polyvalent element, prone to forming various complexes, and can form different chemical forms. In this regard, some of it spreads quite easily in the natural environment. It is therefore understandable that traces of polonium have spread and can be used to trace the source of polonium contamination.
Biological exposure 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 damage to humans by polonium-210 are shown in the table (data from experiments with animals were recalculated to the mass of a person).
The absorption of this substance through the gastrointestinal tract is estimated from 5 to 20%. Through the lungs - it is more effective, but such an administration is extremely inconvenient for hidden poisoning, since this can greatly contaminate others and 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 all organs of the body, but, of course, not quite evenly. And it is excreted from the body with any biological substances: feces, urine, then... The half-life, according to various sources, is from 50 to 100 days. One industrial accident was reported in our country that resulted in the death of a person 13 days after being exposed to 530 MBq (14 mCi) of polonium.
According to indirect data (based on the impact), the amount of polonium introduced into Litvinenko could be (0.2–4) × 10 9 Bq (becquerels), that is, disintegrations per second, by mass it is 1–25 μg, an almost 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 could accidentally fall on people sitting nearby as drops or aerosols, that is, up to 10 5 –10 6 Bk. This does not pose a serious danger to human life, although it exceeds permissible pollution standards. Such an amount can be easily detected, and 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 a dose below 6 mSv (millisieverts), which poses no health risk;
- 17 people received a dose greater than 6 mSv, but not significant enough to cause any illness in the near future; the increase in the risk of disease in the distant future is likely very small. The largest dose, which was nevertheless not life-threatening, was naturally received by Alexander Litvinenko’s wife Marina, with whom he had the most contact.
The permissible dose for professionals working with radioactivity in Russia is 20 mSv/year. The annual doses received by people from natural background radiation are 1–10 mSv/year, and in some places on Earth much higher, and mortality is not increased there. Only exposure to an effective dose of more than 200 mSv over the course of a year is considered potentially dangerous. Thus, claims that the use of polonium created a greater threat to others is an exaggeration.
The press raised the question of whether polonium-210 had been used as a poisonous substance before and whether this could be established. In particular, the poisons with which they may have poisoned Yu. Shchekochikhin and tried to poison A. Politkovskaya remained unknown. If polonium-210 was present in these cases, it had decayed over time to below background levels. However, exhumation may reveal polonium-209, which could have been present as an impurity (see above).
The hypothesis that Yasser Arafat was poisoned with polonium-210 was practically not confirmed. Some excess 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 product of the decay of radon, was found in Arafat's body.
Application
Until now, 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 of the Cosmos satellites were equipped with such devices.
2. As a source of neutrons, in particular, for initiators of a nuclear explosion in atomic bombs. Neutrons are produced when beryllium is irradiated with alpha particles and initiate a nuclear explosion when the mass of uranium-235 or plutonium-239 reaches critical mass. Such sources were also 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. Nowadays it is practically not used for such purposes, since there are much more suitable radionuclides.
4. As an air ionizer in antistatic devices, for example 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 of these devices would have to be processed, which requires a radiochemical laboratory.
Findings relating to Litvinenko's death
Conclusions of a technical nature that may be significant for solving a crime can be divided into two groups: quite definite and those that are very probable, but for an unambiguous statement an investigation is required not only in the UK, but also in Russia.
Quite definite
1. Polonium-210 is a poisonous substance for covert use. 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 is convenient to covertly transport in quantities sufficient to cause poisoning. It is also easy to secretly introduce it into a person’s drink. Other methods of administration (for example, aerosolization or dermal administration) are less effective, unreliable, complex and very dangerous for the poisoner.
3. Accidental contamination of polonium-210 through negligence is almost impossible, since such a degree of contamination requires a huge amount that can only exist in places of mass production of polonium in a factory, and this can be easily determined by the distribution of polonium on the human body.
4. None of the statements made publicly by the UK investigative authorities contain any technical contradictions.
Very probable, but requires confirmation
1. It is most likely that polonium-210 was produced in Russia. It could have been brought to the UK from Russia or the US, where the substance is officially supplied. Other sources are not excluded in principle, but it would be almost impossible to hide such production. Polonium-210 has not been produced in the UK for a long time.
2. Removal from antistatic devices in the USA requires a special radiochemical laboratory, which is extremely difficult to hide under the current control system in the USA. In other countries, such antistatic devices are practically not used.
3. Establishing the origin of polonium through analysis is possible 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 with the existing control system. Previously, several facts of missing polonium were recorded, but all of them were disclosed, since revealing them does not pose a big problem.
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 Marie 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 Marie Skłodowska-Curie's homeland, 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, a new element was first isolated, concentrated 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 (in equilibrium with 1 g of radium there is 0.2 mg of polonium).
The polonium content in the earth's crust is 2-10 -15%. There are seven isotopes of polonium, which are formed in all three naturally radioactive families during the decay of emanations (radon, thoron, actinon) or their decay products. As they decay, they become stable or radioactive isotopes of lead. The main source of 210 Po in the 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)
Atomic 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. Longest lived isotope 209 Po (manufactured artificially), has a half-life of 102 years.
The longest-lived of the natural isotopes, polonium-210 (a natural radionuclide) is an almost pure alpha emitter (T = 138.401 days), formed in the radioactive series of uranium-238. It is one of the products of long-lived active radon residue.
In the overwhelming 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 a tiny fraction (0.00122%) of 210 Po nuclei decays into the excited (803 keV) state of 206 Pb, which decays with the emission of gamma-ray particles. quanta The gamma radiation accompanying such alpha decay can be detected only in a precision experiment. The 210Po isotope is not only the longest-lived among natural ones, i.e. existing on Earth, and not artificially obtained, isotopes of polonium, but also the most common. It is constantly formed due to a chain of isotope decays that begins with 238 U and ends with 206 Pb.
Thus, the source of polonium-210 can be active radon sediment that accumulates in old radon ampoules.
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 uranium production waste. However, in order to obtain a noticeable amount of polonium, an incredible amount of such waste would have to be processed.
In addition to 210 Po, two more artificially radioactive isotopes of polonium have relatively long half-lives - 208 Po (T = 2.898 years) and 209 Po (T = 102 years). These isotopes can be obtained by bombarding lead or bismuth targets with cyclotron-accelerated beams of alpha particles, protons or deuterons. All other polonium isotopes have half-lives 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, is fusible and has a relatively low boiling point; its melting and boiling points are 254 and 962 °C, respectively.
A comparison of the properties of polonium with the properties of sulfur, selenium and tellurium, on the one hand, and bismuth, lead and thallium, on the other, shows that metallic polonium in its physical properties is more likely to resemble elements neighboring in period (Bi) than in group (Te ).
Pure polonium has two allotropic modifications: the low-temperature α-form with a cubic lattice, and the high-temperature β-form with a rhombic lattice. The phase transition from one form to another occurs at 36 °C. Interestingly, at room temperature, freshly prepared polonium is in a high-temperature form. 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 ordinary metal. In terms of fusibility - lead and bismuth. According to electrochemical properties - for noble metals. According to the optical and x-ray spectra - only to himself. And according to their behavior in solutions - to all other radioactive elements: thanks 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 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, density 9.392 g/cm3 (slightly less than that of lead), m.p. 254°C, bp. 962°C, heat of vaporization 24.597 kcal/mol. Thermal coefficient of linear expansion is 2.35*10 -5. The electrical resistivity for the α- and β-forms at 0°C is respectively (μΩ.cm) 42 and 44. In terms of chemical properties, polonium is a direct analogue of sulfur, selenium and tellurium. It exhibits valences of 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 metals. It has amphoteric properties. Forms colloidal hydroxides or basic salts in alkaline, neutral or slightly acidic solutions.
Elementary polonium oxidizes in air. Polonium dioxide (PoO 2)x and polonium monoxide PoO are known. Polonium reacts quickly with oxygen when heated, forming PoO2 dioxide at 250°C. In indicator quantities, acidic polonium trioxide PoO3 and salts of polonium acid, which does not exist in the free state, polonates K 2 PoO 4, were obtained. With halogens, when heated, polonium gives tetrahalides RoG 4. Does not interact with hydrogen and nitrogen. When metallic polonium is heated with metals, polonides are formed, which are isomorphic with the corresponding tellurides. Polonium metal dissolves in nitric and hydrochloric acids.
Polonium metal dissolves readily in concentrated (but not dilute) nitric acid, releasing nitrogen oxides.
Receipt
The isotope 210 Po can be isolated from uranium ores as a by-product during the mining of radium. Typically, 210 Po is obtained from the long-lived radioactive isotope of lead 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 extracted, which is kept for polonium accumulation. Often, for the purpose of extractive 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 deposition of PbS with hydrogen sulfide, as well as crystallization of bromides from concentrated solutions of HBr. Extraction can be carried out by extraction from hydrochloric acid with organic solvents (acetylacetone, tributyl phosphate, etc.). Often, for the purpose of extractive 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. To isolate polonium from large quantities of irradiated bismuth, vacuum sublimation is used, as well as methods based on processes of extraction or coprecipitation of polonium with carriers from molten bismuth. The process of extracting 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. In two successive extractions, this method can recover 99.5% of the polonium.
In practice, the polonium nuclide 210 Po is synthesized artificially in gram quantities by irradiating natural 209 Bi with neutrons in nuclear reactors. The resulting 210 Bi turns into 210 Po due to β-decay.
Application
Radioactive sources of 210 Po are used in both scientific research and technology. While working on the Manhattan Project to create the atomic bomb (USA), polonium
The beryllium neutron source was supposed to be used as a fuse for an 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 for the manufacture of compact and very powerful neutron sources that do not have γ-radiation. To do this, it is fused with an element that has isotopes with a high cross section of the (α,n) reaction, for example, with beryllium or boron. These are sealed metal ampoules containing a polonium-210-coated ceramic tablet made of boron carbide or beryllium carbide. Such neutron sources are lightweight and portable, completely safe to operate 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 electricity generators using 210 Po were successfully used on the Kosmos-84 and Kosmos-85 communications satellites.
The specific energy release of polonium is high - 140 Watt/g. Capsule containing 0.5 g of polonium,heats up to 500° C. (1 cm 3 210 Rho produces 1320 W of heat). This power is very high; it easily brings polonium into a molten state, which is why it is fused, for example, with lead. And although these alloys have a noticeably lower energy density (150 W/cm 3 ), nevertheless more convenient to use and safe.
Such alloys are used to create thermoelectric sources, which are particularly used in spacecraft. For example, the Soviet lunar rover had a polonium heater to heat the instrument compartment.
Polonium is also used in static electricity removal devices. Some devices of this kind may contain polonium with an activity of up to 500 µCi (about 0.1 microgram). This amount is theoretically enough to kill 5,000 people. Polonium-210 can serve in 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 taken into account very strictly, and its storage must be under state control due to the threat of nuclear terrorism.
Polonium is also used in the electrode alloys of automotive spark plugs forreducing the spark voltage, as well as for α-activation analysis. Small amounts of polonium are used to study radiation-chemical processes in liquids under the influence of α-radiation on living organisms.
Sanitary aspects
When working with polonium, you have to be especially careful - it is one of the most dangerous radioelements. Although polonium-210 emits only alpha particles, you should not handle it; the result will be radiation damage to the skin and, possibly, the entire body: polonium penetrates quite easily through the skin. Element No. 84 is also dangerous at a distance exceeding the path length of alpha particles. Its compounds self-heat, become aerosolized and contaminate the air. Therefore, they 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 spreads throughout the tissues through the bloodstream. Polonium is excreted from the body mainly through feces and urine. Most of it is excreted in the first few days. In 50 days, about half of the polonium that enters the body is eliminated. The presence of polonium in people infected with it is identified by the weak gamma radiation of the secretions. Ingestion of one hundred thousandth of a milligram of polonium into the human body leads to death in 50% of cases. Polonium is a very volatile metal; in air, 50% of it evaporates in 45 hours at a temperature of 55°C.
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