Myth 02. The most dangerous radionuclide is strontium
There is a myth that the most dangerous radionuclide is strontium-90. Where did this dark popularity come from? After all, in an operating nuclear reactor, 374 artificial radionuclides are formed, of which one strontium is 10 different isotopes. No, give us not just any strontium, but strontium-90.
Perhaps a vague thought about a mysterious half-life, about long-lived and short-lived radionuclides flashes in the minds of readers? Well, let's try to figure it out. By the way, don’t be afraid of the word radionuclide. Today this term is commonly used to refer to radioactive isotopes. That's right - a radionuclide, and not a distorted "radionuclide" or even a "radionucleotide". 70 years have passed since the explosion of the first atomic bomb, and many terms have been updated. Today, instead of “atomic boiler” we say: “nuclear reactor”, instead of “radioactive rays” - “ionizing radiation”, and instead of “radioactive isotope” - “radionuclide”.
But let's return to strontium. And in fact, national love to strontium-90 is related to its half-life. By the way, what is this: half-life? The fact is that radionuclides differ from stable isotopes in that their nuclei are unstable, unstable. Sooner or later they decay - this is called radioactive decay. At the same time, radionuclides, turning into other isotopes, emit these very ionizing radiations. So, different radionuclides are unstable to varying degrees. Some decay very slowly, over hundreds, thousands, millions and even billions of years. They are called long-lived radionuclides. For example, all natural isotopes of uranium are long-lived. And there are short-lived radionuclides, they decay quickly: within seconds, hours, days, months. But radioactive decay always occurs according to the same law (Fig. 2.1).
Rice. 2.1. Law of Radioactive Decay
No matter how much radionuclide we take (a ton or a milligram), half of this amount always decays in the same (for a given radionuclide) period of time. This is what is called the “half-life” and is designated: T
Let us repeat: this time period is unique and unchanged for each radionuclide. You can do anything with the same strontium-90: heat it, cool it, compress it under pressure, irradiate it with a laser - still half of any portion of strontium will decay in 29.1 years, half of the remaining amount will decay within another 29.1 years, and so on. . It is believed that after 20 half-lives the radionuclide disappears completely.
The faster a radionuclide decays, the more radioactive it is, because each decay is accompanied by the release of one portion of ionizing radiation in the form of an alpha or beta particle, sometimes “accompanied” by gamma radiation (“pure” gamma decay does not exist in nature). But what does “large” or “small” radioactivity mean, and how can it be measured?
For this purpose, the concept of activity is used. Activity allows you to estimate the intensity of radioactive decay in numbers. If one decay occurs per second, they say: “The activity of the radionuclide is equal to one becquerel (1 Bq).” Previously, they used a much larger unit - the curie: 1 Ci = 37 billion Bq. Of course, equal amounts of different radionuclides should be compared, for example 1 kg or 1 mg. The activity per unit mass of a radionuclide is called specific activity. Here it is, this very specific activity, is inversely proportional to the half-life of a given radionuclide (so, you need to take a break). Let's compare these characteristics for the most famous radionuclides (table).
So why is it still strontium-90? It doesn’t seem to stand out in anything special - so, the middle is half and half. And that’s exactly the point! First, let's try to answer one (I warn you right away) provocative question. Which radionuclides are more dangerous: short-lived or long-lived? So, opinions were divided.
Table 2.1. Radiation characteristics of some radionuclides
On the one hand, short-lived ones are more dangerous: they are more active. On the other hand, after the rapid decay of the “short ones,” the problem of radiation disappears. Those who are older remember: immediately after the Chernobyl accident, most of the noise was around radioactive iodine. The short-lived iodine-131 undermined the health of many Chernobyl victims. But today there are no problems with this radionuclide. Just six months after the accident, the iodine-131 released from the reactor disintegrated, not even a trace remained.
Now about long-lived isotopes. Their half-life can be millions or billions of years. Such nuclides are low-active. Therefore, in Chernobyl there were no, there are no and there will not be problems with radioactive contamination of the territories with uranium. Although, in terms of the mass of chemical elements released from the reactor, it was uranium that was in the lead, and by a large margin. But who measures radiation in tons? In terms of activity and becquerels, uranium does not pose a serious danger: it is too long-lived.
And now we come to the answer to the question about strontium-90. This isotope has a half-life of 29 years. A very “disgusting” period, because it is commensurate with the life expectancy of a person. Strontium-90 is long-lived enough to contaminate an area for tens or hundreds of years. But not so long-lived as to have low specific activity. In terms of half-life, cesium-137 is very close to strontium (30 years). That is why during radiation accidents it is this “sweet couple” that creates most of the “long-lasting” problems. By the way, in negative consequences of the Chernobyl accident, gamma-active (bear with me for three pages) cesium is more guilty than the “pure” beta emitter strontium.
And six hundred years will pass, and there will be no cesium or strontium left in the Chernobyl accident zone. And then the first place will come... You already guessed it, right? Plutonium! But we are still far from understanding main problem- health hazards of various radionuclides. After all, the half-life, like the specific activity, is not directly related to such a danger. These properties characterize only the radionuclide itself.
Let's take, for example, the same amounts of uranium-238 and strontium-90: identical in activity, and specifically, a billion becquerels each. For uranium-238 it is about 80 kg, and for strontium-90 it is only 0.2 mg. Will their health risks be different? Like heaven from earth! You can calmly stand next to an uranium ingot weighing 80 kg, you can sit on it without any harm to your health, because almost all the alpha particles formed during the decay of uranium will remain inside the ingot. But an amount of strontium-90 that is the same in activity and at the same time negligibly small in mass is extremely dangerous. If a person is nearby without protective equipment, then in a short time he will receive at least radiation burns to his eyes and skin.
Do you know what specific activity looks like? An analogy arises here - the rate of fire of a weapon. Do you remember that the question about the dangers of long- and short-lived radionuclides is provocative? That's how it is! It’s the same as asking: “Which weapon is more dangerous: one that fires a hundred shots per minute or one shot per hour?” Something else is more important here: the caliber of the weapon, what it shoots and, most importantly, will the bullet reach the target, will it hit it, and what damage will it cause?
Let's start with something simple - with “caliber”. You've probably heard about alpha, beta and gamma radiation before. It is these types of radiation that are formed during radioactive decays (return to Table 1). Such radiations have both general properties, and differences.
General properties: all three types of radiation are classified as ionizing. What does it mean? The radiation energy is extremely high. So much so that when they hit another atom, they knock out an electron from its orbit. In this case, the target atom turns into a positively charged ion (this is why radiation is ionizing). It is high energy that distinguishes ionizing radiation from all other radiation, for example, microwave or ultraviolet.
To make it completely clear, let’s imagine an atom. With enormous magnification, it looks like a poppy seed (nucleus of an atom), surrounded by a thin spherical film like soap bubble several meters in diameter (electronic shell). And now a very tiny speck of dust, an alpha or beta particle, flies out of our grain-nucleus. This is what radioactive decay looks like. When a charged particle is emitted, the charge of the nucleus changes, which means a new chemical element is formed.
And our speck of dust rushes at great speed and crashes into the electron shell of another atom, knocking out an electron from it. The target atom, having lost an electron, turns into a positively charged ion. But the chemical element remains the same: after all, the number of protons in the nucleus has not changed. Such ionization is a chemical process: the same thing happens to metals when dissolved in acids.
It is because of this ability to ionize atoms that different types of radiation are classified as radioactive. Ionizing radiation can arise not only as a result of radioactive decay. Their sources can be: a fission reaction (an atomic explosion or a nuclear reactor), a fusion reaction of light nuclei (the Sun and other stars, a hydrogen bomb), charged particle accelerators and an X-ray tube (these devices themselves are not radioactive). The main difference between radiation is the high energy of ionizing radiation.
The differences between alpha, beta and gamma radiation are determined by their nature. At the end of the 19th century, when radiation was discovered, no one knew what this “beast” was. And the newly discovered “radioactive rays” were simply designated by the first letters of the Greek alphabet.
First, they discovered alpha rays emitted during the decay of heavy radionuclides - uranium, radium, thorium, radon. The nature of alpha particles was clarified after their discovery. It turned out that these were nuclei of helium atoms flying at enormous speed. That is, heavy positively charged “packets” of two protons and two neutrons. These “large-caliber” particles cannot fly far. Even in the air, they travel no more than a few centimeters, and a sheet of paper or, say, the outer dead layer of skin (epidermis) traps them completely.
Beta particles, upon closer examination, turned out to be ordinary electrons, but again traveling at enormous speed. They are much lighter than alpha particles, and they have less electrical charge. Such “small-caliber” particles penetrate deeper into different materials. In the air, beta particles fly several meters; they can be stopped by: a thin sheet of metal, window glass and ordinary clothing. External radiation usually burns the lens of the eye or skin, similar to ultraviolet radiation from the sun.
And finally, gamma radiation. It is of the same nature as visible light, ultraviolet, infrared rays or radio waves. That is, gamma rays are electromagnetic (photon) radiation, but with extremely high photon energy. Or, in other words, with a very short wavelength (Fig. 2.2).
Rice. 2.2. Electromagnetic radiation scale
Gamma radiation has a very high penetrating power. It depends on the density of the irradiated material and is estimated by the thickness of the half-attenuation layer. The denser the material, the better it blocks gamma rays. That is why concrete or lead are often used to protect against gamma radiation. In the air, gamma rays can travel tens, hundreds and even thousands of meters. For other materials, the thickness of the half-attenuation layer is shown in Fig. 2.3.
Rice. 2.3 - Significance of gamma radiation half attenuation layers
When a person is exposed to gamma radiation, both skin and internal organs. If we compared beta radiation to shooting with small-caliber bullets, then gamma radiation is shooting with needles. The nature and properties of gamma radiation are very similar to X-ray radiation. It differs in origin: it is obtained artificially in an X-ray tube.
There are other types of ionizing radiation. For example, during a nuclear outbreak or operation nuclear reactor In addition to gamma radiation, neutron fluxes are formed. In addition to these same radiations, cosmic rays carry protons and much more.
Literature
1. Radiation safety standards NRB-99/2009: sanitary and epidemiological rules and regulations. - M.: Federal Center for Hygiene and Epidemiology of Rospotrebnadzor, 2009. – 100 p.
Please enable JavaScript to view theNatural strontium consists of four stable isotopes 88 Sr (82.56%), 86 Sr (9.86%), 87 Sr (7.02%) and 84 Sr (0.56%). The abundance of strontium isotopes varies due to the formation of 87 Sr due to the decay of natural 87 Rb. For this reason, the exact strontium isotopic composition of a rock or mineral that contains rubidium depends on the age and Rb/Sr ratio of the rock or mineral.
Radioactive isotopes with mass numbers from 80 to 97 have been artificially obtained, including 90 Sr (T 1/2 = 29.12 years), which is formed during the fission of uranium. Oxidation state +2, very rarely +1.
History of the discovery of the element.
Strontium gets its name from the mineral strontianite, found in 1787 in a lead mine near Strontian (Scotland). In 1790, the English chemist Ader Crawford (1748–1795) showed that strontianite contains a new, as yet unknown “earth”. This feature of strontianite was also established by the German chemist Martin Heinrich Klaproth (1743–1817). The English chemist T. Hope in 1791 proved that strontianite contains new element. He clearly differentiated the compounds of barium, strontium and calcium using, among other methods, the characteristic flame colors: yellow-green for barium, bright red for strontium and orange-red for calcium.
Regardless of Western scientists, the St. Petersburg academician Tobias (Toviy Egorovich) Lowitz (1757–1804) in 1792, while studying the mineral barite, came to the conclusion that, in addition to barium oxide, it also contained “strontian earth” as an impurity. He managed to extract more than 100 g of new “earth” from heavy spar and studied its properties. The results of this work were published in 1795. Lovitz wrote then: “I was pleasantly surprised when I read... the excellent article of Mr. Professor Klaproth on strontian earth, about which until then there was a very unclear idea... All the properties of hydrochlorides indicated by him and middle nitrate salts in all points perfectly coincide with the properties of my same salts... I only had to check... the remarkable property of strontium earth is to color the alcohol flame in a carmine-red color, and, indeed, my salt... possessed fully with this property."
Strontium was first isolated in its free form by the English chemist and physicist Humphry Davy in 1808. Metallic strontium was obtained by electrolysis of its moistened hydroxide. The strontium released at the cathode combined with mercury, forming an amalgam. By decomposing the amalgam by heating, Davy isolated the pure metal.
The prevalence of strontium in nature and its industrial production. The strontium content in the earth's crust is 0.0384%. It is the fifteenth most common and follows immediately after barium, slightly behind fluorine. Strontium is not found in free form. It forms about 40 minerals. The most important of them is celestine SrSO 4. Strontianite SrCO 3 is also mined. Strontium is present as an isomorphic impurity in various magnesium, calcium and barium minerals.
Strontium is also found in natural waters. IN sea water its concentration is 0.1 mg/l. This means that the waters of the World Ocean contain billions of tons of strontium. Mineral waters containing strontium are considered promising raw materials for isolating this element. In the ocean, part of the strontium is concentrated in ferromanganese nodules (4900 tons per year). Strontium is also accumulated by the simplest marine organisms - radiolarians, whose skeleton is built from SrSO 4.
The world's industrial strontium resources have not been thoroughly assessed, but they are believed to exceed 1 billion tons.
The largest deposits of celestine are in Mexico, Spain and Turkey. In Russia, there are similar deposits in Khakassia, Perm and Tula regions. However, the needs for strontium in our country are met mainly through imports, as well as processing of apatite concentrate, where strontium carbonate makes up 2.4%. Experts believe that the production of strontium in the recently discovered Kishertskoye deposit (Perm region) can affect the situation on the world market for this product. The price for Permian strontium may be approximately 1.5 times lower than for American strontium, the cost of which is now about $1,200 per ton.
Characteristics of simple substances and industrial production of metal strontium.
Strontium metal has a silvery-white color. In its unrefined state it is colored pale yellow color. It is a relatively soft metal and can be easily cut with a knife. At room temperature, strontium has a face-centered cubic lattice (a-Sr); at temperatures above 231° C it turns into a hexagonal modification (b -Sr); at 623° C it transforms into a cubic body-centered modification (g -Sr). Strontium is a light metal, the density of its a-form is 2.63 g/cm3 (20° C). The melting point of strontium is 768° C, the boiling point is 1390° C.
Being an alkaline earth metal, strontium reacts actively with non-metals. At room temperature, strontium metal is coated with a film of oxide and peroxide. When heated in air, it ignites. Strontium readily forms nitride, hydride and carbide. At elevated temperatures, strontium reacts with carbon dioxide:
5Sr + 2CO 2 = SrC 2 + 4SrO
Strontium metal reacts with water and acids, releasing hydrogen from them:
Sr + 2H 3 O + = Sr 2+ + H 2 + 2H 2 O
The reaction does not occur in cases where poorly soluble salts are formed.
Strontium dissolves in liquid ammonia to form dark blue solutions, from which, upon evaporation, a shiny copper-colored ammonia Sr(NH 3) 6 can be obtained, which gradually decomposes to the amide Sr(NH 2) 2.
To obtain metal strontium from natural raw materials, celestine concentrate is first reduced by heating with coal to strontium sulfide. Strontium sulfide is then treated with hydrochloric acid, and the resulting strontium chloride is dehydrated. The strontianite concentrate is decomposed by firing at 1200° C, and then the resulting strontium oxide is dissolved in water or acids. Often strontianite is immediately dissolved in nitric or hydrochloric acid.
Strontium metal is obtained by electrolysis of a mixture of molten strontium chloride (85%) and potassium or ammonium chloride (15%) on a nickel or iron cathode at 800 ° C. Strontium obtained by this method usually contains 0.3–0.4% potassium.
High-temperature reduction of strontium oxide with aluminum is also used:
4SrO + 2Al = 3Sr + SrO Al 2 O 3
For metallothermic reduction of strontium oxide, silicon or ferrosilicon is also used. The process is carried out at 1000° C in a vacuum in a steel tube. Strontium chloride is reduced with magnesium metal in a hydrogen atmosphere.
The largest producers of strontium are Mexico, Spain, Türkiye and the UK.
Despite its fairly high content in the earth's crust, the metal strontium has not yet found widespread use. Like other alkaline earth metals, it is capable of purifying ferrous metals from harmful gases and impurities. This property gives strontium prospects for use in metallurgy. In addition, strontium is an alloying additive to alloys of magnesium, aluminum, lead, nickel and copper.
Strontium metal absorbs many gases and is therefore used as a getter in vacuum technology.
Strontium compounds.
The predominant oxidation state (+2) for strontium is primarily due to its electronic configuration. It forms numerous binary compounds and salt. Strontium chloride, bromide, iodide, acetate and some other salts of strontium are highly soluble in water. Most strontium salts are slightly soluble; among them are sulfate, fluoride, carbonate, oxalate. Slightly soluble strontium salts are easily obtained by exchange reactions in an aqueous solution.
Many strontium compounds have an unusual structure. For example, isolated molecules of strontium halides are noticeably curved. The bond angle is ~120° for SrF 2 and ~115° for SrCl 2 . This phenomenon can be explained using sd- (rather than sp-) hybridization.
Strontium oxide SrO is obtained by calcination of carbonate or dehydration of hydroxide at red heat temperature. The lattice energy and melting point of this compound (2665° C) are very high.
When calcining strontium oxide in an oxygen environment at high blood pressure peroxide SrO 2 is formed. Yellow superoxide Sr(O 2) 2 was also obtained. When interacting with water, strontium oxide forms hydroxide Sr(OH) 2.
Strontium oxide– a component of oxide cathodes (electron emitters in vacuum devices). It is part of the glass of picture tubes of color televisions (absorbs x-ray radiation), high-temperature superconductors, pyrotechnic mixtures. It is used as a starting material for the production of metal strontium.
In 1920, the American Hill first used a matte glaze, which included oxides of strontium, calcium and zinc, but this fact went unnoticed, and the new glaze did not become a competitor to traditional lead glazes. Only during the Second World War, when lead became especially scarce, did they remember Hill’s discovery. This sparked an avalanche of research: different countries Dozens of strontium glaze recipes appeared. Strontium glazes are not only less harmful than lead glazes, but also more affordable (strontium carbonate is 3.5 times cheaper than red lead). At the same time, they have all the positive qualities of lead glazes. Moreover, products coated with such glazes acquire additional hardness, heat resistance, and chemical resistance.
Enamels - opaque glazes - are also prepared on the basis of silicon and strontium oxides. They are made opaque by the addition of titanium and zinc oxides. Porcelain items, especially vases, are often decorated with crackle glaze. Such a vase seems to be covered with a network of colored cracks. The basis of the crackle technology is the different thermal expansion coefficients of glaze and porcelain. Porcelain coated with glaze is fired at a temperature of 1280–1300° C, then the temperature is reduced to 150–220° C and the still not completely cooled product is dipped into a solution of coloring salts (for example, cobalt salts, if you need to get a black mesh). These salts fill the resulting cracks. After this, the product is dried and heated again to 800–850 ° C - the salts melt in the cracks and seal them.
Strontium hydroxide Sr(OH)2 is considered a moderately strong base. It is not very soluble in water, so it can be precipitated by the action of a concentrated alkali solution:
SrCl 2 + 2KOH(conc) = Sr(OH) 2 Ї + 2KCl
When crystalline strontium hydroxide is treated with hydrogen peroxide, SrO 2 8H 2 O is formed.
Strontium hydroxide can be used to extract sugar from molasses, but the cheaper calcium hydroxide is usually used.
Strontium carbonate SrCO 3 is slightly soluble in water (2·10 –3 g per 100 g at 25° C). In the presence of excess carbon dioxide in solution, it turns into bicarbonate Sr(HCO 3) 2.
When heated, strontium carbonate decomposes into strontium oxide and carbon dioxide. It reacts with acids to release carbon dioxide and form the corresponding salts:
SrCO 2 + 3HNO 3 = Sr(NO 3) 2 + CO 2 + H 2 O
The main areas of strontium carbonate in the modern world are the production of picture tubes for color TVs and computers, ceramic ferrite magnets, ceramic glazes, toothpaste, anti-corrosion and phosphorescent paints, high-tech ceramics, and pyrotechnics. The most intensive areas of consumption are the first two. At the same time, the demand for strontium carbonate in the production of television glass is increasing with the growing popularity of larger television screens. Advances in flat-panel TV technology may reduce demand for strontium carbonate for TV displays, but industry experts believe flat-panel TVs won't become significant competitors to traditional TVs in the next 10 years.
Europe consumes the lion's share of strontium carbonate to produce strontium ferrite magnets, which are used in the automotive industry, where they are used for magnetic latches in car doors and brake systems. In the USA and Japan, strontium carbonate is used primarily in the production of television glass.
For many years, the world's largest producers of strontium carbonate were Mexico and Germany, whose production capacity for this product now amounts to 103 thousand and 95 thousand tons per year, respectively. In Germany, imported celestine is used as a raw material, while Mexican factories use local raw materials. Recently, annual strontium carbonate production capacity has expanded in China (to approximately 140 thousand tons). Chinese strontium carbonate is actively sold in Asia and Europe.
Strontium nitrate Sr(NO 3) 2 is highly soluble in water (70.5 g per 100 g at 20 ° C). It is prepared by reacting strontium metal, strontium oxide, hydroxide or carbonate with nitric acid.
Strontium nitrate is a component of pyrotechnic compositions for signal, lighting and incendiary flares. It colors the flames carmine red. Although other strontium compounds give the flame the same color, nitrate is preferred in pyrotechnics: it not only colors the flame, but also serves as an oxidizer. When decomposed in a flame, it releases free oxygen. In this case, strontium nitrite is first formed, which is then converted into strontium and nitrogen oxides.
In Russia, strontium compounds were widely used in pyrotechnic compositions. During the time of Peter the Great (1672–1725), they were used to produce “amusing fires” that were arranged during various celebrations and celebrations. Academician A.E. Fersman called strontium “the metal of red lights.”
Strontium sulfate SrSO 4 is slightly soluble in water (0.0113 g per 100 g at 0° C). When heated above 1580° C, it decomposes. It is obtained by precipitation from solutions of strontium salts with sodium sulfate.
Strontium sulfate is used as a filler in the manufacture of paints and rubber and a weighting agent in drilling fluids.
Strontium chromate SrCrO 4 precipitates as yellow crystals when solutions of chromic acid and barium hydroxide are mixed.
Strontium dichromate, formed by the action of acids on chromate, is highly soluble in water. To convert strontium chromate to dichromate, a weak acid such as acetic acid is sufficient:
2SrCrO 4 + 2CH 3 COOH = 2Sr 2+ + Cr 2 O 7 2– + 2CH 3 COO – + H 2 O
This way it can be separated from the less soluble barium chromate, which can only be converted into dichromate by the action of strong acids.
Strontium chromate has high light resistance, it is very resistant to high temperatures (up to 1000 ° C), and has good passivating properties in relation to steel, magnesium and aluminum. Strontium chromate is used as a yellow pigment in the production of varnishes and artistic paints. It is called "strontian yellow". It is included in primers based on water-soluble resins and especially primers based on synthetic resins for light metals and alloys (aircraft primers).
Strontium titanate SrTiO 3 does not dissolve in water, but goes into solution under the influence of hot concentrated sulfuric acid. It is obtained by sintering strontium and titanium oxides at 1200–1300° C or coprecipitated sparingly soluble compounds of strontium and titanium above 1000° C. Strontium titanate is used as a ferroelectric; it is part of piezoceramics. In microwave technology, it serves as a material for dielectric antennas, phase shifters and other devices. Strontium titanate films are used in the manufacture of nonlinear capacitors and infrared radiation sensors. With their help, layered dielectric-semiconductor-dielectric-metal structures are created, which are used in photodetectors, storage devices and other devices.
Strontium hexaferrite SrO·6Fe 2 O 3 is obtained by sintering a mixture of iron (III) oxide and strontium oxide. This compound is used as a magnetic material.
Strontium fluoride SrF 2 is slightly soluble in water (slightly more than 0.1 g in 1 liter of solution at room temperature). It does not react with dilute acids, but goes into solution under the influence of hot hydrochloric acid. A mineral containing strontium fluoride, jarlite NaF 3SrF 2 3AlF 3, was found in cryolite mines in Greenland.
Strontium fluoride is used as an optical and nuclear material, a component of special glasses and phosphors.
Strontium chloride SrCl 2 is highly soluble in water (34.6% by weight at 20°C). From aqueous solutions below 60.34° C, SrCl 2 ·6H 2 O hexahydrate crystallizes, spreading in air. With more high temperatures it first loses 4 molecules of water, then another, and at 250 ° C it is completely dehydrated. Unlike calcium chloride hexahydrate, strontium chloride hexahydrate is slightly soluble in ethanol (3.64% by weight at 6°C), which is used for their separation.
Strontium chloride is used in pyrotechnic compositions. It is also used in refrigeration equipment, medicine, and cosmetics.
Strontium bromide SrBr 2 is hygroscopic. In a saturated aqueous solution, its mass fraction is 50.6% at 20° C. Below 88.62° C, SrBr 2 6H 2 O hexahydrate crystallizes from aqueous solutions, above this temperature SrBr 3 H 2 O monohydrate crystallizes. Hydrates are completely dehydrated at 345° C.
Strontium bromide is obtained by reacting strontium with bromine or strontium oxide (or carbonate) with hydrobromic acid. It is used as an optical material.
Strontium iodide SrI 2 is highly soluble in water (64.0% by weight at 20°C), less soluble in ethanol (4.3% by weight at 39°C). Below 83.9° C, SrI 2 6H 2 O hexahydrate crystallizes from aqueous solutions; above this temperature, SrI 2 2H 2 O dihydrate crystallizes.
Strontium iodide serves as a luminescent material in scintillation counters.
Strontium sulfide SrS is produced by heating strontium with sulfur or reducing strontium sulfate with coal, hydrogen and other reducing agents. Its colorless crystals are decomposed by water. Strontium sulfide is used as a component of phosphors, phosphorescent compounds, and hair removers in the leather industry.
Strontium carboxylates can be prepared by reacting strontium hydroxide with the corresponding carboxylic acids. Strontium salts of fatty acids (“strontium soaps”) are used to make special greases.
Organostrontium compounds. Extremely active compounds of the composition SrR 2 (R = Me, Et, Ph, PhCH 2, etc.) can be obtained using HgR 2 (often only at low temperatures).
Bis(cyclopentadienyl)strontium is the product of a direct reaction of the metal with or with cyclopentadiene itself
Biological role of strontium.
Strontium – component microorganisms, plants and animals. In marine radiolarians, the skeleton consists of strontium sulfate - celestine. Seaweeds contain 26–140 mg of strontium per 100 g of dry matter, terrestrial plants – about 2.6, marine animals – 2–50, terrestrial animals – about 1.4, bacteria – 0.27–30. The accumulation of strontium by various organisms depends not only on their type and characteristics, but also on the ratio of the content of strontium and other elements, mainly calcium and phosphorus, in the environment.
Animals receive strontium through water and food. Some substances, such as algae polysaccharides, interfere with the absorption of strontium. Strontium accumulates in bone tissue, the ash of which contains about 0.02% strontium (in other tissues - about 0.0005%).
Strontium salts and compounds are low-toxic substances, but excess strontium affects bone tissue, liver and brain. Being close to calcium in chemical properties, strontium differs sharply from it in its biological action. Excessive content of this element in soils, waters and food products causes “Urov disease” in humans and animals (named after the Urov River in Eastern Transbaikalia) - damage and deformation of joints, growth retardation and other disorders.
Radioactive isotopes of strontium are especially dangerous.
As a result of nuclear tests and accidents at nuclear power plants in environment large quantities of radioactive strontium-90, which has a half-life of 29.12 years, arrived. Until testing of atomic and hydrogen weapons in the three environments was banned, the number of victims of radioactive strontium grew from year to year.
Within a year after completion of atmospheric nuclear explosions As a result of self-purification of the atmosphere, most of the radioactive products, including strontium-90, fell from the atmosphere to the surface of the earth. Pollution of the natural environment due to the removal from the stratosphere of radioactive products of nuclear explosions carried out at the planet's test sites in 1954–1980 now plays a secondary role; the contribution of this process to atmospheric air pollution by 90 Sr is two orders of magnitude less than from the wind lifting of dust from contaminated soil during nuclear tests and as a result of radiation accidents.
Strontium-90, along with cesium-137, are the main polluting radionuclides in Russia. The radiation situation is significantly affected by the presence of contaminated zones that appeared as a result of accidents at the Chernobyl nuclear power plant in 1986 and at the Mayak production facility in the Chelyabinsk region in 1957 (“Kyshtym accident”), as well as in the vicinity of some nuclear fuel cycle enterprises.
Nowadays, average concentrations of 90 Sr in the air outside the areas contaminated as a result of the Chernobyl and Kyshtym accidents have reached levels observed before the accident at the Chernobyl nuclear power plant. Hydrological systems associated with areas contaminated during these accidents are significantly affected by the washout of strontium-90 from the soil surface.
Once in the soil, strontium, together with soluble calcium compounds, enters the plants. Legumes, roots and tubers accumulate the most 90 Sr, while cereals, including grains, and flax accumulate less. Significantly less 90 Sr accumulates in seeds and fruits than in other organs (for example, in the leaves and stems of wheat, 90 Sr is 10 times more than in grain).
From plants, strontium-90 can pass directly or through animals into the human body. Strontium-90 accumulates to a greater extent in men than in women. In the first months of a child’s life, the deposition of strontium-90 is an order of magnitude higher than in an adult; it enters the body with milk and accumulates in rapidly growing bone tissue.
Radioactive strontium accumulates in the skeleton and thus exposes the body to long-term radioactive exposure. The biological effect of 90 Sr is associated with the nature of its distribution in the body and depends on the dose of b-irradiation created by it and its daughter radioisotope 90 Y. With prolonged intake of 90 Sr into the body, even in relatively small quantities, as a result of continuous irradiation of bone tissue, they can develop leukemia and bone cancer. Complete disintegration of strontium-90 released into the environment will occur only after several hundred years.
Application of strontium-90.
The radioisotope of strontium is used in the production of nuclear electric batteries. The operating principle of such batteries is based on the ability of strontium-90 to emit electrons that have high energy, which is then converted into electricity. Elements made of radioactive strontium, connected into a miniature battery (the size of a matchbox), are capable of trouble-free service without recharging for 15–25 years; such batteries are indispensable for space rockets and artificial Earth satellites. And Swiss watchmakers successfully use tiny strontium batteries to power electric watches.
Domestic scientists have created an isotope generator electrical energy for powering automatic weather stations based on strontium-90. Warranty period The service life of such a generator is 10 years, during which it is able to supply electrical current to devices that need it. All its maintenance consists only of preventive examinations– once every two years. The first samples of the generator were installed in Transbaikalia and in the upper reaches of the taiga river Kruchina.
There is a nuclear lighthouse in Tallinn. Its main feature is radioisotope thermoelectric generators, in which, as a result of the decay of strontium-90, thermal energy, which is then converted into light.
Devices that use radioactive strontium are used to measure thickness. This is necessary to monitor and control the production process of paper, fabrics, thin metal strips, plastic films, paint coatings. The strontium isotope is used in instruments for measuring density, viscosity and other characteristics of a substance, in flaw detectors, dosimeters, and alarms. At machine-building enterprises you can often find so-called b-relays; they control the supply of workpieces for processing, check the serviceability of the tool, and the correct position of the part.
In the production of materials that are insulators (paper, fabrics, artificial fiber, plastics, etc.), static electricity occurs due to friction. To avoid this, ionizing strontium sources are used.
Elena Savinkina
The sources are sealed with glue. They consist of a substrate coated with a preparation containing strontium-90+yttrium-90 radionuclides, placed between the body and the source lid.
Scope of application:
Radioisotope instruments
Note:
The strength classes of the sources correspond to C 34444 according to GOST 25926 (ISO 2919). Designated service life is 3.5 years from the date of issue. Tightness control is carried out in accordance with GOST R 51919-2002 (ISO 9978:1992(E)) using the immersion method, the passing limit is 200 Bq (~5 nCi). The sources are supplied in sets consisting of one BIS-R source and one BIS-K source or nine BIS-6A sources and one BIS-F source. Upon request, it is possible to supply individual sources included in the kit.
Main technical characteristics:
They are a substrate with a thickness of 1.1 max mm, on work surface in which (the recess) a layer of radioactive drug is applied, protected by a film of metal oxide. Designated service life is 10 years from the date of issue.
Scope of application:
For verification and calibration of radiometric equipment as measures of radionuclide activity.
Note:
The strength classes of the sources correspond to C 24324 according to GOST 25926 (ISO 2919). Tightness control is carried out in accordance with GOST R 51919-2002 (ISO 9978:1992(E)) using the dry swab method from a non-working surface, the passing limit is 2 Bq (~0.05 nCi). Sources are supplied individually, in sets and in kits.
* The measured values of radionuclide activity do not differ from the nominal values by more than 30%.
Among the artificial isotopes of Strontium, its long-lived radionuclide 90Sr is one of the important components of radioactive contamination of the biosphere. Once in the environment, 90Sr is characterized by the ability to be included (mainly together with Ca) in metabolic processes in plants, animals and humans. Therefore, when assessing 90Sr contamination of the biosphere, it is customary to calculate the 90Sr/Ca ratio in strontium units (1 s.u. = 1 μcurie of 90Sr per 1 g of Ca). When 90Sr and Ca move through biological and food chains, discrimination of Strontium occurs, for the quantitative expression of which the “discrimination coefficient” is found, the ratio of 90Sr/Ca in the subsequent link of the biological or food chain to the same value in the previous link. At the final link of the food chain, the concentration of 90Sr is, as a rule, significantly lower than at the initial link.
90Sr can enter plants directly through direct contamination of leaves or from the soil through the roots (in this case, the type of soil, humidity, pH, Ca content and organic matter etc.). Legumes, roots and tubers accumulate relatively more 90Sr, and cereals, including grains, and flax accumulate less. Significantly less 90Sr accumulates in seeds and fruits than in other organs (for example, in the leaves and stems of wheat, 90Sr is 10 times more than in grain). In animals (comes mainly from plant foods) and humans (comes mainly from cow's milk and fish), 90Sr accumulates mainly in the bones. The amount of 90Sr deposits in the body of animals and humans depends on the age of the individual, the amount of incoming radionuclide, the intensity of growth of new bone tissue, etc. 90Sr poses a great danger to children, into whose bodies it enters with milk and accumulates in rapidly growing bone tissue.
The biological effect of 90Sr is associated with the nature of its distribution in the body (accumulation in the skeleton) and depends on the dose of b-irradiation created by it and its daughter radioisotope 90Y. With prolonged intake of 90Sr into the body, even in relatively small quantities, as a result of continuous irradiation of bone tissue, leukemia and bone cancer can develop. Significant changes in bone tissue are observed when the 90Sr content in the diet is about 1 microcurie per 1 g of Ca. The conclusion in 1963 in Moscow of the Treaty Banning Tests of Nuclear Weapons in the Atmosphere, Space and Underwater led to an almost complete liberation of the atmosphere from 90Sr and a decrease in its mobile forms in the soil.
The main source of environmental pollution with radioactive strontium was nuclear weapons testing and accidents at nuclear power plants.
Therefore, among the radioactive isotopes of strontium, the ones of greatest practical interest are those with mass numbers 89 and 90, the yield of which in large quantities is observed in the fission reactions of uranium and plutonium.
Radioactive strontium that falls on the surface of the Earth ends up in the soil. From the soil, radionuclides enter plants through the root system. It should be noted that at this stage big role The properties of the soil and the type of plant play a role.
Radionuclides falling onto the soil surface can remain in it for many years. upper layers. AND ONLY if the soil is poor in minerals such as calcium, potassium, sodium, phosphorus, favorable conditions are created for the migration of radionuclides in the soil itself and along the soil-plant chain. This primarily applies to soddy-podzolic and sandy-loamy soils. In chernozem soils, the mobility of radionuclides is extremely difficult. Now about the plants. Strontium accumulates in the greatest quantities in legumes, root vegetables, and to a lesser extent (3-7 times) in cereals.
90 Sr-β emitter with a half-life of 28.6 years. As a result of the decay of 90 Sr, 90 Y is formed, also a β-emitter with a half-life of 64.2 hours.
Strontium isotopes falling onto the Earth's surface migrate along biological chains and, ultimately, can enter the human body.
The degree and rate of absorption of strontium from gastrointestinal tract depends on what chemical compound it is part of, on the age of the person and the functional state of the body, on the composition of the diet. Thus, in young people, strontium is absorbed faster and more completely. Increasing the content of calcium salts in the diet reduces the absorption of strontium compounds. When milk is consumed, the absorption of strontium increases. IN different conditions the absorption of strontium from the gastrointestinal tract ranges from 11 to 99%.
Absorbed strontium is actively included in mineral metabolism. Being an analogue of calcium, radioactive strontium is deposited mainly in the bones and bone marrow (critical organs).
Strontium is excreted in feces and urine. The effective half-life is 17.5 years.
IN early dates after the intake of 90 Sr in large quantities, changes are observed in the organs through which it enters or is excreted: the mucous membranes of the mouth, upper respiratory tract, and intestines. Later, liver functions are impaired. When poorly soluble strontium compounds are inhaled, the strontium isotope can be quite firmly fixed in the lungs, which in these cases, together with the respiratory tract, are critical organs. However, in the long term and after inhalation, bones and bone marrow become critical organs, in which up to 90% of all activity is deposited.
During the reaction of hematopoietic tissue to strontium over a long period of time, the morphological composition of the blood changes little. Only when large quantities are ingested does cytopenia develop and progress. No severe cases of damage with acute or subacute course were observed in humans.
With prolonged intake of strontium and subacute radiation sickness, anemia gradually develops, suppression of spermato- and oogenesis, impaired immunity, liver and kidney function, and neuroendocrine system are observed, and life expectancy is reduced.
In the long term, hyper- or hypoplastic processes in the bone marrow, leukemia, and bone sarcomas develop. Less commonly, neoplasms are observed in the pituitary gland and other endocrine organs, in the ovaries, and mammary gland.
The long half-life of 90 Sr determines long-term persistence high levels contamination of territories and environmental objects after contamination with this radionuclide.
Among the nuclear fission products there is also 89 Sr, which is also a β-emitter. However, the half-life of 89 Sr is shorter - 53 days, so the degree of radioactive contamination of objects in this case decreases much faster.
