Strontium 90. Lunch without radionuclides. Basics of healthy eating. From a nuclear reactor to a plate of fruit

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, content of Ca and organic matter, etc. have a great influence). 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 deposition 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 related to 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 the properties of the soil and the type of plant play a big role.

Radionuclides falling onto the soil surface can remain in its upper layers for many years. 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.

Strontium-90 is a pure beta emitter with a half-life of 29.12 years. 90Sr is a pure beta emitter with a maximum energy of 0.54 eV. Upon decay, it forms a daughter radionuclide 90Y with a half-life of 64 hours. Like 137Cs, 90Sr can be found in water-soluble and water-insoluble forms. Features of the behavior of this radionuclide in the human body. Almost all strontium-9O that enters the body is concentrated in bone tissue. This is explained by the fact that strontium is a chemical analogue of calcium, and calcium compounds are the main mineral component of bone. In children, mineral metabolism in bone tissue is more intense than in adults, so strontium-90 accumulates in their skeleton in greater quantities, but is also excreted faster.

For humans, the half-life of strontium-90 is 90-154 days. Strontium-90 deposited in bone tissue primarily affects the red bone marrow - the main hematopoietic tissue, which is also very radiosensitive. Generative tissues are irradiated from strontium-90 accumulated in the pelvic bones. Therefore, low maximum permissible concentrations have been established for this radionuclide - approximately 100 times lower than for cesium-137.

Strontium-90 enters the body only with food, and up to 20% of its intake is absorbed in the intestines. The highest content of this radionuclide in the bone tissue of residents of the northern hemisphere was recorded in 1963-1965. Then this jump was caused by global fallout of radioactive fallout from intensive nuclear weapons testing in the atmosphere in 1961-1962.

After the accident at the Chernobyl nuclear power plant, the entire territory with significant contamination with strontium-90 was within the 30-kilometer zone. A large amount of strontium-90 ended up in water bodies, but in river water its concentration never exceeded the maximum permissible for drinking water (except for the Pripyat River in early May 1986 in its lower reaches).

The biological half-life for strontium-90 from soft tissues is 5-8 days, for bones – up to 150 days (16% is excreted with Teff equal to 3360 days).

Gave. The consequences are signs of perversion and slow bone restructuring, as well as a sharp reduction in its circulatory network.

55. Cesium-137 half-life, entry into the body.

Cesium-137 is a beta emitter with a half-life of 30.174 years. 137Сs was discovered in 1860 by German scientists Kirchhoff and Bunsen. It got its name from the Latin word caesius - blue, based on the characteristic bright line in the blue region of the spectrum. Several isotopes of cesium are currently known. Of greatest practical importance is 137Cs, one of the longest-lived fission products of uranium.

Nuclear power is a source of 137Сs entering the environment. According to published data, in 2000, about 22.2 x 1019 Bq of 137Cs were released into the atmosphere by nuclear power plant reactors in all countries of the world. 137Сs is released not only into the atmosphere, but also into the oceans from nuclear submarines, tankers, and icebreakers equipped with nuclear power plants. In its chemical properties, cesium is close to rubidium and potassium - elements of group 1. Cesium isotopes are well absorbed by any route of entry into the body..

After the Chernobyl accident, 1.0 MCi of cesium-137 was released into the external environment. Currently, it is the main dose-forming radionuclide in the areas affected by the Chernobyl nuclear power plant accident. The suitability of contaminated areas for a full life depends on its content and behavior in the external environment.

The soils of Ukrainian-Belarusian Polesie have a specific feature - cesium-137 is poorly fixed by them and, as a result, it easily enters plants through the root system.

Cesium isotopes, being fission products of uranium, are included in the biological cycle and freely migrate through various biological chains. Currently, 137Cs is found in the body of various animals and humans. It should be noted that stable cesium is included in the human and animal body in quantities from 0.002 to 0.6 μg per 1 g of soft tissue.

Absorption of 137Сs in the gastrointestinal tract of animals and humans is 100%. In certain areas of the gastrointestinal tract, absorption of 137Cs occurs at different rates. Through the respiratory tract, the intake of 137Cs into the human body is 0.25% of the amount supplied with the diet. After oral intake of cesium, significant amounts of absorbed radionuclide are secreted into the intestine and then reabsorbed in the descending intestine. The extent of cesium reabsorption can vary significantly between animal species. Having entered the blood, it is distributed relatively evenly throughout the organs and tissues. The route of entry and the type of animal do not affect the distribution of the isotope.

Determination of 137Cs in the human body is carried out by measuring gamma radiation from the body and beta, gamma radiation from excretions (urine, feces). For this purpose, beta-gamma radiometers and a human radiation counter (HRU) are used. Based on individual peaks in the spectrum corresponding to different gamma emitters, their activity in the body can be determined. In order to prevent radiation injuries from 137Cs, all work with liquid and solid compounds is recommended to be carried out in sealed boxes. To prevent the entry of cesium and its compounds into the body, it is necessary to use personal protective equipment and observe personal hygiene rules.

The effective half-life of long-lived isotopes is determined mainly by the biological half-life, and that of short-lived isotopes by their half-life. The biological half-life is varied - from several hours (krypton, xenon, radon) to several years (scandium, yttrium, zirconium, actinium). The effective half-life ranges from several hours (sodium-24, copper-64), days (iodine-131, phosphorus-23, sulfur-35), to tens of years (radium-226, strontium-90).

The biological half-life for cesium-137 from the body is 70 days, from muscles, lungs and skeleton - 140 days.

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 cover.

Application area:
Radioisotope devices

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 the working surface of which (the recess) a layer of a radioactive drug is applied, protected by a film of metal oxide. Designated service life is 10 years from the date of issue.

Application area:
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%.

Strontium 90 Sr is a silvery calcium-like metal coated with an oxide shell and reacts poorly, being included in the metabolism of the ecosystem as complex Ca - Fe - Al - Sr - complexes are formed. The natural content of the stable isotope in soil, bone tissue, and the environment reaches 3.7 x 10 -2%, in sea water, muscle tissue 7.6 x 10 -4%. Biological functions have not been identified; non-toxic, can replace calcium. There is no radioactive isotope in the natural environment.

Strontium is an element of the main subgroup of the second group, the fifth period of the periodic system of chemical elements of D.I. Mendeleev, with atomic number 38. It is designated by the symbol Sr (lat. Strontium). The simple substance strontium (CAS number: 7440-24-6) is a soft, malleable and ductile alkaline earth metal of silver-white color. It has high chemical activity; in air it quickly reacts with moisture and oxygen, becoming covered with a yellow oxide film.

The new element was discovered in the mineral strontianite, found in 1764 in a lead mine near the Scottish village of Stronshian, which later gave its name to the new element. The presence of a new metal oxide in this mineral was discovered almost 30 years later by William Cruickshank and Ader Crawford. Isolated in its pure form by Sir Humphry Davy in 1808.

Strontium is found in sea water (0.1 mg/l), in soils (0.035 wt%).

In nature, strontium occurs as a mixture of 4 stable isotopes 84 Sr (0.56%), 86 Sr (9.86%), 87 Sr (7.02%), 88 Sr (82.56%).

There are 3 ways to obtain strontium metal:

Thermal decomposition of some compounds

Electrolysis

Reduction of oxide or chloride

The main industrial method for producing strontium metal is the thermal reduction of its oxide with aluminum. Next, the resulting strontium is purified by sublimation.

The electrolytic production of strontium by electrolysis of a melted mixture of SrCl 2 and NaCl is not widespread due to the low current efficiency and contamination of strontium with impurities.

The thermal decomposition of strontium hydride or nitride produces finely dispersed strontium, which is prone to easy ignition.

Strontium is a soft, silvery-white metal that is malleable and ductile and can be easily cut with a knife.

Polymorphic - three of its modifications are known. Up to 215 o C, the cubic face-centered modification (b-Sr) is stable, between 215 and 605 o C - hexagonal (b-Sr), above 605 o C - cubic body-centered modification (g-Sr).

Melting point - 768 o C, Boiling point - 1390 o C.

Strontium in its compounds always exhibits a valence of +2. The properties of strontium are close to calcium and barium, occupying an intermediate position between them.

In the electrochemical series of voltages, strontium is among the most active metals (its normal electrode potential is equal to? 2.89 V. It reacts vigorously with water, forming hydroxide: Sr + 2H 2 O = Sr(OH) 2 + H 2 ^.

Interacts with acids, displaces heavy metals from their salts. It reacts weakly with concentrated acids (H 2 SO 4, HNO 3).

Strontium metal quickly oxidizes in air, forming a yellowish film, in which, in addition to SrO oxide, SrO 2 peroxide and Sr 3 N 2 nitride are always present. When heated in air, it ignites; powdered strontium in air is prone to self-ignition.

Reacts vigorously with non-metals - sulfur, phosphorus, halogens. Interacts with hydrogen (above 200 o C), nitrogen (above 400 o C). Practically does not react with alkalis.

At high temperatures it reacts with CO 2, forming carbide:

5Sr + 2CO 2 = SrC 2 + 4SrO (1)

Easily soluble strontium salts with the anions Cl - , I - , NO 3 - . Salts with anions F -, SO 4 2-, CO 3 2-, PO 4 3- are slightly soluble.

The main areas of application of strontium and its chemical compounds are the radio-electronic industry, pyrotechnics, metallurgy, and the food industry.

Strontium is used for alloying copper and some of its alloys, for introduction into battery lead alloys, for desulfurization of cast iron, copper and steels.

Strontium with a purity of 99.99-99.999% is used for the reduction of uranium.

Hard magnetic strontium ferrites are widely used as materials for the production of permanent magnets.

In pyrotechnics, strontium carbonate, nitrate, and perchlorate are used to color the flame carmine red. The magnesium-strontium alloy has strong pyrophoric properties and is used in pyrotechnics for incendiary and signal compositions.

Radioactive 90 Sr (half-life 28.9 years) is used in the production of radioisotope current sources in the form of strontium titanite (density 4.8 g/cm³, and energy release about 0.54 W/cm³).

Strontium uranate plays an important role in the production of hydrogen (strontium-uranate cycle, Los Alamos, USA) by thermochemical method (atomic-hydrogen energy), and in particular, methods are being developed for the direct fission of uranium nuclei in the composition of strontium uranate to produce heat from the decomposition of water into hydrogen and oxygen.

Strontium oxide is used as a component of superconducting ceramics.

Strontium fluoride is used as a component of solid-state fluorine batteries with enormous energy capacity and energy density.

Strontium alloys with tin and lead are used for casting battery current leads. Strontium-cadmium alloys for galvanic cell anodes.

Radiation characteristics are given in Table 1.

Table 1 - Radiation characteristics of strontium 90

In cases where the isotope enters the environment, the intake of strontium into the body depends on the degree and nature of the inclusion of the metabolite in soil organic structures, food and ranges from 5 to 30%, with greater penetration into the child’s body. Regardless of the route of entry, the emitter accumulates in the skeleton (soft tissues contain no more than 1%). It is excreted from the body extremely poorly, which leads to constant accumulation of the dose due to chronic intake of strontium into the body. Unlike natural β-active analogues (uranium, thorium, etc.), strontium is an effective β-emitter, which changes the spectrum of radiation exposure, including on the gonads, endocrine glands, red bone marrow and brain. Accumulated doses (background) fluctuate within the range (up to 0.2 x 10 -6 µCi/g in bones at doses of the order of 4.5 x 10 -2 mSv/year).

The effect on the human body of natural (non-radioactive, low-toxic and, moreover, widely used for the treatment of osteoporosis) and radioactive isotopes of strontium should not be confused. The strontium isotope 90 Sr is radioactive with a half-life of 28.9 years. 90 Sr undergoes decay, turning into radioactive 90 Y (half-life 64 hours). Complete decay of strontium-90 released into the environment will occur only after several hundred years. 90 Sr is formed during nuclear explosions and emissions from nuclear power plants.

In terms of chemical reactions, radioactive and non-radioactive isotopes of strontium are practically the same. Natural strontium is a component of microorganisms, plants and animals. Regardless of the route and rhythm of entry into the body, soluble strontium compounds accumulate in the skeleton. Less than 1% is retained in soft tissues. The route of entry influences the amount of strontium deposition in the skeleton.

The behavior of strontium in the body is influenced by species, gender, age, as well as pregnancy and other factors. For example, males have higher levels of deposits in their skeletons than females. Strontium is an analogue of calcium. Strontium accumulates at a high rate in the body of children up to the age of four, when bone tissue is actively being formed. Strontium metabolism changes in certain diseases of the digestive system and cardiovascular system. Routes of entry:

Water (the maximum permissible concentration of strontium in water in the Russian Federation is 8 mg/l, and in the USA - 4 mg/l)

Food (tomatoes, beets, dill, parsley, radishes, radishes, onions, cabbage, barley, rye, wheat)

Intratracheal delivery

Through the skin (cutaneous)

Inhalation (through air)

From plants or through animals, strontium-90 can directly pass into the human body.

People whose work involves strontium (in medicine, radioactive strontium is used as applicators in the treatment of skin and eye diseases. The main areas of application of natural strontium are the radio-electronic industry, pyrotechnics, metallurgy, metallothermy, food industry, production of magnetic materials, radioactive - production of atomic electric batteries, atomic-hydrogen energy, radioisotope thermoelectric generators, etc.).

The influence of non-radioactive strontium appears extremely rarely and only under the influence of other factors (calcium and vitamin D deficiency, malnutrition, imbalances in the ratio of microelements such as barium, molybdenum, selenium, etc.). Then it can cause “strontium rickets” and “urological disease” in children - damage and deformation of joints, growth retardation and other disorders. On the contrary, radioactive strontium almost always has a negative effect on the human body:

It is deposited in the skeleton (bones), affects bone tissue and bone marrow, which leads to the development of radiation sickness, tumors of hematopoietic tissue and bones.

Causes leukemia and malignant tumors (cancer) of bones, as well as liver and brain damage

The strontium isotope 90 Sr is radioactive with a half-life of 28.79 years. 90 Sr undergoes β-decay, turning into radioactive yttrium 90 Y (half-life 64 hours). 90 Sr is formed during nuclear explosions and emissions from nuclear power plants.

Strontium is an analogue of calcium and is able to be firmly deposited in bones. Long-term radiation exposure to 90 Sr and 90 Y affects bone tissue and bone marrow, which leads to the development of radiation sickness, tumors of hematopoietic tissue and bones.

Once in the soil, strontium-90, together with soluble calcium compounds, enters plants, from which it can enter the human body directly or through animals. This creates a chain of transmission of radioactive strontium: soil - plants - animals - humans. Penetrating into the human body, strontium accumulates mainly in the bones and thus exposes the body to long-term internal radioactive effects. The result of this exposure, as shown by research conducted by scientists in experiments on animals (dogs, rats, etc.), is a serious illness of the body. Damage to the hematopoietic organs and the development of tumors in the bones come to the fore. Under normal conditions, the “supplier” of radioactive strontium is experimental explosions of nuclear and thermonuclear weapons. Research by American scientists has established that even a small amount of radiation exposure is certainly harmful to a healthy person. If we take into account that even with extremely small doses of this effect, sharp changes occur in those cells of the body on which the reproduction of offspring depends, then it is quite clear that nuclear explosions pose a mortal danger to those who are not yet born! Strontium received its name from the mineral strontianite (carbon dioxide salt of strontium), found in 1787 in Scotland near the village of Strontian. The English researcher A. Crawford, studying strontianite, suggested the presence of a new, as yet unknown “earth” in it. The individual peculiarity of strontianite was also established by Klaproth. The English chemist T. Hope in 1792 proved the presence of a new metal in strontianite, isolated in free form in 1808 by G. Davy.

However, regardless of Western scientists, Russian chemist T.E. Lovitz in 1792, examining the mineral barite, came to the conclusion that, in addition to barium oxide, it also contained “strontian earth” as an impurity. Extremely cautious in his conclusions, Lovitz did not dare to publish them until the completion of the secondary verification of the experiments, which required the accumulation of a large amount of “strontian earth”. Therefore, Lovitz’s research “On strontian earth in heavy spar,” although published after Klaproth’s research, was actually carried out before him. They indicate the discovery of strontium in a new mineral - strontium sulfate, now called celestine. From this mineral, the simplest marine organisms - radiolarians, acantharia - build the spines of their skeleton. From the needles of dying invertebrates, clusters of celestine itself were formed

When talking about radionuclides in food, we primarily mean the dangerous Strontium-90 and Cesium-137. They are the ones that enter the environment in large quantities during accidents at nuclear power plants and nuclear explosions. And given their relatively long half-life (about 30 years), sooner or later they may end up in our dinner.

From a nuclear reactor to a plate of fruit

The human body has a remarkable property - it can recognize “friends” and “strangers”. For example, a portion of jelly will be digested and almost completely absorbed, but accidentally swallowed chewing gum will not. The problem with radionuclides is that our body perceives them as microelements it needs. They are absorbed and participate in metabolism. Radionuclides are absorbed similarly by agricultural plants and animals. Thus, with meat, milk and fruits they end up on our table.

Strontium-90 - harmful to humans

The harm of strontium to humans primarily lies in the fact that our body mistakes it for calcium. Once in the body, the radionuclide takes the place of the calcium we need in the bones, disrupting their structure. The danger of this is easy to imagine: imagine a house built from identical standard bricks. Now imagine that some of them are replaced with aerated concrete blocks, twice the size of a brick.

Bone tissue in which calcium has been replaced by strontium is susceptible to fractures, but this is not the only danger. There is a 100% chance that radioactive decay will occur with the strontium embedded in the bones. This means that it will turn into an atom of another element, while emitting a beta particle - what we call “radiation”, “radiation”, etc. On its way, like a bullet fired at high speed, it can damage structures cells and - most dangerously - DNA, the “basic law” of our body. From such damage, the information recorded in it can be distorted, and such a cell can give rise to a malignant tumor. Considering that strontium in the human body prefers to be in the bones, the bone marrow suffers most from such radio-damage.

If strontium has already entered the body, it is very difficult to remove it, because bone tissue is not renewed every minute. That is why the main thing in the prevention of all radioactive problems is careful selection of food products.

Cesium-137 - harm to humans

Radioactive cesium is a double of potassium, so once it enters the body, it replaces it in all processes. This primarily concerns the muscles - this is where most of the absorbed cesium accumulates. The harm of cesium-137 to humans is primarily associated with its radioactivity. Along the way of its radioactive transformations, it will irradiate surrounding tissues with gamma and beta rays, causing mutations and damage at the cellular level.

The good news is that cesium, unlike strontium, is eliminated from the human body over time. The main credit for this goes to the kidneys. That is why it is recommended to take diuretics in cases where a portion of radioactive cesium has entered the body - after accidents, etc.

Constant exposure to cesium-137 in humans in the long term can cause the appearance of malignant tumors. Absorption of large doses (during accidents and explosions) causes radiation sickness, but this is a radiation safety problem rather than a food safety problem.

Never purchase berries, mushrooms, vegetables and dairy products if their origin is unknown. Be careful with products originating from:
- areas contaminated as a result of the accident at a nuclear power plant - for example, Bryansk;
— Southern Urals;
- Barnaul and Novosibirsk.

River fish can also accumulate radionuclides. In case of minimal doubts, ask the seller for documents confirming the quality of the goods. Radioactivity is one of the indicators that must be checked in food products.