Literature review. Strontium Half-life sr 90

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. When it decays, it forms a daughter radionuclide 90Y with a half-life of 64 hours. Like 137Cs, 90Sr can be found in water-soluble and insoluble forms. Features of the behavior of this radionuclide in the human body. Almost all of the 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.

In 1787, near the Scottish settlement of Strontian, in a lead mine, a hitherto unknown mineral was found. It was named strontianite after the village. And scientists gave the name in honor of this mineral. What are its properties, how can this substance be useful or dangerous?

First studies of strontium

After the discovery of strontianite, scientists classified this mineral into different categories. Some believed that it belonged to fluorites, others - to witherites. However, a little later, clarity regarding this substance was brought by the Scottish chemist T. Hop. At that time it was not yet known that the substance under study could have a half-life. Strontium was also the object of study by the chemist A. Lavoisier, as well as Humphry Davy. A significant contribution to the discovery of this substance was also made by the Russian scientist Tovius Lowitz. He, independently of his Western colleagues, discovered the presence of this metal in heavy spar.

A little theory. What's happened

Everyone knows that today radioactive isotopes are commonly called radionuclides. What are Radionuclides differ from other substances in that their nuclei are unstable. Over time, they decay - a process of radioactive decay occurs. During this process, nuclei are converted into other isotopes and radioactive rays are released. Different radionuclides have different levels of instability. There are short-lived and long-lived isotopes. Short-lived ones decay very quickly: it takes seconds, days or months. Long-lived ones require hundreds, thousands, and sometimes billions of years. No matter how much an isotope is taken, in order for half of its substance to decay, a certain period of time is always required - this is called the half-life.

What is the half-life of strontium-90?

As is known, radionuclides and isotopes are substances very hazardous to health. As for strontium, its stable isotopes pose virtually no danger to humans. But radioactive isotopes are capable of destroying all living things. The reason one dangerous form of strontium, strontium-90, is dangerous is because of its half-life. Strontium-90 decays in 29 years, and this process is always accompanied by the release of a large amount of radiation. This element has the ability to quickly be incorporated into the systems of living organisms and metabolized.

Properties of strontium

In air, strontium reacts very quickly with water, becoming covered with a yellow oxide film. This element does not occur in free form in nature. Its largest deposits are located in Russia, Arizona, and California (USA). Strontium is a very soft metal - it can be easily cut with a simple knife. But its melting point is 768 °C. Alloys containing strontium are used in pyrotechnics. This element is also used to restore uranium.

Penetration of strontium into living organisms

In its chemical properties, strontium is very similar to ordinary calcium - this element is practically its analogue. Strontium-90 is very quickly deposited in bone tissue, teeth, and also in liquids. The decay of this element also produces the daughter isotope yttrium-90, which has a very short half-life. Strontium in this parameter cannot even be compared with yttrium-90, which decays in just 64 hours.

Yttrium-90 is capable of emitting beta particles. It also very quickly attacks bone tissue and the bone marrow, which is especially sensitive to it. Under the influence of powerful radiation, serious physiological changes occur in any living organism. The cellular composition changes, the cell structure is also seriously disrupted, which leads to changes in metabolism. Therefore, the question of what is the half-life of strontium-90 is not at all idle. Ultimately, this element leads to cancer of the blood (leukemia) and bones. It is also capable of exerting a powerful influence on DNA structure and genetics.

Speed ​​of spread in nature

Contamination with strontium-90 occurs quickly because it has a very short half-life. Strontium, formed after man-made disasters, is transmitted through food biological chains, as it contaminates land and water. The isotope also easily penetrates the respiratory tract of animals and humans. From the earth, strontium-90 quickly enters the body of animals, plants, and then into the body of people who take contaminated products. In addition, the isotope is capable of not only infecting a specific organism, but also transmitting deformities to its descendants. Strontium-90 is also passed through mother's milk to her baby.

This isotope takes an active part in plant metabolism. The substance enters them from the soil through the roots. Plant species such as legumes, roots and tubers accumulate very large amounts of strontium. In the human body, strontium accumulates mainly in the skeleton. With age, the amount of deposited strontium decreases. The isotope accumulates more in men than in women.

The most dangerous isotopes

Along with cesium-137, strontium-90 is one of the most dangerous and powerful radioactive pollutants with a fast half-life. Strontium-90 very often enters the environment as a result of accidents at nuclear power plants, as well as nuclear tests. The situation is complicated by the fact that the presence of this isotope is very difficult to determine even in soil samples. Unlike cesium, whose gamma radiation is very easily detected, it takes at least a week to determine the content of strontium-90 in the soil.

During such a study, scientists burn a sample of soil or agricultural products in a special way, and only after that can they say whether this sample contains strontium. This method is absolutely not suitable when it is necessary to determine the amount of isotope absorbed by the human body. For such diagnostics, Belarusian scientists have invented a special helmet that registers beta radiation.

Strontium-90 related element

The metals closest in their properties in this regard are cesium-137 and strontium-90. Cesium-137 has a half-life of 30 years. During radiation disasters, it is these two elements that create the greatest number of problems. It is believed that gamma-active cesium is more to blame for the terrible consequences of the Chernobyl accident than strontium. Taking into account the half-lives of these substances, we can say that at least six hundred years must pass before there are no more of these isotopes left in the Chernobyl zone.

Features of the half-life of isotopes

For each isotope substance, the half-life is strictly defined. Strontium-90 has a period of 28 years. However, this does not mean that all its atoms will disappear after 56 years. The initial amount of the isotope also does not matter. During decay, some of the strontium may change into lighter elements. If the half-life of radioactive strontium is 28 years, then this means the following.

After this period of time, half of the original amount of isotope will remain. After another 28 years - a quarter and so on. It turns out that strontium can pollute the environment for decades. Some scientists round this number to mean that the half-life of strontium is 29 years. After this period of time, half of the substance remains, but this is enough for strontium to spread far beyond the limits of the accident.

Strontium-90 (radiostrontium) is a radioactive strontium nuclide formed in nuclear reactors or during nuclear weapons testing. The half-life of strontium-90 is close to 28.79 years. After decay, another radioactive isotope is formed - yttrium-90. Its half-life is 64 hours.

Place of accumulation of strontium 90 in the body and harm to humans and animals

If cesium-137 replaces potassium and is deposited mainly in the muscles, then strontium-90 acts as an analogue of calcium and remains in the bones of the skeleton and teeth. Bone tissue and bone marrow are also affected. Severe damage leads to the development of radiation sickness, bone tumors, and anemia. The half-life of strontium-90 from the body is about 15 years, which creates a constant source of disease in humans. Just imagine if all the calcium in your bones was replaced with strontium-90, how fragile they would become - only permanent fractures would become a common problem. But at the same time, the issue of constant radioactive radiation on neighboring cells will not be resolved.

At the same time, strontium itself (not the radioactive isotope strontium-90) is very useful for the body, playing a significant role in metabolism. The benefits of ginger have long been proven, especially for older people, who, using it in their diet, increased the strontium content in the body, thereby promoting better absorption of calcium and, as a result, strengthening the condition of their bones and teeth.

Applications of radioactive strontium

Radiostrontium is used in dosimetric instruments for civil and military purposes. It is also used in medicine for radiation therapy of eye tumors or skin lesions. Since strontium-90 radiation is weakly penetrating and is used mainly on superficial foci of diseases.

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 the gastrointestinal tract depends on the chemical compound it is part of, the age of the person and the functional state of the body, and 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. Under 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 the early stages 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 the long-term persistence of high levels of 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.

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 10 different isotopes of one strontium. No, give us not just any strontium, but strontium-90.

Perhaps a vague thought flashes through the minds of readers about a mysterious half-life, about long-lived and short-lived radionuclides? 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. Indeed, the popular love for strontium-90 is associated with 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 are 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, gamma-active (bear with me for three pages) cesium is more guilty of the negative consequences of the Chernobyl accident 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 the main problem - the danger of various radionuclides to health. 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? The way 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 common 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 a soap bubble with a diameter of several meters (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 (atomic explosion or 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 various 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 can be damaged. 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 the operation of a nuclear reactor, in addition to gamma radiation, neutron fluxes are generated. 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 standards. - M.: Federal Center for Hygiene and Epidemiology of Rospotrebnadzor, 2009. – 100 p.