Radioactive iodine half-life. radioactive iodine

All chemical elements form isotopes with unstable nuclei, which emit α-particles, β-particles or γ-rays during their half-life. Iodine has 37 types of nuclei with the same charge, but differing in the number of neutrons that determine the mass of the nucleus and the atom. The charge of all isotopes of iodine (I) is 53. When they mean an isotope with a certain number of neutrons, write this number next to the symbol, through a dash. In medical practice, I-124, I-131, I-123 are used. The normal isotope of iodine (not radioactive) is I-127.

The number of neutrons serves as an indicator for various diagnostic and therapeutic procedures. Radioiodine therapy is based on the varying half-lives of the radioactive isotopes of iodine. For example, an element with 123 neutrons decays in 13 hours, with 124 - in 4 days, and I-131 will have a radioactive effect after 8 days. More often, I-131 is used, during the decay of which γ-rays, inert xenon and β-particles are formed.

The effect of radioactive iodine in the treatment

Iodine therapy is prescribed after the removal of the thyroid gland completely. With partial removal or conservative treatment, this method does not make sense to use. The follicles of the thyroid gland receive iodides from the tissue fluid that surrounds them. Iodides enter the tissue fluid by diffusion or by active transport from the blood. During iodine starvation, secretory cells begin to actively capture radioactive iodine, and degenerate cancer cells do this much more intensively.

β-particles, released during half-life, kill cancer cells.

The striking ability of β-particles acts at a distance of 600 - 2000 nm, which is quite enough to destroy only the cellular elements of malignant cells, and not neighboring tissues.

The main goal of radioiodine therapy is the final removal of all remnants of the thyroid gland, because even the most skillful operation leaves behind these remnants. Moreover, in the practice of surgeons, it has already become customary to leave several gland cells around the parathyroid glands for their normal operation, as well as around the recurrent nerve that innervates the vocal cords. The destruction of the iodine isotope occurs not only in the residual tissues of the thyroid gland, but also metastasis in cancerous tumors, which makes it easier to monitor the concentration of thyroglobulin.

γ-rays do not have a therapeutic effect, but they are successfully used in the diagnosis of diseases. The γ-camera built into the scanner helps to determine the localization of radioactive iodine, which serves as a signal for the recognition of cancerous metastases. The accumulation of the isotope occurs on the surface of the front of the neck (in the place of the former thyroid gland), in the salivary glands, along the entire length of the digestive system, in the bladder. Few, but still there are iodine uptake receptors in the mammary glands. Scanning reveals metastases in trimmed and nearby organs. Most often they are found in the cervical lymph nodes, bones, lungs and tissues of the mediastinum.

Treatment prescriptions for radioactive isotopes

Radioiodine therapy is indicated for use in two cases:

1. If the state of a hypertrophied gland is detected in the form of a toxic goiter (nodular or diffuse). The state of diffuse goiter is characterized by the production of thyroid hormones by the entire secretory tissue of the gland. In nodular goiter, only the nodular tissue secretes hormones. The tasks of introducing radioactive iodine are reduced to the inhibition of the functionality of hypertrophied areas, since the radiation of β-particles destroys precisely those places that are prone to thyrotoxicosis. At the end of the procedure, either the normal function of the gland is restored, or hypothyroidism develops, which is easily normalized when using an analogue of the hormone thyroxine - T4 (L-form).
2. If a malignant neoplasm of the thyroid gland (papillary or follicular cancer) is found, the surgeon determines the degree of risk. In accordance with this, risk groups are distinguished according to the level of tumor progress and possible distant localization of metastases, as well as the need for radioactive iodine treatment.
3. The low-risk group includes patients with a small tumor, not exceeding 2 cm and located in the outline of the thyroid gland. No metastases were found in neighboring organs and tissues (especially in the lymph nodes). Such patients do not need to inject radioactive iodine.
4. Patients with an average risk have a tumor larger than 2 cm, but not exceeding 3 cm. If an unfavorable prognosis develops and the capsule in the thyroid gland germinates, a dose of radioactive iodine of 30-100 mCi is prescribed.
5. The high-risk group has a pronounced aggressive pattern of cancer growth. There is germination in neighboring tissues and organs, lymph nodes, there may be distant metastases. Such patients require treatment with a radioactive isotope greater than 100 millicuries.

Radioiodine Administration Procedure

The radioactive isotope of iodine (I-131) is synthesized artificially. It is taken in the form of gelatin capsules (liquid) orally. Capsules or liquid are odorless and tasteless, swallowed only with a glass of water. After taking the liquid, it is recommended to immediately rinse your mouth with water and swallow it without spitting it out.

In the presence of dentures, it is better to remove them for a while before using liquid iodine.

You can’t eat for two hours, you can (even need) to take a plentiful drink of water or juice. Iodine-131, not absorbed by the thyroid follicles, is excreted in the urine, so urination should occur every hour with the control of the content of the isotope in the urine. Medicines for the thyroid gland are taken no earlier than 2 days later. It is better if the patient's contacts with other people at this time are strictly limited.

Before the procedure, the doctor must analyze the medications taken and stop them at different times: some of them - a week, others at least 4 days before the procedure. If a woman is of childbearing age, then pregnancy planning will have to be postponed for a period determined by the doctor. Previous surgery requires a test for the presence or absence of tissue capable of absorbing iodine-131. 14 days before the start of the introduction of radioactive iodine, a special diet is prescribed, in which the normal isotope of iodine-127 must be completely eliminated from the body. The list of products for the effective removal of iodine will be prompted by the attending physician.

Treatment of cancerous tumors with radioactive iodine

If the iodine-free diet is correctly observed and the period of restrictions on the intake of hormonal drugs is observed, the thyroid cells are completely cleared of iodine residues. With the introduction of radioactive iodine against the background of iodine starvation, cells tend to capture any isotope of iodine and are affected by β-particles. The more actively cells absorb a radioactive isotope, the more they are affected by it. The dose of irradiation of thyroid follicles that capture iodine is several tens of times greater than the effect of a radioactive element on surrounding tissues and organs.

French experts have calculated that almost 90% of patients with lung metastases survived after treatment with a radioactive isotope. Survival within ten years after the application of the procedure was more than 90%. And these are patients with the last (IVc) stage of a terrible disease.

Of course, the described procedure is not a panacea, because complications after its use are not excluded.

First of all, it is sialadenitis (inflammation of the salivary glands), accompanied by swelling, soreness. This disease develops in response to the introduction of iodine and the absence of thyroid cells capable of capturing it. Then the salivary gland has to take over this function. It should be noted that sialadenitis progresses only at high radiation doses (above 80 mCi).

There are cases of violation of the reproductive function of the reproductive system, but with repeated exposures, the total dose of which exceeds 500 mCi.

Treatment after thyroidectomy

Often, cancer patients are prescribed iodine therapy after removal of the thyroid gland. The objective of this procedure is the final defeat of cancer cells remaining after the operation, not only in the thyroid gland, but also in the blood.

After taking the drug, the patient is placed in a single room, which is equipped in accordance with the specifics.

Medical personnel are limited to contact for up to five days. At this time, visitors should not be allowed into the ward, especially pregnant women and children, in order to protect them from the flow of radiation particles. Urine and saliva of the patient are considered radioactive and are subject to special disposal.

Pros and cons of radioactive iodine treatment

The described procedure cannot be called completely “harmless”. Thus, during the action of a radioactive isotope, temporary phenomena are noted in the form of painful sensations in the region of the salivary glands, tongue, and front of the neck. The mouth is dry, itchy in the throat. The patient is sick, there is frequent urge to vomit, swelling, food becomes not tasty. In addition, old chronic diseases become aggravated, the patient becomes lethargic, gets tired quickly, and is prone to depression.

Despite the negative aspects of treatment, the use of radioactive iodine is increasingly used in the treatment of thyroid gland in clinics.

The positive reasons for this pattern are:

• there is no surgical intervention with cosmetic consequences;
• general anesthesia is not required;
• the relative cheapness of European clinics compared to operations with a high quality of service and scanning equipment.

Danger of radiation on contact

It should be remembered that the benefit provided in the process of using radiation is obvious to the patient himself. For the people around him, radiation can play a cruel joke. Not to mention the visitors of the patient, let us mention that medical workers provide care only when necessary and, of course, in protective clothing and gloves.

After discharge, you should not be in contact with a person closer than 1 meter, and with a long conversation, you should move 2 meters away. In the same bed, even after discharge, it is not recommended to sleep in the same bed with another person for 3 days. Sexual contacts and being near a pregnant woman are strictly prohibited within a week from the date of discharge, which occurs five days after the procedure.

How to behave after irradiation with an isotope of iodine?

Eight days after discharge, you should keep children away from you, especially contact. After using the bathroom or toilet, flush three times with water. Hands are washed thoroughly with soap.

It is better for men to sit on the toilet when urinating to prevent splashing of radiation urine. Breastfeeding should be discontinued if the patient is a nursing mother. The clothes in which the patient was on treatment are placed in a bag and washed separately a month or two after discharge. Personal belongings are removed from common areas and storage. In case of emergency admission to the hospital, it is necessary to warn the medical staff about the recent course of iodine-131 irradiation.

Radioactive isotope: Cesium-137

Effect on the body

Cesium-137 is a radioactive isotope of the element cesium and has a half-life of 30 years. This radionuclide was first discovered using optical spectroscopy back in 1860. A solid number of isotopes of this element is known - 39. The longest "half-life" (excuse the pun) is the cesium-135 isotope, a long 2.3 million years.

The most used cesium isotope in nuclear weapons and nuclear reactors is cesium-137, which is obtained from solutions of processed radioactive waste. During nuclear tests or accidents at nuclear power plants, this radionuclide is not averse to getting out into the environment. On nuclear submarines and icebreakers, it is widely used, so from time to time it can enter the waters of the oceans, polluting it.

Cesium-137 enters the human body when a person breathes or eats. Most of all, it likes to settle in muscle tissue (up to 80%), and the rest of its amount is distributed to other tissues and organs.

Cesium-137's closest friends (in terms of chemical composition) are such individuals as potassium and rubidium. In the course of evolution, mankind has learned to widely use cesium-137, for example, in medicine (tumor treatment), in the sterilization of food products, and also in measuring technology.

Looking back at history, it can be seen that industrial accidents have caused the largest releases of cesium into the environment. In 1950, an unplanned accident occurred at the Mayak enterprise, and cesium-137 in the amount of 12.4 PBC (Petabekkerel) broke free. However, the emissions of this dangerous radioactive element during the accident at the Chernobyl nuclear power plant were dozens of times greater - 270 PBC. Radioactive cesium-137, along with other no less dangerous elements, left the reactor torn apart by the explosion and flew into the atmosphere to fall back to the ground and mirrors of rivers and lakes over a large area and very far from the crash site. It is from this isotope that the suitability of soils for living and the ability to engage in agriculture depend. Together with other, no less dangerous radioactive elements, in 1986, cesium-137 made life in the 30-kilometer zone around the destroyed Chernobyl nuclear power plant deadly, and forced people to leave their homes and build their lives anew in a foreign land.

Radioactive isotope: Iodine-131

Iodine-131 has a half-life of 8 days, so this radionuclide poses the greatest danger to all living things within the first month after it enters the environment. Like caesium-137, iodine-131 is usually released after a test of a nuclear weapon or as a result of an accident at a nuclear power plant.

During the accident at the Chernobyl nuclear power plant, all the iodine-131 that was in the nuclear reactor was released into the atmosphere, so the very next day after the disaster, most people in the danger zone received doses of radioactive exposure by inhaling contaminated air and in between taking fresh , but already radioactive cow's milk. The cows had nothing to do with it, and no one raised a hand or opened their mouth to accuse them of having eaten on a pasture of radioactive grass. And even by urgently removing milk from sale, it would not have been possible to save the population from radioactive exposure, since about a third of the population living in the area of ​​the Chernobyl nuclear power plant ate milk obtained from personal cows.

It should be recalled that the contamination of the population with radioactive iodine has already taken place in history long before the Chernobyl disaster. So, in the 50s and 60s of the twentieth century, large-scale nuclear tests were carried out in the United States, and the results were not long in coming. In the state of Nevada, a large number of residents developed cancer, and the reason for this was a simple and unpretentious in all respects radioactive element - iodine-131.

Once in the human body, iodine-131 primarily accumulates in the thyroid gland, so this organ suffers the most. Even a small amount of radioactive iodine, which enters a person mainly with food (especially milk), adversely affects the health of this most important organ and can cause thyroid cancer in old age.

Radioactive isotope: Americium-241

Americium-241 has a fairly long half-life of 432 years. This silvery white metal is named after America, and has the extraordinary ability to glow in the dark thanks to alpha radiation. In industry, americium finds its application, for example, it allows you to create control and measuring instruments capable of measuring the thickness of sheet glass or aluminum and steel tape. In smoke detectors, this isotope also finds its use. A plate of lead only 1 cm thick can reliably protect a person from radioactive radiation emitted by americium. In medicine, americium helps to detect diseases of the human thyroid gland, due to the fact that stable iodine, located in the thyroid gland, begins to emit weak X-rays.

Plutonium-241 is present in significant amounts in weapons-grade plutonium, and it is he who is the main supplier of the americium-241 isotope. As a result of the decay of plutonium, americium gradually accumulates in the original substance.

For example, in freshly produced plutonium, only 1% americium can be found, and in plutonium that has already worked in a nuclear reactor, plutonium-241 can be present in an amount of 25%. And after a few decades, all the plutonium will decay and turn into americium-241. The lifetime of americium can be characterized as rather short, but with a rather high thermal yield and high radioactivity.

When released into the environment, americium-241 exhibits a very high mobility and is highly soluble in water. Therefore, when it enters the human body, these qualities allow it to quickly spread through the organs with the blood stream and settle in the kidneys, liver and bones. The easiest way to get americium into the human body is through the lungs during breathing. After the accident at the Chernobyl nuclear power plant, americium-241 was present not only in the poisoned air, but also settled in the soil, as a result of which it was able to accumulate in plants. For the next generations of the inhabitants of Ukraine, this was not a very happy event, given the 432-year half-life of this radioactive isotope.

Radioactive isotope: Plutonium

In 1940, the element Plutonium with serial number 94 was discovered, in the same year its isotopes were discovered: Plutonium-238, which has a half-life of 90 years, and Plutonium-239, which decays by half in 24 thousand years. In natural uranium, Plutonium-239 can be found in trace amounts, and it is formed there when the nucleus of Plutonium-238 captures one neutron. In cerium ore, extremely small amounts of another isotope of this radionuclide can be found: plutonium-244. This element appears to have formed during the formation of the Earth, with a half-life of 80 million years.

In appearance, Plutonium looks like a silvery metal, very heavy when held in hand. In the presence of even slight humidity, it quickly oxidizes and corrodes, but rusts much more slowly in pure oxygen or in the presence of dry air, since under direct exposure to oxygen, an oxide layer is formed on its surface, which prevents further oxidation. Due to its radioactivity, a piece of plutonium lying in the palm of your hand will be warm to the touch. And if you place such a piece in a thermally isolated space, it will heat up to a temperature in excess of 100 degrees Celsius without outside help.

From an economic point of view, plutonium is not competitive with uranium because low enriched uranium is much cheaper than reprocessing reactor fuel to produce plutonium. The cost of protecting plutonium is very high to prevent its theft in order to create a "dirty" bomb and commit a terrorist act. Added to this is the presence of significant stocks of weapons-grade uranium in the United States and Russia, which, by dilution, becomes suitable for the manufacture of commercial fuel.

Plutonium-238 has a very high thermal power and has a very high alpha radioactivity, is a very serious source of neutrons. Although plutonium-238 rarely contains more than one hundredth of the total plutonium, the amount of neutrons it emits makes it very unpleasant to handle.

Plutonium-239 is the only plutonium isotope suitable for making nuclear weapons. Pure plutonium-239 has a very small critical mass, about 6 kg, that is, even from absolutely pure plutonium it is possible to make a plutonium gun bomb. Due to the relatively short half-life, the decay of this radionuclide releases a significant amount of energy.

Plutonium-240 is the main contaminant of weapons-grade plutonium-239, as it has the ability to rapidly and spontaneously fission. When the content of this radionuclide in plutonium-239 is only 1%, so many neutrons are produced that it becomes impossible to make a stable cannon bomb from such a mixture without the use of implosion. For this reason, plutonium-240 is not allowed in standard weapons-grade plutonium in amounts greater than 6.5%. Otherwise, even when using implosion, the mixture will detonate earlier than it will be necessary for the mass extermination of similar creatures.

Plutonium-241 does not directly affect the usability of plutonium because it has a small neutron background and an average thermal power. This radionuclide decays within 14 years, after which it turns into americium-241, which creates a lot of heat and is not able to intensively divide. If the filling of an atomic bomb contains plutonium-241, it must be taken into account that after ten years of storage, the power of the warhead charge will decrease, and its self-heating will increase.

Plutonium-242 does not fissile well, and at a noticeable concentration it increases the neutron background and the required critical mass. Has the ability to accumulate in reprocessed reactor fuel.

Radioactive isotope: Strontium-90

Strontium-90 decays by half in 29 years and is a pure beta emitter produced by nuclear fission in nuclear weapons and nuclear reactors. After the decay of strontium-90, radioactive yttrium is formed. During the accident at the Chernobyl nuclear power plant, approximately 0.22 MCi of strontium-90 was released into the atmosphere, and it was he who became the object of close attention in the course of developing measures to protect the population of the cities of Chernobyl, Pripyat, as well as residents of settlements located in the 30-kilometer zone around the 4th block of the Chernobyl nuclear power plant from radiation. After all, during a nuclear explosion, 35% of all activity that got into the environment falls on strontium-90, and within 20 years after the explosion - 25% of the activity. However, long before the Chernobyl disaster, an accident occurred at the Mayak production association and a significant amount of the strontium-90 radionuclide entered the atmosphere.

Strontium-90 has a destructive effect on the human body. In chemical composition, it is very similar to calcium, and therefore, when it enters the body, it begins to destroy bone tissue and bone marrow, which leads to radiation sickness. Inside the human body, strontium-90 usually enters with food, and only half of it will take from 90 to 150 days to remove it. In history, the largest amount of this dangerous isotope was recorded in the body of the inhabitants of the northern hemisphere in the 60s of the XX century, after numerous nuclear tests conducted in 1961-1962. After the accident in Pripyat at the Chernobyl nuclear power plant, strontium-90 in large quantities got into water bodies, and the maximum permissible concentration of this radionuclide was recorded in the lower reaches of the Pripyat River in May 1986.



Radioiodine, or rather one of the radioactive (beta and gamma radiation) isotopes of iodine with a mass number of 131 with a half-life of 8.02 days. Iodine-131 is known primarily as a fission product (up to 3%) of uranium and plutonium nuclei, released during accidents at nuclear power plants.

Obtaining radioiodine. Where does it come from

The isotope iodine-131 does not occur in nature. Its appearance is associated only with the work of pharmacological production, as well as nuclear reactors. It is also released during nuclear tests or radioactive disasters. So it increased the content of the iodine isotope in sea and tap water in Japan, as well as in food. The use of special filters helped to reduce the spread of isotopes, as well as to prevent possible provocations at the facilities of the destroyed nuclear power plant. Similar filters are produced in Russia at the NTC Faraday company.

Irradiation of thermal neutron targets in a nuclear reactor makes it possible to obtain iodine-131 with a high content.

Characteristics of iodine-131. Harm

The half-life of radioiodine of 8.02 days, on the one hand, does not make iodine-131 highly active, and on the other hand, allows it to spread over large areas. This is also facilitated by the high volatility of the isotope. So - about 20% of iodine-131 were thrown out of the reactor. For comparison, cesium-137 is about 10%, strontium-90 is 2%.

Iodine-131 forms almost no insoluble compounds, which also helps distribution.

Iodine itself is a deficient element and the organisms of people and animals have learned to concentrate it in the body, the same applies to radioiodine, which is not good for health.

If we talk about the dangers of iodine-131 for humans, then we are talking primarily about the thyroid gland. The thyroid gland does not distinguish ordinary iodine from radioiodine. And with its mass of 12-25 grams, even a small dose of radioactive iodine leads to irradiation of the organ.

Iodine-131 causes mutations and cell death, with an activity of 4.6 10 15 Bq / gram.

Iodine-131. Benefit. Application. Treatment

In medicine, the isotopes iodine-131, as well as iodine-125 and iodine-132, are used to diagnose and even treat thyroid problems, in particular Graves' disease.

During the decay of iodine-131, a beta particle appears with a high flight speed. It is able to penetrate into biological tissues at a distance of up to 2 mm, which causes cell death. In the case of the death of infected cells, this causes a therapeutic effect.

Iodine-131 is also used as an indicator of metabolic processes in the human body.

Release of radioactive iodine 131 in Europe

On February 21, 2017, information appeared in the news bulletins that European stations in more than a dozen countries from Norway to Spain had noticed excess levels of iodine-131 in the atmosphere for several weeks. Assumptions have been made about the sources of the isotope - a release on

Iodine-131 - radionuclide with a half-life of 8.04 days, beta and gamma emitter. Due to its high volatility, almost all of the iodine-131 present in the reactor (7.3 MKi) was released into the atmosphere. Its biological action is associated with the functioning of the thyroid gland. Its hormones - thyroxine and triiodothyroyain - contain iodine atoms. Therefore, normally the thyroid gland absorbs about 50% of the iodine entering the body. Naturally, iron does not distinguish radioactive isotopes of iodine from stable ones. . The thyroid gland of children is three times more active in absorbing radioiodine that has entered the body. In addition, iodine-131 easily crosses the placenta and accumulates in the fetal gland.

The accumulation of large amounts of iodine-131 in the thyroid gland leads to thyroid dysfunction. The risk of malignant degeneration of tissues also increases. The minimum dose at which there is a risk of developing hypothyroidism in children is 300 rad, in adults - 3400 rad. The minimum doses at which there is a risk of developing thyroid tumors are in the range of 10-100 rad. The risk is greatest at doses of 1200-1500 rad. In women, the risk of developing tumors is four times higher than in men, in children three to four times higher than in adults.

The magnitude and rate of absorption, the accumulation of the radionuclide in organs, the rate of excretion from the body depend on age, gender, the content of stable iodine in the diet, and other factors. In this regard, when the same amount of radioactive iodine enters the body, the absorbed doses differ significantly. Especially large doses are formed in the thyroid gland of children, which is associated with the small size of the organ, and can be 2-10 times higher than the dose of irradiation of the gland in adults.

Effectively prevents the entry of radioactive iodine into the thyroid gland by taking stable iodine preparations. At the same time, the gland is completely saturated with iodine and rejects radioisotopes that have entered the body. Taking stable iodine even 6 hours after a single intake of 131I can reduce the potential dose to the thyroid gland by about half, but if iodine prophylaxis is postponed for a day, the effect will be small.

The entry of iodine-131 into the human body can occur mainly in two ways: inhalation, i.e. through the lungs, and orally through consumed milk and leafy vegetables.

The effective half-life of long-lived isotopes is determined mainly by the biological half-life, of short-lived isotopes by the 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 varies 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 of iodine-131 from the whole organism is 138 days, the thyroid gland is 138, the liver is 7, the spleen is 7, the skeleton is 12 days.

Long-term effects - thyroid cancer.