Radiation sickness is a disease that occurs from various types of ionizing radiation.
When irradiated at doses of 1-10 Gy, a typical form of acute radiation sickness develops, in which primary damage occurs bone marrow (bone marrow syndrome ). In the dose range of 10-20 Gy occurs intestinal (nausea, vomiting, bloody diarrhea, increased body temperature, complete paralytic ileus and bloating), at doses of 20-80 Gy - toxicemic (vascular) (disturbances in the intestines and liver, vascular paresis, tachycardia, hemorrhages, severe intoxication and cerebral edema) and at doses above 80 Gy - cerebral form of radiation sickness ( convulsive-paralytic syndrome, disturbance of blood and lymph circulation in the central nervous system, vascular tone and thermoregulation. Functional disorders of the digestive and urinary systems, progressive decrease in blood pressure).
Pathogenesis:
During the course of the disease, four phases are distinguished: 1) primary acute reaction; 2) imaginary clinical well-being (latent phase); 3) the height of the disease; 4) recovery.
1) Primary acute reaction phase The human body develops depending on the dose immediately after irradiation. Some excitement, headache, and general weakness occur. Then dyspeptic disorders occur (nausea, vomiting, loss of appetite), neutrophilic leukocytosis with a shift to the left, lymphocytopenia. Increased excitability of the nervous system, fluctuations in blood pressure, heart rate, etc. are observed. Activation of the pituitary-adrenal system leads to increased secretion of hormones from the adrenal cortex
Chechnikov.
The duration of the primary acute reaction phase is 1-3 days.
2) Phase of imaginary clinical well-being characterized by the inclusion of protective-compensatory reactions. In this regard, the health of patients becomes satisfactory, and clinically visible signs of the disease disappear. The duration of the latent phase depends on the radiation dose and ranges from 10-15 days to 4-5 weeks.
With relatively small doses (up to 1 Gy), the initial mild functional reactions do not develop into a full-blown clinical picture and the disease is limited to the fading phenomena of the initial reactions. In very severe forms of damage there is no latent phase at all.
However, at this time, damage to the blood system increases: lymphocytopenia progresses in the peripheral blood, and the content of reticulocytes and platelets decreases. Devastation (aplasia) develops in the bone marrow.
3) Phase of the height of the disease is characterized by the fact that the patients’ well-being sharply deteriorates again, weakness increases, body temperature rises, bleeding and hemorrhages appear in the skin, mucous membranes, gastrointestinal tract, brain, heart and lungs. As a result of metabolic disorders and dyspeptic disorders, body weight decreases sharply. Profound leukopenia, thrombocytopenia, and severe anemia develop; ESR increases; there is devastation in the bone marrow with initial signs of regeneration. Hypoproteinemia, hypoalbuminemia, increased residual nitrogen and decreased chloride levels are observed. Immunity is suppressed, resulting in the development of infectious complications, autoinfection and autointoxication.
The duration of the phase of pronounced clinical manifestations ranges from several days to 2-3 weeks. When exposed to a dose of more than 2.5 Gy without treatment, death is possible.
4) Recovery phase characterized by gradual normalization of impaired functions, the general condition of patients noticeably improves. Body temperature drops to normal, hemorrhagic and dyspeptic manifestations disappear, from the 2-5th month the function of the sweat and sebaceous glands normalizes, and hair growth resumes. Blood and metabolic parameters are gradually restored.
The recovery period covers 3-6 months; in severe cases, radiation damage can last for 1-3 years, and the disease may become chronic.
Long-term effects of radiation can develop after several years and are non-tumor or tumor in nature.
Non-tumor forms primarily include a reduction in life expectancy, hypoplastic conditions in hematopoietic tissue, mucous membranes of the digestive organs, respiratory tract, skin and other organs; sclerotic processes (liver cirrhosis, nephrosclerosis, atherosclerosis, radiation cataracts, etc.), as well as dishormonal conditions (obesity, pituitary cachexia, diabetes insipidus).
One of the common forms of long-term consequences of radiation injuries is the development of tumors in critical organs with α- and β-radiation, as well as radiation leukemia.
2. Hypoglycemic conditions. Kinds. Mechanisms of development. Consequences for the body. Hypoglycemic coma.
Hypoglycemia is a decrease in blood sugar levels below normal. It develops as a result of insufficient intake of sugar into the blood, its accelerated elimination, or as a result of both.
Hypoglycemic reaction- the body’s response to an acute temporary decrease in the level of HPC below normal.
Causes:
♦ acute hypersecretion of insulin 2-3 days after the start of fasting;
♦ acute hypersecretion of insulin several hours after a glucose load (for diagnostic or therapeutic purposes, as well as after overeating sweets, especially in elderly and senile people).
Manifestations: low level of GPC, slight feeling of hunger, muscle tremors, tachycardia. These symptoms are mild at rest and become apparent with additional physical activity or stress.
One of the characteristic features of radiation injuries is that in people, 10-20 years or more after irradiation, various changes, which are called long-term consequences of irradiation, again appear in the “recovered” and seemingly completely recovered from radiation injury in the body. A feature of diseases related to long-term consequences is that they occur after both local and general (internal and external) irradiation. There are somatic and genetic long-term consequences. Main somatic The consequences of irradiation are a reduction in life expectancy, the occurrence of leukemia, malignant tumors, cataracts, and sterility.
There are non-tumor and tumor forms of long-term consequences.
Non-tumor forms include three types of pathological processes:
1. Hypoplastic conditions - develop mainly in hematopoietic tissue, mucous membranes of the digestive organs, respiratory tract, skin and other organs. These disorders occur with the accumulation of high doses of radiation (3-10 Gy) both during external gamma irradiation and damage from incorporated radionuclides. The main disorders are: hypo- or hyperchromic anemia, leukopenia, atrophy of the mucous membrane of the stomach, intestines, hypo- or anacid gastritis, atrophy of the gonads and infertility (sterility).
2. Sclerotic processes . Extensive and early damage to the vascular network of irradiated organs occurs, and focal or diffuse growths of connective tissue develop in the place of dead parenchymal cells. Main disorders: liver cirrhosis, nephrosclerosis, pneumosclerosis, atherosclerosis, radiation dermatitis, radiation cataracts, bone necrosis, damage to the nervous system.
3. Dishormonal conditions develop without visible dose dependence. Manifestations of dishormonal conditions include obesity, pituitary cachexia, diabetes insipidus, cystic changes in the ovaries, pathological changes in sexual cycles, hyperplasia of the uterine mucosa, parenchyma of the mammary glands (which can lead to the development of tumors), lesions of the thyroid gland (hypothyroidism, neoplasms), diabetes diabetes, etc.
Tumor forms. These include tumors that develop by a direct mechanism (occur more often during irradiation with incorporated alpha and beta emitters) - tumors of bones, liver, kidneys, lungs, and skin. Another type is dishormonal tumors due to an imbalance in the function of the endocrine glands - tumors of the uterus, ovaries, prostate jelly, and the endocrine glands themselves. And finally, there are tumors of complex origin that arise as a result of a combination of direct and dyshormonal mechanisms - leukemia, tumors of the mammary glands.
Let's look at the main somatic long-term consequences. The most common of the long-term effects is reduced life expectancy. A direct proportional relationship has been revealed between the radiation dose and the degree of shortening of the life cycle. It has been experimentally proven that in humans, with a single exposure to radiation, the reduction in life expectancy is 0.1-1.5 days for each millisievert. If radiation acts not immediately, but for a long time, throughout life, continuously, then a reduction in life can be recorded, starting with total weekly doses of 10 rad of gamma radiation or 1 rad of neutron irradiation. The shortening of life of survivors of the atomic bombings in Hiroshima and Nagasaki is due to an increase in the incidence of leukemia and tumors. The UN Commission report for 1964 notes that the incidence of leukemia in Japan from 1946 to 1960 increased from 10.7 to 28 per 1 million inhabitants. Moreover, the probability of illness decreased with increasing distance from the epicenter of the explosion, i.e. with dose reduction.
Malignant neoplasms under the influence of radiation can occur in almost all organs. Most often observed leukemia, the development of which occurs 5-25 years after irradiation. The incidence of leukemia in irradiated patients increases by 5-10 times compared to non-irradiated patients. In the range of 3-15 Gy, each Gy corresponds to an increase in incidence of 50 cases per 1 million people per year.
Later, other cancers arise (thyroid, breast, ovarian, stomach and lung cancer), mainly as a result of general radiation exposure. Tumors of the skin and bones are the result of local irradiation - external (skin) or internal (bones). With chronic exposure to low doses, the development of malignant tumors is 3-10 times lower than with a single exposure to the same dose. Due to anatomical and physiological characteristics and great sensitivity to the effects of ionizing radiation, the children's body is at greater risk (as can be seen in the example of thyroid cancer in children). The time it takes for cancer to appear in children is also reduced compared to adults.
Emergence cataracts (clouding) of the lens– a typical long-term consequence of total body irradiation or local irradiation of the eye and lens. Cataracts appear especially often during prolonged neutron irradiation. In Hiroshima, cataracts occurred in 25-30% of cases in those who were 4 km from the epicenter of the explosion (after several months and up to 12 years or more). The minimum threshold dose of X-rays for a single exposure is 2 Gy; with chronic exposure over several years of irradiation, cataracts develop at doses exceeding 0.3 Sv per year.
Long-term effects of radiation also include nephrosclerosis, developing as a result of damage to renal tissue and its replacement with connective tissue. A persistent increase in blood pressure, characteristic of radiation injury, largely depends on the development of nephrosclerosis.
Radiobiological effects of irradiation of a living organism are divided into threshold (non-stochastic) and non-threshold (stochastic). Radiation effects of a non-stochastic nature should be considered, first of all, acute radiation sickness, local skin damage (burns), radiation cataracts, sterilization, and degenerative damage to various tissues. In this case, there is a certain threshold value of the radiation dose (for example, with a one-time exposure to radiation of 100 rad), below which no visible effect of radiation is observed.
Disorders such as tumors of various locations, leukemia, genetic effects, mental retardation, and deformities are stochastic and non-threshold in nature. The probability of occurrence of these lesions exists at the lowest doses of radiation.
Effect of ionizing radiation on lipids. Lipids are fat-like organic substances that are insoluble in water. They are part of biological membranes and also play the role of reserve nutrients in the body, accumulating in certain parts of the body.
Lipids are the basis of cell membranes. Many cellular metabolic processes occur in membranes. Therefore, lipid peroxidation, which can be caused by irradiation, entails a change in biochemical processes in the cell, and a violation of the integrity of the outer membrane leads to a shift in the ionic balance of the cell.
The effect of ionizing radiation on lipids and the changes that can occur in cells during irradiation are reflected in Appendix B1.
The effect of ionizing radiation on carbohydrates. Carbohydrates (sugars) are a source of energy in the body. As an energy reserve, they are present in the human body in the form of glycogen. The general formula of carbohydrates can be represented as C n (H 2 O) m. Most natural carbohydrates are derivatives of cyclic forms of monosaccharides. Under the influence of radiation, a hydrogen atom can be separated from a carbohydrate molecule. In this case, free radicals are formed, and then peroxides. As a result of irradiation, it is possible to synthesize an organic substance from the breakdown products of carbohydrates, which inhibits the synthesis of DNA and protein and suppresses cell division.
The destruction of carbohydrates reduces the reserves of substances that are sources of energy in the body, which can affect the functioning of many vital systems of the body.
The effect of ionizing radiation on tissues, organs and organ systems. Groups of cells in a multicellular organism, similar in origin, structure and function, together with the intercellular substance form tissues.
In humans, there are four types of tissues: epithelial, connective, muscle and nervous. Tissues form organs (heart, kidneys, liver, stomach, etc.). The cells that make up a tissue or organ are dependent on each other and on the environment.
Organ systems (skeletal, digestive, hematopoietic, etc.) provide the vital functions of the body.
The response of a human tissue, organ or organ system to radiation exposure depends on the disturbances that appear in the cells from which they are built. However, the reaction to the action of ionizing radiation is not limited to the sum of the effects that occur when cells are irradiated. The size of the irradiated area of the body, the features of its structure and functioning, the intensity of blood circulation and other factors also affect the radiosensitivity of a tissue, organ or organ system
Radiosensitivity of organs and tissues. Radiation effects that occur in human biological tissues and organs are directly related to damage and sometimes death of the cells from which they are formed. At the same time, cells have a unique ability to self-heal, and with small doses of radiation, tissues and organs are able to restore their functions.
The relative sensitivity of human tissues and organs to the action of ionizing radiation (their radiosensitivity), as noted earlier, is taken into account using weighting coefficients for tissues and organs (W T).
Based on their ability to divide, all cells of the human body are divided into dividing, weakly dividing and non-dividing (Appendix B3). At an early stage of organism development, all cells are capable of dividing. During the development of an organism, differences arise between cells, and some cells lose the ability to divide. Dividing cells are less resistant to ionizing radiation than non-dividing cells.
The organs of hematopoiesis (bone marrow, lymph nodes, spleen) and digestion (mucous membranes of the stomach and intestines), gonads (testes and ovaries) consist of rapidly dividing cells and are among the most radiosensitive organs. For the same reason, a mature organism is more resistant to radiation than the developing organism of a child or teenager
At high levels of absorbed doses, serious damage occurs in human tissues and organs. Appendix B4 describes disturbances that have mainly been observed at high levels of absorbed doses of gamma or x-ray radiation resulting from a single external exposure to radiation on the human body.
In patients who have suffered acute radiation sickness, residual effects may persist for a long time, sometimes throughout their lives, and long-term consequences may develop.
Residual effects most often manifest themselves as hypoplasia and degeneration of tissues that are most severely damaged by irradiation. They are consequences of incomplete restoration of the damage that underlay the acute lesion: leukopenia, anemia, immunity disorders, sterility, etc. In contrast, long-term consequences are the development of new pathological processes, the signs of which were absent in the acute period, such as cataracts, sclerotic changes, degenerative processes, neoplasms, reduction in life expectancy. The offspring of irradiated parents may develop genetic consequences as a result of mutations in germ cells.
Among the forms of distant radiation pathology the following will be considered:
Non-tumor long-term consequences;
Carcinogenic effects;
Reduced life expectancy.
Non-tumor long-term effects of radiation
Non-tumor (non-stochastic) long-term consequences are among the deterministic effects of radiation, the severity of which depends mainly on the degree of deficiency in the number of cells in the corresponding tissues (hypoplastic processes). The most important components of the complex of causes that determine the development of long-term consequences of radiation include damage to small blood vessels and microcirculation disorders, leading to the development of tissue hypoxia and secondary damage to parenchymal organs. Cellular deficiency in tissues in which proliferation is insufficient to replenish the number of cells killed after irradiation (loose connective tissue, gonads, etc.), and the persistence of changes that occurred during irradiation in cells of non-proliferating and slowly proliferating tissues are also significant.
In most non-critical tissues, severe long-term effects are unlikely to occur after total short-term exposure. Doses that are not absolutely lethal during general irradiation, as a rule, do not exceed the tolerance threshold for non-critical tissues and cannot lead to a significant deficiency of cells in them (the lens and testes can be called exceptions to this general rule). In critical tissues, regenerative processes, if the organism does not die, usually restore the cellular composition quite quickly. Therefore, long-term consequences that develop due to cell deficiency are more typical for local irradiation, when doses exceeding their tolerance can be absorbed in relatively radioresistant tissues. The development of these changes in interaction with natural age-related processes determines the development of functional disorders. Long-term consequences of radiation injury can manifest themselves as functional disorders of regulatory systems: nervous, endocrine, cardiovascular (astheno-neurotic syndrome, vegetative-vascular dystonia).
Long-term non-stochastic effects also include some hyperplastic processes that develop as a compensatory reaction to a decrease in the functions of a certain type of cell. Such reactions are characteristic of endocrine organs. For example, focal hyperplasia of the thyroid tissue with damage to other parts of it in the case of incorporation of radioactive iodine.
Carcinogenic effects of radiation
Radiation carcinogenesis is one of the stochastic effects. The main cause of malignant transformation of an irradiated cell is non-lethal damage to the genetic material. At the beginning of the study of radiation carcinogenesis, the prevailing idea was that the direct cause of malignant transformation of a cell was a mutation that arose as a result of the absorption of a portion of radiation energy by the corresponding part of the cell's genome. While this may be the case in some cases, other possibilities are more likely.
The most common hypothesis is that nuclear DNA instability increases under the influence of radiation. In the process of repairing its non-lethal damage, conditions arise that promote the inclusion of an oncovirus into the genome of a somatic cell or the activation of an oncovirus that was already in a repressed state as part of the genome, followed by cancerous transformation.
Malignant transformation of a cell that remains viable after irradiation can be facilitated by its contact with a large amount of cellular detritus. Due to damage to membrane structures, the sensitivity of cells to regulatory influences from hormones, inhibitors, etc. may change.
Disorders of hormonal regulation are factors contributing to the malignant transformation of cells. This factor is especially important in case of internal radioactive contamination, when radionuclides affect the gland for a long time, disrupting its production of hormones that affect the functions of other organs. As a result, conditions are created for the occurrence of a hormone-dependent tumor (for example, a pituitary tumor in animals with hypoplasia of the thyroid gland caused by the introduction of 131I). The thyroid gland is considered as a critical organ in the formation of long-term pathology when nuclear fission products enter the body.
Immune disorders caused by radiation also contribute to the development of a tumor, as a result of which the development of a tumor not only from cells transformed by radiation, but also from cells in which mutations arose spontaneously or under the influence of other factors is facilitated.
The latent period between radiation exposure and the appearance of a tumor is, on average, 5 - 10 years, but in some cases it can reach 35 years (breast cancer).
The probability of developing a tumor as a result of radiation exposure is estimated as one additional case per 20 people exposed to a dose of 1 Gy. The relative risk of developing a malignant neoplasm throughout life is higher for those exposed in childhood. The yield of tumors per unit dose depends on a number of factors, such as the quality of radiation (the RBE of neutrons for the risk of malignant neoplasms after irradiation at low doses can exceed 10), dose rate, etc.
Shortened life expectancy
An integral indicator of the health status of a population can be the average life expectancy (ALS) of the individuals composing this population. An important manifestation of the long-term consequences of radiation is precisely the reduction in life expectancy.
In rodents it ranges from 1 to 5% per 1 Gy. With long-term exposure to low doses of gamma radiation, a reduction in life expectancy in rodents was observed starting from a daily dose of 0.01 Gy, and the total accumulated dose, after which a reduction in life expectancy began to reliably manifest itself, was at least 2 Gy (for neutrons, the values of the daily dose and total accumulated doses at which life expectancy decreased were an order of magnitude smaller).
When analyzing the phenomenon of lifespan reduction, it is not possible to identify any typical pathological process that directly leads irradiated animals to premature death. In cases where the cause of death in individual individuals could be associated with some specific pathological process, it could be a vascular crisis, a neoplasm, sclerotic changes, leukemia, etc.
The main reason for the reduction in life expectancy after irradiation at sublethal doses is currently considered to be damage to capillaries and small arterioles, microcirculation disorders leading to hypoxia and death of parenchymal cells, mainly in the immune organs and endocrine glands. In part, the reduction in life expectancy may be due to the more frequent development of malignant neoplasms in irradiated patients.
The reduction in human life expectancy can be, according to various estimates, from 100 to 1000 days per 1 Gy with a single short-term exposure and about 8 days with chronic exposure. At the same time, as already noted, at doses below 2 Gy the very presence of a reduction in life expectancy is not recognized by all researchers.
Life expectancy of radiologists in the period 1932 - 1942. was, on average, 60.5 years versus 65.7 years for doctors of other specialties, that is, it was 5.2 years less. Calculations show that over 35 years of practice, the dose accumulated by radiologists at that time could be 5 Gy.
The most common causes of premature death were neoplasms, including leukemia, the mortality rate from which was 3 times higher than among other adult populations, degenerative changes, infectious processes, etc. After 1945, as a result of the introduction of anti-radiation protection measures, differences in The life expectancy of radiologists and doctors of other specialties has disappeared.
A person receives the bulk of ionizing radiation from natural sources of radiation. Most of them are such that it is absolutely impossible to avoid exposure to radiation from them. Throughout the history of the Earth, different types of radiation reach the Earth's surface from space and come from radioactive substances located in the earth's crust.
A person is exposed to radiation in two ways. Radioactive substances can be outside the body and irradiate it from the outside; in this case we talk about external irradiation
. Or they may end up in the air a person breathes, in food or water and enter the body. This method of irradiation is called internal.
Radiation by its very nature is harmful to life. Low doses of radiation can “trigger” an incompletely understood chain of events leading to cancer or genetic damage. At high doses, radiation can destroy cells, damage organ tissue and cause rapid death of the body.
Damage caused by high doses of radiation usually appears within hours or days. Cancers, however, appear many years after irradiation - usually not earlier than one or two decades. And congenital malformations and other hereditary diseases caused by damage to the genetic apparatus, by definition, appear only in the next or subsequent generations: these are children, grandchildren and more distant descendants of an individual exposed to radiation.
While identifying the immediate (“acute”) effects of high doses of radiation is not difficult, detecting long-term effects of low doses of radiation is almost always very difficult. This is partly due to the fact that they take a very long time to manifest. But even if some effects are discovered, it is also necessary to prove that they are explained by the action of radiation, since both cancer and damage to the genetic apparatus can be caused not only by radiation, but also by many other reasons.
To cause acute damage to the body, radiation doses must exceed a certain level, but there is no reason to believe that this rule applies in the case of consequences such as cancer or damage to the genetic apparatus. At least theoretically, the smallest dose is enough for this. However, at the same time, no dose of radiation leads to these consequences in all cases. Even with relatively large doses of radiation, not all people are doomed to these diseases: the repair mechanisms operating in the human body usually eliminate all damage. In the same way, any person exposed to radiation does not necessarily have to develop cancer or become a carrier of hereditary diseases; however, the probability or risk of such consequences occurring is greater for him than for a person who has not been irradiated. And this risk is greater, the higher the radiation dose.
Acute damage to the human body occurs with large doses of radiation. Generally speaking, radiation has a similar effect only starting from a certain minimum, or “threshold” dose of radiation.
The response of human tissues and organs to irradiation is not the same, and the differences are very large. The magnitude of the dose, which determines the severity of damage to the body, depends on whether the body receives it at once or in several doses. Most organs manage to heal radiation damage to one degree or another and therefore tolerate a series of small doses better than the same total radiation dose received at one time.
Impact of ionizing radiation on living cells
Charged particles. A- and b-particles penetrating into the tissues of the body lose energy due to electrical interactions with the electrons of the atoms near which they pass. (g-rays and x-rays transfer their energy to matter in several ways, which ultimately also lead to electrical interactions.)
Electrical Interactions. Within a time of about ten trillionths of a second after the penetrating radiation reaches the corresponding atom in the tissue of the body, an electron is torn off from this atom. The latter is negatively charged, so the rest of the initially neutral atom becomes positively charged. This process is called ionization. The detached electron can further ionize other atoms.
Physico-chemical changes. Both the free electron and the ionized atom usually cannot remain in this state for long and, over the next ten billionths of a second, participate in a complex chain of reactions that result in the formation of new molecules, including such extremely reactive ones as “free radicals.”
Chemical changes. Over the next millionths of a second, the resulting free radicals react with each other and with other molecules and, through a chain of reactions not yet fully understood, can cause chemical modification of biologically important molecules necessary for the normal functioning of the cell.
Biological effects. Biochemical changes can occur within seconds or decades after irradiation and cause immediate cell death or changes in cells that can lead to cancer.
Of course, if the radiation dose is high enough, the exposed person will die. In any case, very large doses of radiation on the order of 100 Gy cause such severe damage to the central nervous system that death usually occurs within a few hours or days. At doses ranging from 10 to 50 Gy for whole-body irradiation, damage to the central nervous system may not be severe enough to be fatal, but the exposed person will still likely die within one to two weeks from gastrointestinal hemorrhages . With even lower doses, serious damage to the gastrointestinal tract may not occur or the body can cope with them, and yet death can occur within one to two months from the moment of irradiation, mainly due to the destruction of red bone marrow cells - the main component of the body's hematopoietic system : from a dose of 3-5 Gy with whole body irradiation, approximately half of all irradiated people die. Thus, in this range of radiation doses, large doses differ from smaller ones only in that death occurs earlier in the first case, and later in the second.
In the human body, ionizing effects cause a chain of reversible and irreversible changes. The triggering mechanism for the effect is the processes of ionization and excitation of atoms and molecules in tissues. An important role in the formation of biological effects is played by free radicals H and OH, which are formed as a result of radiolysis of water (the human body contains up to 70% water). Possessing high activity, they enter into chemical reactions with molecules of protein, enzymes and other elements of biological tissue, which leads to disruption of biochemical processes in the body. The process involves hundreds and thousands of molecules that are not affected by radiation. As a result, metabolic processes are disrupted, tissue growth slows down and stops, and new chemical compounds appear that are not characteristic of the body. This leads to disruption of the vital functions of individual organs and systems of the body. Under the influence of ionizing radiation, the body experiences dysfunction of the hematopoietic organs, increased permeability and fragility of blood vessels, gastrointestinal disorder, decreased body resistance, exhaustion, degeneration of normal cells into malignant ones, etc. The effects develop over different periods of time: from fractions of seconds up to many hours, days, years.
Radiation effects are usually divided into somatic and genetic. Somatic effects manifest themselves in the form of acute and chronic radiation sickness, local radiation damage, such as burns, as well as in the form of long-term reactions of the body, such as leukemia, malignant tumors, and early aging of the body. Genetic effects may appear in subsequent generations.
Acute lesions develop with a single uniform gamma irradiation of the whole body and an absorbed dose of more than 0.25 Gy. At a dose of 0.25...0.5 Gy, temporary changes in the blood may be observed, which quickly normalize. In the dose range of 0.5...1.5 Gy, a feeling of fatigue occurs, less than 10% of those exposed may experience vomiting and moderate changes in the blood. At a dose of 1.5...2.0 Gy, a mild form of acute radiation sickness is observed, which is manifested by a prolonged decrease in the number of lymphocytes in the blood (lymphopenia), vomiting is possible on the first day after irradiation. No deaths are recorded.
Radiation sickness of moderate severity occurs at a dose of 2.5...4.0 Gy. Almost everyone in the first day experiences nausea, vomiting, the content of leukocytes in the blood sharply decreases, subcutaneous hemorrhages appear, in 20% of cases death is possible, death occurs 2...6 weeks after irradiation.
At a dose of 4.0...6.0 Gy, a severe form of radiation sickness develops, leading in 50% of cases to death within the first month. At doses exceeding 6.0...9.0 Gy, in almost 100% of cases the extremely severe form of radiation sickness ends in death due to hemorrhage or infectious diseases.
The data given refers to cases where there is no treatment. Currently, there are a number of anti-radiation agents that, with complex treatment, can eliminate death at doses of about 10 Gy.
Chronic radiation sickness can develop with continuous or repeated exposure to doses significantly lower than those that cause the acute form. The most characteristic signs of the chronic form are changes in the blood, disorders of the nervous system, local skin lesions, damage to the lens, and decreased immunity of the body.
The degree of exposure to radiation depends on whether the exposure is external or internal (when a radioactive isotope enters the body). Internal exposure is possible through inhalation, ingestion of radioisotopes and their penetration into the human body through the skin. Some substances are absorbed and accumulated in specific organs, resulting in high local doses of radiation. For example, calcium, radium, strontium accumulate in bones, iodine isotopes cause damage to the thyroid gland, rare earth elements - mainly liver tumors. Cesium and rubidium isotopes are evenly distributed, causing inhibition of hematopoiesis, damage to the testes, and soft tissue tumors. In internal irradiation, the most dangerous are the alpha-emitting isotopes of polonium and plutonium.
Basic radiation dose limits and permissible levels are established for the following categories of exposed persons:
Personnel - persons working with man-made sources (group A) or who, due to working conditions, are in the sphere of their influence (group B);
The entire population, including personnel, is outside the scope and conditions of their production activities.
For categories of exposed persons, three classes of standards are established: main dose limits (Table 1) and permissible levels corresponding to the main dose limits and control levels.
Dose equivalent H - absorbed dose in an organ or tissue D, multiplied by the appropriate weighting factor for a given radiation W:
H=W*D
The unit of measurement for equivalent dose is J/kg, which has the special name sievert (Sv).
Table 1
Basic dose limits (extracted from NRB-99)
|
Standardized values |
Dose limits, mSv |
|
|
Staff (group A)* |
Population |
|
|
Effective dose |
20 mSv per year on average for any consecutive 5 years, but not more than 50 mSv per year |
1 mSv per year on average for any consecutive 5 years, but not more than 5 mSv per year |
|
Equivalent dose per year in: |
||
|
lens of the eye *** |
||
|
skin**** |
||
|
Hands and feet |
||
* Simultaneous irradiation is allowed up to the specified limits for all standardized values.
** The main dose limits, like all other permissible levels of exposure of personnel in group B, are equal to 1/4 of the values for personnel in group A. Further in the text, all standard values for the category of personnel are given only for group A.
*** Refers to a dose at a depth of 300 mg/cm2.
**** Refers to the average value over an area of 1 cm 2 in the basal layer of skin with a thickness of 5 mg/cm 2 under the cover layer with a thickness of 5 mg/cm 2 . On the palms the thickness of the coating layer is 40 mg/cm. The specified limit allows irradiation of all human skin, provided that within the average irradiation of any 1 cm of skin area, this limit is not exceeded. The dose limit when irradiating the skin of the face ensures that the dose limit to the lens from beta particles is not exceeded.
The values for photons, electrons and ions of any energy are 1, for a - particles, fission fragments, heavy nuclei - 20.
Effective dose is a value used as a measure of the risk of long-term consequences of irradiation of the entire human body and its individual organs, taking into account their radiosensitivity. It represents the sum of the products of the equivalent dose in an organ (tissue) by the corresponding weighting factor for a given organ or tissue:
Basic radiation dose limits do not include doses from natural and medical sources of ionizing radiation, as well as doses due to radiation accidents. There are special restrictions on these types of exposure.
table 2
Permissible levels of general radioactive contamination of working surfaces of skin (during a work shift) (extracted from NRB-96), workwear and personal protective equipment, particles / (cm 2 * min)
|
Object of pollution |
b -Active nucliles |
b -Active nuclides |
|
|
Separate |
other |
||
|
Intact skin, towels, special underwear, the inner surface of the front parts of personal protective equipment |
2 |
2 |
200 |
|
Basic workwear, the inner surface of additional personal protective equipment, the outer surface of safety shoes |
5 |
20 |
2000 |
|
The outer surface of additional personal protective equipment that can be removed in sanitary locks |
50 |
200 |
10000 |
|
Surfaces of permanent premises for personnel and equipment located in them |
5 |
20 |
2000 |
|
Surfaces of premises for periodic stay of personnel and equipment located in them |
50 |
200 |
10000 |
The effective dose for personnel should not exceed 1000 mSv over a working period (50 years), and 70 mSv for the population over a lifetime (70 years). In addition, permissible levels of general radioactive contamination of working surfaces, skin (during a work shift), special clothing and personal protective equipment are set. In table Table 2 shows the numerical values of permissible levels of general radioactive contamination.
2. Ensuring safety when working with ionizing radiation
All work with radionuclides is divided into two types: work with sealed sources of ionizing radiation and work with open radioactive sources.
Sealed sources of ionizing radiation are any sources whose design prevents the entry of radioactive substances into the air of the working area. Open sources of ionizing radiation can pollute the air in the work area. Therefore, requirements for safe work with closed and open sources of ionizing radiation in production have been separately developed.
Ensuring radiation safety requires a set of diverse protective measures, depending on the specific conditions of working with sources of ionizing radiation, as well as on the type of source.
The main danger of closed sources of ionizing radiation is external exposure, determined by the type of radiation, the activity of the source, the radiation flux density and the radiation dose created by it and the absorbed dose. Protective measures to ensure radiation safety conditions when using sealed sources are based on knowledge of the laws of propagation of ionizing radiation and the nature of their interaction with matter. The main ones are the following:
1. The dose of external radiation is proportional to the radiation intensity and duration of action.
2. The intensity of radiation from a point source is proportional to the number of quanta or particles appearing in them per unit time, and inversely proportional to the square of the distance.
3. Radiation intensity can be reduced using screens.
From these laws follow the basic principles of ensuring radiation safety: reducing the power of sources to minimum values (protection in quantity); reduction of time spent working with sources (time-protected); increasing the distance from the source to workers (protection by distance) and shielding radiation sources with materials that absorb ionizing radiation (shielding).
Quantity protection involves working with minimal quantities of radioactive substances, i.e. proportionally reduces the radiation power. However, the requirements of the technological process often do not allow reducing the amount of radioactive substance in the source, which limits the practical application of this protection method.
Time protection is based on reducing the time spent working with the source, which makes it possible to reduce radiation doses to personnel. This principle is especially often used in the direct work of personnel with low activities.
Protection by distance is a fairly simple and reliable method of protection. This is due to the ability of radiation to lose its energy in interactions with matter: the greater the distance from the source, the more processes of interaction of radiation with atoms and molecules, which ultimately leads to a decrease in the radiation dose to personnel.
Shielding is the most effective way to protect against radiation. Depending on the type of ionizing radiation, various materials are used to make screens, and their thickness is determined by the radiation power. The best screens for protection against X-ray and gamma radiation are materials with a large 2, for example lead, which allows you to achieve the desired effect in terms of attenuation factor with the smallest screen thickness. Cheaper screens are made from leaded glass, iron, concrete, barryte concrete, reinforced concrete and water.
According to their purpose, protective screens are divided into five groups:
1. Protective screen containers in which radioactive drugs are placed. They are widely used in the transportation of radioactive substances and radiation sources.
2. Protective Screens for equipment. In this case, the screens completely surround all working equipment when the radioactive drug is in the working position or when the high (or accelerating) voltage is turned on at the source of ionizing radiation.
3. Mobile protective screens. This type of protective screens is used to protect the workplace in various areas of the work area.
4; Protective screens mounted as parts of building structures (walls, floors and ceilings, special doors, etc.). This type of protective screens is intended for protecting premises where personnel are constantly located and the surrounding area.
5. Screens of personal protective equipment (plexiglass shield, sight glasses of pneumatic suits, leaded gloves, etc.).
Protection from open sources of ionizing radiation provides both protection from external radiation and protection of personnel from internal radiation associated with the possible penetration of radioactive substances into the body through the respiratory system, digestion or through the skin. All types of work with open sources of ionizing radiation are divided into 3 classes. The higher the class of work performed, the stricter the hygienic requirements for protecting personnel from internal overexposure.
Methods for protecting personnel are as follows:
1. Use of protection principles applied when working with radiation sources in a closed form.
2. Sealing of production equipment in order to isolate processes that may be sources of radioactive substances entering the external environment.
3. Planning activities. The layout of the premises assumes maximum isolation of work with radioactive substances from other premises and areas that have a different functional purpose. Premises for class I work must be located in separate buildings or an isolated part of the building with a separate entrance. Premises for class II work must be located isolated from other premises; Class III work can be carried out in separate specially designated rooms.
4. Use of sanitary and hygienic devices and equipment, use of special protective materials.
5. Use of personal protective equipment for personnel. All personal protective equipment used for working with open sources is divided into five types: overalls, safety shoes, respiratory protection, insulating suits, and additional protective equipment.
6. Compliance with personal hygiene rules. These rules provide for personal requirements for those working with sources of ionizing radiation: prohibition of smoking in the workplace; zone, thorough cleaning (decontamination) of the skin after finishing work, conducting radiation monitoring of contamination of work clothes, safety shoes and skin. All these measures involve eliminating the possibility of radioactive substances entering the body.
Radiation safety services.
The safety of working with sources of ionizing radiation at enterprises is controlled by specialized services - radiation safety services are staffed by persons who have undergone special training in secondary and higher educational institutions or specialized courses of the Ministry of Atomic Energy of the Russian Federation. These services are equipped with the necessary instruments and equipment that allow them to solve the tasks assigned to them.
The services carry out all types of monitoring based on existing methods, which are constantly being improved as new types of radiation monitoring devices are released.
An important system of preventive measures when working with sources of ionizing radiation is radiation monitoring.
The main tasks determined by national legislation on monitoring the radiation situation, depending on the nature of the work carried out, are as follows:
Monitoring the dose rate of X-ray and gamma radiation, fluxes of beta particles, nitrons, corpuscular radiation in workplaces, adjacent rooms and on the territory of the enterprise and the observed area;
Monitoring the content of radioactive gases and aerosols in the air of workers and other premises of the enterprise;
Control of individual exposure depending on the nature of the work: individual control of external exposure, control of the content of radioactive substances in the body or in a separate critical organ;
Control over the amount of radioactive substances released into the atmosphere;
Control over the content of radioactive substances in wastewater discharged directly into the sewer system;
Control over the collection, removal and neutralization of radioactive solid and liquid waste;
Monitoring the level of pollution of environmental objects outside the enterprise.