Radioactivity and its effect on the human body (Steel Yuri G. Grigoriev)

Radioactivity and its effect on the human body.

 
INTRODUCTION

1.Vidy ionizing radiation

2.Yavlenie radioactivity. The law of radioactive decay

3.Edinitsy measurement of radioactivity

4.Deystvie of ionizing radiation on the human body

5.Osnovnye principles of radiation safety

5.1.Trebovaniya for protection against natural exposure in industrial environments

5.2.Trebovaniya to limit the exposure of the population

5.3.Kriterii intervention in the contaminated territories

5.4. Some measure of protection against external and internal exposure

5.6. Calculation of protection and protective materials

REFERENCES

 INTRODUCTION

Radioactive or, in other words, ionizing radiation combine different physical nature of radiation types. The similarity between them is that they all have a high energy exercise their biological effects through the effects of ionization and the subsequent chemical reactions in biological structures of cells that can lead to its demise. [1] It is important to note that ionizing radiation is not perceived by the senses: we do not see, not hear, and feel no effect on our body.

Ionizing radiation consists of particles (charged and uncharged) and the quantum of electromagnetic energy. With these people in any region of the globe occurs daily. This, above all, the so-called background radiation of the Earth, which is made up of three components:

- Cosmic rays coming to Earth from outer space;

- Radiation from being in the soil, building materials, air and water of natural radionuclides (NRN);

- Radiation from natural radioactive substances, which are food and water to get inside the body, tissues are fixed and can be stored in the body throughout his life.

In addition, a person meets with artificial sources of radiation, commonly used in the national economy. This includes, for example, ionizing radiation used for medical purposes.

The main contribution to natural background radiation environment is made radioactive substances containing radionuclides of the uranium 238, thorium 232, potassium 40, and the emission of radionuclides produced in the interaction of cosmic rays with the elements of the atmosphere and the Earth's crust. This is mainly tritium, carbon-14, beryllium 7, Si 32, Na 22. For mid-latitude cosmic background creates exposure dose on the surface of 1 to 3 mR / hr

In the natural background radiation emit so-called technological change natural background radiation, which is radiation from natural sources, have undergone some changes as a result of human activities. Extracted minerals (phosphates, oil shale, oil, gas and entrained with the water reservoir) render to the surface many of the chemicals, including natural radionuclides. Their quantitative content in terrestrial rocks varies widely, resulting in levels of radioactive contamination in the surrounding areas are different - from a slight excess of natural background to the values ​​that represent a danger to the health of workers and the public. The main sources of population exposure are shown in Table 1 [2].


 

 1.Vidy ionizing radiation



The effectiveness of protection against ionizing radiation is largely dependent on the knowledge of its kinds and properties. All types of ionizing radiation can be divided into two groups: electromagnetic, which include X-ray and g-radiation, and corpuscular or emission of nuclear particles.

X-ray and g-radiation belong to a wide range of electromagnetic radiation and are placed in it after the radio waves, visible light and ultraviolet rays. All these different types of radiation wavelength. The shortest wavelength and, consequently, the highest frequency of electromagnetic oscillations in this range have the g-and X-ray radiation. The smaller the wavelength, the higher the energy emission and the greater its penetrating power. Energy, for example, g-quantum of cobalt-60 is 1.33 MeV.

X-ray source is the sun. But this radiation is absorbed by Earth's atmosphere, otherwise it would have disastrous effect on all living things. X-ray radiation is generated and the corresponding devices (accelerators) for use in the diagnosis and treatment of patients.

Gamma radiation is accompanied by nuclear reactions and decay of many radioactive substances. The energy of g-radiation can have various meanings - from tens of thousands to millions of electron volts. It can pass through the human body. As a protection against g-radiation used effectively lead, concrete or other materials with high specific gravity.

To ionizing radiation are also various kinds of nuclear particles. Among the light nuclear particles include, for example, beta particles, and among heavy - alpha-particles.

Beta radiation - a stream of electrons or positrons. Beta particles have a negative elementary (electron) or positive (positron) charge. They occur in the nuclei of atoms in the radioactive decay and radiate from there. Beta particles can pass through the water layer thickness of 1-2 cm for protection against beta radiation, as a rule, only a sheet of aluminum a few millimeters thick. For external exposure of beta-particles of the human body in the open surface of the skin can form radiation burns of varying severity. In case of sources of beta radiation in the body with food, water and air is internal exposure of the organism, which can lead to severe radiation damage.

Alpha radiation - a stream of heavy positively charged particles. They are 7300 times heavier than beta particles. By its very physical nature of the alpha particle is a nucleus of a helium atom: they consist of two protons and two neutrons, and therefore have two elementary positive electric charge. These particles are emitted during radioactive decay of certain elements of high atomic number (mostly transuranic elements with atomic numbers over 92). Alpha radiation has a high ionizing power, but it penetrates the body tissue at a very shallow depth. Irradiation of human alpha-particles penetrate only to a depth of the surface layer of the skin. They can protect themselves from a sheet of plain paper. Their range in air does not exceed 11 cm Thus, in the case of external exposure to protect against adverse effects of alpha particles is quite simple and they did not seem to pose a serious threat to human health. The situation changes radically in the case of a source of alpha radiation in the human body through food, water or air. In this case, they are extremely dangerous irradiators body from the inside.

Neutrons - neutral, do not carry an electric charge of the particle - in assessing the radiological emergency response may play a significant role. These particles are emitted from the nuclei of atoms in some nuclear reactions, in particular, the reactions of nuclear fission of uranium or plutonium. Neutrons are highly penetrating. The ionization of the medium in the field of neutron radiation by charged particles that arise in the interaction of neutrons with matter. A distinctive feature of the neutron emission is the ability to turn the atoms of stable elements in their radioactive isotopes, which dramatically increases the risk of neutron exposure. Neutron radiation from the hydrogen-containing materials are well protected (paraffin wax, polyethylene).

It is natural that all the protective measures against exposure to ionizing radiation are based on knowledge of the properties of each type of radiation, the characteristics of their penetrating power, the characteristics of ionization effects.


 2.Yavlenie radioactivity. The law of radioactive decay


Radioactivity - a spontaneous transformation of unstable isotopes of one chemical element from the ground or excited state of an isotope of another element, accompanied by the emission of elementary particles and electromagnetic energy. Such nuclei are called atoms or the corresponding radioactive. The very phenomenon is called radioactive decay.

The amount of any radioactive isotope decreases with time due to radioactive decay, which occurs spontaneously as a result of intranuclear processes. For each of the radioactive substances decay rate of the nuclei of its atoms is constant, unchanging, and is typical only for this isotope. All radionuclides decay in the same manner and subject to the law of radioactive decay. The essence of law lies in the fact that per unit time into the same part of the available atomic nuclei of a radioactive isotope.

To characterize the rate of decay of radioactive elements in practice, instead of the decay constant? enjoy a half-life T1 / 2, which represents the time during which splits half the original number of radioactive nuclei. For the various radioactive elements have half-lives range from fractions of a second to billions of years.


 

 

 3.Edinitsy measurement of radioactivity


Activity (A) - a measure of the radioactivity of a number of radionuclides present in the energy state at a given time:

 A = dN / dt,

where dN - the expected number of spontaneous nuclear transitions from that energy state occurring during the time interval dt. In the SI unit of activity is the reciprocal second (s-1), which has a special name becquerel (Bq). 1 Bq = 1 disintegration / s.

Used and the international non-systemic activity unit curie (Ci). Curie - a radioactive isotope is the amount in which the number of radioactive disintegrations per second is equal to 3.7? 1010. The unit of curies of radioactivity corresponds to one gram of radium. In units of becquerel and curie express - and b-activity.

To characterize the g-activity put another unit - the equivalent of one milligram of radium (226Ra). Milligram equivalent of radium - is the activity of any radioactive source, g-rays which creates the same exposure dose, as g-radiation of one milligram of radium in the Russian State standard platinum filter 0.5 mm. A point source of one milligram (1mKi) of radium, after the initial filtration through a 0.5 mm platinum, creates in the air at a distance of 1 cm dose rate of 8.4 R / h This quantity is called the ionization constant g-Ra (K), which is adopted as the standard dose of radiation. Since it is compared to other radioactive isotopes. g-equivalent isotope M is related to its activity through a g-ionization constant expression:

M = A * K / 8.4

which allows us to recalculate the activity of a radioactive substance, expressed in meq. radium to the activity, expressed as Ki, and vice versa.

To characterize the X-ray emission, and g determine the so-called exposition dose (X) of ionizing radiation. It characterizes the ability of ionizing x-ray and g-radiation in the air. In practice, off-system unit - X-rays. This is the amount of radiation, which in one cm3 of air (0.001293 g) at atmospheric pressure of 760 torr and a temperature of 0 ° C, 2.08 h109 formed ion pairs.

The unit of exposure dose in the International System of Units (SI) adopted a pendant per kilogram (C / kg), ie this amount of energy x-ray and g-radiation, which forms a kg of dry air ions carrying a total charge of 1 coulomb of electricity each sign. A P = 2.58 x10-4 C / kg, 1 C / kg = 3880 R.

The exposure dose does not account for the energy of ionizing radiation that is absorbed by the irradiated object. To determine the effect of exposure to ionizing radiation in a substance introduced the concept of absorbed dose (D) - the fundamental dosimetric quantity defined as:

 D = de / dm,

where the de - the average energy transferred to matter by ionizing radiation, located in the elementary volume; dm - mass of a substance in unit volume.

In SI units the absorbed dose is measured in joules divided by the kilogram (J / kg) and has a special name - the gray (Gy).

Common Units of measurement of absorbed dose is the rad. The unit rad (rad - radiation absorbed dose) - this is such a dose at which the mass of one gram of irradiated material is absorbed by the energy of any type of radiation equal to 100 ergs.

Because, at one and the same dose of energy g-rays and particles in one gram of varying the composition of biological tissue is absorbed by different amounts of energy, the absorbed dose in such cases are calculated:

 D = A? F,

where D - the absorbed dose, X - the exposure dose of P at the same point; f - coefficient of the transition.

If the air dose of radiation equivalent to a P 88 ergs / g, the absorbed energy for this environment will be 88/100 = 0.88 rad. Thus, for air absorbed dose equal to 0.88 rad corresponds to the exposure dose of 1 R.

The transition factor f is usually determined empirically on the phantom. For water and soft-tissue factor f rounded received per unit (in fact, it is 0.93). Consequently, the absorbed dose in rads numerically equal to the corresponding exposure dose in roentgens. For bone tissue factor f varies from 2 to 5.

The biological effect of the same doses of various types of radiation are not the same. This is due to specific ionization radiation. The higher the specific ionization, the higher the coefficient of relative biological effectiveness (RBE), or weighting factor (WR). This ratio shows how many times the efficiency of the biological action of this type of radiation above the X-ray or g-radiation at the same absorbed dose in tissue.

To evaluate the biological effects of radiation introduced the concept of equivalent dose - is the absorbed dose in an organ or tissue multiplied by the appropriate weighting factor for that radiation WR:

HTR = WR? DTR, where, DTR - the average absorbed dose in an organ or tissue T, and WR - weighting factor for radiation R. If the radiation field is composed of several radiations with different values ​​of WR, then the equivalent dose is defined as:

The unit of equivalent dose is J / kg, with a special name - the sievert (Sv). Common Units of measurement of equivalent dose is the biological equivalent of glad - rem.


 4.Deystvie of ionizing radiation on the human body



As a result of exposure to ionizing radiation on the human body can occur in the tissues of the complex physical, chemical and biological processes.

The primary physical act of interaction of ionizing radiation with biological object is ionization. It is through the ionization energy is transferred to the object.


 

 

It is known that the biological tissue of 60-70% by weight of water. As a result of ionization of water molecules form free radicals H and OH


In the presence of oxygen free radical is also formed hydroperoxide (H2O-) and hydrogen peroxide (H2O), which are strong oxidants ..

Obtained in the process of water radiolysis free radicals and oxidants, possessing high chemical activity, enter into chemical reactions with molecules of proteins, enzymes and other structural elements of biological tissue, which leads to a change in the biological processes in the body. As a result, violated the metabolic processes inhibited the activity of enzyme systems, slows down and stops the growth of tissue, new chemical compounds that are not inherent in the body - toxins. This leads to impaired activity of individual functions or systems of the body as a whole. Depending on the magnitude of the absorbed dose and индивидуальныхособенностей the body caused by the changes can be reversible or irreversible.

Some radioactive substances are accumulated in some internal organs. For example, sources of alpha - radiation (radium, uranium, plutonium), beta - radiation (strontium and yttrium) and gamma-radiation (zirconium) are deposited in bone. All of these substances is difficult to leave the body.

Features of ionizing radiation action on living organism

In studying the effect of radiation on the organism identified the following features:

- High efficiency of the absorbed energy. Small quantities of absorbed radiation energy can cause profound biological changes in the body;
the presence of latent or incubation, the manifestations of the effects of ionizing radiation. This period is often called the period of an imaginary being. The duration of irradiation is reduced with large doses;
- The action of small doses can add up or accumulate. This effect is called cumulation;
- Radiation affects not only at the living organism, but also his offspring. This so-called genetic effect;
- The various organs of a living organism has its own sensitivity to radiation. With daily exposure doses of 0.02-0.05 P has come changes in the blood;
- Not every body as a whole responds to the same exposure.