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Study of radioactivity of drugs. Radioactive drugs

Radiation can be used either to assess the metabolism of the isotope-labeled substance in the body, or to inhibit tissues that have absorbed the isotope. Designed for biomedical research, radioisotope diagnostics and treatment of various diseases, mainly for radiation therapy of malignant tumors.

For diagnostic purposes, radioisotopes are used, which, when introduced into the body, participate in the types of metabolism being studied or the activity of organs and systems being studied, and at the same time can be recorded by radiometric methods. Such radioactive drugs, if possible, have a short effective half-life and low-energy radiation that is weakly absorbed in tissues, which causes an insignificant radiation load on the body of the subject.

Criteria for selecting radioactive drugs intended for radiation therapy malignant neoplasms, is the possibility of creating the required therapeutic dose ionizing radiation in the area of neoplasm with minimal impact on healthy tissue. This effect is achieved both by choosing the type and duration of irradiation and by choosing the method of delivering the radiopharmaceutical to the target. Delivery is possible both through the body’s metabolism with selective accumulation of the radioactive isotope in the tissues to be irradiated, and by surgical means in the form of granules, probes, application dressings, etc.

Classification

Radioactive drugs are divided into open and closed:

IN closed In preparations, the radioactive material is enclosed in a protective coating or capsule that prevents radioactive contamination of the environment and contact with the radioactive compound of the patient and personnel.
IN open In preparations, direct contact of the radioactive substance with the tissues of the body and the environment occurs.

List of radioisotopes used

Isotope	Half life	Type and energy of radiation [average value]		Application
11 C	20,385 min	β+	1982.1 keV	Diagnostics using . Metabolic state of the heart, assessment of amino acid consumption (methionine, leucine) and protein synthesis, diagnosis of brain tumors, assessment of the metabolic state of the parathyroid gland, metabolic rate fatty acids in the myocardium
13N	9.97 min	β+	1200.3 keV	Diagnosis using positron emission tomography. Blood flow measurement, myocardial perfusion assessment
15 O	122.24 s	β+	1731.9 keV	Diagnosis using positron emission tomography. Study of lung function, central and peripheral hemodynamics, etc.
18 F	109,771 min	β+	633.5 keV	Diagnosis using positron emission tomography. Visualization of tumors of various locations, assessment of glucose metabolism in the myocardium, lungs, brain, diagnosis of Alzheimer's disease, diagnosis of diffuse Lewy body disease, diagnosis of Parkinson's disease, localization of the epileptic focus.
32P	14,262 days	β−	1710.66 keV	Interstitial and intracavitary radiation therapy of tumors; treatment of polycythemia and related disorders. 33 P can be used for the same purposes.
60Co	5.2714 years	β−	317.88 keV	in the treatment of tumors of the female genital organs, cancer of the oral and lung mucosa, brain tumors, etc.
60Co	5.2714 years	γ	1173.237 keV 1332.501 keV
85 Kr	10,756 years	β−	687.4 keV	study of pulmonary function, central and peripheral hemodynamics, etc.
90 Y	64.1 hours	β−	2280.1 keV	for interstitial and intracavitary radiation therapy (in the treatment of tumors of the female genital organs, cancer of the oral and lung mucosa, brain tumors, etc.)
99m Tc	6.01 hours	γ	140.511 keV	Diagnosis of brain tumors using gamma cameras, study of central and peripheral hemodynamics, etc.; examination of the lungs, liver, brain, etc.
111 In	2.8047 days.	γ	171.28 keV 245.40 keV	examination of the lungs, liver, brain, etc.
113m In	1.6582 h.	γ	391.69 keV	liver examination, etc.
123 I	13 o'clock	γ	160 keV	Diagnosis using gamma cameras of the thyroid gland and nervous system hearts.
125 I	59.5 days	γ	35 keV	Treatment of prostate cancer using the method

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Introduction

We humans live in a world that can be called radioactive. There are no places where there is an absolute absence of radioactivity in nature, the habitat of animals, or people. Radioactivity is a natural formation, cosmic rays scattered in environment radioactive nuclides, that is, substances that create the radioactive background in which we live. During evolution, all living things have adapted to this background level. You also need to take into account that the level of radioactivity on Earth is decreasing all the time; every 10-15 thousand years the level of radioactivity decreases by about half. In general, only major accidents in a certain area associated, as a rule, with nuclear power plants violate this intermediate level. And the most dangerous set of circumstances for a person is considered to be when radionuclides enter the human body. Moreover, during internal irradiation, the most dangerous effect is produced by α-particles. It is generally accepted that this danger of α-irradiation is caused by their large mass compared to electrons and increased ionizing ability due to their double charge.

Relevance of the work is that the idea of the absolute danger of any radioactive exposure is practically fixed in the public consciousness, and therefore it seems necessary to consider physical nature pathological effects of radioactivity on living organisms and assessment of risk and hazard levels.

Purpose of the work: make an attempt to evaluate the brake electromagnetic radiation alpha particles as a factor of pathological effects on a living organism during internal irradiation.

Tasks:

1. Familiarize yourself with the nature of radioactivity and methods of its research;

2. Investigate the possibility of using school physical equipment;

3. Design an experiment and investigate its result.

Hypothesis: one of the components of the pathological effect on the body during internal irradiation is electromagnetic radiation caused by braking (movement with negative acceleration) on the track, and leading to damage to DNA molecules due to the high radiation power density in a group of cells near the track with the subsequent development of cancer.

Object of study:α-particle during its inhibition in biological tissues during internal irradiation.

Subject of research: component of the energy loss of an α-particle to electromagnetic radiation.

Part 1. On the nature of radiation.

1. Rice. 1. A. Becquereli
  discovery of radioactivity and its biological effects

1896 French physicist A. Becquerel, studying the phenomenon of luminescence of uranium salts, found that uranium salt emits rays of an unknown type that pass through paper, wood, thin metal plates, and ionize the air. In February 1896, Becquereli was unable to conduct another experiment due to cloudy weather. Becquerel put the record in the desk drawer, placing a copper cross coated with uranium salt on top of it. Having developed the plate two days later, just in case, he discovered blackening on it in the form of a distinct shadow of a cross. This meant that uranium salts spontaneously, without any external phenomena, create some kind of radiation. Intensive research began.

1898 Marie Sklodowska-Curie, while studying uranium ores, discovered new chemical elements: polonium, radium. It turned out that all chemical elements, starting with serial number 83, are radioactive. The phenomenon of spontaneous transformation of unstable isotopes into stable ones, accompanied by the emission of particles and the emission of energy, is called natural radioactivity.

1. Forms of radioactivity

1898 Exposure to radioactive radiation magnetic field, E. Rutherford identified two types of rays: α-rays - heavy positively charged particles (nuclei of helium atoms) and β-rays - light negatively charged particles (identical to electrons). Two years later, P. Willard discovered gamma rays. Gamma rays are electromagnetic waves with a wavelength of Gamma rays are not deflected by electric and magnetic fields.

Rice. 3. Alpha radiation

Rice. 2. The influence of the magnetic field on the trajectory of particles

Rice. 4. Beta radiation

After Rutherford established the structure of the atom, it became clear that radioactivity is a nuclear process. 1902 E. Rutherford and F. Soddy proved that as a result of radioactive decay, the transformation of atoms of one chemical element into the atoms of another chemical element, accompanied by the emission of various particles.

Alpha particles and beta particles ejected from the nucleus have significant kinetic energy and, acting on the substance, on the one hand, produce its ionization, and on the other, penetrate to a certain depth. Interacting with matter, they lose this energy, mainly as a result of elastic interactions with atomic nuclei or electrons, giving them all or part of their energy, causing ionization or excitation of atoms (i.e. transfer of an electron from a closer to a more distant orbit from the nucleus ). Ionization and penetration to a certain depth are of fundamental importance for assessing the effects of ionizing radiation on biological tissue various types radiation. Knowing the properties of different types of radiation to penetrate different materials, a person can use them for his protection.

Part 2. Alpha radiation and its characteristics

2.1. Pathogenicity and danger of α-radiation

Alpha radiation is a stream of nuclei of helium atoms. Occurs as a result of the decay of atoms of heavy elements such as uranium, radium and thorium. A type of radioactive decay of a nucleus, which results in the emission of a helium 4 He nucleus - an alpha particle. In this case, the mass number of the nucleus decreases by 4, and the atomic number by 2.

IN general view The alpha decay formula is as follows:

Example of alpha decay for the isotope 238 U:

Fig.5. Alpha decay of uranium 238

Alpha particles formed during nuclear decay have an initial kinetic energy in the range of 1.8-15 MeV. When an alpha particle moves in a substance, it creates strong ionization of the surrounding atoms, as a result of which it very quickly loses energy. The energy of alpha particles resulting from radioactive decay is not enough to even penetrate the dead layer of skin, so there is no radiation risk from external exposure to such alpha particles. External alpha radiation is dangerous to health only in the case of high-energy alpha particles (with energies above tens of MeV), the source of which is an accelerator. However, the penetration of alpha-active radionuclides inside the body, when living tissues of the body are directly exposed to irradiation, is very dangerous for health, since the high ionization density along the particle track severely damages biomolecules. It is believed that with equal energy release (absorbed dose), the equivalent dose accumulated during internal irradiation with alpha particles with energies characteristic of radioactive decay is 20 times higher than during irradiation with gamma and x-ray quanta. Thus, α-particles with energies of 10 MeV and higher, sufficient to overcome the dead stratum corneum of the skin, can pose a danger to humans during external irradiation. A much greater danger to humans is represented by α-particles that arise from the alpha decay of radionuclides that enter the body (in particular, through the respiratory tract or digestive tract). A microscopic amount of α-radioactive substance is enough to cause acute radiation sickness in a victim, often with a fatal outcome.

Being quite heavy and positively charged, alpha particles from radioactive decay have a very short range in matter and, when moving through a medium, quickly lose energy at a short distance from the source. This leads to the fact that all the radiation energy is released in a small volume of the substance, which increases the chances of cell damage when the radiation source enters the body. However, external radiation from radioactive sources is harmless because alpha particles can be effectively trapped by a few centimeters of air or tens of micrometers dense matter- for example, a sheet of paper and even the dead stratum corneum of the epidermis, without reaching living cells. Even touching a source of pure alpha radiation is not dangerous, although it should be remembered that many sources of alpha radiation also emit much more penetrating types of radiation (beta particles, gamma rays, sometimes neutrons). However, if an alpha source enters the body, it results in significant radiation exposure.

Rice. 6. Penetrating ability of alpha, beta particles and gamma quanta.

2.2. Calculation of α-particle characteristics

The existence of electromagnetic waves was a major prediction. J.C. Maxwell (1876), this theory is presented in the section of the school physics course - electrodynamics. “Electrodynamics” is the science of electromagnetic waves, the nature of their occurrence, propagation in different media, interaction with various substances and structures.

And in this science there is one of the fundamental statements that any electric charge a particle moving with acceleration is a source of electromagnetic radiation.

It is precisely because of this that X-ray waves are generated in X-ray installations when the flow of electrons is quickly stopped, which, after being accelerated in the device, are decelerated when they collide with the anode of the X-ray tube.

Something similar happens in a very short time with α-particles if their source is the nuclei of radioactive atoms located in the medium. Having a high speed when leaving the nucleus and having traveled only from 5 to 40 microns, the α-particle stops. At the same time, experiencing enormous deceleration and having a double charge, they cannot help but create an electromagnetic pulse.

Using the usual school laws of mechanics and the law of conservation of energy, I calculated the initial speed of α-particles, the magnitude of negative acceleration, the time it took the α-particle to move before stopping, the resistance force of its movement and the power it developed.

It is clear that the energy of the α particle is used to destroy the cells of the body, ionize atoms, in one case more, when leaving other radioactive nuclei less, but the radiation energy created in a short flight time of approximately 5 to 40 microns cannot exceed the energy α -particles they have upon departure.

In the calculations I used as initial known characteristics, only the energy of α-particles (this is its kinetic energy) and the average path length in biological tissues of the body (L= 5 - 40 µm). I found the mass of the α-particle and its composition in the reference book.

The energy of their α particles is 4-10 MeV. It was for such alpha particles that I carried out calculations.

The mass of an α particle is 4 amu; 1 amu=1.660·10 -27 kg;

m = 4·1.660·10 -27 = 6.64·10 -27 kg - the mass of the α-particle.

α-particle track length.

q = 2 1.6 = 3.2 - charge

E k = 7 MeV = 7·10 6 ·1.6·10 -19 = 11.2·10 -13 J - kinetic energy of the α particle.

F = ma = 6.64·10 -27 ·8.4·10 18 =5.5 ·10 -8 N - resistance force of the α-particle.

Table 1 characteristics of α-particles.

.3.Power of α-radiation and electromagnetic safety standards

Data from the directory:

1. The depth δ of penetration of electromagnetic waves with a frequency of 10 GHz in biological tissues with a high water content (water is an absorber of electromagnetic waves) is 3.43 mm (343 μm). When an electromagnetic wave penetrates to a depth δ, its power density decreases by e=2.71 times.

2. From safety standards, with an exposure time of less than 0.2 hours, the power density (critical) should not exceed

In (1) the penetration depths and attenuation of the electromagnetic wave are indicated for a frequency of 10 GHz. In our case, a single pulse of an electromagnetic wave can be interpreted as positive part one period, i.e. the closest frequency value would be 230 GHz.

For biological tissue in maximum purity specified in the reference book equal to 10 GHz. According to our calculations, a single pulse of an electromagnetic wave can be represented as a short pulse of frequency 230 GHz. From the reference book we can conclude that as the frequency of electromagnetic waves increases, the thickness δ decreases. Let us estimate the thickness δ for our case. The frequency of 230 GHz exceeds the 10 GHz given in the reference book by 23 times. Assuming that the frequency ratio of 23 times will be constant for the previous section of the range (10 GHz will be 23 times the frequency of 433 MHz) - for which (i.e. 10 times). Then for a frequency of 230 GHz we can take δ = 34 μm.

Assuming that, passing from the center of the sphere, the radiation through the surfaces of mentally constructed spheres with a common center and with the distance between them is equal to δ, then, having passed through n such surfaces, the initial intensity (power) of the electromagnetic wave will be reduced by a factor. In order for the calculations to be close to the truth, we take n with the number of layers equal to 8; Then

Because; The initial energy of electromagnetic waves can be estimated as 0.01; because the mechanical energy of an alpha particle is mainly spent on the formation of a track of ionized particles. Therefore it can be accepted.

They will be killed by the impulse of the wave. This is confirmed by quantitative estimates.

Because the calculated power density of radiation emanating from the center of the sphere and passing through it with a sphere radius (8δ = 272 μm) with an area of 4.65 will be comparable to the critical radiation power density of the required SanPiN norm, it can be argued that inside this sphere, in its volume all cells will die.

That. Our estimates lead to the result that all biological cells in the volume of the sphere to the surface of which radiation from the center of the sphere passes from the α-particle track will die, i.e. they will be located in space, the volume through which passes electromagnetic wave with a radiation power density exceeding the critical radiation density determined by SanPiN standards. These dead cells (or rather their remains), due to the body’s regeneration mechanisms, will be removed from the body practically without any consequences.

The most dangerous of the consequences of such an electromagnetic shock for cells will be that in a certain spherical layer of cells surrounding the dangerous sphere there will be such half-dead cells, the correct functioning of some will certainly be disrupted by the electromagnetic pulse that “broke” (teared, disrupted) the DNA structure , which is responsible for the “correct” regeneration of a given cell.

Part 3. Design and conduct of experiments

3.1. Measurement of radioactive background on the territory of Municipal Budget Educational Institution Secondary School No. 11

Purpose: to measure the radioactive background on the territory of Municipal Budget Educational Institution Secondary School No. 11.

Hypothesis: precipitation and wind carry different types particles (in our case we are interested in radioactive particles).

Equipment: dosimeter.

Digital radiation monitor

For the experiments, I used an ionizing radiation sensor (dosimeter). An ionizing radiation sensor (dosimeter) is designed to automatically count the number of ionizing particles that have entered it. The device can be used to measure alpha, beta and gamma radiation levels. Since the device is equipped with its own screen, it can be used independently of a computer and other data recording devices in the field to determine radiation levels.

Rice. 7 Ionizing radiation sensor (dosimeter)

TECHNICAL SPECIFICATIONS 1. Measuring ranges: . X1: 0 - 0.5 mR/h; 0 - 500 cycles/min (CPM); . X2: 0 - 5 mR/h; 0 - 5000 cycles/min (CPM); . X3: 0 - 50 mR/h; 0 - 50000 cycles/min (CPM). 2. Sensitivity: 1000 cycles/min/mR/H relative to cesium-137. 3. Accuracy: . with visual calibration: ± 20% of full scale; . for instrument calibration: ± 10% of full scale. 4. Calibration: Cesium-137 is used. 5. Operating temperature range: 0 - 50 °C. 6. Power supply: . battery (9V); . average battery life: 2000 hours at normal levels of background radiation.

Progress of work: To do this, we measured the background radiation of our school in different months. In winter, the wind direction is directed to the south (side AB).

Rice. 8 Plan of MBOU Secondary School No. 11

Table 2. Radioactive background of the territory of MBOU Secondary School No. 11.

Results

On the southern side, the measured radioactive background is higher than on the northern side, which means that wind and precipitation actually carry different types of particles.

I also took measurements near the sewer (these are points F and K) and the dosimeter readings were slightly higher there, and this proves that it is water that carries radionuclides.

3.2.Study of the dependence of the absorbed dose on the distance to the geometric center of the drug for flat geometry.

Purpose of the work: to study the dependence of the absorbed dose on the distance to the geometric center of the drug in flat geometry.

Equipment: ruler, dosimeter, potassium hydroxide.

Progress of work: measure the radioactive level, moving the drug away from the dosimeter every centimeter.

Rice. 9 Results of the dependence of the absorbed dose on the distance to the geometric center of the drug for flat geometry.

Experiment shows that with flat geometry radioactive drug the dependence of the absorbed dose on the distance to the center of the preparation differs from quadratic in the case of a point preparation. With flat geometry, this dependence on distance is weaker.

Conclusion.

Estimates and calculations show that the radiation power density in the tissue area, the immediate environment of the track, exceeds tens of times the permissible electromagnetic safety standards, which leads to the complete death of cells in this area. But the existing regeneration mechanism will restore dead cells and preserve all the functions of these cells. Main danger for the body - the presence of a spherical layer of cells surrounding this central region. The cells of the spherical layer remain alive, but a powerful electromagnetic pulse can affect their DNA molecules, which can lead to their abnormal development and the formation of their replicas with oncological pathology.

Literature

1. Sh.A.Gorbushkin - ABC of physics

2. G.D. Luppov - Basic notes and test tasks(“Educational literature”, 1996);

3.P.V.Glinskaya - For those entering universities (“Grinin Brothers”, 1995);

Chemical Encyclopedia (Soviet Encyclopedia, 1985);

4. Gusev N. G., Klimanov V. A., Mashkovich V. P., Suvorov A. P. - Protection against ionizing radiation;

5. Abramov A. I., Kazansky Yu. A., Matusevich E. S. Fundamentals experimental methods nuclear physics (3rd ed., revised and expanded. M., Energoatomizdat, 1985);

6. Radiation safety standards (NRB-99/2009) (Ministry of Health of Russia, 2009);

7. Moiseev A. A., Ivanov V. I. Handbook on dosimetry and radiation hygiene (2nd ed., revised and expanded. M., Atomizdat, 1974);

8.Physical encyclopedia ( Soviet encyclopedia, 1994. T. 4. Poynting-Robertson);

9.Mukhin K.N. - Experimental nuclear physics(Book 1. Physics of the atomic nucleus. Part I. Properties of nucleons, nuclei and radioactive radiation. - M.: Energoatomizdat, 1993);

10. Biophysical characteristics of human tissues. Directory/Berezovsky V.A. etc.; Kyiv: Naukova Dumka, 1990.-224 p.

This examination method is based on the ability of radioactive isotopes to emit. Nowadays, computer radioisotope research is most often performed - scintigraphy. First, the patient is injected with a radioactive substance into a vein, into the mouth, or by inhalation. Most often, compounds of the short-lived isotope technetium with various organic substances are used.

Radiation from the isotopes is captured by a gamma camera, which is placed above the organ being examined. This radiation is converted and transmitted to a computer, on the screen of which an image of the organ is displayed. Modern gamma cameras make it possible to obtain layer-by-layer “slices”. The result is a color picture that is understandable even to non-professionals. The study is carried out for 10-30 minutes, and all this time the image on the screen changes. Therefore, the doctor has the opportunity to see not only the organ itself, but also observe its work.

All other isotope studies are gradually being replaced by scintigraphy. Thus, scanning, which before the advent of computers was the main method of radioisotope diagnostics, is used less and less today. When scanning, the image of the organ is displayed not on a computer, but on paper in the form of colored shaded lines. But with this method, the image turns out flat and also provides little information about the functioning of the organ. And the scanning causes certain inconvenience for the patient - it requires him to be completely immobile for thirty to forty minutes.

Right on target

With the advent of scintigraphy, radioisotope diagnostics received a second life. This is one of the few methods that detects the disease at an early stage. For example, cancer metastases in bones are detected by isotopes six months earlier than by x-ray. These six months can cost a person his life.

In some cases, isotopes are generally the only method that can give the doctor information about the condition of the diseased organ. With their help, kidney diseases are detected when nothing is detected on an ultrasound; microinfarctions of the heart, invisible on an ECG and echocardiogram, are diagnosed. Sometimes a radioisotope study allows the doctor to “see” pulmonary embolism, which is not visible on an x-ray. Moreover, this method provides information not only about the shape, structure and structure of the organ, but also allows you to assess its functional state, which is extremely important.

If previously only the kidneys, liver, gallbladder and thyroid gland were examined using isotopes, now the situation has changed. Radioisotope diagnostics is used in almost all areas of medicine, including microsurgery, neurosurgery, and transplantology. Besides this diagnostic technique allows not only to make and clarify the diagnosis, but also to evaluate the results of treatment, including constant monitoring of postoperative patients. For example, scintigraphy is indispensable when preparing a patient for coronary artery bypass surgery. And in the future it helps to evaluate the effectiveness of the operation. Isotopes detect conditions that threaten human life: myocardial infarction, stroke, pulmonary embolism, traumatic brain hemorrhages, bleeding and acute diseases of the abdominal organs. Radioisotope diagnostics helps to distinguish cirrhosis from hepatitis, discern a malignant tumor at the first stage, and identify signs of rejection of transplanted organs.

Under control

There are almost no contraindications to radioisotope research. To carry it out, an insignificant amount of short-lived isotopes that quickly leave the body is introduced. The amount of the drug is calculated strictly individually, depending on the patient’s weight and height and the condition of the organ being tested. And the doctor must select a gentle examination regimen. And most importantly: radiation exposure during a radioisotope study is usually even less than during an x-ray study. Radioisotope testing is so safe that it can be performed several times a year and combined with x-rays.

In case of an unexpected breakdown or accident, the isotope department in any hospital is reliably protected. As a rule, it is located far from the medical departments - on the ground floor or in the basement. The floors, walls and ceilings are very thick and covered with special materials. Stock radioactive substances is located deep underground in special lead-lined vaults. And the preparation of radioisotope preparations is carried out in fume hoods with lead screens.

Constant radiation monitoring is also carried out using numerous counters. The department employs trained personnel who not only determine the level of radiation, but also know what to do in the event of a leak of radioactive substances. In addition to the department employees, the radiation level is monitored by specialists from SES, Gosatomnadzor, Moskompriroda and the Department of Internal Affairs.

Simplicity and reliability

The patient must adhere to certain rules during a radioisotope study. It all depends on which organ is supposed to be examined, as well as on the age and physical condition of the sick person. Thus, when examining the heart, the patient must be prepared for physical activity on a bicycle ergometer or on a walking track. The study will be of better quality if done on an empty stomach. And, of course, you should not take medications several hours before the test.

Before the bone scintigraphy, the patient will have to drink a lot of water and urinate frequently. This flushing will help remove isotopes from the body that have not settled in the bones. When examining your kidneys, you also need to drink plenty of fluids. Scintigraphy of the liver and biliary tract is done on an empty stomach. And the thyroid gland, lungs and brain are examined without any preparation at all.

Radioisotope testing may be interfered with by metal objects placed between the body and the gamma camera. After introducing the drug into the body, you must wait until it reaches the desired organ and is distributed in it. During the examination itself, the patient should not move, otherwise the result will be distorted.

The simplicity of radioisotope diagnostics makes it possible to examine even extremely sick patients. It is also used in children starting from the age of three; they mainly examine the kidneys and bones. Although, of course, children require additional training. Before the procedure, they are given a sedative so that they do not fidget during the examination. But pregnant women are not subject to radioisotope testing. This is due to the fact that the developing fetus is very sensitive to even minimal radiation.

There are radioactive drugs for biomedical research, diagnostic, therapeutic and radiation sources for gamma devices.
Hundreds of inorganic and organic compounds labeled with 14C, 3H, 32P, 35S, 131J and other radioactive isotopes can be used in biomedical research. Highest value have labeled amino acids, their analogs and derivatives, alkaloids, vitamins, antibiotics, carbohydrates and their derivatives, nucleic acid components, steroids and steroid hormones.
To label diagnostic radioactive drugs, as a rule, radioactive isotopes with a short half-life are used. In the case of labeling with long-lived isotopes, compounds that are quickly eliminated from the body are used (vitamin B12-Co58, neohydrin-Hg2O3, etc.). Some diagnostic short-lived radioactive preparations with the isotopes yttrium-90, technetium-99m, iodine-132, gallium-68, indium-115m are obtained through simple manipulations directly in medical institutions from special generators as daughter products of the decay of the corresponding long-lived radioactive isotopes. Diagnostic radioactive drugs are labeled with gamma, beta and positron emitters. Radioactive drugs that emit alpha particles are not suitable for this purpose. Radioactive drugs are used in the form of true and colloidal solutions, suspensions, proteins, fats, gases, etc. Therapeutic radioactive drugs are intended for radiation therapy of mainly malignant tumors, as well as some skin diseases. These include dispersed radioactive drugs (colloidal solutions, suspensions, emulsins), discrete radiation sources (applicators, point and linear sources-drugs that are absorbed in the body), organotropic and tumorotropic substances (chemical elements with tropism for certain organs and tissues, antibodies , complexing agents, etc.). Beta and gamma active isotopes (60Co, 137Cs, 32P, 90Sr, 90Y, 198Au, etc.) are used in therapeutic radioactive preparations. In some cases, these drugs make it possible to provide irradiation of the tumor in a sufficient tissue dose with minimal radiation exposure to surrounding healthy tissue. Depending on the location of the pathological focus, radioactive drugs are used in the form of applications to the skin and mucous membranes or injected into tissues, cavities, intravenously or into lymphatic vessels. To charge gamma therapy devices, sources made from cobalt-60 and cesium-137 are used. They have the most advantageous properties for gamma therapy: a relatively long half-life, monochromaticity and high energy of gamma radiation, and a more favorable deep distribution of absorbed energy in the irradiated tissues compared to conventional X-ray radiation.
The same isotopes are used in installations for radiation sterilization.

The radioactivity of drugs can be determined by the absolute, calculated and relative (comparative) method. The latter is the most common.

Absolute method. A thin layer of the material under study is applied to a special thin film (10-15 μg/cm²) and placed inside the detector, as a result of which the full solid angle (4p) is used to register emitted beta particles, for example, and almost 100% counting efficiency is achieved. When working with a 4p counter, you do not need to introduce numerous corrections, as with the calculation method.

The activity of the drug is expressed immediately in units of activity Bq, Ku, mKu, etc.

The absolute activity of alpha and beta emitting isotopes is determined using a calculation method using conventional gas-discharge or scintillation counters.

A number of correction factors are introduced into the formula for determining the activity of a sample, taking into account radiation losses during measurement.

A = N/w×e×k×r×q×r×g m×2.22×10¹²

A is the activity of the drug in Ku;

N is the counting rate in pulses/min minus the background;

w - correction for geometric measurement conditions (solid angle);

e- correction for the resolution time of the counting installation;

k - correction for absorption of radiation in the air layer and in the window (or wall) of the counter;

r - correction for self-absorption in the drug layer;

q - correction for backscattering from the substrate;

r - correction for the decay scheme;

g - correction for gamma radiation with mixed beta - gamma radiation;

m is the weighed portion of the measuring preparation in mg;

2.22×10¹² - conversion factor from the number of disintegrations per minute to Ci (1 Ci = 2.22*10¹² disintegrations/min).

To determine the specific activity, it is necessary to convert the activity per 1 mg to 1 kg.

Aud = A*106, (Ku/kg)

Preparations for radiometry can be prepared with a thin, thick or intermediate layer of the material being studied.

If the material under study has a half-attenuation layer - D1/2,

then thin - at d<0,1D1/2, промежуточные - 0,1D1/24D1/2.

All correction factors themselves, in turn, depend on many factors and, in turn, are calculated using complex formulas. Therefore, the calculation method is very labor-intensive.

The relative (comparative) method has found wide application in determining the beta activity of drugs. It is based on comparing the count rate from a standard (a drug with known activity) with the count rate of the drug being measured.

In this case, there must be completely identical conditions when measuring the activity of the standard and the test drug.

Apr = Aet* Npr/Net, where

Aet is the activity of the reference drug, dispersion/min;

Apr - radioactivity of the drug (sample), dispersion/min;

Net - counting speed from the standard, imp/min;

Npr - counting rate from the drug (sample), imp/min.

Data sheets for radiometric and dosimetric equipment usually indicate the error with which measurements are made. The maximum relative measurement error (sometimes called the main relative error) is indicated as a percentage, for example ± 25%. For different types of instruments it can be from ± 10% to ± 90% (sometimes the error of the type of measurement for different sections of the scale is indicated separately).

Based on the maximum relative error ± d%, the maximum absolute measurement error can be determined. If readings from instrument A are taken, then the absolute error is DA=±Ad/100. (If A = 20 mR, and d = ± 25%, then in reality A = (20 ± 5) mR. That is, in the range from 15 to 25 mR.

Veterinary and sanitary examination of milk and eggs for radiation injuries.

Entering the body of animals, radioisotopes begin to be excreted from it in significant quantities already in the first hours and days, appearing in feces, urine, milk, eggs, and wool. It has been established that cows can excrete with milk: iodine-131 - up to 8% of the dose received, strontium-90 - up to 1.9%, cesium-137 - up to 9.3. In cows with a daily milk yield of 15-20 kg, the relative amount of isotopes is greater than in low-yielding cows. The release of isotopes also increases when feeding animals succulent feed (sometimes by 70%), and when feeding beets, rutabaga and other vegetables of the cabbage family containing thiacyanate, the excretion of iodine-131 decreases. According to G.K. Vokken (1973), the introduction of stable iodine into the diet up to 2.0 g per day. can reduce the yield of iodine-131 in milk by 50%. At the same time, the susceptibility of the thyroid gland is reduced. The excretion of strontium-90 is greater in the first months of lactation.
Radiation injuries significantly affect the productivity of dairy animals and the composition of milk. When cows are internally irradiated with a dose of 3 Ci, milk yield decreases by 33% on the first day, by 52% on the 10th day, and by 85% on the 30th day (N.N. Akimov, V.G. Ilyin, 1984). In case of severe radiation sickness from external irradiation by 7 days. productivity drops by 50% within a few days. until death - stops completely.
The composition of milk also changes: SNF (1.5 times), specific gravity, acidity, and amount of calcium increase; fat content is reduced (by 20%) and antibacterial properties. During the veterinary and sanitary assessment of milk from animals suffering from radiation sickness caused by internal irradiation, radiometric data are additionally taken into account. If the maximum permissible levels of contamination of milk with radioisotopes are exceeded, it is subject to decontamination. The same is done with the milk of healthy animals that have been subjected to mechanical contamination with radioactive substances during storage or

Transportation induced by radioactivity. Milk obtained from animals suffering from radiation sickness from external irradiation, with a positive overall assessment of its good quality, can be used without restrictions.
Radioisotopes of iodine-131 and strontium-90 are 80-90% associated with the protein fraction of milk, cesium-137 is in ionic form. These data are of significant importance when decontaminating milk.
This results in relatively clean butter and cottage cheese. The serum is assessed as confiscated, subject to either further decontamination through ion exchange resin filters, or dilution with “pure” serum to acceptable levels of radioactivity and feeding to animals. A reduction in the radioactivity of milk due to the decay of short-lived isotopes during long-term storage can be achieved by processing it into condensed and dry milk. If milk is contaminated with long-lived isotopes, it is deactivated by filtration through ion exchange resins or by ionite separation.
Without the danger of causing radiation damage to animals, animals can be grazed at a radiation level of 0.5 R/h, but to obtain milk uncontaminated with radioisotopes - only at a radiation level of 0.1 R/h.
In case of contact contamination with radioisotopes (deposition on the surface of finished products), solid dairy products, butter, cheeses, etc., their decontamination is carried out by cutting off the surface layer to a depth of 2-3 mm. This is done with thin steel wire, a long knife or scraper. After that, control dosimetry of the product is carried out.
The ovary of chickens is a critical organ for iodine-131, equivalent to the thyroid gland, therefore, when RV enters the body of chickens, up to 3.25% of the radioiodine introduced into the body is deposited in the yolk of the egg. Up to 9.25% of cesium-137 will be deposited in the protein, and up to 37.5% of strontium-89 and strontium-90 will be deposited in the shell. In total, the activity of the egg can be up to 50% of the total activity of the daily dose in the first day after the explosion. On the 19th day, if we take the activity of the egg as 100%, it will change as follows: strontium will account for 93.4%, cesium - 2.9, iodine - 3.7%.
Contamination of the shell with strontium can also be mechanical (on the surface) during the passage of the egg through the cloaca, where the unreserved part of strontium enters with feces.
With a single dose of 3 mCi/kg, egg laying may stop on the 19th day. If the same dose is administered fractionally over 10 days, egg laying stops after 41 days.
Eggs are decontaminated due to the self-disintegration of isotopes during long-term storage. Taking into account the tropism of certain isotopes to different parts of the egg and their different physical decay constants, the white and yolk are processed separately into egg powder and stored until the activity declines within acceptable values. In this case, the radioactivity of the egg white decreases 10 times in 43 days, and the yolk - in 14 days. storage Egg shells, which contain a significant amount of strontium-90, pose a risk of repeated internal irradiation of chickens due to their consumption, which is possible if there is a lack of calcium in the diet. It is best to bury it with a layer of soil covering at least 70 cm and installing a sign in this place “Infected with RV. Date and radiation level.” (In peacetime, all contaminated waste is disposed of in the manner prescribed by special instructions.)
In the case of external irradiation of chickens, egg laying remains almost unchanged. With severe radiation sickness, it stops with the onset of peak time. Eggs obtained from chickens under external irradiation are released for food purposes without restrictions.
According to V.A. Verkholetov and V.P. Frolov, in the hair follicles, sebaceous glands and other elements of the skin when animals are irradiated, structural and morphological changes of atrophic order occur, which with external irradiation lead to hair loss (wool), especially in sheep. These changes contribute to a decrease in the quality of hides and wool. Thus, with mild and moderate degrees of radiation sickness, the incorporation of iodine-131 reduces the shearing of wool, its density, length, fineness, thickness and strength of sheepskin. When radioisotopes come into direct contact with the skin, beta burns occur. If animals are internally irradiated, the skin contains a significant amount of isotopes that create an activity almost equal to the specific activity of muscle tissue. A certain amount of isotopes (less than in the skin) is also deposited in the hair. Consequently, skin and wool are subject to radiometric and dosimetric control.
The main method of decontamination of wool is the self-decomposition of isotopes during long-term storage, and for hides, in addition, wet salting or pickling.

The radioactivity of drugs can be determined by the absolute, calculated and relative (comparative) method. The latter is the most common.

Absolute method. A thin layer of the material under study is applied to a special thin film (10-15 μg/cm²) and placed inside the detector, as a result of which the full solid angle (4) is used to register emitted, for example, beta particles and almost 100% counting efficiency is achieved. When working with a 4 counter, you do not need to introduce numerous corrections, as with the calculation method.

The activity of the drug is expressed immediately in units of activity Bq, Ku, mKu, etc.

By calculation method determine the absolute activity of alpha and beta emitting isotopes using conventional gas-discharge or scintillation counters.

A number of correction factors are introduced into the formula for determining the activity of a sample, taking into account radiation losses during measurement.

A =N/  q r m 2,22  10 ¹²

A- activity of the drug in Ku;

N- counting rate in imp/min minus background;

 - correction for geometric measurement conditions (solid angle);

-correction for the resolving time of the counting installation;

-correction for radiation absorption in the air layer and in the window (or wall) of the counter;

-correction for self-absorption in the drug layer;

q-correction for backscattering from the substrate;

r- correction for the decay scheme;

-correction for gamma radiation with mixed beta and gamma radiation;

m- weighed portion of the measuring drug in mg;

2,22  10 ¹² - conversion factor from the number of disintegrations per minute to Ci (1Ci = 2.22*10¹²dissolution/min).

To determine the specific activity, it is necessary to convert the activity per 1 mg to 1 kg .

Audi= A*10 6 , (TOu/kg)

Preparations for radiometry can be prepared thin, thick or intermediate layer the material being studied.

If the material being tested has half attenuation layer - 1/2,

That thin - at d<0,11/2, intermediate - 0,11/2thick (thick-layer preparations) d>41/2.

All correction factors themselves, in turn, depend on many factors and, in turn, are calculated using complex formulas. Therefore, the calculation method is very labor-intensive.

Relative (comparative) method has found wide application in determining the beta activity of drugs. It is based on comparing the counting rate from a standard (a drug with known activity) with the counting rate of the measured drug.

In this case, there must be completely identical conditions when measuring the activity of the standard and the test drug.

Apr = Aet*Npr/Nthis, Where

Aet - activity of the reference drug, dis/min;

Apr - radioactivity of the drug (sample), dispersion/min;

Net is the counting rate from the standard, imp/min;

Npr - counting rate from the drug (sample), imp/min.

The passports for radiometric and dosimetric equipment usually indicate with what error the measurements are made. Maximum relative error measurements (sometimes called the main relative error) is indicated as a percentage, for example,  25%. For different types of instruments it can be from  10% to  90% (sometimes the error of the type of measurement is indicated separately for different sections of the scale).

Based on the maximum relative error ± %, you can determine the maximum absolute measurement error. If readings from instrument A are taken, then the absolute error A = A/100. (If A = 20 mR, a =25%, then in reality A = (205) mR. That is, in the range from 15 to 25 mR.

Detectors of ionizing radiation. Classification. Principle and operating diagram of a scintillation detector.

Radioactive radiation can be detected (isolated, detected) using special devices - detectors, the operation of which is based on the physical and chemical effects that arise when radiation interacts with matter.

Types of detectors: ionization, scintillation, photographic, chemical, calorimetric, semiconductor, etc.

The most widely used detectors are based on measuring the direct effect of the interaction of radiation with matter - ionization of the gaseous medium. These are: - ionization chambers;

- proportional counters;

- Geiger-Muller counters (gas-discharge counters);

- corona and spark counters,

as well as scintillation detectors.

Scintillation (luminescent) The radiation detection method is based on the property of scintillators to emit visible light radiation (light flashes - scintillations) under the influence of charged particles, which are converted by a photomultiplier into electric current pulses.

Cathode Dynodes Anode The scintillation counter consists of a scintillator and

PMT. Scintillators can be organic and

inorganic, in solid, liquid or gas

condition. This is lithium iodide, zinc sulfide,

sodium iodide, angracene single crystals, etc.

100 +200 +400 +500 volts

PMT operation:- Under the influence of nuclear particles and gamma quanta

In the scintillator, atoms are excited and emit quanta of visible color - photons.

Photons bombard the cathode and knock photoelectrons out of it:

Photoelectrons are accelerated by the electric field of the first dynode, knock out secondary electrons from it, which are accelerated by the field of the second dynode, etc., until an avalanche flow of electrons is formed that hits the cathode and is recorded by the electronic circuit of the device. The counting efficiency of scintillation counters reaches 100%. The resolution is much higher than in ionization chambers (10 v-5 - !0 v-8 versus 10¯³ in ionization chambers). Scintillation counters find very wide application in radiometric equipment

Radiometers, purpose, classification.

By appointment.

Radiometers - devices intended for:

Measurements of the activity of radioactive drugs and radiation sources;

Determination of flux density or intensity of ionizing particles and quanta;

Surface radioactivity of objects;

Specific activity of gases, liquids, solids and granular substances.

Radiometers mainly use gas-discharge counters and scintillation detectors.

They are divided into portable and stationary.

As a rule, they consist of: - a detector-pulse sensor; - a pulse amplifier; - a converting device; - an electromechanical or electronic numerator; - a high voltage source for the detector; - a power supply for all equipment.

In order of improvement, the following were produced: radiometers B-2, B-3, B-4;

dekatron radiometers PP-8, RPS-2; automated laboratories “Gamma-1”, “Gamma-2”, “Beta-2”; equipped with computers that allow the calculation of up to several thousand sample samples with automatic printing of results. DP-100 installations, KRK-1, SRP-68 radiometers are widely used -01.

Indicate the purpose and characteristics of one of the devices.

Dosimeters, purpose, classification.

The industry produces a large number of types of radiometric and dosimetric equipment, which can be classified:

By the method of recording radiation (ionization, scintillation, etc.);

By type of detected radiation (,,,n,p)

Power source (mains, battery);

By place of application (stationary, field, individual);

By appointment.

Dosimeters - devices that measure exposure and absorbed dose (or dose rate) of radiation. Basically consist of a detector, an amplifier and a measuring device. The detector can be an ionization chamber, a gas-discharge counter or a scintillation counter.

Divided into dose rate meters- these are DP-5B, DP-5V, IMD-5, and individual dosimeters- measure the radiation dose over a period of time. These are DP-22V, ID-1, KID-1, KID-2, etc. They are pocket dosimeters, some of them are direct reading.

There are spectrometric analyzers (AI-Z, AI-5, AI-100) that allow you to automatically determine the radioisotope composition of any samples (for example, soils).

There are also a large number of alarms indicating excess background radiation and the degree of surface contamination. For example, SZB-03 and SZB-04 signal that the amount of hand contamination with beta-active substances is exceeded.

Indicate the purpose and characteristics of one of the devices

Equipment for the radiological department of the veterinary laboratory. Characteristics and operation of the SRP-68-01 radiometer.

Staff equipment for radiological departments of regional veterinary laboratories and special district or inter-district radiological groups (at regional veterinary laboratories)

Radiometer DP-100

Radiometer KRK-1 (RKB-4-1em)

Radiometer SRP 68-01

Radiometer “Besklet”

Radiometer - dosimeter -01Р

Radiometer DP-5V (IMD-5)

Set of dosimeters DP-22V (DP-24V).

Laboratories can be equipped with other types of radiometric equipment.

Most of the above radiometers and dosimeters are available at the department in the laboratory.

Periodization of hazards during a nuclear power plant accident.

Nuclear reactors use intranuclear energy released during fission chain reactions of U-235 and Pu-239. During a fission chain reaction, both in a nuclear reactor and in an atomic bomb, about 200 radioactive isotopes of about 35 chemical elements are formed. In a nuclear reactor, the chain reaction is controlled, and nuclear fuel (U-235) “burns out” in it gradually over 2 years. Fission products - radioactive isotopes - accumulate in the fuel element (fuel element). An atomic explosion can neither theoretically nor practically occur in a reactor. At the Chernobyl nuclear power plant, as a result of personnel errors and a gross violation of technology, a thermal explosion occurred, and radioactive isotopes were released into the atmosphere for two weeks, carried by winds in different directions and, settling over vast areas, creating spotty pollution of the area. Of all the r/a isotopes, the most biologically hazardous were: Iodine-131(I-131) – with a half-life (T 1/2) 8 days, Strontium - 90(Sr-90) - T 1/2 -28 years and Cesium - 137(Cs-137) - T 1/2 -30 years. As a result of the accident, 5% of the fuel and accumulated radioactive isotopes were released at the Chernobyl nuclear power plant - 50 MCi of activity. For cesium-137, this is equivalent to 100 pieces. 200 Kt. atomic bombs. Now there are more than 500 reactors in the world, and a number of countries provide themselves with 70-80% of their electricity from nuclear power plants, in Russia 15%. Taking into account the depletion of organic fuel reserves in the foreseeable future, the main source of energy will be nuclear.

Periodization of hazards after the Chernobyl accident:

1. period of acute iodine danger (iodine - 131) for 2-3 months;

2. period of surface contamination (short- and medium-lived radionuclides) - until the end of 1986;

3. period of root entry (Cs-137, Sr-90) - from 1987 for 90-100 years.