Chapter VII New research in all fields. On methods of radiation protection in medicine and pseudo-methods of removing radiation from the body Study of the radioactivity of drugs
The radioactivity of preparations can be determined by the absolute, calculated and relative (comparative) methods. The latter is the most common.
absolute method. A thin layer of the test material is applied to a special very thin film (10-15 μg/cm²) and placed inside the detector, as a result of which the full solid angle (4) of registration of emitted, for example, beta particles is used and almost 100% counting efficiency is achieved. When working with a 4 counter, it is not necessary to introduce numerous corrections, as with the calculation method.
The activity of the drug is immediately expressed in units of activity Bq, Ku, mKu, etc.
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 the loss of radiation during the measurement.
A =N/ q r m 2,22 10 ¹²
A- activity of the drug in Ku;
N- counting rate in pulses/min minus the background;
- correction for geometric measurement conditions (solid angle);
-correction for the resolution time of the counting unit;
-correction for radiation absorption in the air layer and in the window (or wall) of the counter;
-correction for self-absorption in the preparation layer;
q-correction for backscattering from the substrate;
r- correction for the decay scheme;
-correction for gamma radiation with mixed beta, gamma radiation;
m- weight of the measuring preparation in mg;
2,22 10 ¹² - conversion factor from the number of disintegrations per minute to Ki (1Ki = 2.22 * 10¹² dis / min).
To determine the specific activity, it is necessary to convert the activity per 1 mg to 1 kg .
Aud= A*10 6 , (TOu/kg)
Preparations for radiometry can be prepared thin, thick or intermediate layer the material under study.
If the test material has half attenuation layer - 1/2,
then thin
- at d<0,11/2,
intermediate
- 0,11/2
All correction factors themselves, in turn, depend on many factors and, in turn, are calculated using complex formulas. Therefore, the calculation method is very laborious.
Relative (comparative) method has found wide application in determining the beta activity of drugs. It is based on comparing the count rate from a reference (drug of known activity) with the count rate of the drug being measured.
In this case, there should be completely identical conditions for measuring the activity of the reference and the test preparation.
Apr \u003d Aet *Netc/Nthis, where
Aet is the activity of the reference preparation, rasp/min;
Apr is the radioactivity of the preparation (samples), rasp/min;
Net-counting rate from the standard, imp/min;
Npr - counting rate from the preparation (samples), imp/min.
In passports for radiometric and dosimetric equipment, it is usually indicated with what error the measurements are made. Limit 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 parts of the scale).
According to the limiting relative error ± %, it is possible to determine the limit absolute measurement error. If the readings of instrument A are taken, then the absolute error А=А/100. (If A=20 mR, a=25%, then actually A= (205) mR. That is, within the range of 15 to 25mR.
Detectors of ionizing radiation. Classification. The principle and scheme of operation of the scintillation detector.
Radioactive radiation can be detected (isolated, detected) using special devices - detectors, whose operation is based on the physicochemical effects that occur when radiation interacts with matter.
Types of detectors: ionization, scintillation, photographic, chemical, calorimetric, semiconductor, etc.
The most widespread are detectors based on measuring the direct effect of the interaction of radiation with matter - the 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 registration method is based on the property of scintillators to emit visible light radiation (light flashes - scintillations) under the action of charged particles, which are converted by a photomultiplier into electric current pulses.
Cathode Dinodes Anode The scintillation counter consists of a scintillator and
FEU. Scincillators can be organic and
inorganic, in solid, liquid or gas
condition. It is lithium iodide, zinc sulfide,
sodium iodide, angracene single crystals, etc.
100 +200 +400 +500 volts
PMT work:- Under the influence of nuclear particles and gamma quanta
Atoms are excited in the scintillator and emit visible color quanta - photons.
Photons bombard the cathode and knock out photoelectrons from 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 enters the cathode and is recorded by the electronic circuit of the device. The counting efficiency of scintillation counters reaches 100%. Scintillation counters are widely used in radiometric equipment.
Radiometers, purpose, classification.
By appointment.
radiometers - devices intended for:
Measurements of the activity of radioactive preparations and radiation sources;
Determining the flux density or intensity of ionizing particles and quanta;
Surface radioactivity of objects;
Specific activity of gases, liquids, firmaments and bulk substances.
Radiometers mainly use gas-discharge counters and scintillation detectors.
They are divided into portable and stationary.
As a rule, they consist of: - a pulse detector; - a pulse amplifier; - a counting device; - an electromechanical or electronic numerator; - a high voltage source for the detector; - a power supply for all equipment.
In order to improve, the following were produced: radiometers B-2, B-3, B-4;
decatron radiometers PP-8, RPS-2; automated laboratories "Gamma-1", "Gamma-2", "Beta-2", equipped with a computer, allowing to calculate up to several thousand samples with automatic printing of results. DP-100 installations, radiometers KRK-1, SRP-68 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:
According to the method of registration of radiation (ionization, scintillation, etc.);
By type of detected radiation (,,,n,p)
Power source (mains, battery);
At the place of application (stationary, field, individual);
By appointment.
Dosimeters - devices that measure the exposure and absorbed dose (or dose rate) of radiation. They mainly 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.
Subdivided 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 signaling devices for exceeding the radiation background, the degree of contamination of surfaces. For example, SZB-03 and SZB-04 signal the excess of contamination of hands with beta-active substances.
Indicate the purpose and characteristics of one of the devices
Equipment of the radiological department of the veterinary laboratory. Characteristics and operation of the SRP-68-01 radiometer.
Standard equipment of 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 “Beresklet”
Radiometer - dosimeter -01R
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 in case of an accident at a nuclear power plant.
Nuclear reactors use intranuclear energy released during chain reactions of U-235 and Pu-239 fission. In 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 a TVEL (fuel element). In a reactor, an atomic explosion cannot occur either theoretically or practically. 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 territories, created patchy 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. At the Chernobyl nuclear power plant, as a result of the accident, 5% of the fuel and accumulated radioactive isotopes were thrown out - this is 50 MCi of activity. For cesium-137, this is equivalent to 100 pcs. 200 ct. atomic bombs. Now there are more than 500 reactors in the world, and a number of countries provide themselves with electricity by 70-80% at the expense of nuclear power plants, in Russia 15%. Taking into account the depletion of organic fuel reserves in the foreseeable future, nuclear energy will be the main source of energy.
Periodization of hazards after the Chernobyl accident:
1. period of acute iodine hazard (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 income (Cs-137, Sr-90) - from 1987 for 90-100 years.
Natural sources of ionizing radiation. Cosmic radiation and natural RV. Dose from ERF.
RADIOACTIVE DRUGS- radioactive substances containing radioactive nuclides, manufactured in various forms and intended for various purposes. In medicine R. items are used for diagnosis of diseases, and also treatment of hl. arr. malignant neoplasms.
Distinguish two groups of R. of the item - closed and open.
Closed R. p. enclosed in a shell of non-toxic material (platinum, gold, stainless steel, etc.), which prevents direct contact of the radioactive substance with the environment. At gamma-emitting R. of the item the cover carries out function of the filter for beta radiation (see) and low-energy gamma radiation (see). These drugs are used for application, interstitial and intracavitary radiation therapy (see). The most frequently used are gamma-emitting radionuclides, in which artificial radioactive isotopes of cobalt (60 Co), gold (198 Au), tantalum (182 Ta), cesium (131 Cs), and others are used as radionuclides. natural radioactive nuclide radium. Also used are preparations of the radioactive isotope California (252 Cf), which is mainly a source of fast neutrons (see Neutron therapy). Closed R. of the item differ in a big variety of an external form. The most widely used linear R. items in the form of needles and tubes (cylinders). The needles are hollow cylinders, one end of which is pointed, and the other has an eye for pulling the thread. Pieces of wire (pins) with a diameter, as a rule, less than 1 mm, made of an alloy of nickel and cobalt containing radioactive 60Co, are placed inside the needle. The length of the pin is called the active length of the R. p. Standard sets include cobalt needles with a pin length from 5 to 50 mm, and the total length of the needles is from 13.5 to 58.5 mm. Tubes (cylinders) differ from needles in that they do not have a pointed end, their active length ranges from 10 to 60 mm. In linear R. p., the radionuclide is distributed either evenly along the entire length - 0.0625 microcurie / mm (2.3 MBq / mm), or unevenly with increased linear activity at the ends. A variety of linear R. p. are pieces of cobalt, tantalum or iridium wire of very small size (diameter 0.7 mm, length 3 mm), coated with a layer of gold or platinum, which are inserted into nylon hollow threads (tubes). Use also preparations 198Au, having the form of granules to dia. 0.8 mm and 2.5 mm long, the surface of which is coated with a layer of platinum. The activity of each granule is about 3.5 microcuries (130 MBq). In addition to linear, closed R. items can have a spherical shape with a through hole in the center for threading (radioactive beads).
Sometimes, for surface applications, a dummy is preliminarily made from an easily molded material (wax, plastic) that repeats the shape of the part of the surface being irradiated. This dummy with the closed R. of the item introduced into it is called a radioactive mask. During interstitial radiation therapy, closed R. p. in the form of needles, pins, granules, nylon threads are introduced directly into the tumor tissue using special tools (see Radiological Instrumentation, Radiosurgery). With intracavitary radiation therapy (see Gamma therapy), a closed R. p. of a linear form is introduced into the endostat - a hollow tube previously inserted into the uterus, bladder, rectum, etc.
Open R. p.- radionuclides that are in various states of aggregation (true and colloidal solutions, gases, suspensions, absorbable threads and films), which, when used, come into direct contact with organs and tissues, i.e., involved in the metabolism and activity of individual organs and systems. Open R. items are used for diagnostic and therapeutic purposes. For diagnosis use preparations of radionuclides with a short effective half-life (see), which causes a slight radiation load on the body. They are characterized by the absence of toxic effects and the presence of beta or gamma radiation, which can be registered by radiometric methods (see). The most widely used in the study of the functions of the kidneys, liver, brain, lungs and other organs, central and peripheral hemodynamics, various compounds labeled with isotopes of technetium (99m Tc), iodine (131 I), indium (111 In, 113m In), as well as gaseous R. p. of xenon (133 Xe), krypton (85 Kr), oxygen (15 O), etc. The introduction of R. p., depending on their form, is carried out by ingestion, intravenous administration, inhalation, etc. (see. radiopharmaceuticals).
With to lay down. the purpose open R. of the item is most often used in the form of colloidal solutions (see. Radioactive colloids ). The choice of a radionuclide is determined by a short (preferably no more than a few days) half-life, a small effective half-life of the compound, suitable physical properties of the radiation used, and the absence of a toxic effect on the body. The radioactive isotopes of yttrium (90 Y), phosphorus (32 P), and gold (198 Au) meet these requirements most completely. Open R. p. are injected into the tumor tissue by injection using protective syringes (see Beta therapy),
R. items are made industrially and delivered to lay down. institutions. R. items are kept in special protective rooms - storages, from where they are delivered in transport lead containers to radio manipulation rooms (see the Radiological Department). The preparation and breeding of open R. p. is carried out in special boxes, fume hoods and radio manipulation chambers to exclude the possibility of radioactive isotopes getting on the surface of the body or inside the body of medical staff as a result of contamination of hands, tools, inhaled air (see Radiation protection, Radiological protective technological equipment).
Bibliography: Zedgenidze G. A. and Zubovsky G. A. Clinical radioisotope diagnostics, M., 1968; Pavlov A. S. Interstitial gamma and beta therapy of malignant tumors, M., 1967; Afterloading, 20 years of experience, 1955-1975, ed. by B. Hilaris, N. Y., 1975.
V. S. Datsenko, M. A. Fadeeva.
Artificial radioactive drugs
A woman who had just left the examination table was operated on for a tumor six months ago. Now she reappeared, as she again felt unwell, and although the professor at first said nothing to his assistants about this case, they knew what was the matter. The patient obviously had a relapse, the resumption of growth of a malignant tumor, because of which she appeared.
We will give her a radioactive drug, - the professor said to the young doctors; turning to the patient, he added: - This will put you in order again.
The drug that the professor was talking about, a metal artificially made radioactive, placed in the body of a sick person, emits rays, as you know, capable of destroying cells, and above all the more sensitive cells of a cancerous tumor. Ever since scientists learned about this, artificially made radioactive substances have played an important role in medicine. But if we want to talk about their essence and structure, we must first talk about isotopes, special substances, once again indicating that modern man is able to do a lot.
When Wilhelm Conrad Roentgen discovered rays in 1895, later named after him, not only physicists, but the whole world was deeply excited by this revolution, and they immediately began to expect great practical benefits from it.
The French physicist Henri Becquerel, in search of highly fluorescent substances, turned his attention to potassium uranium compounds, which at that time were much talked about in scientific circles. Radium was not yet known at that time.
And it turned out that the uranium compounds of potassium, subjected to the action of light, actually emitted rays. At first, scientists thought that these were x-rays, but then it turned out that this was not true. Becquerel discovered a special kind of rays that are capable of penetrating through paper and thin tin and causing a blackening of a photographic plate placed behind a sheet of tin. These rays were first called becquerel rays, and then radioactive.
The physicist Pierre Curie also learned about the work of Becquerel, who suggested that his young wife Maria, nee Sklodowska, study Becquerel rays as the topic of his doctoral work. What this advice led to is known: Marie Curie discovered radium and proposed the now accepted name "radioactive radiation" for Becquerel's rays.
There is no need to tell a novel about radium here. It is known to most readers. Marie Curie also discovered other radioactive substances, such as polonium, which she named after her homeland, Poland. It was one of the greatest scientific discoveries. Since that time, thousands of researchers have studied radium, wanting to find out its properties. They found that its radiation weakens extremely slowly and the substance is used up by half only within 1580 years. It was further discovered that in this case a gas is formed, the so-called emanation, which also emits rays, but with a duration of action much shorter than that of radium itself. Finally, it was established that the radiation of radium is a mixture of three types of rays, which were designated by the first three letters of the Greek alphabet. Alpha rays are positively charged helium nuclei, which are ejected with great force by the latter; beta rays have a high penetrating power, allowing them to pass through wood and thin tin; gamma rays are endowed with this ability to an even greater extent, are hard rays and resemble x-rays.
With further study of radioactivity, it was established that a chemical element is not something absolutely unified, but sometimes consists of atoms of several types. Such elements are called isotopes. They differ from one another not in different special properties, but in different atomic weights. All this would hardly be of interest to physicians if, in 1934, the daughter of the great Marie Curie, Irene Curie, and her husband Frederic Joliot had failed to create an artificial radioactive substance. They subjected a piece of aluminum to the action of alpha rays, destroyed the nuclei of aluminum atoms by such bombardment and obtained an isotope of phosphorus - a substance that does not exist in nature. It was the first man-made radioactive drug. Subsequently, many others were created, and new, better methods were naturally developed to obtain them. It soon became clear that artificial isotopes should be of great importance for medicine, in particular, radioactive phosphorus, radioactive iodine, and others. At first, diagnostic studies and physiological observations were meant to study, for example, the metabolic process in the body, the rate of blood flow in the body and in individual organs, especially in the heart, which would make it possible to identify defects in it. The use of artificial radioactive preparations can sometimes be supplemented by x-ray studies.
Man-made radioactive drugs have some properties that X-rays do not have. They require contrast agents that they cannot penetrate. If a person swallows an iron nail, it is directly visible on the screen and is very clear in the picture. But with a stomach ulcer, the situation is different: the contrast must be created artificially. Therefore, a patient undergoing X-ray examination should drink a suspension of barium sulfate, which absorbs X-rays. Thanks to this, the doctor sees on the screen the corresponding changes in the gastric mucosa and can make a diagnosis.
When using an artificial radioactive preparation, the situation is somewhat different. Take, for example, the thyroid gland, which is known to be a very complex organ. We know that she voraciously consumes iodine. Wanting to know the path of iodine in the thyroid gland, we can give a sick person radioactive iodine. This drug breaks down in a natural way and emits rays; we, however, are not able to see them, but we can establish their presence, measure and thereby trace the fate of the introduced iodine with the help of special apparatus. Radioactive iodine is used to destroy a neoplasm (tumor) of the thyroid gland, malignant goiter. If you give such a patient radioactive iodine, then the latter, greedily absorbed by the thyroid gland, disintegrates within a short time and emits rays into the surrounding tissues, that is, into the cancer cells of the tumor, and these rays, as already mentioned, have destructive power. In this way, you can try to save the life of the patient, or at least prolong it.
This area of expertise has grown enormously, and most clinics already have isotope treatment units. With many diseases, this is still the only way that can lead to success. In addition to iodine, a number of other elements are currently used that have been converted into radioactive and have the necessary effect.
Of course, these should be elements that have some kind of relationship, "affinity", to the relevant organs. Such "inclinations", "affinity", are observed often. Just as the thyroid gland needs iodine and therefore absorbs it, so the bone marrow needs phosphorus. Therefore, in this case, radioactive phosphorus can be used and introduced into the body, since it will be eagerly absorbed by the bones and bone marrow.
Radioactive gold preparations are of great importance for the treatment of various diseases and, in particular, some malignant tumors. They are resorted to when surgical treatment is impossible or not indicated. But this method of treatment requires certain caution and control by the doctor. The blood and bone marrow can also give an unfavorable reaction, and with disorders of the liver and kidneys, or with more significant circulatory disorders, treatment with radioactive gold is poorly tolerated by patients.
There is another metal, also very suitable for the treatment of malignant neoplasms, if it is artificially made radioactive. This is cobalt. It can be given radioactivity in a nuclear reactor. The radioactivity of cobalt persists for a long time, for several years. In addition, in some cases, cobalt treatment is more convenient than X-ray treatment, since cobalt can be injected into various body cavities. The greatest value is the treatment of cancer of the female genital organs with cobalt. Radioactive cobalt has the property that its rays are able to penetrate the skin and act on the formations located under it, which must be destroyed or damaged.
There are other isotopes used in medicine. Undoubtedly, this chapter of hers is still far from being completed. It will be necessary to find metals and other elements that have a special affinity and inclination for certain organs, like the affinity between iodine and the thyroid gland. Then it will be easy to artificially make these elements radioactive and use them to treat a number of diseases.
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Introduction
We humans live in a world that can be called radioactive. Places where there is an absolute absence of radioactivity, in nature, in the habitat of animals, there are no people. Radioactivity is a natural formation, cosmic rays, radioactive nuclides scattered in the environment, 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 some area, usually associated with nuclear power plants, violate this average level. And the most dangerous combination of circumstances for a person is when radionuclides enter the human body. Moreover, with 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 the increased ionizing power due to the double charge.
The relevance of the work lies in the fact that the idea of the absolute danger of any radioactive exposure is practically fixed in the public mind, and therefore it seems necessary to consider the physical nature of the pathological effects of radioactivity on living organisms and assess the levels of risk and danger.
Objective: to make an attempt to evaluate the bremsstrahlung of 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 for its study;
2. Explore the possibility of using school physical equipment;
3.Develop 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 deceleration (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 oncological disease.
Object of study:α-particle during its deceleration in biological tissues under internal irradiation.
Subject of study: component of energy loss of an α-particle due to electromagnetic radiation.
Part 1. On the nature of radiation.
-
Rice. 1. A. Becquereli
discovery of radioactivity and its biological action
-
1896 French physicist A. Becquerel, studying the phenomenon of luminescence of uranium salts, found that uranium salt emits rays of an unknown type, which pass through paper, wood, thin metal plates, ionize the air. In February 1896, Becquereli failed to conduct another experiment due to cloudy weather. Becquerel put the record in a drawer, placing on top of it a copper cross covered with uranium salt. Having shown the plate, just in case, two days later, he found 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 Maria Skłodowska-Curie, exploring uranium ores, discovered new chemical elements: polonium, radium. It turned out that all chemical elements, starting with the serial number 83, have radioactivity. 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.
- Forms of radioactivity
1898 Exposing radioactive radiation to the action of a magnetic field, E. Rutherford singled out 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 from Gamma rays that are not deflected by electric and magnetic fields.
Rice. 3. Alpha radiation
Rice. 2. Effect of a magnetic field on the trajectory of particle motion
Rice. 4. Beta radiation
After Rutherforth established the structure of the atom, it became clear that radioactivity is a nuclear process. In 1902, E. Rutherford and F. Soddy proved that as a result of radioactive decay, the atoms of one chemical element are transformed into atoms of another chemical element, accompanied by the emission of various particles.
Alpha particles, beta particles, ejected from the nucleus, have significant kinetic energy and, acting on matter, 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 an orbit closer to an orbit more distant from the nucleus ). Ionization and penetration to a certain depth are of fundamental importance for assessing the impact of ionizing radiation on biological tissue of various types of radiation. Knowing the properties of different types of radiation to penetrate different materials, a person can use them for his own 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. Arises as a result of the decay of atoms of heavy elements such as uranium, radium and thorium. A type of radioactive decay of the nucleus, as a result of which the helium nucleus 4 He is emitted - an alpha particle. In this case, the mass number of the nucleus decreases by 4, and the atomic number - by 2.
In general, the alpha decay formula looks like this:
An example of alpha decay for the isotope 238 U:
Fig.5. Alpha decay of uranium 238
Alpha particles formed during the decay of the nucleus have an initial kinetic energy in the range of 1.8-15 MeV. When an alpha particle moves in a substance, it creates a strong ionization of the surrounding atoms, as a result, it loses energy very quickly. The energy of alpha particles resulting from radioactive decay is not enough even to overcome the dead layer of the skin, so there is no radiation risk from external exposure to such alpha particles. External alpha radiation is hazardous to health only in the case of high-energy alpha particles (with energies above tens of MeV), the source of which is the accelerator. However, the penetration of alpha-active radionuclides inside the body, when living tissues of the body are directly exposed to radiation, is very dangerous for health, since a high ionization density along the particle track severely damages biomolecules. It is believed that with equal energy release (absorbed dose), the equivalent dose gained during internal irradiation with alpha particles with energies characteristic of radioactive decay is 20 times higher than with 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 arising from the alpha decay of radionuclides that have entered the body (in particular, through the respiratory tract or the digestive tract). A microscopic amount of α-radioactive substance is enough to cause acute radiation sickness in the 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 matter, which increases the chances of cell damage when the radiation source enters the body. However, external radiation from radioactive sources is harmless, since alpha particles can be effectively trapped by several centimeters of air or tens of micrometers of dense matter - for example, a sheet of paper and even the horny dead layer 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 quanta, 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 the characteristics of an α-particle
The existence of electromagnetic waves was the main prediction. J.K. Maxwell (1876), this theory is presented in the section of the school course in physics - electrodynamics. "Electrodynamics" is the science of electromagnetic waves, the nature of their occurrence, propagation in different media, interaction with various substances, structures.
And in this science there is one of the fundamental statements that any particle with an electric charge, 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 quickly stops, which, after acceleration 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 run only from 5 to 40 microns, the α-particle stops. At the same time, experiencing a tremendous slowdown and having a double charge, they cannot but create an electromagnetic impulse.
I, using the usual school laws of mechanics and the law of conservation of energy, calculated the initial speed of α-particles, the magnitude of negative acceleration, the time of movement of the α-particle to a stop, the resistance force of its movement and the power developed by it.
It is clear that the energy of the α-particle goes to the destruction of the cells of the body, the ionization of atoms, in one case more, when leaving other radioactive nuclei it is less, but the radiation energy created in a short time of flight from about 5 to 40 microns cannot exceed the energy α -particles that they have when they fly out.
When calculating, I used as initial known characteristics only the energy of α-particles (this is its kinetic energy) and the average path length in the biological tissues of the body (L= 5 - 40 microns). The mass of the α-particle and its composition, I found in the reference book.
The energy of their α-particles is 4-10 MeV. It was for such α-particles that I carried out the calculations.
The mass of an α-particle is 4 amu; 1 amu = 1.660 10 -27 kg;
m \u003d 4 1.660 10 -27 \u003d 6.64 10 -27 kg - the mass of the α-particle.
Track length of an α-particle.
q = 2 1.6 = 3.2 - charge
E k \u003d 7 MeV \u003d 7 10 6 1.6 10 -19 \u003d 11.2 10 -13 J is the kinetic energy of the α-particle.
F \u003d ma \u003d 6.64 10 -27 8.4 10 18 \u003d 5.5 10 -8 N is the drag force of the α-particle.
Table 1 characterization of the α-particle.
.3. α-radiation power and electromagnetic safety standardsInformation from the directory:
1. The penetration depth δ 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 microns). 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 depths of penetration, attenuation of the electromagnetic wave for a frequency of 10 GHz are indicated. In our case, a single pulse of an electromagnetic wave can be interpreted as a positive part of one period, i.e. the closest frequency would be 230 GHz.
For biological tissue in the maximum purity specified in the handbook equal to 10 GHz. According to our calculations, a single pulse of an electromagnetic wave can be represented as a short pulse with a frequency of 230 GHz. From the handbook, we can conclude that with an increase in the frequency of electromagnetic waves, 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 band (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 also 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 a distance between them are equal to δ, then after passing through n such surfaces, the initial intensity (power) of the electromagnetic wave will be reduced by a factor of . 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 the alpha particle is mainly spent on the formation of a track of ionized particles. Therefore, you can accept.
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 at a sphere radius (8δ \u003d 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 track of the α-particle will die, i.e. they will be located in a space, a volume through which an electromagnetic wave passes with a radiation power density exceeding the critical radiation density defined by the SanPiN norms. These dead cells (more precisely, their remains) will be removed from the body almost without any consequences due to the mechanisms of regeneration of the body.
The most dangerous of the consequences of such an electromagnetic shock for cells will be that in some spherical layer of cells surrounding the dangerous sphere there will be such half-killed cells, the correct functioning of some will most likely be disrupted by the electromagnetic pulse that “broke” (broke, broke) the structure of DNA , which is responsible for the "correct" regeneration of this cell.
Part 3: Designing and Conducting Experiments
3.1. Measurement of radioactive background on the territory of MBOU secondary school No. 11
Purpose: to measure the radioactive background on the territory of MBOU secondary school No. 11.
Hypothesis: precipitation and wind carry different types of particles (in our case, we are interested in radioactive particles).
Equipment: dosimeter.
Digital radiation monitor
For 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 fallen into it. The device can be used to measure the level of alpha, beta and gamma radiation. 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 the level of radiation.
Rice. 7 Sensor of ionizing radiation (dosimeter)
TECHNICAL CHARACTERISTICS 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 against Cesium-137. 3. Accuracy: . for visual calibration: ± 20% of full scale; . with instrumental 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 background radiation levels.
Progress of work: To do this, we measured the radiation background of our school in different months. In winter, the wind direction is south (side AB).
Rice. 8 Plan MBOU secondary school No. 11
Table 2. Radioactive background of the territory of MBOU secondary school No. 11.
results
In the south side, the measured background radiation is greater than in the north side, which means that wind and precipitation do carry different types of particles.
I also took measurements at the sewer (these are points F and K) and the dosimeter readings are slightly higher there, and this proves that it is water that is the carrier of radionuclides.
3.2. Study of the dependence of the absorbed dose on the distance to the geometric center of the drug in a flat geometry.
The purpose of the work: to study the dependence of the absorbed dose on the distance to the geometric center of the drug in a flat geometry.
Equipment: ruler, dosimeter, potassium hydroxide.
Progress of work: measure the radioactive level, moving the drug away from the dosimeter for every centimeter.
Rice. 9 The results of the dependence of the absorbed dose on the distance to the geometric center of the drug with a flat geometry.
The experiment shows that with a flat geometry of a radioactive preparation, the dependence of the absorbed dose on the distance to the center of the preparation differs from the quadratic one in the case of a point preparation. For flat geometry, this distance dependence is weaker.
Conclusion.
Estimates and calculations show that the radiation power density in the tissue area, the immediate environment of the track, exceeds ten times the permissible electromagnetic safety standards, which leads to complete cell death in this area. But the existing mechanism of regeneration will restore the dead cells and preserve all the functions of these cells. The main danger to the body is the presence of a spherical layer of cells surrounding this central area. 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 an oncological pathology.
Literature
1. Sh.A. Gorbushkin - ABC of physics
2. GD Luppov - Supporting notes and test tasks ("Educational literature", 1996);
3. P.V. Glinskaya - For applicants to universities ("Brothers Grinin", 1995);
Chemical Encyclopedia (Soviet Encyclopedia, 1985);
4. Gusev N. G., Klimanov V. A., Mashkovich V. P., Suvorov A. P. - Protection from ionizing radiation;
5. A. I. Abramov, Yu. A. Kazansky, E. S. Matusevich. Fundamentals of experimental methods of nuclear physics (3rd ed., revised and supplemented. M., Energoatomizdat, 1985);
6. Radiation safety standards (NRB-99/2009) (Ministry of Health of Russia, 2009);
7. Moiseev A. A., Ivanov V. I. Handbook of dosimetry and radiation hygiene (2nd ed., revised and supplemented by M., Atomizdat, 1974);
8. Physical Encyclopedia (Soviet Encyclopedia, 1994. Vol. 4. Poynting-Robertson);
9. Mukhin KN - 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. and etc.; Kiev: Naukova Dumka, 1990.-224 p.
The work was added to the site site: 2016-06-20Order writing a unique work
" xml:lang="en-EN" lang="en-EN">Topic: Methods for determining the radioactivity of drugs
" xml:lang="en-EN" lang="en-EN">Questions:
" xml:lang="en-EN" lang="en-EN">1. Absolute method for measuring radioactivity2. Calculation method for measuring radioactivity
" xml:lang="en-EN" lang="en-EN"> 3. Relative method for measuring radioactivity
" xml:lang="en-EN" lang="en-EN">Absolute method for measuring radioactivity
The absolute method is used in the absence of the necessary reference sources for measuring preparations by the relative method or in the case of an unknown isotopic composition of radionuclides contained in the test sample.
In the radiometry of preparations by the absolute method, installations are used that make it possible to register all beta particles formed during the decay of radionuclides, or a precisely established part of them. Such devices include installations with end or 4
- counters (for example, radiometer 2154-1M "Protoka", UMF-3, etc.). The measured drug is placed inside the counter and surrounded on all sides by the working volume of gas. Due to this, almost all beta particles emitted from the preparation are captured and recorded, i.e., almost 100% counting efficiency is practically achieved. Thus, when working with such a counter, corrections for absorption and scattering in the preparation and substrate are minimized. But detectors of this type are more complex than gas-discharge counters." xml:lang="en-EN" lang="en-EN">To determine the absolute activity on installations with 4
;font-family:"Symbol"" xml:lang="en-EN" lang="en-EN">" xml:lang="en-EN" lang="en-EN">-counters the test material is applied in a thin layer on special films (acetate, colloid, etc.) with a thickness of 10-15 µg/cm;vertical-align:super" xml:lang="en-EN" lang="en-EN">2"xml:lang="en-EN" lang="en-EN">. To improve the measurement accuracy (better than 10-15%), the substrate films are metallized by applying a metal layer using special sputtering units, for example, the universal vacuum spraying unit UVR- 2. The thickness of the applied metal layer should be 5-7 µg/cm;vertical-align:super" xml:lang="en-EN" lang="en-EN">2" xml:lang="en-EN" lang="en-EN">. The conversion factor (K) in this case will be 4.5;font-family:"Symbol"" xml:lang="en-EN" lang="en-EN">" xml:lang="en-EN" lang="en-EN">10;vertical-align:super" xml:lang="en-EN" lang="en-EN">-13" xml:lang="en-EN" lang="en-EN"> Ki/(imp/min).Calculation method for measuring radioactivity
The calculation method is used if installations with end counters are used for measurement. To do this, the drugs are placed under the counter window at a distance of 20-30 mm from it. Beta emitters with low energy should be located at a distance of 6-7 mm from the counter. To compare the count rate with the activity, a number of correction factors are introduced into the measurement results that take into account radiation losses during radiometry.
" xml:lang="en-EN" lang="en-EN">Absolute activity of preparations A
;vertical-align:sub" xml:lang="en-EN" lang="en-EN">pr"xml:lang="en-EN" lang="en-EN">(Ki) of the thin and intermediate layers is determined by the formula:" xml:lang="en-EN" lang="en-EN">
" xml:lang="en-US" lang="en-US">N;vertical-align:sub" xml:lang="en-EN" lang="en-EN">0" xml:lang="en-EN" lang="en-EN">A
;vertical-align:sub" xml:lang="en-EN" lang="en-EN">pr" xml:lang="en-EN" lang="en-EN">=" xml:lang="en-EN" lang="en-EN"> 2.22
;font-family:"Symbol"" xml:lang="en-EN" lang="en-EN">" xml:lang="en-EN" lang="en-EN">10;vertical-align:super" xml:lang="en-EN" lang="en-EN">12;font-family:"Symbol"" xml:lang="en-US" lang="en-US">" xml:lang="en-US" lang="en-US">KP;font-family:"Symbol"" xml:lang="en-US" lang="en-US">" xml:lang="en-US" lang="en-US">mqr;vertical-align:super" xml:lang="en-EN" lang="en-EN">" xml:lang="en-EN" lang="en-EN">where
" xml:lang="en-US" lang="en-US">N;vertical-align:sub" xml:lang="en-EN" lang="en-EN">0" xml:lang="en-EN" lang="en-EN"> - drug counting rate (without background), imp/min;;font-family:"Symbol"" xml:lang="en-US" lang="en-US">" xml:lang="en-EN" lang="en-EN"> - coefficient taking into account the geometric factor of measurement;;font-family:"Symbol"" xml:lang="en-US" lang="en-US">" xml:lang="en-EN" lang="en-EN"> - correction for the resolution time of the counter; K - coefficient that takes into account the absorption of beta radiation in the air layer and the material of the counter window; P - coefficient of self-absorption of beta radiation in drug material;;font-family:"Symbol"" xml:lang="en-US" lang="en-US">" xml:lang="en-EN" lang="en-EN"> - correction for gamma radiation at mixed radiation;" xml:lang="en-US" lang="en-US">m" xml:lang="en-EN" lang="en-EN"> – mass of the measured preparation;" xml:lang="en-US" lang="en-US">q" xml:lang="en-EN" lang="en-EN"> - coefficient that takes into account the backscattering of beta radiation from the aluminum substrate;" xml:lang="en-US" lang="en-US">r;vertical-align:super" xml:lang="en-EN" lang="en-EN">" xml:lang="en-EN" lang="en-EN"> - correction for decay scheme.coefficient r , which takes into account the correction for the decay scheme, i.e. the relative content of beta radiation in the preparation, for many beta emitters is 1. For the potassium-40 radionuclide, the coefficient r is 0.88, since 88% of 100% decay acts are beta decay, and 12% - to K-capture, accompanied by gamma radiation.
When determining the specific activity, the formula takes the form:
" xml:lang="en-EN" lang="en-EN"> 1
;font-family:"Symbol"" xml:lang="en-EN" lang="en-EN">" xml:lang="en-EN" lang="en-EN">10;vertical-align:super" xml:lang="en-EN" lang="en-EN">6;font-family:"Symbol"" xml:lang="en-EN" lang="en-EN">" xml:lang="en-EN" lang="en-EN">" xml:lang="en-US" lang="en-US">N;vertical-align:sub" xml:lang="en-EN" lang="en-EN">0" xml:lang="en-EN" lang="en-EN">A
;vertical-align:sub" xml:lang="en-EN" lang="en-EN">pr" xml:lang="en-EN" lang="en-EN">=" xml:lang="en-EN" lang="en-EN"> 2.22
;font-family:"Symbol"" xml:lang="en-EN" lang="en-EN">" xml:lang="en-EN" lang="en-EN">10;vertical-align:super" xml:lang="en-EN" lang="en-EN">12;font-family:"Symbol"" xml:lang="en-US" lang="en-US">" xml:lang="en-US" lang="en-US">KP;font-family:"Symbol"" xml:lang="en-US" lang="en-US">" xml:lang="en-US" lang="en-US">mqr;vertical-align:super" xml:lang="en-EN" lang="en-EN">where, 1 10 6 - conversion factor when converted to 1 kg when measuring m in mg.
Relative method for measuring radioactivity
The relative method for determining the radioactivity of preparations is based on the comparison of the counting rate from a standard (drug with known activity) with the counting rate of the measured preparation. The advantage of this method is simplicity, efficiency and satisfactory reliability. As a standard, radionuclides are used that are identical or close in physical properties radionuclides contained in the measured preparations (radiation energy, decay pattern, half-life). Measurements of the standard and the preparation are carried out under the same conditions (on the same installation, with the same counter, at the same distance from the counter, on a substrate of the same material and the same thickness, the preparation and the standard must have the same geometric parameters: area, shape and thickness).
" xml:lang="en-EN" lang="en-EN">It is desirable to have a long-lived radioactive isotope as a reference, since it can be used long time without amendment. For radiometry of samples of environmental objects containing beta-emitting radionuclides, potassium-40, strontium-90 + yttrium-90, T
" xml:lang="en-US" lang="en-US">h" xml:lang="en-EN" lang="en-EN">-234. For the manufacture of a standard from potassium-40, chemically pure salts of KC1 or" xml:lang="en-US" lang="en-US">K;vertical-align:sub" xml:lang="en-EN" lang="en-EN">2" xml:lang="en-US" lang="en-US">SO;vertical-align:sub" xml:lang="en-EN" lang="en-EN">4" xml:lang="en-EN" lang="en-EN">.;vertical-align:sub" xml:lang="en-EN" lang="en-EN">" xml:lang="en-EN" lang="en-EN">First, the count rate is measured from the standard" xml:lang="en-US" lang="en-US">N;vertical-align:sub" xml:lang="en-EN" lang="en-EN">et" xml:lang="en-EN" lang="en-EN"> then the count rate from the drug" xml:lang="en-US" lang="en-US">N;vertical-align:sub" xml:lang="en-EN" lang="en-EN">pr" xml:lang="en-EN" lang="en-EN">. Based on the fact that the count rate from the standard is proportional to the activity of the standard, and the count rate from the drug is proportional to the activity of the drug, the radioactivity of the test drug is found.A floor N pr
A floor N floor \u003d A pr N pr A pr \u003d
" xml:lang="en-EN" lang="en-EN">
" xml:lang="en-US" lang="en-US">N;vertical-align:sub" xml:lang="en-EN" lang="en-EN">et" xml:lang="en-EN" lang="en-EN">where A
;vertical-align:sub" xml:lang="en-EN" lang="en-EN">et" xml:lang="en-EN" lang="en-EN"> - radioactivity of the standard, dist/min; A;vertical-align:sub" xml:lang="en-EN" lang="en-EN">pr" xml:lang="en-EN" lang="en-EN"> - radioactivity of the drug (samples), dis/min;" xml:lang="en-US" lang="en-US">N;vertical-align:sub" xml:lang="en-EN" lang="en-EN">et" xml:lang="en-EN" lang="en-EN">- counting rate from the standard, imp/min;" xml:lang="en-US" lang="en-US">N;vertical-align:sub" xml:lang="en-EN" lang="en-EN">pr" xml:lang="en-EN" lang="en-EN"> -count rate from the drug (sample), imp/min." xml:lang="en-EN" lang="en-EN">The comparative method gives results that are satisfactory in terms of accuracy, if it is known that the radionuclide composition of the measured sample is the same or close to the reference one.