Monoenergetic ionizing radiation- ionizing radiation, consisting of photons of the same energy or particles of the same type with the same kinetic energy.

Mixed ionizing radiation- ionizing radiation, consisting of particles of various types or of particles and photons.

Directional ionizing radiation ionizing radiation with a dedicated direction of propagation.

Natural radiation background- ionizing radiation created by cosmic radiation and radiation of naturally distributed natural radioactive substances (on the Earth's surface, in the near-ground atmosphere, in food, water, in the human body, etc.).

Background - ionizing radiation, consisting of a natural background and ionizing radiation from extraneous sources.

Cosmic radiation- ionizing radiation, which consists of primary radiation coming from outer space and secondary radiation resulting from the interaction of primary radiation with the atmosphere.

Narrow beam of radiation- such geometry of radiation in which the detector registers only unscattered radiation from the source.

Wide beam of radiation- such geometry of radiation, in which the detector registers unscattered and scattered radiation from the source.

Ionizing radiation field- spatio-temporal distribution of ionizing radiation in the considered environment.

Flux of ionizing particles (photons)- the ratio of the number of ionizing particles (photons) dN passing through a given surface during the time interval dt to this interval: F = dN / dt.

Particle energy flow- the ratio of the energy of the incident particles to the time interval Ψ = dЕ / dt.

The flux density of ionizing particles (photons)- the ratio of the flux of ionizing particles (photons) dF

penetrating into the volume of an elementary sphere, to the area of ​​the central cross-section dS of this sphere: φ = dF / dS = d 2 N / dtdS. (The energy flux density of the particles is determined in a similar way).

Fluence (transfer) of ionizing particles (photons) is the ratio of the number of ionizing particles (photons) dN penetrating into the volume of an elementary sphere to the area of ​​the central cross-section dS of this sphere: Ф = dN / dS.

Energy spectrum of ionizing particles- the distribution of ionizing particles by their energy. Effective photon energy is the photon energy of such a monoenergetic photon

radiation, the relative attenuation of which in an absorber of a certain composition and a certain thickness is the same as that of the considered non-monoenergetic photon radiation.

Boundary energy of the spectrumβ -radiation - the highest energy of β -particles in continuous energy spectrumβ-radiation of a given radionuclide.

Albedo of radiation is the ratio of the number of particles (photons) reflected from the interface between two media to the number of particles (photons) incident on the interface.

Delayed emission: particles emitted by decay products, as opposed to particles (neutrons and gamma rays) that arise directly at the time of fission.

Ionization in gases: detachment from an atom or gas molecule of one or more electrons. As a result of ionization, free charge carriers (electrons and ions) appear in the gas and it acquires the ability to conduct electricity.

The term "radiation" encompasses the range of electromagnetic waves, including the visible spectrum, infrared and ultraviolet regions, as well as radio waves, electric current and ionizing radiation. All the dissimilarity of these phenomena is due only to the frequency (wavelength) of the radiation. Ionizing radiation can be hazardous to human health. AND onizing radiation(radiation) - a type of radiation that changes the physical state of atoms or atomic nuclei, turning them into electrically charged ions or products of nuclear reactions. Under certain circumstances, the presence of such ions or products of nuclear reactions in the tissues of the body can change the course of processes in cells and molecules, and when these events accumulate, it can disrupt the course of biological reactions in the body, i.e. pose a danger to human health.

2. TYPES OF RADIATION

Distinguish between corpuscular radiation, consisting of particles with a mass other than zero, and electromagnetic (photon) radiation.

2.1. Corpuscular radiation

Corpuscular ionizing radiation includes alpha radiation, electron, proton, neutron and meson radiation. Corpuscular radiation, consisting of a stream of charged particles (α-, β-particles, protons, electrons), the kinetic energy of which is sufficient to ionize atoms at

collision, belongs to the class of directly ionizing radiation. Neutrons and other elementary particles do not directly ionize, but in the process of interacting with the medium, they release charged particles (electrons, protons) that can ionize the atoms and molecules of the medium through which they pass.

Accordingly, corpuscular radiation, consisting of a stream of uncharged particles, is called indirectly ionizing radiation.

Fig. 1. Decay scheme for 212 Bi.

2.1.1 Alpha radiation

Alpha particles (α - particles) are the nuclei of a helium atom, emitted during α - decay by some radioactive atoms. α - particle consists of two protons and two neutrons.

Alpha radiation is a flux of nuclei of helium atoms (positively charged and

relatively heavy particles).

Natural alpha radiation as a result of radioactive decay of the nucleus is characteristic of unstable nuclei of heavy elements, starting with an atomic number of more than 83, i.e. for natural radionuclides of the series of uranium and thorium, as well as for artificially obtained transuranium elements.

A typical scheme of α-decay of a natural radionuclide is shown in Fig. 1, and the energy spectrum of α -particles formed during the decay of a radionuclide is shown in

Fig. 2.

Fig. 2 Energy spectrum of α -particles

The possibility of α-decay is associated with the fact that the mass (and, therefore, the total energy of ions) of the α-radioactive nucleus is greater than the sum of the masses of the α-particle and the daughter nucleus formed after α-decay. The excess energy of the original (mother) nucleus is released in the form of the kinetic energy of the α-particle and the recoil of the daughter nucleus. α-particles are positively charged nuclei of helium - 2 He4 and fly out of the nucleus at a speed of 15-20 thousand km / sec. On their way, they produce strong ionization of the environment,

ripping electrons out of the orbits of atoms.

The range of α-particles in air is about 5-8 cm, in water - 30-50 microns, in metals - 10-20 microns. During ionization by α-rays, chemical changes are observed in the substance, and the crystal structure is disturbed solids... Since there is electrostatic repulsion between the α-particle and the nucleus, the probability of nuclear reactions under the influence of α-particles of natural radionuclides (the maximum energy is 8.78 MeV for 214 Po) is very small, and is observed only on light nuclei (Li, Be, B, C , N, Na, Al) with the formation of radioactive isotopes and free neutrons.

2.1.2 Proton radiation

Proton radiation- radiation generated in the process of spontaneous decay of neutron-deficient atomic nuclei or as an output beam of an ion accelerator (for example, synchrophasotoron).

2.1.3 Neutron radiation

Neutron radiation - a flux of neutrons that convert their energy in elastic and inelastic interactions with atomic nuclei. With inelastic interactions, secondary radiation arises, which can consist of both charged particles and gamma quanta (gamma radiation). In elastic interactions, the usual ionization of matter is possible.

Sources of neutron radiation are: spontaneously fissioning radionuclides; specially made radionuclide neutron sources; accelerators of electrons, protons, ions; nuclear reactors; cosmic radiation.

From the point of view of biological Neutrons are formed in nuclear reactions (in nuclear reactors and in other industrial and laboratory installations, as well as in nuclear explosions).

Neutrons have no electrical charge. Conventionally, neutrons, depending on the kinetic energy, are divided into fast (up to 10 MeV), ultrafast, intermediate, slow and thermal. Neutron radiation has a high penetrating power. Slow and thermal neutrons enter into nuclear reactions, as a result, stable or radioactive isotopes can be formed.

A free neutron is an unstable, electrically neutral particle with the following

properties:

These properties of the neutron make it possible to use it, on the one hand, as an object that is being studied and, on the other hand, as a tool for conducting research. In the first case, we investigate unique properties neutron, which is relevant and makes it possible to most reliably and accurately determine the fundamental parameters of the electroweak interaction and, thereby, either confirm or refute Standard model... The presence of a magnetic moment in a neutron already indicates its complex structure, i.e. its "non-elementarity". In the second case, the interaction of unpolarized and polarized neutrons different energies with nuclei allows them to be used in the physics of nuclei and elementary particles. The study of the effects of violation of spatial parity and invariance with respect to time reversal in various processes - from neutron optics to fission of nuclei by neutrons - is by no means a complete list of the most urgent research directions.

The fact that thermal reactor neutrons have wavelengths comparable to the interatomic distances in matter makes them an indispensable tool for studying condensed matter. The interaction of neutrons with atoms is relatively weak, which allows neutrons to penetrate deep enough into matter - this is their significant advantage over X-rays and γ-rays, as well as beams of charged particles. due to the presence of mass, neutrons at the same momentum (hence, at the same wavelength) have significantly less energy than X-rays and γ-rays, and this energy turns out to be comparable to the energy of thermal vibrations of atoms and molecules in matter, which makes it possible to study not only the average static atomic structure of a substance, but also the dynamic processes occurring in it. The presence of a magnetic moment in neutrons makes it possible to use them to study the magnetic structure and magnetic excitations of matter, which is very important for understanding the properties and nature of magnetism of materials.

Scattering of neutrons by atoms is mainly due to nuclear forces, therefore, the cross sections for their coherent scattering are in no way related to the atomic number (in contrast to X-ray and γ-rays). Therefore, irradiation of materials with neutrons makes it possible to distinguish the positions of atoms of light (hydrogen, oxygen, etc.) elements, the identification of which is almost impossible using X-rays and γ - rays. For this reason, neutrons are successfully used in the study of biological objects, in materials science, in medicine, and other fields. In addition, the difference in neutron scattering cross sections for different isotopes makes it possible not only to distinguish elements with similar atomic numbers in a material, but also to study their isotopic composition. The presence of isotopes with a negative amplitude of coherent scattering provides a unique opportunity to contrast the media under study, which is also very often used in biology and medicine.

Coherent scattering- scattering of radiation with conservation of frequency and with a phase that differs by π from the phase of the primary radiation. The scattered wave can interfere with the incident wave or other coherently scattered waves.

For those who are not familiar with physics or are just starting to study it, the question of what is radiation is difficult. But with the given physical phenomenon we meet almost every day. To put it simply, radiation is the process of energy propagation in the form of electromagnetic waves and particles, or, in other words, it is energy waves propagating around.

Radiation source and its types

The source of electromagnetic waves can be both artificial and natural. For example, X-rays are referred to as artificial radiation.

You can feel the radiation without even leaving your home: you just have to hold your hand over a burning candle, and immediately you will feel the radiation of heat. It can be called thermal, but besides it, there are several other types of radiation in physics. Here is some of them:

• Ultraviolet - a person can feel this radiation on himself while sunbathing.
• X-rays have the shortest wavelengths, these are called X-rays.
• Even a person can see infrared rays, an example of this is an ordinary children's laser. This type of radiation is formed when microwave radio emissions and visible light coincide. Infrared radiation is often used in physiotherapy.
• Radioactive radiation is generated during the decay of radioactive chemical elements. You can learn more about radiation from the article.
• Optical radiation is nothing more than light radiation, light in the broadest sense of the word.
• Gamma radiation is a type of electromagnetic radiation with a short wavelength. Used, for example, in radiation therapy.

Scientists have long known that some radiation has a detrimental effect on the human body. How strong this effect will be depends on the duration and power of the radiation. If you expose yourself long time radiation, this may lead to changes in cellular level... All electronic equipment that surrounds us, be it a mobile phone, a computer or a microwave oven - all this has an impact on health. Therefore, you need to be careful not to expose yourself to unnecessary radiation.

A person is constantly under the influence of various external factors. Some of them are visible, such as weather conditions, and their impact can be controlled. Others are not visible to the human eye and are called radiation. Everyone should know the types of radiation, their role and applications.

A person can meet some types of radiation everywhere. Radio waves are a prime example. They represent vibrations of an electromagnetic nature that are capable of being distributed in space at the speed of light. Such waves carry energy from generators.

The sources of radio waves can be divided into two groups.

1. Natural, these include lightning and astronomical units.
2. Artificial, that is, man-made. They include alternating current emitters. These can be radio communication devices, broadcasting devices, computers and navigation systems.

Human skin is capable of depositing this type of waves on its surface, therefore there are a number of negative consequences of their impact on humans. Radio wave radiation can slow down the activity of brain structures, as well as cause mutations at the genetic level.

For persons with a pacemaker installed, such exposure is fatal. These devices have a clear maximum allowable level of radiation, the rise above it introduces an imbalance in the operation of the stimulator system and leads to its breakdown.

All the effects of radio waves on the body have been studied only in animals, there is no direct evidence of their negative effect on humans, but scientists are still looking for ways of protection. As such, there are no effective methods yet. The only advice is to stay away from dangerous devices. Since household appliances connected to the network also create a radio wave field around them, it is simply necessary to turn off the power to devices that a person does not use at the moment.

Infrared emission

All types of radiation are related in one way or another. Some of them are visible to the human eye. Infrared radiation adjoins the part of the spectrum that the human eye can catch. It not only illuminates the surface, but is also capable of heating it.

The main natural source of infrared rays is the sun. Man has created artificial emitters, through which the necessary thermal effect is achieved.

Now we need to figure out how useful or harmful this type of radiation is for humans. Almost all long-wave infrared radiation is absorbed by the upper layers of the skin, therefore it is not only safe, but also capable of increasing immunity and enhancing regenerative processes in tissues.

As for short waves, they can go deep into tissues and cause overheating of organs. The so-called heatstroke is a consequence of exposure to short infrared waves. The symptoms of this pathology are known to almost everyone:

• the appearance of spinning in the head;
• feeling of nausea;
• increase in heart rate;
• visual disturbances characterized by darkening in the eyes.

How can you protect yourself from dangerous influences? It is necessary to observe safety precautions when using heat-protective clothing and screens. The use of short-wave heaters should be accurately dosed, the heating element should be covered with a heat-insulating material, with the help of which the radiation of soft long waves.

If you think about it, all types of radiation can penetrate tissues. But it was X-ray radiation that made it possible to use this property in practice in medicine.

If we compare the rays of X-ray origin with the rays of light, then the former are very long, which allows them to penetrate even through opaque materials. Such rays are not able to be reflected and refracted. This type of spectrum has a soft and hard component. Soft consists of long waves that can be completely absorbed by human tissues. Thus, constant exposure to long waves leads to cell damage and DNA mutation.

There are a number of structures that are unable to transmit X-rays through them. These include, for example, bone and metals. Based on this, images of human bones are taken in order to diagnose their integrity.

Currently, devices have been created that allow not only to take a fixed picture, for example, of a limb, but also to observe the changes taking place with it “online”. These devices help the doctor to perform surgical intervention on the bones under visual control, without making wide traumatic incisions. With the help of such devices, it is possible to study the biomechanics of the joints.

As for the negative impact x-rays, then prolonged contact with them can lead to the development of radiation sickness, which manifests itself in a number of signs:

• neurological disorders;
• dermatitis;
• decreased immunity;
• oppression of normal hematopoiesis;
• development of oncological pathology;
• infertility.

To protect yourself from terrible consequences, when in contact with this type of radiation, you need to use shielding shields and pads made of materials that do not let the rays through.

People used to call this type of rays simply - light. This type of radiation is able to be absorbed by the object of influence, partially passing through it and partially reflected. Such properties are widely used in science and technology, especially in the manufacture of optical devices.

All sources of optical radiation are divided into several groups.

1. Thermal ones with a continuous spectrum. Heat is released in them due to the current or the combustion process. These can be electric and halogen incandescent lamps, as well as pyrotechnic products and electric lighting devices.
2. Luminescent, containing gases excited by streams of photons. Such sources are energy saving devices and cathodoluminescent devices. As for radio- and chemiluminescent sources, fluxes in them are excited due to the products of radioactive decay and chemical reactions respectively.
3. Plasma, whose characteristics depend on the temperature and pressure of the plasma formed in them. These can be gas discharge, mercury tube and xenon lamps. Spectral sources, as well as devices of a pulsed nature, are no exception.

Optical radiation on the human body acts in combination with ultraviolet radiation, which provokes the production of melanin in the skin. Thus, the positive effect lasts until the threshold value of exposure is reached, beyond which the risk of burns and cutaneous oncopathology is located.

The most famous and widely used radiation, the effects of which can be found everywhere, is ultraviolet radiation. This radiation has two spectra, one of which reaches the earth and participates in all processes on earth. The second is trapped by a layer of ozone and does not pass through it. The ozone layer neutralizes this spectrum, thereby fulfilling a protective role. The destruction of the ozone layer is dangerous by the penetration of harmful rays to the surface of the earth.

The natural source of this type of radiation is the Sun. A huge number of artificial sources have been invented:

• Erythema lamps, activating the production of vitamin D in the layers of the skin and helping to treat rickets.
• Solariums, not only allowing sunbathing, but also having a healing effect for people with pathologies caused by a lack of sunlight.
• Laser emitters used in biotechnology, medicine and electronics.

As for the impact on the human body, it is twofold. On the one hand, a lack of ultraviolet radiation can cause various diseases. Dosed loading with such radiation helps the immune system, the work of muscles and lungs, and also prevents hypoxia.

All types of influences are divided into four groups:

• the ability to kill bacteria;
• removal of inflammation;
• restoration of damaged tissues;
• reduction of pain.

The negative effects of ultraviolet radiation include the ability to provoke skin cancer with prolonged exposure. Melanoma of the skin is an extremely malignant type of tumor. Such a diagnosis means almost 100 percent impending death.

With regard to the organ of vision, excessive exposure to ultraviolet rays damages the retina, cornea and the lining of the eye. Thus, this type of radiation should be used in moderation. If, under certain circumstances, you have to be in contact with a source of ultraviolet rays for a long time, then you must protect your eyes with glasses, and your skin with special creams or clothing.

These are the so-called cosmic rays, which carry the nuclei of atoms of radioactive substances and elements. The flux of gamma radiation has a very high energy and is able to quickly penetrate the cells of the body, ionizing their contents. Destroyed cellular elements act like poisons, decomposing and poisoning the entire body. The process necessarily involves the cell nucleus, which leads to mutations in the genome. Healthy cells are destroyed, and in their place mutant cells are formed, unable to fully provide the body with everything it needs.

This radiation is dangerous because a person does not feel it in any way. The consequences of exposure do not appear immediately, but have a long-term effect. First of all, cells of the hematopoietic system, hair, genitals and lymphoid system are affected.

Radiation is very dangerous by the development of radiation sickness, but even this spectrum has found useful applications:

• it is used to sterilize products, equipment and medical instruments;
• measuring the depth of underground wells;
• measuring the path length of spacecraft;
• impact on plants in order to identify productive varieties;
• in medicine, such radiation is used to conduct radiation therapy in the treatment of oncology.

In conclusion, it must be said that all types of rays are successfully applied by man and are necessary. Thanks to them, plants, animals and people exist. Protection from overexposure should be a priority rule when working.

Radiation

in a broad sense, the emission of rapidly moving charged particles or waves and the formation of their fields. I. - a form of release and distribution of energy. Exists different kinds I. Mechanical I. includes noise, infrasound, and ultrasound. The second group consists of electromagnetic and corpuscular I. The main characteristics of mechanical and electromagnetic I. are frequency and wavelength, the action of any I. depends on their energy. I. are also divided into ionizing and non-ionizing. There are a number of forms of I., in particular: visible - optical I. with a wavelength from 740 nm (red light) to 400 nm (violet light), which determines the visual sensations of a person; ultraviolet - electromagnetic radiation invisible to the eye within the wavelength range from 400 to 10 nm; infrared - optical radiation with a wavelength of 770 nm (that is, more than visible), emitted by heated bodies; sound - excitement sound waves in an elastic (solid liquid and gas) medium, including audible sound (from 16 to 20 kHz), infrasound (less than 16 kHz), ultrasound (from 21 kHz to 1 GHz) and hyperevuk (more than 1 GHz); ionizing - electromagnetic (X-rays and gamma rays) and corpuscular (alpha and beta particles, flux of protons and neutrons) radiation, to one degree or another penetrates into living tissues and produces changes in them associated or with "knocking out") electrons from atoms and molecules, or with direct and indirect generation of ions; electromagnetic - the process of emission of electromagnetic waves and the alternating field of these waves.

EdwART. Glossary of terms of the Ministry of Emergency Situations, 2010

Antonyms:

See what "Radiation" is in other dictionaries:

Electromagnetic, classic electrodynamics education el. magn. waves with accelerated moving charge. chsami (or alternating currents); into a quantum. the theory of the creation of photons when the state of a quantum changes. systems; the term "I." also used for ... ... Physical encyclopedia

The process of emission and propagation of energy in the form of waves and particles. In the overwhelming majority of cases, radiation is understood as electromagnetic radiation, which in turn can be divided by radiation sources into thermal radiation, ... ... Wikipedia

Outpouring, outpouring, effusion, light, emission, emanation, radiation, radiation, sheaf, vibroacoustic treatment. Dictionary of Russian synonyms. radiation emanation (book) Dictionary of synonyms of the Russian language. Practical guide. M .: Russian language. Z. E. ... ... Synonym dictionary

RADIATION, radiation, cf. (book). Action according to ch. radiate radiate and radiate radiate. Radiation of heat from the sun. Heat radiation. Non-thermal radiation. Radioactive radiation. Explanatory dictionary Ushakov. D.N. Ushakov. 1935 1940 ... Ushakov's Explanatory Dictionary

Modern encyclopedia

Electromagnetic free formation process electromagnetic field; the free electromagnetic field itself is also called radiation. Emitting accelerated moving charged particles (eg, bremsstrahlung, synchrotron radiation, ... ... Big Encyclopedic Dictionary

Radiation- electromagnetic, the process of formation of a free electromagnetic field, as well as the free electromagnetic field itself, which exists in the form of electromagnetic waves. Radiation is emitted by accelerated moving charged particles, as well as atoms, ... ... Illustrated Encyclopedic Dictionary

RADIATION, energy transfer by ELEMENTARY PARTICLES OR ELECTROMAGNETIC WAVES. Any ELECTROMAGNETIC RADIATION passes through VACUUM, which distinguishes it from such phenomena as THERMAL CONDUCTIVITY, CONVECTION and sound transmission. In a vacuum ... ... Scientific and technical encyclopedic dictionary

radiation- working electronic equipment. Topics information security EN emanation ... Technical translator's guide

RADIATE, ayu, ayu; not sov. that. Emit rays, emit radiant energy. I. light I. warm. The eyes radiate tenderness (trans.). Ozhegov's Explanatory Dictionary. S.I. Ozhegov, N.Yu. Shvedova. 1949 1992 ... Ozhegov's Explanatory Dictionary

Radiation, radiation (Radiation, emanation) the body's return to space of the energy contained in it in the form of electromagnetic waves. Samoilov K.I. Marine vocabulary... M. L .: State Naval Publishing House of the NKVMF of the USSR, 1941 ... Marine dictionary

Books

• Radiation in astrophysical plasma, Zheleznyakov VV. In the monograph, from a unified point of view, the general principles of generation and transfer of radiation in astrophysical plasma are presented. It meets the needs of both radio and X-ray ...

To use the preview of presentations, create yourself a Google account (account) and log into it: https://accounts.google.com

Slide captions:

Radiation

Radiation e - the transfer of energy by the emission of electromagnetic waves. It can be the sun's rays, as well as the rays emitted by heated bodies around us. These rays are called heat radiation. When radiation, spreading from the source body, reaches other bodies, then part of it is reflected, and part is absorbed by them. When absorbed, the energy of thermal radiation is converted into the internal energy of bodies, and they are heated. All objects around us radiate heat to one degree or another.

What dress is hot in summer

With an increase in body temperature, thermal radiation increases, i.e. the higher the body temperature, the more intense the heat radiation. How fantastic would look the world if we could see the thermal radiation of other bodies inaccessible to our eye!

DO YOU KNOW? Snakes perfectly perceive heat radiation, but not with their eyes, but with their skin. Therefore, in complete darkness, they are able to detect a warm-blooded victim.

Materials have been created that can be used to convert thermal radiation into visible radiation. They are used in the manufacture of special photographic film for shooting in absolute darkness and in night vision devices - thermal imagers.

night vision devices thermal imagers

1) Which of the types of heat transfer is accompanied by the transfer of matter A) Thermal conductivity B) Convection C) Radiation Test on the topic: types of heat transfer

2) With heat transfer by radiation A) Energy is transferred by jets and streams of matter B) Energy is transferred through layers of stationary matter C) Energy can be transferred in airless space

3) How is the transfer of energy from the Sun to the Earth A) Thermal conductivity B) Convection C) Radiation

4) After turning on the table lamp and with the lamp, the book lying on the table warmed up. Choose the correct statement A) The book is heated by convection in the air B) The book is heated by radiation C) The book gets hotter the lighter the cover

5) Heat transfer by radiation and convection is possible through A) Atmospheric air B) Down duvet C) Metal plate

6) What determines the intensity of convection A) From the speed of movement of molecules B) From the temperature difference C) From the strength of the wind

7) Thanks to what method of heat transfer can you warm yourself near a fire? A) Thermal conductivity B) Convection C) Radiation

8) What kind of heat transfer is NOT accompanied by the transfer of matter? A) Convection and thermal conductivity; B) Radiation and convection; B) Thermal conductivity and radiation

9) What is the name of the type of convection in which warm air from the battery rises up A) Artificial B) Natural C) Forced

10) What is the name of the type of convection when we mix hot tea with a spoon for cooling A) Artificial B) Natural C) Forced