Since the middle of the last century, a new word has come into science - radiation. Its discovery made a revolution in the minds of physicists around the world and allowed to discard some of the Newtonian theories and make bold assumptions about the structure of the universe, its formation and our place in it. But that's all for the experts. The townsfolk only sigh and try to put together such disparate knowledge about this subject. Complicating the process is the fact that there are quite a few units of radiation measurement, and all of them are eligible.
Terminology
The first term to get acquainted with is, in fact, radiation. This is the name given to the process of radiation by some substance of the smallest particles, such as electrons, protons, neutrons, helium atoms and others. Depending on the type of particle, the properties of radiation differ from each other. Radiation is observed either during the decay of substances into simpler ones, or during their synthesis.
Radiation units are conventional concepts that indicate how many elementary particles are released from matter. At the moment, physics operates on a familydifferent units and their combinations. This allows you to describe the various processes that occur with matter.
Radioactive decay is an arbitrary change in the structure of unstable atomic nuclei by releasing microparticles.
The decay constant is a statistical concept that predicts the probability of an atom being destroyed over a given period of time.
The half-life is the time interval during which half of the total amount of a substance decays. For some elements, it is calculated in minutes, while for others it is years, and even decades.
How is radiation measured
Radiation units are not the only ones used to evaluate the properties of radioactive materials. In addition to them, such quantities are used as:
- activity of the radiation source;- flux density (number of ionizing particles per unit area).
In addition, there is a difference in the description of the effects of radiation on living and non-living objects. So, if the substance is inanimate, then the concepts apply to it:
- absorbed dose;- exposure dose.
If the radiation affected living tissue, then the following terms are used:
- equivalent dose;
- effective equivalent dose;- dose rate.
The units of radiation measurement are, as mentioned above, conditional numerical values adopted by scientists to facilitate calculations and build hypotheses and theories. Perhaps that is why there is no single generally accepted unit of measure.
Curie
One of the units of radiation is the curie. It does not belong to the system (does not belong to the SI system). In Russia, it is used in nuclear physics and medicine. The activity of a substance will be equal to one curie if 3.7 billion radioactive decays occur in it in one second. That is, we can say that one curie is equal to three billion seven hundred million becquerels.
This number was due to the fact that Marie Curie (who introduced this term into science) conducted her experiments on radium and took its decay rate as a basis. But over time, physicists decided that the numerical value of this unit is better tied to another - the becquerel. This made it possible to avoid some errors in mathematical calculations.
In addition to curies, you can often find multiples or submultiples, such as:
- megacurie (equal to 3.7 times 10 to the 16th power of becquerels);
- kilocurie (3, 7 thousand billion becquerels);
- millicurie (37 million becquerels);- microcurie (37 thousand becquerels).
Using this unit, you can express the volume, surface or specific activity of a substance.
Becquerel
The becquerel unit of radiation dose is systemic and is included in the International System of Units (SI). It is the simplest, because a radiation activity of one becquerel means that there is only one radioactive decay per second in matter.
It got its name in honor of Antoine Henri Becquerel, a French physicist. The title wasapproved at the end of the last century and is still used today. Since this is a fairly small unit, decimal prefixes are used to indicate activity: kilo-, milli-, micro- and others.
Recently, non-systemic units such as curie and rutherford have been used along with becquerels. One rutherford is equal to one million becquerels. In the description of volumetric or surface activity, one can find the designations becquerel per kilogram, becquerel per meter (square or cubic) and their various derivatives.
X-ray
The unit of measurement of radiation, X-ray, is also not systemic, although it is used everywhere to indicate the exposure dose of received gamma radiation. One roentgen is equal to such a radiation dose at which one cubic centimeter of air at standard atmospheric pressure and zero temperature carries a charge equal to 3.3(10-10). This is equal to two million pairs of ions.
Despite the fact that under the legislation of the Russian Federation most non-systemic units are prohibited, X-rays are used in the marking of dosimeters. But they will soon cease to be used, since it turned out to be more practical to write down and calculate everything in grays and sieverts.
Rad
The unit of measurement of radiation is rad, which is outside the SI system and is equal to the amount of radiation at which one millionth of a joule of energy is transferred to one gram of a substance. That is, one rad is 0.01 joule per kilogram of matter.
The material that absorbs energy can be either living tissue or other organic andinorganic substances and substances: soil, water, air. As an independent unit, the rad was introduced in 1953 and in Russia has the right to be used in physics and medicine.
Gray
This is another unit of measure for the level of radiation, which is recognized by the International System of Units. It reflects the absorbed dose of radiation. A substance is considered to have received a dose of one gray if the energy that was transferred with radiation is equal to one joule per kilogram.
This unit got its name in honor of the English scientist Lewis Gray and was officially introduced into science in 1975. According to the rules, the full name of the unit is written with a small letter, but its abbreviated designation is capitalized. One gray is equal to one hundred rads. In addition to simple units, multiple and submultiple equivalents are also used in science, such as kilogray, megagray, decigray, centigray, microgray and others.
Sievert
The sievert unit of radiation is used to denote effective and equivalent doses of radiation and is also part of the SI system, like gray and becquerel. Used in science since 1978. One sievert is equal to the energy absorbed by a kilogram of tissue after exposure to one heating of gamma rays. The name of the unit was in honor of Rolf Sievert, a scientist from Sweden.
By definition, sieverts and grays are equal, that is, equivalent and absorbed doses have the same size. But there is still a difference between them. When determining the equivalent doseit is necessary to take into account not only the quantity, but also other properties of the radiation, such as wavelength, amplitude, and which particles represent it. Therefore, the numerical value of the absorbed dose is multiplied by the radiation quality factor.
So, for example, all other things being equal, the absorbed effect of alpha particles will be twenty times stronger than the same dose of gamma radiation. In addition, it is necessary to take into account the tissue coefficient, which shows how the organs respond to radiation. Therefore, the equivalent dose is used in radiobiology, and the effective dose is used in occupational he alth (to normalize exposure to radiation).
Solar constant
There is a theory that life on our planet appeared due to solar radiation. The units of measurement of radiation from a star are calories and watts divided by a unit of time. This was decided because the amount of radiation from the Sun is determined by the amount of heat that objects receive, and the intensity with which it comes. Only half a millionth of the total amount of energy emitted reaches the Earth.
Radiation from stars propagates in space at the speed of light and enters our atmosphere in the form of rays. The spectrum of this radiation is quite wide - from "white noise", that is, radio waves, to X-rays. Particles that also get along with the radiation are protons, but sometimes there may be electrons (if the energy release was large).
The radiation received from the Sun is the driving force of all living processes onplanet. The amount of energy we receive depends on the season, the position of the star above the horizon, and the transparency of the atmosphere.
Effect of radiation on living beings
If living tissues with the same characteristics are irradiated with different types of radiation (at the same dose and intensity), the results will vary. Therefore, to determine the consequences, only the absorbed or exposure dose is not enough, as is the case with inanimate objects. Units of penetrating radiation appear on the scene, such as sieverts rems and grays, which indicate the equivalent dose of radiation.
Equivalent is the dose absorbed by living tissue and multiplied by a conditional (table) coefficient, which takes into account how dangerous this or that type of radiation is. The most commonly used measure is the sievert. One sievert is equal to one hundred rems. The higher the coefficient, the more dangerous the radiation, respectively. So, for photons this is one, and for neutrons and alpha particles it is twenty.
Since the accident at the Chernobyl nuclear power plant in Russia and other CIS countries, special attention has been paid to the level of radiation exposure to humans. The equivalent dose from natural radiation sources should not exceed five millisieverts per year.
The action of radionuclides on non-living objects
Radioactive particles carry a charge of energy that they transfer to matter when they collide with it. And the more particles come into contact on their way witha certain amount of matter, the more energy it will receive. Its quantity is estimated in doses.
- Absorbed dose is the amount of radioactive radiation that was received by a unit of a substance. It is measured in grays. This value does not take into account the fact that the effect of different types of radiation on matter is different.
- Exposure dose - is the absorbed dose, but taking into account the degree of ionization of the substance from the effects of various radioactive particles. It is measured in coulombs per kilogram or roentgens.
