Аннотация: natural emission that ionizes atoms and molecules, or the low-energy photons survived since the BigBang; also may refer to any kind of emission of any waves
Background radiation - natural phenomenon of ionization of atoms and molecules by the high-energy particles (usually, electrons, alpha-particles and photons) that come from the space (cosmic rays), from the Sun (solar wind) or from the radioactive decay of unstable isotopes.
Also, the Background radiation refers to the radio-waves, that come from the space. To avoid the ambiguity, for this meaning, the term Cosmic microwave background radiation should be used in all cases then the confusion may occur.
In general, the term radiation may refer to emission of waves of any kind - electromagnetic, acoustic, gravitation, electrons, ions, etc.
In the narrow sense, radiation refers to the emission of ionizing particles that may affect the biological objects, electronic cirquits and other machines and devices.
Usually, the background radiation refers to the ionization of atoms and molecules by the particles emitted by the natural radioactive decay of minerals (mainly, compounds of uranium) and the decay of unstable isotope of carbon, created in the upper layers of the atmosphere by the cosmic rays and the solar wind from the nitrogen atoms.
The comparable contribution to the background radiation is due to the unstable isotopes of carbon. In the atmospheric carbon dioxide (CO2). There are three naturally occurring isotopes of carbon.
Of order of 0.99 of the carbon is carbon-12,
of order of 0.01 is carbon-13,
and carbon-14 occurs in small amount of order of 10-12.
The measurement of the concentration of the unstable carbon allows the rough estimate of the age of the carbon-containing objects made of biological origin. Actually, such an analysis refers to the date when the plant had absorbed the atmospheric CO2 with "natural" concentrations. Then, 14C decays with the half-life of 5730 years, giving the relation between its concentration and the age of the object. Even at the careful measurement, the error of such a dating is usually of order of several tens of years.
The background radiation can be used for the rough calibration of the home-made Geiger counters. Such counters become popular in the USSR after the Chernobyl disaster. In the simplest case, it is assumed, that the natural level of the background radiation corresponds to 1 particle per square cm per second; at the low-efficient Geiger tube of diameter 1 cm and length 10 cm, this gives of order of 15 counts per minute. Roughly, this corresponds to the dose 15 microroentgen per hour (of order of 0.15 millierg of absorbed energy per gram per hour). The most of contribution into this background radiation is due to beta-particles of energy of order of
10-13 Joule (id est, 10-5 erg ).
The "standard" counting rate due to the background radiation depends on the kind of the Geiger tube; but the sizes of the tube, namely, the product of the length and the radius, determines the order of magnitude of the counting rate due to the background radiation; and the only the correction coefficient of order of unity
should be applied to take into account the probability of detection of a particle while it corosses the tube.
The increase of the counting rate after the thunderstorms may be attributed to the mixing of the atmosphere, delivering unstable isotopes from the upper layers to the ground. Similar increase of the counting rate one can observe in the airplane at the altitude of order of 10 km or higher. For the Geiger tubes mentioned, usually the counting rate does not increase to more than 1 count per second.
The higher counting rates (so fast that it cannot be counted by human and sounds like a cracking wood) indicates the approaching the contaminated region, or that some contaminated object is in vicinity, for example, boots or cloths, used while visiting the contaminated regions. In the most of cases (the visitor did not tried to evacuate the radioactive materials from the working nuclear reactor for the reason of the wild fire emergency), the radioactive dirt can be removed completely by the strong washing; at least, it becomes difficult to detect it above the standard noise due to the background radiation.
Persons who may have opportunity to get exposed to the ionizing radiation are recommended to calibrate their Geiger counters before the exposition to the radiation, in order to be able to compare the change of the counting rate above the level of the background radiation due to the radioactive contamination.
The rough measurement of the flux of beta-particle from the cloths is usually sufficient to confirm or negate their danger for the human body.
As for the food, the more careful measurement may necessary because some unstable isotopes (especially those of cesium, strontium, polonium and plutonium) tend to accumulate in the human tissues and the more careful analysis of products should be performed at the permanent consuming. In addition, some Geiger tubes have too thick walls and are not sensitive to the alpha-particles. In the civilized countries, such an analysis of the food is performed by default. In the Soviet Union, the use of the radioactive Turkish tea for calibration of radiometers was reported.
The analysis of the food and drink with the alpha-counter (which usually counts the beta-particles too) allows to detect the lethal amount of the radioactive poison. Such a tests are recommended for all the people who are in conflict with terroristic organizations as the KGB or "Edinaya Rossia". Would Alexander Litvinenko know this, he wold have opportunity to save his life.
In 2010, while the mass fires were reported in Russia, several authors had indicated the increase of the level of radiation in Moscow above the usual background level. This could be attributed to the burning of the forests contaminated during the Chernobyl disaster in 1986, as well as to the emergency evacuation of the radioactive materials from Sarov nuclear center.
No results of the systematic measurements of the radiation in Moscow are reported, so, it is difficult to guess the level of radiation and the most important source of it.