Here μ0 is the linear absorption coefficient of gamma radiation.

Here μ0 is the linear absorption coefficient of gamma radiation.

Thus, during the decay of a resting π0 meson, gamma radiation with an energy of ~ 70 MeV arises. Gamma radiation from the decay of elementary particles also forms a linear spectrum. Elementary particles, which, however, experience decay, often move at speeds comparable to the speed of light. As a result, there is a Doppler extension of the line and the spectrum of gamma radiation is blurred in a wide range of energies.

Gamma radiation, which is formed during the passage of fast charged particles through matter, is caused by their inhibition to the Coulomb field of atomic nuclei of matter. Inhibitory gamma radiation, as well as X-ray radiation, is characterized by a continuous spectrum, the upper limit of which coincides with the energy of a charged particle, such as an electron. In charged particle accelerators, braking gamma radiation with a maximum energy of up to several tens of Gev is obtained.

In outer space, gamma radiation can result from collisions of quanta of softer long-wavelength, electromagnetic radiation, such as light, with electrons accelerated by the magnetic fields of space objects. In this case, the fast electron transmits its energy to electromagnetic radiation and visible light is converted into harder gamma radiation.

A similar phenomenon can occur in terrestrial conditions when high-energy electrons produced by accelerators collide with photons of visible light in intense light beams generated by lasers. An electron transmits energy to a light photon, which is converted into a γ-quantum. Thus, it is possible in practice to convert individual photons of light into quanta of high-energy gamma radiation.

Gamma radiation has a high penetrating power, ie it can penetrate through large layers of matter without noticeable attenuation. The main processes that occur during the interaction of gamma radiation with matter are photoelectric absorption (photoeffect), Compton scattering (Compton effect) and the creation of an electron-positron pair.

In the photo effect, the γ-quantum is absorbed by one of the electrons of the atom, and the energy of the γ-quantum is converted (minus the binding energy of the electron in the atom) into the kinetic energy of the electron flying out of the atom. The probability of the photoeffect is directly proportional to the fifth degree of the atomic number of the element and inversely proportional to the 3rd degree of the energy of gamma radiation. Thus, the photoeffect predominates in the region of low-energy γ-quanta (£ 100 keV) on heavy elements (Pb, U).

In the Compton effect, the γ-quantum is scattered by one of the electrons weakly bound in the atom. In contrast to the photoeffect, in the compton effect the γ-quantum does not disappear, but only changes the energy (wavelength) and direction of propagation. As a result of the compton effect, the narrow beam of gamma rays becomes wider, and the radiation itself becomes softer (long-wavelength).

The intensity of Compton scattering is proportional to the number of electrons in 1 cm3 of matter, and therefore the probability of this process is proportional to the atomic number of matter. The Compton effect becomes noticeable in substances with a small atomic number and at energies of gamma radiation exceeding the binding energy of electrons in atoms. Thus, in the case of Pb, the probability of Compton scattering is comparable to the probability of photoelectric absorption at an energy of ~ 0.5 MeV.

In the case of Al, the compton effect predominates at much lower energies. If the energy of the γ-quantum exceeds 1.02 MeV, the process of formation of electron-positron pairs in the electric field of nuclei becomes possible. The probability of pair formation is proportional to the square of the atomic number and increases with increasing hν. Therefore, at hν ~ 10 MeV, the main process in any substance is the formation of pairs.


The reverse process of electron-positron vapor annihilation is a source of gamma radiation

To characterize the attenuation of gamma radiation in a substance usually use the absorption coefficient, which shows at what thickness X of the absorber the intensity I0 of the incident beam of gamma radiation is weakened by e times:

I = I0e-μ0x.

Here μ0 is the linear absorption coefficient of gamma radiation. Sometimes a mass absorption coefficient equal to the ratio of μ0 to the absorber density is introduced.

The exponential law of attenuation of gamma radiation is valid for the narrow direction of the gamma ray beam, when any process, both absorption and scattering, removes gamma radiation from the composition of the primary beam. However, at high energies, the process of passing gamma radiation through matter becomes much more complicated.

Secondary electrons and positrons have a high energy and therefore can, in turn, create gamma radiation due to the processes of inhibition and annihilation. Thus, a number of alternating generations of secondary gamma radiation, electrons and positrons arise in matter, ie, a cascade downpour develops. The number of secondary particles in such a shower initially increases with thickness, reaching a maximum. However, then the absorption processes begin to prevail over the processes of particle reproduction and the downpour fades.

The ability of gamma radiation to develop a downpour depends on the ratio between its energy and the so-called critical energy, after which the downpour in this substance almost loses the ability to develop.

To change the energy of gamma radiation in experimental physics, gamma spectrometers of various types are used, based mainly on measuring the energy of secondary electrons. The main types of gamma-ray spectrometers: magnetic, scintillation, semiconductor, crystal diffraction.

The study of the spectra of nuclear gamma radiation provides important information about the structure of nuclei. Observation of the effects associated with the influence of the external environment on the properties of nuclear gamma radiation is used to study the properties of solids.

Gamma radiation is used in technology, for example to detect defects in metal parts – gamma flaw detection. In radiation chemistry, gamma radiation is used to initiate chemical transformations, such as polymerization processes. Gamma radiation is used in the food industry to sterilize food. The main sources of gamma radiation are natural and artificial radioactive isotopes, as well as electronic accelerators.

The effect on the body of gamma radiation is similar to the effect of other types of ionizing radiation. Gamma radiation can cause radiation damage to the body, up to its death. The nature of the effect of gamma radiation depends on the energy of γ-quanta and the spatial features of the radiation, such as external or internal. The relative biological efficiency of gamma radiation is 0.7-0.9.

In industrial conditions (chronic action in small radiation doses) the relative biological efficiency of gamma radiation is taken equal to 1. Gamma is used in medicine for the treatment of tumors, for sterilization of premises, equipment and drugs. Gamma radiation is also used to obtain mutations with the subsequent selection of economically useful forms. This leads to high-yielding varieties of microorganisms (for example, to obtain antibiotics) and plants.

Modern possibilities of radiation therapy have expanded primarily due to the means and methods of remote gamma therapy. The success of remote gamma therapy has been achieved as a result of extensive work in the use of powerful artificial radioactive sources of gamma radiation (cobalt-60, cesium-137), as well as new gamma drugs.

The great importance of remote gamma therapy is also explained by the comparative availability and ease of use of gamma devices. The latter, as well as X-ray, are designed forstatic and mobile irradiation. With the help of mobile irradiation tend to create a large dose in the tumor with scattered irradiation of healthy tissues. Constructive improvements of gamma devices have been made, aimed at reducing partial shade, improving the homogenization of fields, the use of blind filters and the search for additional protection options.

The use of nuclear radiation in crop production has opened up new, broad opportunities to change the metabolism of agricultural plants, increase their yields, accelerate development and improve quality.

As a result of the first studies of radio biologists, it was found that ionizing radiation is a powerful factor in the growth, development and metabolism of living organisms. Under the influence of gamma radiation in plants, animals or microorganisms changes the coordinated metabolism, accelerates or slows down (depending on the dose) the course of physiological processes, there are changes in growth, development, crop formation.

It should be noted that the gamma radiation in the seeds do not get radioactive substances. Irradiated seeds, as well as the crop grown from them, are non-radioactive. Optimal doses of radiation only accelerate the normal processes occurring in the plant, and therefore completely unfounded any fears and warnings against the use in food of crops obtained from seeds that have been subjected to pre-sowing irradiation.

Ionizing radiation began to be used to increase the shelf life of agricultural products and to kill various pests. For example, if the grain is passed through a hopper where a powerful radiation source is installed before loading into the elevator, the possibility of insect pest reproduction will be eliminated and the grain will be able to be stored for a long time without any losses.

The grain itself as a nutrient does not change at such doses. Its use for feed of four generations of experimental animals did not cause any abnormalities in growth, ability to reproduce and other pathological abnormalities.

Radiosensitivity and levels of radiosensitivity. Radiosensitivity is the ability of living organisms to respond to stimuli caused by the absorbed energy of ionizing radiation. Radiosensitivity is most often assessed by the lethal effects of radiation.

In 1906, Bergogne and Tribondo studied the effects of radiation on the testicles of rats and found that germ cells were significantly damaged by radiation, while interstitial cells remained intact.