X-rays were discovered by V.K. Roentgen in 1895 and called X-rays. Over the next two years, the scientist was engaged in their research. During this period, the first x-ray tubes were created . They are the most common source of radiation.
It was found that hard X-rays can penetrate various materials, as well as human soft tissues. The latter fact quickly found application in medicine.
The discovery of x-rays at that time attracted the attention of scientists around the world. The following year, after their discovery, a huge number of works on their study and use were published.
Many scientists have studied the properties of x-rays.
J. Stokes predicted their electromagnetic nature, which was experimentally confirmed by C. Barcl, who also discovered polarization. German physicists Knipping, Friedrich, Laue revealed diffraction (phenomena associated with a deviation from rectilinear propagation). In 1913, Bragg and Wulf independently discovered a simple relationship between wavelength, diffraction angle, and the distance between nearby atomic planes on the crystal. All the above works formed the basis of structural x-ray analysis. The use of spectra for elemental material analysis began in the 1920s. A major role in the development of the study and application of radiation belongs to the Physicotechnical Institute, which was founded by A.F. Ioffe.
The most common source of rays is an x-ray tube. However, the sources may be individual radioactive isotopes. In this case, some directly emit x-rays, while in others nuclear radiation (a-particles or electrons) bombard the emitting radiation metal target. The tube has a significantly higher radiation intensity than isotopic sources. At the same time, the dimensions, cost, and weight of isotope sources are incomparably less than that of a tube installation.
Sources of soft x-ray radiation can become synchrotrons and electronic storage devices. The radiation intensity of synchrotrons is two to three orders of magnitude higher than the radiation of the tube in a certain region of the spectrum.
The natural sources that emit x-rays include the Sun and other objects in space.
In accordance with the mechanism of occurrence, the spectra and the radiation itself can be characteristic (linear) and inhibitory (continuous).
In the second case, fast particles (charged) are emitted by means of the X-ray spectrum due to their deceleration in the process of interaction with target atoms.
Linear radiation is formed as a result of atomic ionization with the ejection of an electron from one of the shells of the atom. Such a phenomenon can result from the collision of an atom and a fast particle, for example, with an electron (primary x-ray radiation), or the absorption of a photon by an atom (fluorescence x-ray).
The interaction of rays with matter can create a photoelectric effect that accompanies their absorption or scattering. This phenomenon is detected when, when an atom absorbs a photon, the first one emits one of the internal electrons. Then, either the radiative transition of an atom with the emission of a photon of characteristic radiation or the ejection of a second electron during a non-radiative transition can occur.
Under the influence of X-rays on non-metallic crystals (for example, rock salt) , ions with a positive additional charge are formed at some sites in the atomic lattice, and excess electrons appear close to them.