X-rays are also called röntgen rays, from the name of the German physicist Konrad Wilhelm Röntgen who discovered them in 1895, demonstrating their existence by means of a radiogram of the consort's hand.
X-rays, passing through matter, produce ions, therefore they are called ionizing radiations. These radiations dissociate the molecules and, if they belong to cells of living organisms, produce cellular lesions. Because of their properties, X-rays are used in the treatment of certain types of tumors. They are also used in medical diagnostics to obtain x-rays, or "photographs" of the internal organs, made possible by the fact that the different tissues are otherwise opaque to X-rays, that is, they absorb them more or less intensely depending on their composition. Therefore, when they pass through matter, X-rays undergo an attenuation the greater the higher the thickness and specific weight of the material crossed, both dependent on the atomic number (Z) of the material itself.
In general, a radiation is made up of quanta of electromagnetic waves (photons), or of particles with mass (corpuscular radiations). A radiation, consisting of photons or corpuscles, is called ionizing when it causes the formation of ions along its path.
X-rays are made up of electromagnetic radiations, which in turn are of different types: radio waves, microwaves, infrared, visible light, ultraviolet light, X-rays and gamma rays. The path of radiation depends essentially on their interaction with the material encountered during the journey. The more energy they have, the faster they move. If they hit an object, the energy is transferred to the object itself.
Thus, passing through matter ionizing radiations give up all or part of their energy, producing ions which, in turn, if they acquire sufficient energy, produce further ions: a swarm of ions develops on the trajectory of the incident radiation that proceeds up to exhaustion of initial energy. Typical examples of ionizing radiation are X-rays and γ-rays, while corpuscular radiations can be made up of different particles: negative electrons (βˉ radiation), positive electrons or positrons (β + radiation), protons, neutrons, nuclei of the atom of helium (α radiation).
X-rays and medicine
X-rays are used in diagnostics (radiographs), while other radiations are also used in therapy (radiotherapy). These radiations are present in nature, or they are artificially produced by means of radiogenic devices and particle accelerators. The energy of X-rays is between about 100 eV (electronvolt) as regards diagnostic radiology and 108 eV as regards radiotherapy.
X-rays have the ability to penetrate through opaque biological tissues to light radiations, resulting only partially absorbed. Therefore, radiopacity of the material means the ability to absorb photons X and radiolucency means the ability to let them pass. The number of photons that can cross the thickness of a subject depends on the energy of the photons themselves, on the atomic number and on the density of the means that compose it. Thus, the resulting image results in a map of the attenuation differences of the incident photon beam, which in turn depends on the inhomogeneous structure, hence on the radiopacity of the examined body section. Radiopacities, therefore, are different between a limb, soft tissues, and a bone segment. They also differ in the chest, between the lung fields (full of air) and the mediastinum. There are also causes of pathological variation of the normal radiopacity of a tissue; for example, its increase in the case of a lung mass, or its decrease in the bone in the event of a fracture.
