X-rays are a form of electromagnetic radiation at high frequency whose wavelength is between approximately 5 and 10 nanometers picometers. The energy of these photons range from a few eV (electron volt) to several tens of MeV. Ionizing radiation is used in many applications including medical imaging and crystallography.
X-rays were discovered in 1895 by German physicist Wilhelm Röntgen, who received it for the first Nobel Prize in physics. He named these rays X, because of their unknown nature at the time.
Production of X-rays
X-rays are production of energy conversion. It is product of two processes, general radiation and characteristic radiation. However only 1% of the energy converted during these two procedures is useful and produces x-rays, while the remaining 99% changes into heat.
General radiation (Bremsstralung) :
In this process, x-rays are produced by deflection. When an electron passes close to the positively charged nucleus of another atom, it is attracted to it, changing its path and slows down. While slowing down, the electron releases energy in the form of x-ray. The created photon has an energy varying from zero (minimal or no deflection) to full energy of the incoming electron. Thus it has a broad spectrum.
In this process, x-rays are produced by collision. When an electron hits the inner shell electron of the target atom, it knocks it off from the electron cloud. Consequently, a higher shell atom descends to fill this gap and during its transition it releases energy producing one x-ray. This ray has the energy of the difference between the energy of the two shells. Thus it is a characteristic of the atom, and has a narrow spectrum.
Interaction of X-rays with target:
When we discuss x-rays and their effect on a target object, we mention incident, absorbed, transmitted and deviated rays.
Incident ray: these are the rays that originate from the source, before hitting the subject.
Absorbed rays: these rays disappear after transferring all its energy to the subject. The absorption of x-rays increase with an increase in the density of the subject. However these are the rays that cause most damage to the subject.
Transmitted rays: these rays pass through the body without any interaction. These are the rays that are photographed and assess the density of different types of organs. High transmission rate means low body density and vice-versa.
Scatter rays: these rays deviate when in contact with the target, with little or no loss of energy. They are undesirable, since they interfere with transmitted rays and reduce the quality of the image. Thus they are frequently filtered out.
X-rays are produced when a beam of electrons at high speed meets a target material. During the interaction between electrons and matter, the kinetic energy of electrons is transformed into electromagnetic energy. X-ray tube consists of a cathode, responsible for the emission of electrons and an anode, a source of X-ray production. The tube is surrounded by a protective cover providing a electrical insulation, and preventing the dispersion of X-rays emitted.