The Invention of X-rays were done by a German physicist called Wilhelm Roentgen. In 1895 Roentgen discovered X-rays almost by accident. Whilst doing some experiments in which he passed an electric current through Crookes tubes (special tubes containing a cathode and electrode from which the air has been removed), Roentgen noticed that photographic plates nearby began to grow fogged.

When a stream of very fast high-energy electrons strikes a metallic electrode (anode), the electrons are slowed down, and some of them penetrate into the metal (Fig.1). The sudden braking of the electron produces an electromagnetic radiation of very short wavelength: X-rays or Roentgen rays. This radiation is generated by electrons penetrating into the metal and interacting with the metal atoms.

To discover why this occurred he placed black paper on the tube and then switched on the current. Nearby a screen coated with barium began to glow. This caused Roentgen to believe that unknown rays produced inside the tube were passing through the paper to make this fluorescent substance give out light. These he named X-rays since x is a scientific number for anything that is unknown.

The main use of X-rays is in medicine. A common application is in the form of X-ray machines, which take photos of a patient’s body. If an arm or leg were broken for example, then this limb would be put in front of the X-ray with a piece of photographic film behind. The X –ray is turned on briefly and goes through to the film. The rays go through the skin and flesh easily, showing up as dark areas on the film, but with more difficulty through bone. They are slowed down and so these areas are much lighter. X-rays can also be used to kill cancer cells, but also kill healthy cells, so must be used with much care.

Other uses are in industry, at airports to check customers and baggage and by art historians to see if a picture has been painted on top of an older one. X-ray diffraction is also very important in spectroscopy and as a basis for X-ray crystallography. The diffraction of X-rays by a crystal where the wavelength of X-rays is comparable in size to the distances between atoms in most crystals is used to disperse X-rays in a spectrometer and to determine the structure of crystals or molecules.

It shows well-defined wavelengths which are characteristic of the structure of the metal forming the anode: a high-energy electron which penetrates into the metal atom may dislodge one of the inner electrons of that atom: the vacant place is taken by one of the outer electrons which thus leaps from an outer to an inner “shell” and in doing so, emits energy in the form of radiation, i.e., X-rays.

X-rays was created whenever high-energy electrons suddenly gave up energy. Machines produce x-rays by accelerating electrons to extremely high speeds and then crashing them into a piece of solid material called a target. There, the electrons rapidly slowed down because they collide with atoms in the target, and part of the energy is changed into x-rays.

As a rule, the stream of electrons (such electrons issuing from a cathode are called cathode rays ) is not directed against the actual anode, but against the anticathode, which forms a target for bombardment. The impingement of the electrons against the anticathode causes the latter to become very hot, and it may be necessary to cool it or to design it as a rotating anode, so that the cathode rays are always beamed on a fresh area of the anode surface.

Because of their short wavelength (10 8 to 10 12 cm) X-rays can pass through objects which are opaque to ordinary light, and shadow images of such objects can be made visible on a fluorescent screen coated with barium platinocyanide. When X-rays pass through crystalline substances, diffraction phenomena occur which reveal the wave character of this radiation. An interference pattern composed of a regular arrangement of dots can be formed on a photographic plate, and these provide information as to the crystal structure of the material concerned. Such diffraction patterns were first studied scientifically by M. Von Laue, and they are known as Laue X-ray patterns (Fig.5).

A danger associated with X-rays is the extremely high voltage that occurs. In human beings an overdose exposure of X-rays may produce cancer, skin burns, and a reduction of the blood supply or other serious conditions. In plants or animals they may damage or even destroy living tissue.

Most X-rays from sources in space are absorbed by the atmosphere before they reach the earth .Sometimes a harmless substance is injected into the body to make certain organs stand out clearly on a radiograph or fluoroscopic image. The Japanese satellite provided astronomers with data that indicates the X-rays in the universe came from a larger number of galaxies than previously thought. Observations indicated that X-rays were emitted from a small number of galaxies with black holes.