X-rays and their properties
X-rays or x-radiation are part of the electromagnetic spectrum with shorter wavelengths (higher frequency) than visible light. X-radiation wavelength ranges from 0.01 to 10 nanometers, or frequencies from 3×1016 Hz to 3×1019 Hz. This puts the x-ray wavelength between ultraviolet light and gamma rays. The distinction between x-ray and gamma rays may be based on wavelength or on radiation source. Sometimes x-radiation is considered to be radiation emitted by electrons, while gamma radiation is emitted by the atomic nucleus.
German scientist Wilhelm Röntgen was the first to study x-rays (1895), although he was not the first person to observe them. X-rays had been observed emanating from Crookes tubes, which were invented circa 1875. Röntgen called the light “X-radiation” to indicate it was a previously unknown type. Sometimes the radiation is called Röntgen or Roentgen radiation, after the scientist. Accepted spellings include x rays, x-rays, xrays, and X rays (and radiation).
The term x-ray is also used to refer to a radiographic image formed using x-radiation and to the method used to produce the image.
Sources of X-Rays
X-rays may be emitted whenever sufficiently energetic charged particles strike matter. Accelerated electrons are used to produce x-radiation in an x-ray tube, which is a vacuum tube with a hot cathode and a metal target. Protons or other positive ions may also be used. For example, proton-induced x-ray emission is an analytical technique. Natural sources of x-radiation include radon gas, other radioisotopes, lightning, and cosmic rays.
How X-Radiation Interacts With Matter
The three ways x-rays interact with matter are Compton scattering, Rayleigh scattering, and photoabsorption. Compton scattering is the primary interaction involving high energy hard x-rays, while photoabsorption is the dominant interaction with soft x-rays and lower energy hard x-rays. Any x-ray has sufficient energy to overcome the binding energy between atoms in molecules, so the effect depends on the elemental composition of matter and not its chemical properties.
Most people are familiar with x-rays because of their use in medical imaging, but there are many other applications of the radiation:
In diagnostic medicine, x-rays are used to view bone structures. Hard x-radiation is used to minimize absorption of low energy x-rays. A filter is placed over the x-ray tube to prevent transmission of the lower energy radiation. The high atomic mass of calcium atoms in teeth and bones absorbs x-radiation, allowing most of the other radiation to pass through the body. Computer tomography (CT scans), fluoroscopy, and radiotherapy are other x-radiation diagnostic techniques. X-rays may also be used for therapeutic techniques, such as cancer treatments.
X-rays are used for crystallography, astronomy, microscopy, industrial radiography, airport security, spectroscopy, fluorescence, and to implode fission devices. X-rays may be used to create art and also to analyze paintings. Banned uses include x-ray hair removal and shoe-fitting fluoroscopes, which were both popular in the 1920s.