what is X-ray? How does it work?
X-rays are a form of electromagnetic radiation, as are radio waves, infrared radiation, visible light, ultraviolet radiation and microwaves. One of the most common and beneficial uses of X-rays is for medical imaging. X-rays are also used in treating cancer and in exploring the cosmos.
Electromagnetic radiation is transmitted in waves or particles at different wavelengths and frequencies. This broad range of wavelengths is known as the electromagnetic spectrum. The EM spectrum is generally divided into seven regions in order of decreasing wavelength and increasing energy and frequency. The common designations are: radio waves, microwaves, infrared (IR), visible light, ultraviolet (UV), X-rays and gamma-rays.
The electromagnetic spectrum is generally divided into seven regions, in order of decreasing wavelength and increasing energy and frequency: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays.
The electromagnetic spectrum is generally divided into seven regions, in order of decreasing wavelength and increasing energy and frequency: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays.
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X-rays are roughly classified into two types: soft X-rays and hard X-rays. Soft X-rays fall in the range of the EM spectrum between (UV) light and gamma-rays. Soft X-rays have comparatively high frequencies — about 3 × 1016 cycles per second, or hertz, to about 1018 Hz — and relatively short wavelengths — about 10 nanometers (nm), or 4 × 10−7 inches, to about 100 picometers (pm), or 4 × 10−8 inches. (A nanometer is one-billionth of a meter; a picometer is one-trillionth of a meter.) Hard X-rays have frequencies of about 1018 Hz to higher than 1020 Hz and wavelengths of about 100 pm (4 × 10−9 inches) to about 1 pm (4 × 10−11 inches). Hard X-rays occupy the same region of the EM spectrum as gamma-rays. The only difference between them is their source: X-rays are produced by accelerating electrons, while gamma-rays are produced by atomic nuclei.
History of X-rays
X-rays were discovered in 1895 by Wilhelm Conrad Röentgen, a professor at Würzburg University in Germany. According to the Nondestructive Resource Center's "History of Radiography" Web page, Röentgen noticed crystals near a high-voltage cathode-ray tube exhibiting a fluorescent glow, even when he shielded them with dark paper. Some form of energy was being produced by the tube, and it was penetrating the paper and causing the crystals to glow. Röentgen called the unknown energy "X-radiation." Experiments showed that this radiation could penetrate soft tissues but not bone, and would produce shadow images on photographic plates.
For this discovery, Röentgen was awarded the very first Nobel Prize in Physics, in 1901. During World War I, X-rays were already being used for medical purposes.
X-ray sources and effects
According to NobelPrize.org, "X-rays are produced when electrons strike a metal target. The electrons are liberated from the heated filament and accelerated by a high voltage towards the metal target." When the electrons strike the target, their energy is converted to X-rays.
X-rays can also be produced by a synchrotron, a type of particle accelerator that causes charged particles to move in a closed, circular path. When high-speed electrons are forced to move in a circular path by a magnetic field, the angular acceleration causes the particles to emit photons. If the energy is great enough, the electrons will emit X-rays.
Synchrotron radiation was seen for the first time at General Electric in the United States in 1947, according to the European Synchrotron Radiation Facility. This radiation was considered a nuisance because it caused the particles to lose energy, but it was later recognized in the 1960s as light with exceptional properties that overcame the shortcomings of X-ray tubes. One interesting feature of synchrotron radiation is that it is polarized; that is, the electric and magnetic fields of the photons all oscillate in the same direction, which can be either linear or circular.
X-ray imaging
Due to their ability to penetrate certain materials, X-rays are used for a number of nondestructive evaluation and testing (NDE/NDT) applications, particularly for identifying flaws or cracks in structural components. According to the NDT Resource Center, "Radiation is directed through a part and onto [a] film or other detector. The resulting shadowgraph shows the internal features" and whether the part is sound.
X-rays are also essential for transportation security inspections of cargo, luggage and passengers. Electronic imaging detectors allow for real-time visualization of the content of packages and items that passengers might carry on their persons.
The original use of X-rays was for imaging bones, which were easily distinguishable from soft tissues on the film that was available at that time.