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X-ray

This article is about the nature, production, and uses of the radiation. For the method of imaging, see Radiography. For the medical specialty, see Radiology. For other meanings, see X-ray (disambiguation).
Not to be confused with X-wave or X-band.

An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz (30×1015 Hz to30×1018 Hz) and energies in the range 124 eV to 124 keV. X-ray wavelengths are shorter than those of UV rays and typically longer than those of gamma rays. In many languages, X-radiation is referred to as Röntgen radiation, after the German scientist Wilhelm Conrad Röntgen, who discovered it on November 8, 1895. He named it X-radiation to signify an unknown type of radiation. Spellings of X-ray(s) in English include the variants x-ray(s), xray(s), and X ray(s).

X-rays are part of the electromagnetic spectrum, with wavelengths shorter than UV light. Different applications use different parts of the X-ray spectrum.
X-ray image of human lungs

Contents

Pre-Röntgen observations and research

Example of a Crookes tube, a type of discharge tube that emitted X-rays

Before their discovery in 1895, X-rays were just a type of unidentified radiation emanating from experimental discharge tubes. They were noticed by scientists investigating cathode rays produced by such tubes, which are energetic electron beams that were first observed in 1869. Many of the early Crookes tubes (invented around 1875) undoubtedly radiated X-rays, because early researchers noticed effects that were attributable to them, as detailed below. Crookes tubes created free electrons by ionization of the residual air in the tube by a high DC voltage of anywhere between a few kilovolts and 100 kV. This voltage accelerated the electrons coming from the cathode to a high enough velocity that they created X-rays when they struck the anode or the glass wall of the tube.

The earliest experimenter thought to have (unknowingly) produced X-rays was actuary William Morgan. In 1785 he presented a paper to the Royal Society of London describing the effects of passing electrical currents through a partially evacuated glass tube, producing a glow created by X-rays. This work was further explored by Humphry Davy and his assistant Michael Faraday.

When Stanford University physics professor Fernando Sanford created his "electric photography" he also unknowingly generated and detected X-rays. From 1886 to 1888 he had studied in the Hermann Helmholtz laboratory in Berlin, where he became familiar with the cathode rays generated in vacuum tubes when a voltage was applied across separate electrodes, as previously studied by Heinrich Hertz and Philipp Lenard. His letter of January 6, 1893 (describing his discovery as "electric photography") to The Physical Review was duly published and an article entitled Without Lens or Light, Photographs Taken With Plate and Object in Darkness appeared in the San Francisco Examiner.

Starting in 1888, Philipp Lenard conducted experiments to see whether cathode rays could pass out of the Crookes tube into the air. He built a Crookes tube with a "window" at the end made of thin aluminum, facing the cathode so the cathode rays would strike it (later called a "Lenard tube"). He found that something came through, that would expose photographic plates and cause fluorescence. He measured the penetrating power of these rays through various materials. It has been suggested that at least some of these "Lenard rays" were actually X-rays.

In 1889 Ukrainian-born Ivan Puluj, a lecturer in experimental physics at the Prague Polytechnic who since 1877 had been constructing various designs of gas-filled tubes to investigate their properties, published a paper on how sealed photographic plates became dark when exposed to the emanations from the tubes.

Hermann von Helmholtz formulated mathematical equations for X-rays. He postulated a dispersion theory before Röntgen made his discovery and announcement. He based it on the electromagnetic theory of light.{{Full citation needed|date=October }2021} However, he did not work with actual X-rays.

In 1894 Nikola Tesla noticed damaged film in his lab that seemed to be associated with Crookes tube experiments and began investigating this invisible, radiant energy. After Röntgen identified the X-ray, Tesla began making X-ray images of his own using high voltages and tubes of his own design, as well as Crookes tubes.

Discovery by Röntgen

On November 8, 1895, German physics professor Wilhelm Röntgen stumbled on X-rays while experimenting with Lenard tubes and Crookes tubes and began studying them. He wrote an initial report "On a new kind of ray: A preliminary communication" and on December 28, 1895, submitted it to Würzburg's Physical-Medical Society journal. This was the first paper written on X-rays. Röntgen referred to the radiation as "X", to indicate that it was an unknown type of radiation. The name stuck, although (over Röntgen's great objections) many of his colleagues suggested calling them Röntgen rays. They are still referred to as such in many languages, including German, Hungarian, Ukrainian, Danish, Polish, Bulgarian, Swedish, Finnish, Estonian, Turkish, Russian, Latvian, Lithuanian, Japanese, Dutch, Georgian, Hebrew and Norwegian. Röntgen received the first Nobel Prize in Physics for his discovery.

There are conflicting accounts of his discovery because Röntgen had his lab notes burned after his death, but this is a likely reconstruction by his biographers: Röntgen was investigating cathode rays from a Crookes tube which he had wrapped in black cardboard so that the visible light from the tube would not interfere, using a fluorescent screen painted with barium platinocyanide. He noticed a faint green glow from the screen, about 1 meter away. Röntgen realized some invisible rays coming from the tube were passing through the cardboard to make the screen glow. He found they could also pass through books and papers on his desk. Röntgen threw himself into investigating these unknown rays systematically. Two months after his initial discovery, he published his paper.

Hand mit Ringen (Hand with Rings): print of Wilhelm Röntgen's first "medical" X-ray, of his wife's hand, taken on 22 December 1895 and presented to Ludwig Zehnder of the Physik Institut, University of Freiburg, on 1 January 1896

Röntgen discovered their medical use when he made a picture of his wife's hand on a photographic plate formed due to X-rays. The photograph of his wife's hand was the first photograph of a human body part using X-rays. When she saw the picture, she said "I have seen my death."

The discovery of X-rays stimulated a veritable sensation. Röntgen's biographer Otto Glasser estimated that, in 1896 alone, as many as 49 essays and 1044 articles about the new rays were published. This was probably a conservative estimate, if one considers that nearly every paper around the world extensively reported about the new discovery, with a magazine such as Science dedicating as many as 23 articles to it in that year alone. Sensationalist reactions to the new discovery included publications linking the new kind of rays to occult and paranormal theories, such as telepathy.

Advances in radiology

Taking an X-ray image with early Crookes tube apparatus, late 1800s. The Crookes tube is visible in center. The standing man is viewing his hand with a fluoroscope screen. The seated man is taking a radiograph of his hand by placing it on a photographic plate. No precautions against radiation exposure are taken; its hazards were not known at the time.
Surgical removal of a bullet whose location was diagnosed with X-rays (see inset) in 1897

Röntgen immediately noticed X-rays could have medical applications. Along with his 28 December Physical-Medical Society submission he sent a letter to physicians he knew around Europe (January 1, 1896). News (and the creation of "shadowgrams") spread rapidly with Scottish electrical engineer Alan Archibald Campbell-Swinton being the first after Röntgen to create an X-ray (of a hand). Through February there were 46 experimenters taking up the technique in North America alone.

The first use of X-rays under clinical conditions was by John Hall-Edwards in Birmingham, England on 11 January 1896, when he radiographed a needle stuck in the hand of an associate. On February 14, 1896, Hall-Edwards was also the first to use X-rays in a surgical operation. In early 1896, several weeks after Röntgen's discovery, Ivan Romanovich Tarkhanov irradiated frogs and insects with X-rays, concluding that the rays "not only photograph, but also affect the living function".

The first medical X-ray made in the United States was obtained using a discharge tube of Pului's design. In January 1896, on reading of Röntgen's discovery, Frank Austin of Dartmouth College tested all of the discharge tubes in the physics laboratory and found that only the Pului tube produced X-rays. This was a result of Pului's inclusion of an oblique "target" of mica, used for holding samples of fluorescent material, within the tube. On 3 February 1896 Gilman Frost, professor of medicine at the college, and his brother Edwin Frost, professor of physics, exposed the wrist of Eddie McCarthy, whom Gilman had treated some weeks earlier for a fracture, to the X-rays and collected the resulting image of the broken bone on gelatin photographic plates obtained from Howard Langill, a local photographer also interested in Röntgen's work.

1896 plaque published in "Nouvelle Iconographie de la Salpetrière", a medical journal. In the left a hand deformity, in the right same hand seen using radiography. The authors named the technique Röntgen photography.

Many experimenters, including Röntgen himself in his original experiments, came up with methods to view X-ray images "live" using some form of luminescent screen. Röntgen used a screen coated with barium platinocyanide. On February 5, 1896, live imaging devices were developed by both Italian scientist Enrico Salvioni (his "cryptoscope") and Professor McGie of Princeton University (his "Skiascope"), both using barium platinocyanide. American inventor Thomas Edison started research soon after Röntgen's discovery and investigated materials' ability to fluoresce when exposed to X-rays, finding that calcium tungstate was the most effective substance. In May 1896 he developed the first mass-produced live imaging device, his "Vitascope", later called the fluoroscope, which became the standard for medical X-ray examinations. Edison dropped X-ray research around 1903, before the death of Clarence Madison Dally, one of his glassblowers. Dally had a habit of testing X-ray tubes on his own hands, developing a cancer in them so tenacious that both arms were amputated in a futile attempt to save his life; in 1904, he became the first known death attributed to X-ray exposure. During the time the fluoroscope was being developed, Serbian American physicist Mihajlo Pupin, using a calcium tungstate screen developed by Edison, found that using a fluorescent screen decreased the exposure time it took to create an X-ray for medical imaging from an hour to a few minutes.

In 1901, U.S. President William McKinley was shot twice in an assassination attempt. While one bullet only grazed his sternum, another had lodged somewhere deep inside his abdomen and could not be found. A worried McKinley aide sent word to inventor Thomas Edison to rush an X-ray machine to Buffalo to find the stray bullet. It arrived but was not used. While the shooting itself had not been lethal, gangrene had developed along the path of the bullet, and McKinley died of septic shock due to bacterial infection six days later.

Hazards discovered

With the widespread experimentation with x‑rays after their discovery in 1895 by scientists, physicians, and inventors came many stories of burns, hair loss, and worse in technical journals of the time. In February 1896, Professor John Daniel and Dr. William Lofland Dudley of Vanderbilt University reported hair loss after Dr. Dudley was X-rayed. A child who had been shot in the head was brought to the Vanderbilt laboratory in 1896. Before trying to find the bullet an experiment was attempted, for which Dudley "with his characteristic devotion to science" volunteered. Daniel reported that 21 days after taking a picture of Dudley's skull (with an exposure time of one hour), he noticed a bald spot 2 inches (5.1 cm) in diameter on the part of his head nearest the X-ray tube: "A plate holder with the plates towards the side of the skull was fastened and a coin placed between the skull and the head. The tube was fastened at the other side at a distance of one-half inch from the hair."

In August 1896 Dr. HD. Hawks, a graduate of Columbia College, suffered severe hand and chest burns from an x-ray demonstration. It was reported in Electrical Review and led to many other reports of problems associated with x-rays being sent in to the publication. Many experimenters including Elihu Thomson at Edison's lab, William J. Morton, and Nikola Tesla also reported burns. Elihu Thomson deliberately exposed a finger to an x-ray tube over a period of time and suffered pain, swelling, and blistering. Other effects were sometimes blamed for the damage including ultraviolet rays and (according to Tesla) ozone. Many physicians claimed there were no effects from X-ray exposure at all. On August 3, 1905, in San Francisco, California, Elizabeth Fleischman, an American X-ray pioneer, died from complications as a result of her work with X-rays.

20th century and beyond

A patient being examined with a thoracic fluoroscope in 1940, which displayed continuous moving images. This image was used to argue that radiation exposure during the X-ray procedure would be negligible.

The many applications of X-rays immediately generated enormous interest. Workshops began making specialized versions of Crookes tubes for generating X-rays and these first-generation cold cathode or Crookes X-ray tubes were used until about 1920.

A typical early 20th century medical x-ray system consisted of a Ruhmkorff coil connected to a cold cathode Crookes X-ray tube. A spark gap was typically connected to the high voltage side in parallel to the tube and used for diagnostic purposes. The spark gap allowed detecting the polarity of the sparks, measuring voltage by the length of the sparks thus determining the "hardness" of the vacuum of the tube, and it provided a load in the event the X-ray tube was disconnected. To detect the hardness of the tube, the spark gap was initially opened to the widest setting. While the coil was operating, the operator reduced the gap until sparks began to appear. A tube in which the spark gap began to spark at around 2 1/2 inches was considered soft (low vacuum) and suitable for thin body parts such as hands and arms. A 5-inch spark indicated the tube was suitable for shoulders and knees. A 7–9 inch spark would indicate a higher vacuum suitable for imaging the abdomen of larger individuals. Since the spark gap was connected in parallel to the tube, the spark gap had to be opened until the sparking ceased in order to operate the tube for imaging. Exposure time for photographic plates was around half a minute for a hand to a couple of minutes for a thorax. The plates may have a small addition of fluorescent salt to reduce exposure times.

Crookes tubes were unreliable. They had to contain a small quantity of gas (invariably air) as a current will not flow in such a tube if they are fully evacuated. However, as time passed, the X-rays caused the glass to absorb the gas, causing the tube to generate "harder" X-rays until it soon stopped operating. Larger and more frequently used tubes were provided with devices for restoring the air, known as "softeners". These often took the form of a small side tube that contained a small piece of mica, a mineral that traps relatively large quantities of air within its structure. A small electrical heater heated the mica, causing it to release a small amount of air, thus restoring the tube's efficiency. However, the mica had a limited life, and the restoration process was difficult to control.

In 1904, John Ambrose Fleming invented the thermionic diode, the first kind of vacuum tube. This used a hot cathode that caused an electric current to flow in a vacuum. This idea was quickly applied to X-ray tubes, and hence heated-cathode X-ray tubes, called "Coolidge tubes", completely replaced the troublesome cold cathode tubes by about 1920.

In about 1906, the physicist Charles Barkla discovered that X-rays could be scattered by gases, and that each element had a characteristic X-ray spectrum. He won the 1917 Nobel Prize in Physics for this discovery.

In 1912, Max von Laue, Paul Knipping, and Walter Friedrich first observed the diffraction of X-rays by crystals. This discovery, along with the early work of Paul Peter Ewald, William Henry Bragg, and William Lawrence Bragg, gave birth to the field of X-ray crystallography.

In 1913, Henry Moseley performed crystallography experiments with X-rays emanating from various metals and formulated Moseley's law which relates the frequency of the X-rays to the atomic number of the metal.

The Coolidge X-ray tube was invented the same year by William D. Coolidge. It made possible the continuous emissions of X-rays. Modern X-ray tubes are based on this design, often employing the use of rotating targets which allow for significantly higher heat dissipation than static targets, further allowing higher quantity X-ray output for use in high powered applications such as rotational CT scanners.

Chandra's image of the galaxy cluster Abell 2125 reveals a complex of several massive multimillion-degree-Celsius gas clouds in the process of merging.

The use of X-rays for medical purposes (which developed into the field of radiation therapy) was pioneered by Major John Hall-Edwards in Birmingham, England. Then in 1908, he had to have his left arm amputated because of the spread of X-ray dermatitis on his arm.

Medical science also used the motion picture to study human physiology. In 1913, a motion picture was made in Detroit showing a hard-boiled egg inside a human stomach. This early x-ray movie was recorded at a rate of one still image every four seconds. Dr Lewis Gregory Cole of New York was a pioneer of the technique, which he called "serial radiography". In 1918, x-rays were used in association with motion picture cameras to capture the human skeleton in motion. In 1920, it was used to record the movements of tongue and teeth in the study of languages by the Institute of Phonetics in England.

In 1914 Marie Curie developed radiological cars to support soldiers injured in World War I. The cars would allow for rapid X-ray imaging of wounded soldiers so battlefield surgeons could quickly and more accurately operate.

From the early 1920s through to the 1950s, X-ray machines were developed to assist in the fitting of shoes and were sold to commercial shoe stores. Concerns regarding the impact of frequent or poorly controlled use were expressed in the 1950s, leading to the practice's eventual end that decade.

The X-ray microscope was developed during the 1950s.

The Chandra X-ray Observatory, launched on July 23, 1999, has been allowing the exploration of the very violent processes in the universe which produce X-rays. Unlike visible light, which gives a relatively stable view of the universe, the X-ray universe is unstable. It features stars being torn apart by black holes, galactic collisions, and novae, and neutron stars that build up layers of plasma that then explode into space.

An X-ray laser device was proposed as part of the Reagan Administration's Strategic Defense Initiative in the 1980s, but the only test of the device (a sort of laser "blaster" or death ray, powered by a thermonuclear explosion) gave inconclusive results. For technical and political reasons, the overall project (including the X-ray laser) was de-funded (though was later revived by the second Bush Administration as National Missile Defense using different technologies).

Dog hip xray posterior view
Phase-contrast X-ray image of spider

Phase-contrast X-ray imaging refers to a variety of techniques that use phase information of a coherent X-ray beam to image soft tissues. It has become an important method for visualizing cellular and histological structures in a wide range of biological and medical studies. There are several technologies being used for X-ray phase-contrast imaging, all utilizing different principles to convert phase variations in the X-rays emerging from an object into intensity variations. These include propagation-based phase contrast, Talbot interferometry, refraction-enhanced imaging, and X-ray interferometry. These methods provide higher contrast compared to normal absorption-contrast X-ray imaging, making it possible to see smaller details. A disadvantage is that these methods require more sophisticated equipment, such as synchrotron or microfocus X-ray sources, X-ray optics, and high resolution X-ray detectors.

Soft and hard X-rays

X-rays with high photon energies above 5–10 keV (below 0.2–0.1 nm wavelength) are called hard X-rays, while those with lower energy (and longer wavelength) are called soft X-rays. The intermediate range with photon energies of several keV is often referred to as tender X-rays. Due to their penetrating ability, hard X-rays are widely used to image the inside of objects, e.g., in medical radiography and airport security. The term X-ray is metonymically used to refer to a radiographic image produced using this method, in addition to the method itself. Since the wavelengths of hard X-rays are similar to the size of atoms, they are also useful for determining crystal structures by X-ray crystallography. By contrast, soft X-rays are easily absorbed in air; the attenuation length of 600 eV (~2 nm) X-rays in water is less than 1 micrometer.

Gamma rays

There is no consensus for a definition distinguishing between X-rays and gamma rays. One common practice is to distinguish between the two types of radiation based on their source: X-rays are emitted by electrons, while gamma rays are emitted by the atomic nucleus. This definition has several problems: other processes also can generate these high-energy photons, or sometimes the method of generation is not known. One common alternative is to distinguish X- and gamma radiation on the basis of wavelength (or, equivalently, frequency or photon energy), with radiation shorter than some arbitrary wavelength, such as 10−11 m (0.1 Å), defined as gamma radiation. This criterion assigns a photon to an unambiguous category, but is only possible if wavelength is known. (Some measurement techniques do not distinguish between detected wavelengths.) However, these two definitions often coincide since the electromagnetic radiation emitted by X-ray tubes generally has a longer wavelength and lower photon energy than the radiation emitted by radioactive nuclei. Occasionally, one term or the other is used in specific contexts due to historical precedent, based on measurement (detection) technique, or based on their intended use rather than their wavelength or source. Thus, gamma-rays generated for medical and industrial uses, for example radiotherapy, in the ranges of 6–20 MeV, can in this context also be referred to as X-rays.

Ionizing radiation hazard symbol

X-ray photons carry enough energy to ionize atoms and disrupt molecular bonds. This makes it a type of ionizing radiation, and therefore harmful to living tissue. A very high radiation dose over a short period of time causes radiation sickness, while lower doses can give an increased risk of radiation-induced cancer. In medical imaging, this increased cancer risk is generally greatly outweighed by the benefits of the examination. The ionizing capability of X-rays can be utilized in cancer treatment to kill malignant cells using radiation therapy. It is also used for material characterization using X-ray spectroscopy.

Attenuation length of X-rays in water showing the oxygen absorption edge at 540 eV, the energy−3 dependence of photoabsorption, as well as a leveling off at higher photon energies due to Compton scattering. The attenuation length is about four orders of magnitude longer for hard X-rays (right half) compared to soft X-rays (left half).

Hard X-rays can traverse relatively thick objects without being much absorbed or scattered. For this reason, X-rays are widely used to image the inside of visually opaque objects. The most often seen applications are in medical radiography and airport security scanners, but similar techniques are also important in industry (e.g. industrial radiography and industrial CT scanning) and research (e.g. small animal CT). The penetration depth varies with several orders of magnitude over the X-ray spectrum. This allows the photon energy to be adjusted for the application so as to give sufficient transmission through the object and at the same time provide good contrast in the image.

X-rays have much shorter wavelengths than visible light, which makes it possible to probe structures much smaller than can be seen using a normal microscope. This property is used in X-ray microscopy to acquire high-resolution images, and also in X-ray crystallography to determine the positions of atoms in crystals.

X-rays interact with matter in three main ways, through photoabsorption, Compton scattering, and Rayleigh scattering. The strength of these interactions depends on the energy of the X-rays and the elemental composition of the material, but not much on chemical properties, since the X-ray photon energy is much higher than chemical binding energies. Photoabsorption or photoelectric absorption is the dominant interaction mechanism in the soft X-ray regime and for the lower hard X-ray energies. At higher energies, Compton scattering dominates.

Photoelectric absorption

The probability of a photoelectric absorption per unit mass is approximately proportional to Z3/E3, where Z is the atomic number and E is the energy of the incident photon. This rule is not valid close to inner shell electron binding energies where there are abrupt changes in interaction probability, so called absorption edges. However, the general trend of high absorption coefficients and thus short penetration depths for low photon energies and high atomic numbers is very strong. For soft tissue, photoabsorption dominates up to about 26 keV photon energy where Compton scattering takes over. For higher atomic number substances this limit is higher. The high amount of calcium (Z = 20) in bones, together with their high density, is what makes them show up so clearly on medical radiographs.

A photoabsorbed photon transfers all its energy to the electron with which it interacts, thus ionizing the atom to which the electron was bound and producing a photoelectron that is likely to ionize more atoms in its path. An outer electron will fill the vacant electron position and produce either a characteristic X-ray or an Auger electron. These effects can be used for elemental detection through X-ray spectroscopy or Auger electron spectroscopy.

Compton scattering

Compton scattering is the predominant interaction between X-rays and soft tissue in medical imaging. Compton scattering is an inelastic scattering of the X-ray photon by an outer shell electron. Part of the energy of the photon is transferred to the scattering electron, thereby ionizing the atom and increasing the wavelength of the X-ray. The scattered photon can go in any direction, but a direction similar to the original direction is more likely, especially for high-energy X-rays. The probability for different scattering angles is described by the Klein–Nishina formula. The transferred energy can be directly obtained from the scattering angle from the conservation of energy and momentum.

Rayleigh scattering

Rayleigh scattering is the dominant elastic scattering mechanism in the X-ray regime. Inelastic forward scattering gives rise to the refractive index, which for X-rays is only slightly below 1.

Whenever charged particles (electrons or ions) of sufficient energy hit a material, X-rays are produced.

Production by electrons

Characteristic X-ray emission lines for some common anode materials.
Anode
material
Atomic
number
Photon energy [keV] Wavelength [nm]
Kα1 Kβ1 Kα1 Kβ1
W 74 59.3 67.2 0.0209 0.0184
Mo 42 17.5 19.6 0.0709 0.0632
Cu 29 8.05 8.91 0.154 0.139
Ag 47 22.2 24.9 0.0559 0.0497
Ga 31 9.25 10.26 0.134 0.121
In 49 24.2 27.3 0.0512 0.455
Spectrum of the X-rays emitted by an X-ray tube with a rhodium target, operated at 60 kV. The smooth, continuous curve is due to bremsstrahlung, and the spikes are characteristic K lines for rhodium atoms.

X-rays can be generated by an X-ray tube, a vacuum tube that uses a high voltage to accelerate the electrons released by a hot cathode to a high velocity. The high velocity electrons collide with a metal target, the anode, creating the X-rays. In medical X-ray tubes the target is usually tungsten or a more crack-resistant alloy of rhenium (5%) and tungsten (95%), but sometimes molybdenum for more specialized applications, such as when softer X-rays are needed as in mammography. In crystallography, a copper target is most common, with cobalt often being used when fluorescence from iron content in the sample might otherwise present a problem.

The maximum energy of the produced X-ray photon is limited by the energy of the incident electron, which is equal to the voltage on the tube times the electron charge, so an 80 kV tube cannot create X-rays with an energy greater than 80 keV. When the electrons hit the target, X-rays are created by two different atomic processes:

  1. Characteristic X-ray emission (X-ray electroluminescence): If the electron has enough energy, it can knock an orbital electron out of the inner electron shell of the target atom. After that, electrons from higher energy levels fill the vacancies, and X-ray photons are emitted. This process produces an emission spectrum of X-rays at a few discrete frequencies, sometimes referred to as spectral lines. Usually, these are transitions from the upper shells to the K shell (called K lines), to the L shell (called L lines) and so on. If the transition is from 2p to 1s, it is called Kα, while if it is from 3p to 1s it is Kβ. The frequencies of these lines depend on the material of the target and are therefore called characteristic lines. The Kα line usually has greater intensity than the Kβ one and is more desirable in diffraction experiments. Thus the Kβ line is filtered out by a filter. The filter is usually made of a metal having one proton less than the anode material (e.g., Ni filter for Cu anode or Nb filter for Mo anode).
  2. Bremsstrahlung: This is radiation given off by the electrons as they are scattered by the strong electric field near the high-Z (proton number) nuclei. These X-rays have a continuous spectrum. The frequency of bremsstrahlung is limited by the energy of incident electrons.

So, the resulting output of a tube consists of a continuous bremsstrahlung spectrum falling off to zero at the tube voltage, plus several spikes at the characteristic lines. The voltages used in diagnostic X-ray tubes range from roughly 20 kV to 150 kV and thus the highest energies of the X-ray photons range from roughly 20 keV to 150 keV.

Both of these X-ray production processes are inefficient, with only about one percent of the electrical energy used by the tube converted into X-rays, and thus most of the electric power consumed by the tube is released as waste heat. When producing a usable flux of X-rays, the X-ray tube must be designed to dissipate the excess heat.

A specialized source of X-rays which is becoming widely used in research is synchrotron radiation, which is generated by particle accelerators. Its unique features are X-ray outputs many orders of magnitude greater than those of X-ray tubes, wide X-ray spectra, excellent collimation, and linear polarization.

Short nanosecond bursts of X-rays peaking at 15-keV in energy may be reliably produced by peeling pressure-sensitive adhesive tape from its backing in a moderate vacuum. This is likely to be the result of recombination of electrical charges produced by triboelectric charging. The intensity of X-ray triboluminescence is sufficient for it to be used as a source for X-ray imaging.

Production by fast positive ions

X-rays can also be produced by fast protons or other positive ions. The proton-induced X-ray emission or particle-induced X-ray emission is widely used as an analytical procedure. For high energies, the production cross section is proportional to Z12Z2−4, where Z1 refers to the atomic number of the ion, Z2 refers to that of the target atom. An overview of these cross sections is given in the same reference.

Production in lightning and laboratory discharges

X-rays are also produced in lightning accompanying terrestrial gamma-ray flashes. The underlying mechanism is the acceleration of electrons in lightning related electric fields and the subsequent production of photons through Bremsstrahlung. This produces photons with energies of some few keV and several tens of MeV. In laboratory discharges with a gap size of approximately 1 meter length and a peak voltage of 1 MV, X-rays with a characteristic energy of 160 keV are observed. A possible explanation is the encounter of two streamers and the production of high-energy run-away electrons; however, microscopic simulations have shown that the duration of electric field enhancement between two streamers is too short to produce a significant number of run-away electrons. Recently, it has been proposed that air perturbations in the vicinity of streamers can facilitate the production of run-away electrons and hence of X-rays from discharges.

Main article: X-ray detector

X-ray detectors vary in shape and function depending on their purpose. Imaging detectors such as those used for radiography were originally based on photographic plates and later photographic film, but are now mostly replaced by various digital detector types such as image plates and flat panel detectors. For radiation protection direct exposure hazard is often evaluated using ionization chambers, while dosimeters are used to measure the radiation dose a person has been exposed to. X-ray spectra can be measured either by energy dispersive or wavelength dispersive spectrometers. For X-ray diffraction applications, such as x-ray crystallography, hybrid photon counting detectors are widely used.

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X-ray.
A chest radiograph of a female, demonstrating a hiatal hernia

Since Röntgen's discovery that X-rays can identify bone structures, X-rays have been used for medical imaging. The first medical use was less than a month after his paper on the subject. Up to 2010, five billion medical imaging examinations had been conducted worldwide. Radiation exposure from medical imaging in 2006 made up about 50% of total ionizing radiation exposure in the United States.

Projectional radiographs

Plain radiograph of the right knee

Projectional radiography is the practice of producing two-dimensional images using x-ray radiation. Bones contain a high concentration of calcium, which, due to its relatively high atomic number, absorbs x-rays efficiently. This reduces the amount of X-rays reaching the detector in the shadow of the bones, making them clearly visible on the radiograph. The lungs and trapped gas also show up clearly because of lower absorption compared to tissue, while differences between tissue types are harder to see.

Projectional radiographs are useful in the detection of pathology of the skeletal system as well as for detecting some disease processes in soft tissue. Some notable examples are the very common chest X-ray, which can be used to identify lung diseases such as pneumonia, lung cancer, or pulmonary edema, and the abdominal x-ray, which can detect bowel (or intestinal) obstruction, free air (from visceral perforations) and free fluid (in ascites). X-rays may also be used to detect pathology such as gallstones (which are rarely radiopaque) or kidney stones which are often (but not always) visible. Traditional plain X-rays are less useful in the imaging of soft tissues such as the brain or muscle. One area where projectional radiographs are used extensively is in evaluating how an orthopedic implant, such as a knee, hip or shoulder replacement, is situated in the body with respect to the surrounding bone. This can be assessed in two dimensions from plain radiographs, or it can be assessed in three dimensions if a technique called '2D to 3D registration' is used. This technique purportedly negates projection errors associated with evaluating implant position from plain radiographs.

Dental radiography is commonly used in the diagnoses of common oral problems, such as cavities.

In medical diagnostic applications, the low energy (soft) X-rays are unwanted, since they are totally absorbed by the body, increasing the radiation dose without contributing to the image. Hence, a thin metal sheet, often of aluminium, called an X-ray filter, is usually placed over the window of the X-ray tube, absorbing the low energy part in the spectrum. This is called hardening the beam since it shifts the center of the spectrum towards higher energy (or harder) x-rays.

To generate an image of the cardiovascular system, including the arteries and veins (angiography) an initial image is taken of the anatomical region of interest. A second image is then taken of the same region after an iodinated contrast agent has been injected into the blood vessels within this area. These two images are then digitally subtracted, leaving an image of only the iodinated contrast outlining the blood vessels. The radiologist or surgeon then compares the image obtained to normal anatomical images to determine whether there is any damage or blockage of the vessel.

Computed tomography

Main article: CT scan
Head CT scan (transverse plane) slice – a modern application of medical radiography

Computed tomography (CT scanning) is a medical imaging modality where tomographic images or slices of specific areas of the body are obtained from a large series of two-dimensional X-ray images taken in different directions. These cross-sectional images can be combined into a three-dimensional image of the inside of the body and used for diagnostic and therapeutic purposes in various medical disciplines....

Fluoroscopy

Main article: Fluoroscopy

Fluoroscopy is an imaging technique commonly used by physicians or radiation therapists to obtain real-time moving images of the internal structures of a patient through the use of a fluoroscope. In its simplest form, a fluoroscope consists of an X-ray source and a fluorescent screen, between which a patient is placed. However, modern fluoroscopes couple the screen to an X-ray image intensifier and CCD video camera allowing the images to be recorded and played on a monitor. This method may use a contrast material. Examples include cardiac catheterization (to examine for coronary artery blockages) and barium swallow (to examine for esophageal disorders and swallowing disorders).

Radiotherapy

The use of X-rays as a treatment is known as radiation therapy and is largely used for the management (including palliation) of cancer; it requires higher radiation doses than those received for imaging alone. X-rays beams are used for treating skin cancers using lower energy x-ray beams while higher energy beams are used for treating cancers within the body such as brain, lung, prostate, and breast.

Abdominal radiograph of a pregnant woman, a procedure that should be performed only after proper assessment of benefit versus risk

Diagnostic X-rays (primarily from CT scans due to the large dose used) increase the risk of developmental problems and cancer in those exposed. X-rays are classified as a carcinogen by both the World Health Organization's International Agency for Research on Cancer and the U.S. government. It is estimated that 0.4% of current cancers in the United States are due to computed tomography (CT scans) performed in the past and that this may increase to as high as 1.5–2% with 2007 rates of CT usage.

Experimental and epidemiological data currently do not support the proposition that there is a threshold dose of radiation below which there is no increased risk of cancer. However, this is under increasing doubt. It is estimated that the additional radiation from diagnostic X-rays will increase the average person's cumulative risk of getting cancer by age 75 by 0.6–3.0%. The amount of absorbed radiation depends upon the type of X-ray test and the body part involved. CT and fluoroscopy entail higher doses of radiation than do plain X-rays.

To place the increased risk in perspective, a plain chest X-ray will expose a person to the same amount from background radiation that people are exposed to (depending upon location) every day over 10 days, while exposure from a dental X-ray is approximately equivalent to 1 day of environmental background radiation. Each such X-ray would add less than 1 per 1,000,000 to the lifetime cancer risk. An abdominal or chest CT would be the equivalent to 2–3 years of background radiation to the whole body, or 4–5 years to the abdomen or chest, increasing the lifetime cancer risk between 1 per 1,000 to 1 per 10,000. This is compared to the roughly 40% chance of a US citizen developing cancer during their lifetime. For instance, the effective dose to the torso from a CT scan of the chest is about 5 mSv, and the absorbed dose is about 14 mGy. A head CT scan (1.5mSv, 64mGy) that is performed once with and once without contrast agent, would be equivalent to 40 years of background radiation to the head. Accurate estimation of effective doses due to CT is difficult with the estimation uncertainty range of about ±19% to ±32% for adult head scans depending upon the method used.

The risk of radiation is greater to a fetus, so in pregnant patients, the benefits of the investigation (X-ray) should be balanced with the potential hazards to the fetus. In the US, there are an estimated 62 million CT scans performed annually, including more than 4 million on children. Avoiding unnecessary X-rays (especially CT scans) reduces radiation dose and any associated cancer risk.

Medical X-rays are a significant source of human-made radiation exposure. In 1987, they accounted for 58% of exposure from human-made sources in the United States. Since human-made sources accounted for only 18% of the total radiation exposure, most of which came from natural sources (82%), medical X-rays only accounted for 10% of total American radiation exposure; medical procedures as a whole (including nuclear medicine) accounted for 14% of total radiation exposure. By 2006, however, medical procedures in the United States were contributing much more ionizing radiation than was the case in the early 1980s. In 2006, medical exposure constituted nearly half of the total radiation exposure of the U.S. population from all sources. The increase is traceable to the growth in the use of medical imaging procedures, in particular computed tomography (CT), and to the growth in the use of nuclear medicine.

Dosage due to dental X-rays varies significantly depending on the procedure and the technology (film or digital). Depending on the procedure and the technology, a single dental X-ray of a human results in an exposure of 0.5 to 4 mrem. A full mouth series of X-rays may result in an exposure of up to 6 (digital) to 18 (film) mrem, for a yearly average of up to 40 mrem.

Financial incentives have been shown to have a significant impact on X-ray use with doctors who are paid a separate fee for each X-ray providing more X-rays.

Early photon tomography or EPT (as of 2015) along with other techniques are being researched as potential alternatives to X-rays for imaging applications.

Other notable uses of X-rays include:

Each dot, called a reflection, in this diffraction pattern forms from the constructive interference of scattered X-rays passing through a crystal. The data can be used to determine the crystalline structure.
Using X-ray for inspection and quality control: the differences in the structures of the die and bond wires reveal the left chip to be counterfeit.
  • Authentication and quality control of packaged items.
  • Industrial CT (computed tomography), a process that uses X-ray equipment to produce three-dimensional representations of components both externally and internally. This is accomplished through computer processing of projection images of the scanned object in many directions.
  • Airport security luggage scanners use X-rays for inspecting the interior of luggage for security threats before loading on aircraft.
  • Border control truck scanners and domestic police departments use X-rays for inspecting the interior of trucks.
X-ray fine art photography of needlefish by Peter Dazeley

While generally considered invisible to the human eye, in special circumstances X-rays can be visible. Brandes, in an experiment a short time after Röntgen's landmark 1895 paper, reported after dark adaptation and placing his eye close to an X-ray tube, seeing a faint "blue-gray" glow which seemed to originate within the eye itself. Upon hearing this, Röntgen reviewed his record books and found he too had seen the effect. When placing an X-ray tube on the opposite side of a wooden door Röntgen had noted the same blue glow, seeming to emanate from the eye itself, but thought his observations to be spurious because he only saw the effect when he used one type of tube. Later he realized that the tube which had created the effect was the only one powerful enough to make the glow plainly visible and the experiment was thereafter readily repeatable. The knowledge that X-rays are actually faintly visible to the dark-adapted naked eye has largely been forgotten today; this is probably due to the desire not to repeat what would now be seen as a recklessly dangerous and potentially harmful experiment with ionizing radiation. It is not known what exact mechanism in the eye produces the visibility: it could be due to conventional detection (excitation of rhodopsin molecules in the retina), direct excitation of retinal nerve cells, or secondary detection via, for instance, X-ray induction of phosphorescence in the eyeball with conventional retinal detection of the secondarily produced visible light.

Though X-rays are otherwise invisible, it is possible to see the ionization of the air molecules if the intensity of the X-ray beam is high enough. The beamline from the wiggler at the ID11 at the European Synchrotron Radiation Facility is one example of such high intensity.

The measure of X-rays ionizing ability is called the exposure:

  • The coulomb per kilogram (C/kg) is the SI unit of ionizing radiation exposure, and it is the amount of radiation required to create one coulomb of charge of each polarity in one kilogram of matter.
  • The roentgen (R) is an obsolete traditional unit of exposure, which represented the amount of radiation required to create one electrostatic unit of charge of each polarity in one cubic centimeter of dry air. 1 roentgen =2.58×10−4 C/kg.

However, the effect of ionizing radiation on matter (especially living tissue) is more closely related to the amount of energy deposited into them rather than the charge generated. This measure of energy absorbed is called the absorbed dose:

  • The gray (Gy), which has units of (joules/kilogram), is the SI unit of absorbed dose, and it is the amount of radiation required to deposit one joule of energy in one kilogram of any kind of matter.
  • The rad is the (obsolete) corresponding traditional unit, equal to 10 millijoules of energy deposited per kilogram. 100 rad = 1 gray.

The equivalent dose is the measure of the biological effect of radiation on human tissue. For X-rays it is equal to the absorbed dose.

  • The Roentgen equivalent man (rem) is the traditional unit of equivalent dose. For X-rays it is equal to the rad, or, in other words, 10 millijoules of energy deposited per kilogram. 100 rem = 1 Sv.
  • The sievert (Sv) is the SI unit of equivalent dose, and also of effective dose. For X-rays the "equivalent dose" is numerically equal to a Gray (Gy). 1 Sv= 1 Gy. For the "effective dose" of X-rays, it is usually not equal to the Gray (Gy).
Ionizing radiation related quantitiesview talk edit
Quantity Unit Symbol Derivation Year SI equivalence
Activity (A) becquerel Bq s−1 1974 SI unit
curie Ci 3.7 × 1010 s−1 1953 3.7×1010 Bq
rutherford Rd 106 s−1 1946 1,000,000 Bq
Exposure (X) coulomb per kilogram C/kg C⋅kg−1 of air 1974 SI unit
röntgen R esu / 0.001293 g of air 1928 2.58 × 10−4 C/kg
Absorbed dose (D) gray Gy J⋅kg−1 1974 SI unit
erg per gram erg/g erg⋅g−1 1950 1.0 × 10−4 Gy
rad rad 100 erg⋅g−1 1953 0.010 Gy
Equivalent dose (H) sievert Sv J⋅kg−1 × WR 1977 SI unit
röntgen equivalent man rem 100 erg⋅g−1 x WR 1971 0.010 Sv
Effective dose (E) sievert Sv J⋅kg−1 × WR × WT 1977 SI unit
röntgen equivalent man rem 100 erg⋅g−1 × WR × WT 1971 0.010 Sv
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X-ray
X ray Language Watch Edit This article is about the nature production and uses of the radiation For the method of imaging see Radiography For the medical specialty see Radiology For other meanings see X ray disambiguation Not to be confused with X wave or X band An X ray or much less commonly X radiation is a penetrating form of high energy electromagnetic radiation Most X rays have a wavelength ranging from 10 picometers to 10 nanometers corresponding to frequencies in the range 30 petahertz to 30 exahertz 30 1015 Hz to 30 1018 Hz and energies in the range 124 eV to 124 keV X ray wavelengths are shorter than those of UV rays and typically longer than those of gamma rays In many languages X radiation is referred to as Rontgen radiation after the German scientist Wilhelm Conrad Rontgen who discovered it on November 8 1895 1 He named it X radiation to signify an unknown type of radiation 2 Spellings of X ray s in English include the variants x ray s xray s and X ray s 3 X rays are part of the electromagnetic spectrum with wavelengths shorter than UV light Different applications use different parts of the X ray spectrum X ray image of human lungs Contents 1 History 1 1 Pre Rontgen observations and research 1 2 Discovery by Rontgen 1 3 Advances in radiology 1 4 Hazards discovered 1 5 20th century and beyond 2 Energy ranges 2 1 Soft and hard X rays 2 2 Gamma rays 3 Properties 4 Interaction with matter 4 1 Photoelectric absorption 4 2 Compton scattering 4 3 Rayleigh scattering 5 Production 5 1 Production by electrons 5 2 Production by fast positive ions 5 3 Production in lightning and laboratory discharges 6 Detectors 7 Medical uses 7 1 Projectional radiographs 7 2 Computed tomography 7 3 Fluoroscopy 7 4 Radiotherapy 8 Adverse effects 9 Other uses 10 Visibility 11 Units of measure and exposure 12 See also 13 References 14 External linksHistory EditPre Rontgen observations and research Edit Example of a Crookes tube a type of discharge tube that emitted X rays Before their discovery in 1895 X rays were just a type of unidentified radiation emanating from experimental discharge tubes They were noticed by scientists investigating cathode rays produced by such tubes which are energetic electron beams that were first observed in 1869 Many of the early Crookes tubes invented around 1875 undoubtedly radiated X rays because early researchers noticed effects that were attributable to them as detailed below Crookes tubes created free electrons by ionization of the residual air in the tube by a high DC voltage of anywhere between a few kilovolts and 100 kV This voltage accelerated the electrons coming from the cathode to a high enough velocity that they created X rays when they struck the anode or the glass wall of the tube 4 The earliest experimenter thought to have unknowingly produced X rays was actuary William Morgan In 1785 he presented a paper to the Royal Society of London describing the effects of passing electrical currents through a partially evacuated glass tube producing a glow created by X rays 5 6 This work was further explored by Humphry Davy and his assistant Michael Faraday When Stanford University physics professor Fernando Sanford created his electric photography he also unknowingly generated and detected X rays From 1886 to 1888 he had studied in the Hermann Helmholtz laboratory in Berlin where he became familiar with the cathode rays generated in vacuum tubes when a voltage was applied across separate electrodes as previously studied by Heinrich Hertz and Philipp Lenard His letter of January 6 1893 describing his discovery as electric photography to The Physical Review was duly published and an article entitled Without Lens or Light Photographs Taken With Plate and Object in Darkness appeared in the San Francisco Examiner 7 Starting in 1888 Philipp Lenard conducted experiments to see whether cathode rays could pass out of the Crookes tube into the air He built a Crookes tube with a window at the end made of thin aluminum facing the cathode so the cathode rays would strike it later called a Lenard tube He found that something came through that would expose photographic plates and cause fluorescence He measured the penetrating power of these rays through various materials It has been suggested that at least some of these Lenard rays were actually X rays 8 In 1889 Ukrainian born Ivan Puluj a lecturer in experimental physics at the Prague Polytechnic who since 1877 had been constructing various designs of gas filled tubes to investigate their properties published a paper on how sealed photographic plates became dark when exposed to the emanations from the tubes 9 Hermann von Helmholtz formulated mathematical equations for X rays He postulated a dispersion theory before Rontgen made his discovery and announcement He based it on the electromagnetic theory of light 10 Full citation needed date October 2021 However he did not work with actual X rays In 1894 Nikola Tesla noticed damaged film in his lab that seemed to be associated with Crookes tube experiments and began investigating this invisible radiant energy 11 12 After Rontgen identified the X ray Tesla began making X ray images of his own using high voltages and tubes of his own design 13 as well as Crookes tubes Discovery by Rontgen Edit Wilhelm Rontgen On November 8 1895 German physics professor Wilhelm Rontgen stumbled on X rays while experimenting with Lenard tubes and Crookes tubes and began studying them He wrote an initial report On a new kind of ray A preliminary communication and on December 28 1895 submitted it to Wurzburg s Physical Medical Society journal 14 This was the first paper written on X rays Rontgen referred to the radiation as X to indicate that it was an unknown type of radiation The name stuck although over Rontgen s great objections many of his colleagues suggested calling them Rontgen rays They are still referred to as such in many languages including German Hungarian Ukrainian Danish Polish Bulgarian Swedish Finnish Estonian Turkish Russian Latvian Lithuanian Japanese Dutch Georgian Hebrew and Norwegian Rontgen received the first Nobel Prize in Physics for his discovery 15 There are conflicting accounts of his discovery because Rontgen had his lab notes burned after his death but this is a likely reconstruction by his biographers 16 17 Rontgen was investigating cathode rays from a Crookes tube which he had wrapped in black cardboard so that the visible light from the tube would not interfere using a fluorescent screen painted with barium platinocyanide He noticed a faint green glow from the screen about 1 meter away Rontgen realized some invisible rays coming from the tube were passing through the cardboard to make the screen glow He found they could also pass through books and papers on his desk Rontgen threw himself into investigating these unknown rays systematically Two months after his initial discovery he published his paper 18 Hand mit Ringen Hand with Rings print of Wilhelm Rontgen s first medical X ray of his wife s hand taken on 22 December 1895 and presented to Ludwig Zehnder of the Physik Institut University of Freiburg on 1 January 1896 19 20 Rontgen discovered their medical use when he made a picture of his wife s hand on a photographic plate formed due to X rays The photograph of his wife s hand was the first photograph of a human body part using X rays When she saw the picture she said I have seen my death 21 The discovery of X rays stimulated a veritable sensation Rontgen s biographer Otto Glasser estimated that in 1896 alone as many as 49 essays and 1044 articles about the new rays were published 22 This was probably a conservative estimate if one considers that nearly every paper around the world extensively reported about the new discovery with a magazine such as Science dedicating as many as 23 articles to it in that year alone 23 Sensationalist reactions to the new discovery included publications linking the new kind of rays to occult and paranormal theories such as telepathy 24 25 Advances in radiology Edit Taking an X ray image with early Crookes tube apparatus late 1800s The Crookes tube is visible in center The standing man is viewing his hand with a fluoroscope screen The seated man is taking a radiograph of his hand by placing it on a photographic plate No precautions against radiation exposure are taken its hazards were not known at the time Surgical removal of a bullet whose location was diagnosed with X rays see inset in 1897 Rontgen immediately noticed X rays could have medical applications Along with his 28 December Physical Medical Society submission he sent a letter to physicians he knew around Europe January 1 1896 26 News and the creation of shadowgrams spread rapidly with Scottish electrical engineer Alan Archibald Campbell Swinton being the first after Rontgen to create an X ray of a hand Through February there were 46 experimenters taking up the technique in North America alone 26 The first use of X rays under clinical conditions was by John Hall Edwards in Birmingham England on 11 January 1896 when he radiographed a needle stuck in the hand of an associate On February 14 1896 Hall Edwards was also the first to use X rays in a surgical operation 27 In early 1896 several weeks after Rontgen s discovery Ivan Romanovich Tarkhanov irradiated frogs and insects with X rays concluding that the rays not only photograph but also affect the living function 28 The first medical X ray made in the United States was obtained using a discharge tube of Pului s design In January 1896 on reading of Rontgen s discovery Frank Austin of Dartmouth College tested all of the discharge tubes in the physics laboratory and found that only the Pului tube produced X rays This was a result of Pului s inclusion of an oblique target of mica used for holding samples of fluorescent material within the tube On 3 February 1896 Gilman Frost professor of medicine at the college and his brother Edwin Frost professor of physics exposed the wrist of Eddie McCarthy whom Gilman had treated some weeks earlier for a fracture to the X rays and collected the resulting image of the broken bone on gelatin photographic plates obtained from Howard Langill a local photographer also interested in Rontgen s work 29 1896 plaque published in Nouvelle Iconographie de la Salpetriere a medical journal In the left a hand deformity in the right same hand seen using radiography The authors named the technique Rontgen photography Many experimenters including Rontgen himself in his original experiments came up with methods to view X ray images live using some form of luminescent screen 26 Rontgen used a screen coated with barium platinocyanide On February 5 1896 live imaging devices were developed by both Italian scientist Enrico Salvioni his cryptoscope and Professor McGie of Princeton University his Skiascope both using barium platinocyanide American inventor Thomas Edison started research soon after Rontgen s discovery and investigated materials ability to fluoresce when exposed to X rays finding that calcium tungstate was the most effective substance In May 1896 he developed the first mass produced live imaging device his Vitascope later called the fluoroscope which became the standard for medical X ray examinations 26 Edison dropped X ray research around 1903 before the death of Clarence Madison Dally one of his glassblowers Dally had a habit of testing X ray tubes on his own hands developing a cancer in them so tenacious that both arms were amputated in a futile attempt to save his life in 1904 he became the first known death attributed to X ray exposure 26 During the time the fluoroscope was being developed Serbian American physicist Mihajlo Pupin using a calcium tungstate screen developed by Edison found that using a fluorescent screen decreased the exposure time it took to create an X ray for medical imaging from an hour to a few minutes 30 26 In 1901 U S President William McKinley was shot twice in an assassination attempt While one bullet only grazed his sternum another had lodged somewhere deep inside his abdomen and could not be found A worried McKinley aide sent word to inventor Thomas Edison to rush an X ray machine to Buffalo to find the stray bullet It arrived but was not used While the shooting itself had not been lethal gangrene had developed along the path of the bullet and McKinley died of septic shock due to bacterial infection six days later 31 Hazards discovered Edit With the widespread experimentation with x rays after their discovery in 1895 by scientists physicians and inventors came many stories of burns hair loss and worse in technical journals of the time In February 1896 Professor John Daniel and Dr William Lofland Dudley of Vanderbilt University reported hair loss after Dr Dudley was X rayed A child who had been shot in the head was brought to the Vanderbilt laboratory in 1896 Before trying to find the bullet an experiment was attempted for which Dudley with his characteristic devotion to science 32 33 34 volunteered Daniel reported that 21 days after taking a picture of Dudley s skull with an exposure time of one hour he noticed a bald spot 2 inches 5 1 cm in diameter on the part of his head nearest the X ray tube A plate holder with the plates towards the side of the skull was fastened and a coin placed between the skull and the head The tube was fastened at the other side at a distance of one half inch from the hair 35 In August 1896 Dr HD Hawks a graduate of Columbia College suffered severe hand and chest burns from an x ray demonstration It was reported in Electrical Review and led to many other reports of problems associated with x rays being sent in to the publication 36 Many experimenters including Elihu Thomson at Edison s lab William J Morton and Nikola Tesla also reported burns Elihu Thomson deliberately exposed a finger to an x ray tube over a period of time and suffered pain swelling and blistering 37 Other effects were sometimes blamed for the damage including ultraviolet rays and according to Tesla ozone 38 Many physicians claimed there were no effects from X ray exposure at all 37 On August 3 1905 in San Francisco California Elizabeth Fleischman an American X ray pioneer died from complications as a result of her work with X rays 39 40 41 20th century and beyond Edit A patient being examined with a thoracic fluoroscope in 1940 which displayed continuous moving images This image was used to argue that radiation exposure during the X ray procedure would be negligible The many applications of X rays immediately generated enormous interest Workshops began making specialized versions of Crookes tubes for generating X rays and these first generation cold cathode or Crookes X ray tubes were used until about 1920 A typical early 20th century medical x ray system consisted of a Ruhmkorff coil connected to a cold cathode Crookes X ray tube A spark gap was typically connected to the high voltage side in parallel to the tube and used for diagnostic purposes 42 The spark gap allowed detecting the polarity of the sparks measuring voltage by the length of the sparks thus determining the hardness of the vacuum of the tube and it provided a load in the event the X ray tube was disconnected To detect the hardness of the tube the spark gap was initially opened to the widest setting While the coil was operating the operator reduced the gap until sparks began to appear A tube in which the spark gap began to spark at around 2 1 2 inches was considered soft low vacuum and suitable for thin body parts such as hands and arms A 5 inch spark indicated the tube was suitable for shoulders and knees A 7 9 inch spark would indicate a higher vacuum suitable for imaging the abdomen of larger individuals Since the spark gap was connected in parallel to the tube the spark gap had to be opened until the sparking ceased in order to operate the tube for imaging Exposure time for photographic plates was around half a minute for a hand to a couple of minutes for a thorax The plates may have a small addition of fluorescent salt to reduce exposure times 42 Crookes tubes were unreliable They had to contain a small quantity of gas invariably air as a current will not flow in such a tube if they are fully evacuated However as time passed the X rays caused the glass to absorb the gas causing the tube to generate harder X rays until it soon stopped operating Larger and more frequently used tubes were provided with devices for restoring the air known as softeners These often took the form of a small side tube that contained a small piece of mica a mineral that traps relatively large quantities of air within its structure A small electrical heater heated the mica causing it to release a small amount of air thus restoring the tube s efficiency However the mica had a limited life and the restoration process was difficult to control In 1904 John Ambrose Fleming invented the thermionic diode the first kind of vacuum tube This used a hot cathode that caused an electric current to flow in a vacuum This idea was quickly applied to X ray tubes and hence heated cathode X ray tubes called Coolidge tubes completely replaced the troublesome cold cathode tubes by about 1920 In about 1906 the physicist Charles Barkla discovered that X rays could be scattered by gases and that each element had a characteristic X ray spectrum He won the 1917 Nobel Prize in Physics for this discovery In 1912 Max von Laue Paul Knipping and Walter Friedrich first observed the diffraction of X rays by crystals This discovery along with the early work of Paul Peter Ewald William Henry Bragg and William Lawrence Bragg gave birth to the field of X ray crystallography In 1913 Henry Moseley performed crystallography experiments with X rays emanating from various metals and formulated Moseley s law which relates the frequency of the X rays to the atomic number of the metal The Coolidge X ray tube was invented the same year by William D Coolidge It made possible the continuous emissions of X rays Modern X ray tubes are based on this design often employing the use of rotating targets which allow for significantly higher heat dissipation than static targets further allowing higher quantity X ray output for use in high powered applications such as rotational CT scanners Chandra s image of the galaxy cluster Abell 2125 reveals a complex of several massive multimillion degree Celsius gas clouds in the process of merging The use of X rays for medical purposes which developed into the field of radiation therapy was pioneered by Major John Hall Edwards in Birmingham England Then in 1908 he had to have his left arm amputated because of the spread of X ray dermatitis on his arm 43 Medical science also used the motion picture to study human physiology In 1913 a motion picture was made in Detroit showing a hard boiled egg inside a human stomach This early x ray movie was recorded at a rate of one still image every four seconds 44 Dr Lewis Gregory Cole of New York was a pioneer of the technique which he called serial radiography 45 46 In 1918 x rays were used in association with motion picture cameras to capture the human skeleton in motion 47 48 49 In 1920 it was used to record the movements of tongue and teeth in the study of languages by the Institute of Phonetics in England 50 In 1914 Marie Curie developed radiological cars to support soldiers injured in World War I The cars would allow for rapid X ray imaging of wounded soldiers so battlefield surgeons could quickly and more accurately operate 51 From the early 1920s through to the 1950s X ray machines were developed to assist in the fitting of shoes 52 and were sold to commercial shoe stores 53 54 55 Concerns regarding the impact of frequent or poorly controlled use were expressed in the 1950s 56 57 leading to the practice s eventual end that decade 58 The X ray microscope was developed during the 1950s The Chandra X ray Observatory launched on July 23 1999 has been allowing the exploration of the very violent processes in the universe which produce X rays Unlike visible light which gives a relatively stable view of the universe the X ray universe is unstable It features stars being torn apart by black holes galactic collisions and novae and neutron stars that build up layers of plasma that then explode into space An X ray laser device was proposed as part of the Reagan Administration s Strategic Defense Initiative in the 1980s but the only test of the device a sort of laser blaster or death ray powered by a thermonuclear explosion gave inconclusive results For technical and political reasons the overall project including the X ray laser was de funded though was later revived by the second Bush Administration as National Missile Defense using different technologies Dog hip xray posterior view Phase contrast X ray image of spider Phase contrast X ray imaging refers to a variety of techniques that use phase information of a coherent X ray beam to image soft tissues It has become an important method for visualizing cellular and histological structures in a wide range of biological and medical studies There are several technologies being used for X ray phase contrast imaging all utilizing different principles to convert phase variations in the X rays emerging from an object into intensity variations 59 60 These include propagation based phase contrast 61 Talbot interferometry 60 refraction enhanced imaging 62 and X ray interferometry 63 These methods provide higher contrast compared to normal absorption contrast X ray imaging making it possible to see smaller details A disadvantage is that these methods require more sophisticated equipment such as synchrotron or microfocus X ray sources X ray optics and high resolution X ray detectors Energy ranges EditSoft and hard X rays Edit X rays with high photon energies above 5 10 keV below 0 2 0 1 nm wavelength are called hard X rays while those with lower energy and longer wavelength are called soft X rays 64 The intermediate range with photon energies of several keV is often referred to as tender X rays Due to their penetrating ability hard X rays are widely used to image the inside of objects e g in medical radiography and airport security The term X ray is metonymically used to refer to a radiographic image produced using this method in addition to the method itself Since the wavelengths of hard X rays are similar to the size of atoms they are also useful for determining crystal structures by X ray crystallography By contrast soft X rays are easily absorbed in air the attenuation length of 600 eV 2 nm X rays in water is less than 1 micrometer 65 Gamma rays Edit There is no consensus for a definition distinguishing between X rays and gamma rays One common practice is to distinguish between the two types of radiation based on their source X rays are emitted by electrons while gamma rays are emitted by the atomic nucleus 66 67 68 69 This definition has several problems other processes also can generate these high energy photons or sometimes the method of generation is not known One common alternative is to distinguish X and gamma radiation on the basis of wavelength or equivalently frequency or photon energy with radiation shorter than some arbitrary wavelength such as 10 11 m 0 1 A defined as gamma radiation 70 This criterion assigns a photon to an unambiguous category but is only possible if wavelength is known Some measurement techniques do not distinguish between detected wavelengths However these two definitions often coincide since the electromagnetic radiation emitted by X ray tubes generally has a longer wavelength and lower photon energy than the radiation emitted by radioactive nuclei 66 Occasionally one term or the other is used in specific contexts due to historical precedent based on measurement detection technique or based on their intended use rather than their wavelength or source Thus gamma rays generated for medical and industrial uses for example radiotherapy in the ranges of 6 20 MeV can in this context also be referred to as X rays 71 Properties Edit Ionizing radiation hazard symbol X ray photons carry enough energy to ionize atoms and disrupt molecular bonds This makes it a type of ionizing radiation and therefore harmful to living tissue A very high radiation dose over a short period of time causes radiation sickness while lower doses can give an increased risk of radiation induced cancer In medical imaging this increased cancer risk is generally greatly outweighed by the benefits of the examination The ionizing capability of X rays can be utilized in cancer treatment to kill malignant cells using radiation therapy It is also used for material characterization using X ray spectroscopy Attenuation length of X rays in water showing the oxygen absorption edge at 540 eV the energy 3 dependence of photoabsorption as well as a leveling off at higher photon energies due to Compton scattering The attenuation length is about four orders of magnitude longer for hard X rays right half compared to soft X rays left half Hard X rays can traverse relatively thick objects without being much absorbed or scattered For this reason X rays are widely used to image the inside of visually opaque objects The most often seen applications are in medical radiography and airport security scanners but similar techniques are also important in industry e g industrial radiography and industrial CT scanning and research e g small animal CT The penetration depth varies with several orders of magnitude over the X ray spectrum This allows the photon energy to be adjusted for the application so as to give sufficient transmission through the object and at the same time provide good contrast in the image X rays have much shorter wavelengths than visible light which makes it possible to probe structures much smaller than can be seen using a normal microscope This property is used in X ray microscopy to acquire high resolution images and also in X ray crystallography to determine the positions of atoms in crystals Interaction with matter EditX rays interact with matter in three main ways through photoabsorption Compton scattering and Rayleigh scattering The strength of these interactions depends on the energy of the X rays and the elemental composition of the material but not much on chemical properties since the X ray photon energy is much higher than chemical binding energies Photoabsorption or photoelectric absorption is the dominant interaction mechanism in the soft X ray regime and for the lower hard X ray energies At higher energies Compton scattering dominates Photoelectric absorption Edit The probability of a photoelectric absorption per unit mass is approximately proportional to Z3 E3 where Z is the atomic number and E is the energy of the incident photon 72 This rule is not valid close to inner shell electron binding energies where there are abrupt changes in interaction probability so called absorption edges However the general trend of high absorption coefficients and thus short penetration depths for low photon energies and high atomic numbers is very strong For soft tissue photoabsorption dominates up to about 26 keV photon energy where Compton scattering takes over For higher atomic number substances this limit is higher The high amount of calcium Z 20 in bones together with their high density is what makes them show up so clearly on medical radiographs A photoabsorbed photon transfers all its energy to the electron with which it interacts thus ionizing the atom to which the electron was bound and producing a photoelectron that is likely to ionize more atoms in its path An outer electron will fill the vacant electron position and produce either a characteristic X ray or an Auger electron These effects can be used for elemental detection through X ray spectroscopy or Auger electron spectroscopy Compton scattering Edit Compton scattering is the predominant interaction between X rays and soft tissue in medical imaging 73 Compton scattering is an inelastic scattering of the X ray photon by an outer shell electron Part of the energy of the photon is transferred to the scattering electron thereby ionizing the atom and increasing the wavelength of the X ray The scattered photon can go in any direction but a direction similar to the original direction is more likely especially for high energy X rays The probability for different scattering angles is described by the Klein Nishina formula The transferred energy can be directly obtained from the scattering angle from the conservation of energy and momentum Rayleigh scattering Edit Rayleigh scattering is the dominant elastic scattering mechanism in the X ray regime 74 Inelastic forward scattering gives rise to the refractive index which for X rays is only slightly below 1 75 Production EditWhenever charged particles electrons or ions of sufficient energy hit a material X rays are produced Production by electrons Edit Characteristic X ray emission lines for some common anode materials 76 77 Anode material Atomic number Photon energy keV Wavelength nm Ka1 Kb1 Ka1 Kb1W 74 59 3 67 2 0 0209 0 0184Mo 42 17 5 19 6 0 0709 0 0632Cu 29 8 05 8 91 0 154 0 139Ag 47 22 2 24 9 0 0559 0 0497Ga 31 9 25 10 26 0 134 0 121In 49 24 2 27 3 0 0512 0 455 Spectrum of the X rays emitted by an X ray tube with a rhodium target operated at 60 kV The smooth continuous curve is due to bremsstrahlung and the spikes are characteristic K lines for rhodium atoms X rays can be generated by an X ray tube a vacuum tube that uses a high voltage to accelerate the electrons released by a hot cathode to a high velocity The high velocity electrons collide with a metal target the anode creating the X rays 78 In medical X ray tubes the target is usually tungsten or a more crack resistant alloy of rhenium 5 and tungsten 95 but sometimes molybdenum for more specialized applications such as when softer X rays are needed as in mammography In crystallography a copper target is most common with cobalt often being used when fluorescence from iron content in the sample might otherwise present a problem The maximum energy of the produced X ray photon is limited by the energy of the incident electron which is equal to the voltage on the tube times the electron charge so an 80 kV tube cannot create X rays with an energy greater than 80 keV When the electrons hit the target X rays are created by two different atomic processes Characteristic X ray emission X ray electroluminescence If the electron has enough energy it can knock an orbital electron out of the inner electron shell of the target atom After that electrons from higher energy levels fill the vacancies and X ray photons are emitted This process produces an emission spectrum of X rays at a few discrete frequencies sometimes referred to as spectral lines Usually these are transitions from the upper shells to the K shell called K lines to the L shell called L lines and so on If the transition is from 2p to 1s it is called Ka while if it is from 3p to 1s it is Kb The frequencies of these lines depend on the material of the target and are therefore called characteristic lines The Ka line usually has greater intensity than the Kb one and is more desirable in diffraction experiments Thus the Kb line is filtered out by a filter The filter is usually made of a metal having one proton less than the anode material e g Ni filter for Cu anode or Nb filter for Mo anode Bremsstrahlung This is radiation given off by the electrons as they are scattered by the strong electric field near the high Z proton number nuclei These X rays have a continuous spectrum The frequency of bremsstrahlung is limited by the energy of incident electrons So the resulting output of a tube consists of a continuous bremsstrahlung spectrum falling off to zero at the tube voltage plus several spikes at the characteristic lines The voltages used in diagnostic X ray tubes range from roughly 20 kV to 150 kV and thus the highest energies of the X ray photons range from roughly 20 keV to 150 keV 79 Both of these X ray production processes are inefficient with only about one percent of the electrical energy used by the tube converted into X rays and thus most of the electric power consumed by the tube is released as waste heat When producing a usable flux of X rays the X ray tube must be designed to dissipate the excess heat A specialized source of X rays which is becoming widely used in research is synchrotron radiation which is generated by particle accelerators Its unique features are X ray outputs many orders of magnitude greater than those of X ray tubes wide X ray spectra excellent collimation and linear polarization 80 Short nanosecond bursts of X rays peaking at 15 keV in energy may be reliably produced by peeling pressure sensitive adhesive tape from its backing in a moderate vacuum This is likely to be the result of recombination of electrical charges produced by triboelectric charging The intensity of X ray triboluminescence is sufficient for it to be used as a source for X ray imaging 81 Production by fast positive ions Edit X rays can also be produced by fast protons or other positive ions The proton induced X ray emission or particle induced X ray emission is widely used as an analytical procedure For high energies the production cross section is proportional to Z12Z2 4 where Z1 refers to the atomic number of the ion Z2 refers to that of the target atom 82 An overview of these cross sections is given in the same reference Production in lightning and laboratory discharges Edit X rays are also produced in lightning accompanying terrestrial gamma ray flashes The underlying mechanism is the acceleration of electrons in lightning related electric fields and the subsequent production of photons through Bremsstrahlung 83 This produces photons with energies of some few keV and several tens of MeV 84 In laboratory discharges with a gap size of approximately 1 meter length and a peak voltage of 1 MV X rays with a characteristic energy of 160 keV are observed 85 A possible explanation is the encounter of two streamers and the production of high energy run away electrons 86 however microscopic simulations have shown that the duration of electric field enhancement between two streamers is too short to produce a significant number of run away electrons 87 Recently it has been proposed that air perturbations in the vicinity of streamers can facilitate the production of run away electrons and hence of X rays from discharges 88 89 Detectors EditMain article X ray detector X ray detectors vary in shape and function depending on their purpose Imaging detectors such as those used for radiography were originally based on photographic plates and later photographic film but are now mostly replaced by various digital detector types such as image plates and flat panel detectors For radiation protection direct exposure hazard is often evaluated using ionization chambers while dosimeters are used to measure the radiation dose a person has been exposed to X ray spectra can be measured either by energy dispersive or wavelength dispersive spectrometers For X ray diffraction applications such as x ray crystallography hybrid photon counting detectors are widely used 90 Medical uses EditThis section needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources X ray news newspapers books scholar JSTOR November 2017 Learn how and when to remove this template message X ray A chest radiograph of a female demonstrating a hiatal hernia Since Rontgen s discovery that X rays can identify bone structures X rays have been used for medical imaging 91 The first medical use was less than a month after his paper on the subject 29 Up to 2010 five billion medical imaging examinations had been conducted worldwide 92 Radiation exposure from medical imaging in 2006 made up about 50 of total ionizing radiation exposure in the United States 93 Projectional radiographs Edit Main article Projectional radiography Plain radiograph of the right knee Projectional radiography is the practice of producing two dimensional images using x ray radiation Bones contain a high concentration of calcium which due to its relatively high atomic number absorbs x rays efficiently This reduces the amount of X rays reaching the detector in the shadow of the bones making them clearly visible on the radiograph The lungs and trapped gas also show up clearly because of lower absorption compared to tissue while differences between tissue types are harder to see Projectional radiographs are useful in the detection of pathology of the skeletal system as well as for detecting some disease processes in soft tissue Some notable examples are the very common chest X ray which can be used to identify lung diseases such as pneumonia lung cancer or pulmonary edema and the abdominal x ray which can detect bowel or intestinal obstruction free air from visceral perforations and free fluid in ascites X rays may also be used to detect pathology such as gallstones which are rarely radiopaque or kidney stones which are often but not always visible Traditional plain X rays are less useful in the imaging of soft tissues such as the brain or muscle One area where projectional radiographs are used extensively is in evaluating how an orthopedic implant such as a knee hip or shoulder replacement is situated in the body with respect to the surrounding bone This can be assessed in two dimensions from plain radiographs or it can be assessed in three dimensions if a technique called 2D to 3D registration is used This technique purportedly negates projection errors associated with evaluating implant position from plain radiographs 94 95 Dental radiography is commonly used in the diagnoses of common oral problems such as cavities In medical diagnostic applications the low energy soft X rays are unwanted since they are totally absorbed by the body increasing the radiation dose without contributing to the image Hence a thin metal sheet often of aluminium called an X ray filter is usually placed over the window of the X ray tube absorbing the low energy part in the spectrum This is called hardening the beam since it shifts the center of the spectrum towards higher energy or harder x rays To generate an image of the cardiovascular system including the arteries and veins angiography an initial image is taken of the anatomical region of interest A second image is then taken of the same region after an iodinated contrast agent has been injected into the blood vessels within this area These two images are then digitally subtracted leaving an image of only the iodinated contrast outlining the blood vessels The radiologist or surgeon then compares the image obtained to normal anatomical images to determine whether there is any damage or blockage of the vessel Computed tomography Edit Main article CT scan Head CT scan transverse plane slice a modern application of medical radiography Computed tomography CT scanning is a medical imaging modality where tomographic images or slices of specific areas of the body are obtained from a large series of two dimensional X ray images taken in different directions 96 These cross sectional images can be combined into a three dimensional image of the inside of the body and used for diagnostic and therapeutic purposes in various medical disciplines Fluoroscopy Edit Main article Fluoroscopy Fluoroscopy is an imaging technique commonly used by physicians or radiation therapists to obtain real time moving images of the internal structures of a patient through the use of a fluoroscope In its simplest form a fluoroscope consists of an X ray source and a fluorescent screen between which a patient is placed However modern fluoroscopes couple the screen to an X ray image intensifier and CCD video camera allowing the images to be recorded and played on a monitor This method may use a contrast material Examples include cardiac catheterization to examine for coronary artery blockages and barium swallow to examine for esophageal disorders and swallowing disorders Radiotherapy Edit The use of X rays as a treatment is known as radiation therapy and is largely used for the management including palliation of cancer it requires higher radiation doses than those received for imaging alone X rays beams are used for treating skin cancers using lower energy x ray beams while higher energy beams are used for treating cancers within the body such as brain lung prostate and breast 97 98 Adverse effects Edit Abdominal radiograph of a pregnant woman a procedure that should be performed only after proper assessment of benefit versus risk Diagnostic X rays primarily from CT scans due to the large dose used increase the risk of developmental problems and cancer in those exposed 99 100 101 X rays are classified as a carcinogen by both the World Health Organization s International Agency for Research on Cancer and the U S government 92 102 It is estimated that 0 4 of current cancers in the United States are due to computed tomography CT scans performed in the past and that this may increase to as high as 1 5 2 with 2007 rates of CT usage 103 Experimental and epidemiological data currently do not support the proposition that there is a threshold dose of radiation below which there is no increased risk of cancer 104 However this is under increasing doubt 105 It is estimated that the additional radiation from diagnostic X rays will increase the average person s cumulative risk of getting cancer by age 75 by 0 6 3 0 106 The amount of absorbed radiation depends upon the type of X ray test and the body part involved 107 CT and fluoroscopy entail higher doses of radiation than do plain X rays To place the increased risk in perspective a plain chest X ray will expose a person to the same amount from background radiation that people are exposed to depending upon location every day over 10 days while exposure from a dental X ray is approximately equivalent to 1 day of environmental background radiation 108 Each such X ray would add less than 1 per 1 000 000 to the lifetime cancer risk An abdominal or chest CT would be the equivalent to 2 3 years of background radiation to the whole body or 4 5 years to the abdomen or chest increasing the lifetime cancer risk between 1 per 1 000 to 1 per 10 000 108 This is compared to the roughly 40 chance of a US citizen developing cancer during their lifetime 109 For instance the effective dose to the torso from a CT scan of the chest is about 5 mSv and the absorbed dose is about 14 mGy 110 A head CT scan 1 5mSv 64mGy 111 that is performed once with and once without contrast agent would be equivalent to 40 years of background radiation to the head Accurate estimation of effective doses due to CT is difficult with the estimation uncertainty range of about 19 to 32 for adult head scans depending upon the method used 112 The risk of radiation is greater to a fetus so in pregnant patients the benefits of the investigation X ray should be balanced with the potential hazards to the fetus 113 114 In the US there are an estimated 62 million CT scans performed annually including more than 4 million on children 107 Avoiding unnecessary X rays especially CT scans reduces radiation dose and any associated cancer risk 115 Medical X rays are a significant source of human made radiation exposure In 1987 they accounted for 58 of exposure from human made sources in the United States Since human made sources accounted for only 18 of the total radiation exposure most of which came from natural sources 82 medical X rays only accounted for 10 of total American radiation exposure medical procedures as a whole including nuclear medicine accounted for 14 of total radiation exposure By 2006 however medical procedures in the United States were contributing much more ionizing radiation than was the case in the early 1980s In 2006 medical exposure constituted nearly half of the total radiation exposure of the U S population from all sources The increase is traceable to the growth in the use of medical imaging procedures in particular computed tomography CT and to the growth in the use of nuclear medicine 93 116 Dosage due to dental X rays varies significantly depending on the procedure and the technology film or digital Depending on the procedure and the technology a single dental X ray of a human results in an exposure of 0 5 to 4 mrem A full mouth series of X rays may result in an exposure of up to 6 digital to 18 film mrem for a yearly average of up to 40 mrem 117 118 119 120 121 122 123 Financial incentives have been shown to have a significant impact on X ray use with doctors who are paid a separate fee for each X ray providing more X rays 124 Early photon tomography or EPT 125 as of 2015 along with other techniques 126 are being researched as potential alternatives to X rays for imaging applications Other uses EditOther notable uses of X rays include Each dot called a reflection in this diffraction pattern forms from the constructive interference of scattered X rays passing through a crystal The data can be used to determine the crystalline structure X ray crystallography in which the pattern produced by the diffraction of X rays through the closely spaced lattice of atoms in a crystal is recorded and then analysed to reveal the nature of that lattice A related technique fiber diffraction was used by Rosalind Franklin to discover the double helical structure of DNA 127 X ray astronomy which is an observational branch of astronomy which deals with the study of X ray emission from celestial objects X ray microscopic analysis which uses electromagnetic radiation in the soft X ray band to produce images of very small objects X ray fluorescence a technique in which X rays are generated within a specimen and detected The outgoing energy of the X ray can be used to identify the composition of the sample Industrial radiography uses X rays for inspection of industrial parts particularly welds Radiography of cultural objects most often x rays of paintings to reveal underdrawing pentimenti alterations in the course of painting or by later restorers and sometimes previous paintings on the support Many pigments such as lead white show well in radiographs X ray spectromicroscopy has been used to analyse the reactions of pigments in paintings For example in analysing colour degradation in the paintings of van Gogh 128 Using X ray for inspection and quality control the differences in the structures of the die and bond wires reveal the left chip to be counterfeit 129 Authentication and quality control of packaged items Industrial CT computed tomography a process that uses X ray equipment to produce three dimensional representations of components both externally and internally This is accomplished through computer processing of projection images of the scanned object in many directions Airport security luggage scanners use X rays for inspecting the interior of luggage for security threats before loading on aircraft Border control truck scanners and domestic police departments use X rays for inspecting the interior of trucks X ray fine art photography of needlefish by Peter Dazeley X ray art and fine art photography artistic use of X rays for example the works by Stane Jagodic X ray hair removal a method popular in the 1920s but now banned by the FDA 130 Shoe fitting fluoroscopes were popularized in the 1920s banned in the US in the 1960s in the UK in the 1970s and later in continental Europe Roentgen stereophotogrammetry is used to track movement of bones based on the implantation of markers X ray photoelectron spectroscopy is a chemical analysis technique relying on the photoelectric effect usually employed in surface science Radiation implosion is the use of high energy X rays generated from a fission explosion an A bomb to compress nuclear fuel to the point of fusion ignition an H bomb Visibility EditWhile generally considered invisible to the human eye in special circumstances X rays can be visible Brandes in an experiment a short time after Rontgen s landmark 1895 paper reported after dark adaptation and placing his eye close to an X ray tube seeing a faint blue gray glow which seemed to originate within the eye itself 131 Upon hearing this Rontgen reviewed his record books and found he too had seen the effect When placing an X ray tube on the opposite side of a wooden door Rontgen had noted the same blue glow seeming to emanate from the eye itself but thought his observations to be spurious because he only saw the effect when he used one type of tube Later he realized that the tube which had created the effect was the only one powerful enough to make the glow plainly visible and the experiment was thereafter readily repeatable The knowledge that X rays are actually faintly visible to the dark adapted naked eye has largely been forgotten today this is probably due to the desire not to repeat what would now be seen as a recklessly dangerous and potentially harmful experiment with ionizing radiation It is not known what exact mechanism in the eye produces the visibility it could be due to conventional detection excitation of rhodopsin molecules in the retina direct excitation of retinal nerve cells or secondary detection via for instance X ray induction of phosphorescence in the eyeball with conventional retinal detection of the secondarily produced visible light Though X rays are otherwise invisible it is possible to see the ionization of the air molecules if the intensity of the X ray beam is high enough The beamline from the wiggler at the ID11 at the European Synchrotron Radiation Facility is one example of such high intensity 132 Units of measure and exposure EditThe measure of X rays ionizing ability is called the exposure The coulomb per kilogram C kg is the SI unit of ionizing radiation exposure and it is the amount of radiation required to create one coulomb of charge of each polarity in one kilogram of matter The roentgen R is an obsolete traditional unit of exposure which represented the amount of radiation required to create one electrostatic unit of charge of each polarity in one cubic centimeter of dry air 1 roentgen 2 58 10 4 C kg However the effect of ionizing radiation on matter especially living tissue is more closely related to the amount of energy deposited into them rather than the charge generated This measure of energy absorbed is called the absorbed dose The gray Gy which has units of joules kilogram is the SI unit of absorbed dose and it is the amount of radiation required to deposit one joule of energy in one kilogram of any kind of matter The rad is the obsolete corresponding traditional unit equal to 10 millijoules of energy deposited per kilogram 100 rad 1 gray The equivalent dose is the measure of the biological effect of radiation on human tissue For X rays it is equal to the absorbed dose The Roentgen equivalent man rem is the traditional unit of equivalent dose For X rays it is equal to the rad or in other words 10 millijoules of energy deposited per kilogram 100 rem 1 Sv The sievert Sv is the SI unit of equivalent dose and also of effective dose For X rays the equivalent dose is numerically equal to a Gray Gy 1 Sv 1 Gy For the effective dose of X rays it is usually not equal to the Gray Gy Ionizing radiation related quantities view talk edit Quantity Unit Symbol Derivation Year SI equivalenceActivity A becquerel Bq s 1 1974 SI unitcurie Ci 3 7 1010 s 1 1953 3 7 1010 Bqrutherford Rd 106 s 1 1946 1 000 000 BqExposure X coulomb per kilogram C kg C kg 1 of air 1974 SI unitrontgen R esu 0 001293 g of air 1928 2 58 10 4 C kgAbsorbed dose D gray Gy J kg 1 1974 SI uniterg per gram erg g erg g 1 1950 1 0 10 4 Gyrad rad 100 erg g 1 1953 0 010 GyEquivalent dose H sievert Sv J kg 1 WR 1977 SI unitrontgen equivalent man rem 100 erg g 1 x WR 1971 0 010 SvEffective dose E sievert Sv J kg 1 WR WT 1977 SI unitrontgen equivalent man rem 100 erg g 1 WR WT 1971 0 010 SvSee also Edit Medical portal Physics portal Backscatter X ray Detective quantum efficiency High energy X rays Macintyre s X Ray Film 1896 documentary radiography film N ray Neutron radiation NuSTAR Radiographer Reflection physics Resonant inelastic X ray scattering RIXS Small angle X ray scattering SAXS The X Rays 1897 British short silent comedy film X ray absorption spectroscopy X ray marker X ray nanoprobe X ray reflectivity X ray vision X ray weldingReferences Edit X Rays Science Mission Directorate NASA Novelline Robert 1997 Squire s Fundamentals of Radiology Harvard University Press 5th edition ISBN 0 674 83339 2 X ray Oxford English Dictionary Online ed Oxford University Press Subscription or participating institution membership required Filler Aaron 2009 The History Development and Impact of Computed Imaging in Neurological Diagnosis and Neurosurgery CT MRI and DTI Nature Precedings doi 10 1038 npre 2009 3267 5 Morgan William 1785 02 24 Electrical Experiments Made in Order to Ascertain the Non Conducting Power of a Perfect Vacuum amp c Philosophical Transactions of the Royal Society Royal Society of London 75 272 278 doi 10 1098 rstl 1785 0014 Anderson J G January 1945 William Morgan and X rays Transactions of the Faculty of Actuaries 17 219 221 doi 10 1017 s0071368600003001 Wyman Thomas Spring 2005 Fernando Sanford and the Discovery of X rays Imprint from the Associates of the Stanford University Libraries 5 15 Thomson Joseph J 1903 The Discharge of Electricity through Gasses USA Charles Scribner s Sons pp 182 186 Gaida Roman et al 1997 Ukrainian Physicist Contributes to the Discovery of X Rays Mayo Clinic Proceedings Mayo Foundation for Medical Education and Research 72 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11 Als Nielsen Jens Mcmorrow Des 2001 Elements of Modern X Ray Physics John Wiley amp Sons Ltd pp 40 41 ISBN 978 0 471 49858 2 External links EditWikimedia Commons has media related to X ray Look up x ray in Wiktionary the free dictionary On a New Kind of Rays Nature 53 1369 274 276 January 1896 doi 10 1038 053274b0 Ion X Ray tubes The Cathode Ray Tube site Index of Early Bremsstrahlung Articles Shade Tree Physics 12 Apr 2010 Samuel Jean Jacques 20 October 2013 La decouverte des rayons X par Rontgen Bibnum Education in French Rontgen s discovery of X rays English translation Retrieved from https en wikipedia org w index php title X ray amp oldid 1050460269, wikipedia, wiki, book,

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