HOME

TheInfoList




An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy
electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. ...

electromagnetic radiation
. Most X-rays have a
wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase (waves), phase on the wave, such as two adja ...

wavelength
ranging from 10 
picometers The picometre (international American and British English spelling differences#-re, -er, spelling as used by the International Bureau of Weights and Measures; SI symbol: pm) or picometer (American and British English spelling differences#-re, -er ...
to 10 
nanometers one nanometric Scanning_Tunneling_Microscope.html"_;"title="carbon_nano_tube,_photographed_with_Scanning_Tunneling_Microscope">carbon_nano_tube,_photographed_with_Scanning_Tunneling_Microscope_ file:EM_Spectrum_Properties_edit.svg.html" ;"title= ...
, corresponding to
frequencies Frequency is the number of occurrences of a repeating event per unit of time A unit of time is any particular time Time is the indefinite continued sequence, progress of existence and event (philosophy), events that occur in an apparent ...

frequencies
in the range 30 
petahertz The hertz (symbol: Hz) is the SI derived unit, derived unit of frequency in the International System of Units (SI) and is defined as one cycle (geometry), cycle per second. It is named after Heinrich Hertz, Heinrich Rudolf Hertz, the first per ...

petahertz
to 30 
exahertz The hertz (symbol: Hz) is the SI derived unit, derived unit of frequency in the International System of Units (SI) and is defined as one cycle (geometry), cycle per second. It is named after Heinrich Hertz, Heinrich Rudolf Hertz, the first per ...

exahertz
( to ) and energies in the range 124  eV to 124 
keV In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular suc ...
. X-ray wavelengths are shorter than those of
UV
UV
rays and typically longer than those of
gamma ray A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, it ...
s. In many languages, X-radiation is referred to as Röntgen radiation, after the German scientist
Wilhelm Conrad Röntgen
Wilhelm Conrad Röntgen
, who discovered it on November 8, 1895. He named it ''X-radiation'' to signify an unknown type of radiation.Novelline, Robert (1997). ''Squire's Fundamentals of Radiology''. Harvard University Press. 5th edition. . Spellings of ''X-ray(s)'' in English include the variants ''x-ray(s)'', ''xray(s)'', and ''X ray(s)''.


History


Pre-Röntgen observations and research

Before their discovery in 1895, X-rays were just a type of unidentified radiation emanating from experimental
discharge tube A gas-filled tube, also commonly known as a discharge tube or formerly as a Plücker tube, is an arrangement of electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconducto ...

discharge tube
s. They were noticed by scientists investigating
cathode ray Cathode rays (electron beam or e-beam) are streams of electron The electron is a subatomic particle In physical sciences, subatomic particles are smaller than atom An atom is the smallest unit of ordinary matter In classical ...
s produced by such tubes, which are energetic
electron The electron is a subatomic particle (denoted by the symbol or ) whose electric charge is negative one elementary charge. Electrons belong to the first generation (particle physics), generation of the lepton particle family, and are general ...

electron
beams that were first observed in 1869. Many of the early
Crookes tube A Crookes tube (also Crookes–Hittorf tube) is an early experimental electrical discharge tube A gas-filled tube, also commonly known as a discharge tube or formerly as a Plücker tube, is an arrangement of electrode An electrode is an elec ...

Crookes tube
s (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 Ionization or ionisation is the process by which an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday ...
of the residual air in the tube by a high DC
voltage Voltage, electric potential difference, electric pressure or electric tension is the difference in electric potential The electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is the ...

voltage
of anywhere between a few
kilovolt The volt (symbol: V) is the derived unit for electric potential The electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is the amount of work energy needed to move a unit of electric ...
s and 100 kV. This voltage accelerated the electrons coming from the
cathode A cathode is the from which a leaves a polarized electrical device. This definition can be recalled by using the ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in which positive charges move. Electrons ha ...
to a high enough velocity that they created X-rays when they struck the
anode An anode is an electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor A semiconductor material has an Electrical resistivity and conductivity, electrical conductivit ...

anode
or the glass wall of the tube. The earliest experimenter thought to have (unknowingly) produced X-rays was actually William Morgan. In 1785, he presented a paper to the
Royal Society of London The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. Founded on 28 November 1660, it was granted a royal charter by Charles II of ...
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 Sir Humphry Davy, 1st Baronet (17 December 177829 May 1829) was a Cornish people, Cornish chemist and inventor who invented the Davy lamp and a very early form of arc lamp. He is also remembered for isolating, by using electricity, a series of ...

Humphry Davy
and his assistant
Michael Faraday Michael Faraday (; 22 September 1791 – 25 August 1867) was an English scientist A scientist is a person who conducts scientific research The scientific method is an Empirical evidence, empirical method of acquiring knowledge ...

Michael Faraday
. When
Stanford University Stanford University, officially Leland Stanford Junior University, is a private Private or privates may refer to: Music * "In Private "In Private" was the third single in a row to be a charting success for United Kingdom, British singer Du ...

Stanford University
physics professor
Fernando Sanford Fernando Sanford (February 12, 1854 – May 21, 1948) was an American physicist A physicist is a scientist A scientist is a person who conducts Scientific method, scientific research to advance knowledge in an Branches of science, area of int ...
created his "electric photography", he also unknowingly generated and detected X-rays. From 1886 to 1888, he had studied in the
Hermann Helmholtz Hermann Ludwig Ferdinand von Helmholtz (31 August 1821 – 8 September 1894) was a German physicist A physicist is a scientist A scientist is a person who conducts Scientific method, scientific research to advance knowledge in an Branc ...
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 Heinrich Rudolf Hertz ( ; ; 22 February 1857 – 1 January 1894) was a German physicist A physicist is a scientist A scientist is a person who conducts scientific research The scientific method is an Empirical evidence, empi ...

Heinrich Hertz
and
Philipp Lenard Philipp Eduard Anton Von Lenard (7 June 1862 – 20 May 1947) was a Hungarian-born German physicist A physicist is a scientist A scientist is a person who conducts Scientific method, scientific research to advance knowledge in an Branche ...

Philipp Lenard
. His letter of January 6, 1893 (describing his discovery as "electric photography") to The
Physical Review ''Physical Review'' is a peer-reviewed Peer review is the evaluation of work by one or more people with similar competencies as the producers of the work ( peers). It functions as a form of self-regulation by qualified members of a profession ...
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 The ''San Francisco Examiner'' is a newspaper distributed in and around San Francisco, California, and published since 1863. The longtime "Monarch of the Dailies" and flagship of the Hearst Corporation chain, the ''Examiner'' converted to free di ...

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 aluminium, 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 Ukrainian may refer to: * Something of, from, or related to Ukraine * Something relating to Ukrainians an East Slavic people from Eastern Europe * Something relating to Demographics of Ukraine, in terms of demography: population of Ukraine * Somethi ...
-born
Ivan Puluj
Ivan Puluj
, a lecturer in experimental physics at the Prague Polytechnic who since 1877 had been constructing various designs of
gas-filled tube A gas-filled tube, also commonly known as a discharge tube or formerly as a tube, is an arrangement of s in a within an , temperature-resistant . Gas-filled tubes exploit phenomena related to , and operate by the gas with an applied suffici ...
s 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 Hermann Ludwig Ferdinand von Helmholtz (31 August 1821 – 8 September 1894) was a German physicist A physicist is a scientist A scientist is a person who conducts Scientific method, scientific research to advance knowledge in an Branch ...

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. However, he did not work with actual X-rays. In 1894,
Nikola Tesla Nikola Tesla ( ; sr-cyr, Никола Тесла, ; 10 July 1856 – 7 January 1943) was a Serbian-American inventor, electrical engineer, mechanical engineer, and futurist best known for his contributions to the design of the moder ...

Nikola Tesla
noticed damaged film in his lab that seemed to be associated with Crookes tube experiments and began investigating this invisible,
radiant energy In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. "Ph ...
. 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 German(s) may refer to: Common uses * of or related to Germany * Germans, Germanic ethnic group, citizens of Germany or people of German ancestry * For citizens of Germany, see also German nationality law * German language The German la ...

German
physics professor
Wilhelm Röntgen Wilhelm Conrad Röntgen (; ; 27 March 184510 February 1923) was a German mechanical engineer Mechanical may refer to: Machine * Mechanical system, a system that manages the power of forces and movements to accomplish a task * Machine (mechanica ...

Wilhelm Röntgen
stumbled on X-rays while experimenting with Lenard tubes and
Crookes tube A Crookes tube (also Crookes–Hittorf tube) is an early experimental electrical discharge tube A gas-filled tube, also commonly known as a discharge tube or formerly as a Plücker tube, is an arrangement of electrode An electrode is an elec ...

Crookes tube
s 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 Würzburg (; Main-Franconian: ) is a List of cities and towns in Germany, city in the traditional region of Franconia in the north of the Germany, German state of Bavaria. Würzburg is the administrative seat of the ''Regierungsbezirk'' Lower Fra ...

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 German(s) may refer to: Common uses * of or related to Germany * Germans, Germanic ethnic group, citizens of Germany or people of German ancestry * For citizens of Germany, see also German nationality law * German language The German la ...

German
,
HungarianHungarian may refer to: * Hungary, a country in Central Europe * Kingdom of Hungary, state of Hungary, existing between 1000 and 1946 * Hungarians, ethnic groups in Hungary * Hungarian algorithm, a polynomial time algorithm for solving the assignmen ...
,
Ukrainian Ukrainian may refer to: * Something of, from, or related to Ukraine * Something relating to Ukrainians an East Slavic people from Eastern Europe * Something relating to Demographics of Ukraine, in terms of demography: population of Ukraine * Somethi ...
,
Danish Danish may refer to: * Something of, from, or related to the country of Denmark * A national or citizen of Denmark, also called a "Dane", see Demographics of Denmark * Danish people or Danes, people with a Danish ancestral or ethnic identity * Danis ...
,
Polish Polish may refer to: * Anything from or related to Poland Poland ( pl, Polska ), officially the Republic of Poland ( pl, Rzeczpospolita Polska, links=no ), is a country located in Central Europe. It is divided into 16 Voivodeships of Pol ...
,
Bulgarian Bulgarian may refer to: * Something of, from, or related to the country of Bulgaria * Bulgarians, a South Slavic ethnic group * Bulgarian language, a Slavic language * Bulgarian alphabet * A citizen of Bulgaria, see Demographics of Bulgaria * Bulg ...

Bulgarian
,
Swedish Swedish or ' may refer to: * Anything from or related to Sweden, a country in Northern Europe * Swedish language, a North Germanic language spoken primarily in Sweden and Finland * Swedish alphabet, the official alphabet used by the Swedish langua ...
,
Finnish Finnish may refer to: * Something or someone from, or related to Finland * Finnish culture * Finnish people or Finns, the primary ethnic group in Finland * Finnish language, the national language of the Finnish people * Finnish cuisine See also

...
,
Estonian Estonian may refer to: *Something of, from, or related to Estonia, a country in the Baltic region in northern Europe *Estonians, people from Estonia, or of Estonian descent *Estonian language *Estonian cuisine *Estonian culture See also

* * La ...
,
Turkish Turkish may refer to: * of or about Turkey Turkey ( tr, Türkiye ), officially the Republic of Turkey, is a country straddling Southeastern Europe and Western Asia. It shares borders with Greece Greece ( el, Ελλάδα, , ), offi ...

Turkish
,
Russian Russian refers to anything related to Russia, including: *Russians (русские, ''russkiye''), an ethnic group of the East Slavic peoples, primarily living in Russia and neighboring countries *Rossiyane (россияне), Russian language term ...
, Latvian,
Lithuanian Lithuanian may refer to: * Lithuanians Lithuanians ( lt, lietuviai, singular ''lietuvis/lietuvė'') are a Balts, Baltic ethnic group. They are native to Lithuania, where they number around 2,561,300 people. Another million or more make up the Lith ...
,
Japanese Japanese may refer to: * Something from or related to Japan , image_flag = Flag of Japan.svg , alt_flag = Centered deep red circle on a white rectangle , image_coat = Imperial Seal of J ...

Japanese
,
Dutch Dutch commonly refers to: * Something of, from, or related to the Netherlands * Dutch people () * Dutch language () *Dutch language , spoken in Belgium (also referred as ''flemish'') Dutch may also refer to:" Castle * Dutch Castle Places * ...
,
Georgian Georgian may refer to: Common meanings * Anything related to, or originating from Georgia (country) **Georgians, an indigenous Caucasian ethnic group **Georgian language, a Kartvelian language spoken by Georgians **Georgian scripts, three scripts ...
,
Hebrew Hebrew (, , or ) is a Northwest Semitic languages, Northwest Semitic language of the Afroasiatic languages, Afroasiatic language family. Historically, it is regarded as the language of the Israelites, Judeans and their ancestors. It is the o ...
, and
Norwegian Norwegian, Norwayan, or Norsk may refer to: *Something of, from, or related to Norway, a country in northwestern Europe *Norwegians, both a nation and an ethnic group native to Norway *Demographics of Norway *The Norwegian language, including the t ...
. Röntgen received the first
Nobel Prize in Physics The Nobel Prize in Physics is a yearly award given by the Royal Swedish Academy of Sciences for those who have made the most outstanding contributions for mankind in the field of physics. It is one of the five Nobel Prizes established by the will ...
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 light. Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon ener ...

fluorescent
screen painted with barium
platinocyanidePlatinocyanide, also known as tetracyanoplatinate (IUPAC), cyanoplatinate, or platinocyanate, is a polyatomic ion A polyatomic ion, also known as a molecular ion, is a covalently bonded set of two or more atoms, or of a metal complex, that can b ...
. He noticed a faint green glow from the screen, about 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. 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

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 Alan Archibald Campbell-Swinton FRS FRS may also refer to: Government and politics * Facility Registry System, a centrally managed Environmental Protection Agency database that identifies places of environmental interest in the United States ...
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 Birmingham ( ) is a city A city is a large .Goodall, B. (1987) ''The Penguin Dictionary of Human Geography''. London: Penguin.Kuper, A. and Kuper, J., eds (1996) ''The Social Science Encyclopedia''. 2nd edition. London: Routledge. It can ...

Birmingham
,
England England is a that is part of the . It shares land borders with to its west and to its north. The lies northwest of England and the to the southwest. England is separated from by the to the east and the to the south. The country cover ...

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". At around the same time, the zoological illustrator James Green began to use X-rays to examine fragile specimens.
George Albert Boulenger George Albert Boulenger (19 October 1858 – 23 November 1937) was a Belgian Belgian may refer to: * Something of, or related to, Belgium Belgium, ; french: Belgique ; german: Belgien officially the Kingdom of Belgium, is a country in ...
first mentioned this work in a paper he delivered before the
Zoological Society of London The Zoological Society of London (ZSL) is a charity devoted to the worldwide and their . It was founded in 1826. History On 29 November 1822, the birthday of , "the father of modern zoology", a meeting held in the in Soho Square led by R ...

Zoological Society of London
in May 1896. The book ''Sciagraphs of British Batrachians and Reptiles'' (sciagraph is an obsolete name for an X-ray photograph), by Green and James H. Gardiner, with a foreword by Boulenger, was published in 1897. 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 Dartmouth College ( ) is a private Private or privates may refer to: Music * "In Private "In Private" was the third single in a row to be a charting success for United Kingdom, British singer Dusty Springfield, after an absence of nearly t ...
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 Micas ( ) are a group of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs natural ...

mica
, used for holding samples of
fluorescent light. Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon ener ...

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. 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
platinocyanidePlatinocyanide, also known as tetracyanoplatinate (IUPAC), cyanoplatinate, or platinocyanate, is a polyatomic ion A polyatomic ion, also known as a molecular ion, is a covalently bonded set of two or more atoms, or of a metal complex, that can b ...
. On February 5, 1896, live imaging devices were developed by both Italian scientist Enrico Salvioni (his "cryptoscope") and Professor McGie of
Princeton University Princeton University is a private Private or privates may refer to: Music * "In Private "In Private" was the third single in a row to be a charting success for United Kingdom, British singer Dusty Springfield, after an absence of nearly tw ...

Princeton University
(his "Skiascope"), both using barium platinocyanide. American inventor
Thomas Edison Thomas Alva Edison (February 11, 1847October 18, 1931) was an American inventor and businessman. He developed many devices in fields such as electric power generation Electricity generation is the process of generating electric power from s ...

Thomas Edison
started research soon after Röntgen's discovery and investigated materials' ability to fluoresce when exposed to X-rays, finding that was the most effective substance. In May 1896, he developed the first mass-produced live imaging device, his "Vitascope", later called the
fluoroscope A barium swallow exam taken via fluoroscopy. Fluoroscopy () is an imaging technique that uses X-rays to obtain real-time moving images of the interior of an object. In its primary application of medical imaging, a fluoroscope () allows a physicia ...

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 Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumor A benign tumor is a mass of cells Cell most often refers to: * Cell (biolo ...

cancer
in them so tenacious that both arms were
amputated Amputation is the removal of a Limb (anatomy), limb by Physical trauma, trauma, medical illness, or surgery. As a surgical measure, it is used to control pain or a disease process in the affected limb, such as cancer, malignancy or gangrene. In som ...

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 Mihajlo Idvorski Pupin ( sr-cyr, Михајло Идворски Пупин, ; 4 October 1858Although Pupin's birth year is sometimes given as 1854 (and Serbia and Montenegro issued a postage stamp in 2004 to commemorate the 150th anniversary of ...

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 Assassination is the act of murder, deliberately killing a prominent or important person, such as heads of state, head of government, heads of government, politicians, Monarchy, royalty, celebrity, celebrities, journalists, or CEOs. An assassin ...

assassination
attempt. While one bullet only grazed his
sternum The sternum or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, human lung, lungs, and major blood vessels from in ...

sternum
, another had lodged somewhere deep inside his
abdomen The abdomen (colloquially called the belly, tummy, midriff or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the Trunk (anatomy) ...

abdomen
and could not be found. A worried McKinley aide sent word to inventor Thomas Edison to rush an
X-ray machine An X-ray machine is any machine A machine is any physical system with ordered structural and functional properties. It may represent human-made or naturally occurring device molecular machine A molecular machine, nanite, or nanomachine is a ...
to Buffalo to find the stray bullet. It arrived but was not used. While the shooting itself had not been lethal,
gangrene Gangrene is a type of tissue death Necrosis (from Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roug ...
had developed along the path of the bullet, and McKinley died of
septic shock Septic shock (namely, '' infection throughout the body'') is a potentially fatal medical condition that occurs when sepsis, which is organ injury or damage in response to infection An infection is the invasion of an organism's body Tissue (b ...
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 William Lofland Dudley (April 16, 1859 – September 8, 1914) was an American chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: ...
of
Vanderbilt University Vanderbilt University (informally Vandy or VU) is a private Private or privates may refer to: Music * "In Private "In Private" was the third single in a row to be a charting success for United Kingdom, British singer Dusty Springfield, aft ...
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 The skull is a bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North A ...

skull
(with an exposure time of one hour), he noticed a bald spot 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 A coin is a small, flat, (usually, depending on the country or value) round piece of metal A metal (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hell ...

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 Elihu Thomson (March 29, 1853 – March 13, 1937) was an English-born American engineer Engineers, as practitioners of engineering Engineering is the use of scientific method, scientific principles to design and build machines, str ...
at Edison's lab, William J. Morton, and
Nikola Tesla Nikola Tesla ( ; sr-cyr, Никола Тесла, ; 10 July 1856 – 7 January 1943) was a Serbian-American inventor, electrical engineer, mechanical engineer, and futurist best known for his contributions to the design of the moder ...

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.Kathern, Ronald L. and Ziemer, Paul L
The First Fifty Years of Radiation Protection
physics.isu.edu
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 San Francisco (; Spanish language, Spanish for "Francis of Assisi, Saint Francis"), officially the City and County of San Francisco, is a cultural, commercial, and financial center in the U.S. state of California. Located in Northern Califo ...

San Francisco
,
California California is a U.S. state, state in the Western United States. With over 39.3million residents across a total area of approximately , it is the List of states and territories of the United States by population, most populous and the List of ...

California
, Elizabeth Fleischman, an American X-ray pioneer, died from complications as a result of her work with X-rays. Hall-Edwards developed a cancer (then called X-ray dermatitis) sufficiently advanced by 1904 to cause him to write papers and give public addresses on the dangers of X-rays. He lost his personal battle and his left arm had to be amputated at the elbow in 1908, and four fingers on his right arm soon thereafter, leaving only a thumb. He died of cancer in 1926. His left hand is kept at
Birmingham University Birmingham ( ) is a city A city is a large human settlement.Goodall, B. (1987) ''The Penguin Dictionary of Human Geography''. London: Penguin.Kuper, A. and Kuper, J., eds (1996) ''The Social Science Encyclopedia''. 2nd edition. London: Routl ...
.


20th century and beyond

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 A cold cathode is a that is not electrically heated by a .A negatively charged emits s or is the positively charged terminal. For more, see . A cathode may be considered "cold" if it emits more electrons than can be supplied by alone. It is u ...
or Crookes X-ray tubes were used until about 1920. A typical early 20th century medical X-ray system consisted of a
Ruhmkorff coil An induction coil or "spark coil" (archaism, archaically known as an inductorium or Ruhmkorff coil after Heinrich Rühmkorff) is a type of electrical transformer used to produce high-voltage pulses from a low-voltage direct current (DC) supply. ...
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 was considered soft (low vacuum) and suitable for thin body parts such as hands and arms. A spark indicated the tube was suitable for shoulders and knees. An 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 Micas ( ) are a group of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs natural ...

mica
, a
mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

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 Sir John Ambrose Fleming (29 November 1849 – 18 April 1945) was an English and who invented the first or , designed the with which the first transatlantic radio transmission was made, and also established the used in physics. He was ...
invented the
thermionic diode Various semiconductor diodes. Bottom: A bridge rectifier. In most diodes, a white or black painted band identifies the cathode into which electrons will flow when the diode is conducting. Electron flow is the reverse of conventional current flow ...
, the first kind of
vacuum tube A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied. The type kn ...
. This used a
hot cathode In s and s, a hot cathode or thermionic cathode is a electrode which is heated to make it emit s due to . This is in contrast to a , which does not have a heating element. The heating element is usually an heated by a separate passing throug ...

hot cathode
that caused an
electric current An electric current is a stream of charged particle In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, ...
to flow in a
vacuum A vacuum is a space Space is the boundless three-dimensional Three-dimensional space (also: 3-space or, rarely, tri-dimensional space) is a geometric setting in which three values (called parameter A parameter (from the Ancient Gree ...

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 Charles Glover Barkla FRS FRSE (7 June 1877 – 23 October 1944) was a British physicist A physicist is a scientist A scientist is a person who conducts Scientific method, scientific research to advance knowledge in an Branches of scie ...
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 The Nobel Prize in Physics is a yearly award given by the Royal Swedish Academy of Sciences for those who have made the most outstanding contributions for mankind in the field of physics. It is one of the five Nobel Prizes established by the will ...
for this discovery. In 1912,
Max von Laue Max Theodor Felix von Laue (; 9 October 1879 – 24 April 1960) was a German physicist who received the Nobel Prize in Physics in 1914 for his discovery of the diffraction of X-rays by crystals. In addition to his scientific endeavors with co ...

Max von Laue
, Paul Knipping, and Walter Friedrich first observed the
diffraction Diffraction refers to various phenomena that occur when a wave In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that ...

diffraction
of X-rays by crystals. This discovery, along with the early work of
Paul Peter Ewald Paul Peter Ewald, FRS (January 23, 1888 in Berlin Berlin (; ) is the Capital city, capital and List of cities in Germany by population, largest city of Germany by both area and population. Its 3,769,495 inhabitants, as of 31 December 2019 ma ...
,
William Henry Bragg Sir William Henry Bragg (2 July 1862 – 12 March 1942) was an English physicist, chemist, mathematician, and active sportsman who uniquelyThis is still a unique accomplishment, because no other parent-child combination has yet shared a Nobel P ...

William Henry Bragg
, and
William Lawrence Bragg Sir William Lawrence Bragg, (31 March 1890 – 1 July 1971) was an Australian-born British physicist and X-ray crystallographer, discoverer (1912) of Bragg's law of X-ray diffraction, which is basic for the determination of crystal struc ...
, gave birth to the field of
X-ray crystallography X-ray crystallography (XRC) is the experimental science determining the atomic and molecular structure of a crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a ...

X-ray crystallography
. In 1913,
Henry Moseley Henry Gwyn Jeffreys Moseley (; 23 November 1887 – 10 August 1915) was an English physicist A physicist is a scientist A scientist is a person who conducts Scientific method, scientific research to advance knowledge in an Branches of sc ...
performed crystallography experiments with X-rays emanating from various metals and formulated
Moseley's law Moseley's law is an empirical law concerning the characteristic X-ray#Physics, x-rays emitted by atoms. The law had been discovered and published by the English physicist Henry Moseley in 1913-1914. Until Moseley's work, "atomic number" was merely ...
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. The use of X-rays for medical purposes (which developed into the field of
radiation therapy Radiation therapy or radiotherapy, often abbreviated RT, RTx, or XRT, is a therapy using ionizing radiation Ionizing radiation (or ionising radiation), including nuclear radiation, consists of s or s that have sufficient to s or s by detachi ...

radiation therapy
) was pioneered by Major John Hall-Edwards in
Birmingham, England Birmingham ( ) is a city A city is a large human settlement.Goodall, B. (1987) ''The Penguin Dictionary of Human Geography''. London: Penguin.Kuper, A. and Kuper, J., eds (1996) ''The Social Science Encyclopedia''. 2nd edition. London: Routl ...
. 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 Marie Salomea Skłodowska Curie ( ; ; , born Maria Salomea Skłodowska ; 7 November 1867 – 4 July 1934) was a Polish and naturalized-French physicist A physicist is a scientist A scientist is a person who conducts Scientific meth ...

Marie Curie
developed radiological cars to support soldiers injured in
World War I World War I, often abbreviated as WWI or WW1, also known as the First World War or the Great War, was a global war A world war is "a war engaged in by all or most of the principal nations of the world". The term is usually reserved for ...

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 An X-ray microscope uses electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and ...
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 presidency of Ronald Reagan, 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 defunded (though was later revived by the second presidency of George W. Bush, Bush Administration as National Missile Defense using different technologies). 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 effect, 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 X-ray tube#Microfocus X-ray tubes, microfocus X-ray sources, X-ray optics, and high resolution X-ray detectors.


Energy ranges


Soft and hard X-rays

X-rays with high photon energy, 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 metonymy, 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 X-ray crystallography (XRC) is the experimental science determining the atomic and molecular structure of a crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a ...

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 ray A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, it ...
s. One common practice is to distinguish between the two types of radiation based on their source: X-rays are emitted by
electron The electron is a subatomic particle (denoted by the symbol or ) whose electric charge is negative one elementary charge. Electrons belong to the first generation (particle physics), generation of the lepton particle family, and are general ...

electron
s, 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 Angstrom, 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 atomic nucleus, 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.


Properties

X-ray photons carry enough energy to Ionization, ionize atoms and disrupt molecular bonds. This makes it a type of ionizing radiation, and therefore harmful to living tissue (biology), 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 oncology, cancer treatment to kill malignant cell (biology), cells using
radiation therapy Radiation therapy or radiotherapy, often abbreviated RT, RTx, or XRT, is a therapy using ionizing radiation Ionizing radiation (or ionising radiation), including nuclear radiation, consists of s or s that have sufficient to s or s by detachi ...

radiation therapy
. It is also used for material characterization using X-ray spectroscopy. Hard X-rays can traverse relatively thick objects without being much absorption (electromagnetic radiation), absorbed or scattering, scattered. For this reason, X-rays are widely used to imaging science, 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 imaging#Micro-CT, 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 Transmittance, transmission through the object and at the same time provide good contrast (vision), 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 X-ray crystallography (XRC) is the experimental science determining the atomic and molecular structure of a crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a ...

X-ray crystallography
to determine the positions of atoms in crystals.


Interaction with matter

X-rays interact with matter in three main ways, through photoelectric effect, 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 ''Z''3/''E''3, 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 conservation of momentum, 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.


Production

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


Production by electrons

X-rays can be generated by an X-ray tube, a
vacuum tube A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied. The type kn ...
that uses a high voltage to accelerate the
electron The electron is a subatomic particle (denoted by the symbol or ) whose electric charge is negative one elementary charge. Electrons belong to the first generation (particle physics), generation of the lepton particle family, and are general ...

electron
s released by a
hot cathode In s and s, a hot cathode or thermionic cathode is a electrode which is heated to make it emit s due to . This is in contrast to a , which does not have a heating element. The heating element is usually an heated by a separate passing throug ...

hot cathode
to a high velocity. The high velocity electrons collide with a metal target, the
anode An anode is an electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor A semiconductor material has an Electrical resistivity and conductivity, electrical conductivit ...

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: # ''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). # ''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 effect, 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 (physics), 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 electronvolt, 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 streamer discharge, streamers and the production of high-energy Runaway electrons, 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.


Detectors

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 data, 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 energy spectrum, spectra can be measured either by energy dispersive or wavelength dispersive spectrometers. For X-ray diffraction applications, such as
X-ray crystallography X-ray crystallography (XRC) is the experimental science determining the atomic and molecular structure of a crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a ...

X-ray crystallography
, hybrid pixel detector, hybrid photon counting detectors are widely used.


Medical uses

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

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 bone, skeletal system as well as for detecting some disease processes in soft tissue. Some notable examples are the very common chest radiograph, 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 obstruction, 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 radiodensity, 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 human brain, brain or muscle. One area where projectional radiographs are used extensively is in evaluating how an orthopedic Implant (medicine), 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 dental caries, 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#Human cardiovascular system, 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 radiocontrast agent, 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 radiology, 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

Computed tomography (CT scanning) is a medical imaging modality where tomography, 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 space, three-dimensional image of the inside of the body and used for diagnostic and therapeutic purposes in various medical disciplines.


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 charge-coupled device, 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 circulation, 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 Radiation therapy or radiotherapy, often abbreviated RT, RTx, or XRT, is a therapy using ionizing radiation Ionizing radiation (or ionising radiation), including nuclear radiation, consists of s or s that have sufficient to s or s by detachi ...

radiation therapy
and is largely used for the management (including palliation) of
cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumor A benign tumor is a mass of cells Cell most often refers to: * Cell (biolo ...

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.


Adverse effects

Diagnostic X-rays (primarily from CT scans due to the large dose used) increase the risk of developmental problems and
cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumor A benign tumor is a mass of cells Cell most often refers to: * Cell (biolo ...

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 linear no-threshold model, 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.Radiologyinfo.org
Radiological Society of North America and American College of Radiology
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 (1.5 mSv, 64 mGy)Shrimpton, P.C; Miller, H.C; Lewis, M.A; Dunn, M
Doses from Computed Tomography (CT) examinations in the UK – 2003 Review
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.Medical Radiation Exposure Of The U.S. Population Greatly Increased Since The Early 1980s
Science Daily, March 5, 2009
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 uses

Other notable uses of X-rays include: *
X-ray crystallography X-ray crystallography (XRC) is the experimental science determining the atomic and molecular structure of a crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a ...

X-ray crystallography
in which the pattern produced by the
diffraction Diffraction refers to various phenomena that occur when a wave In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that ...

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 helix, double helical structure of DNA. *X-ray astronomy, which is an observational branch of astronomy, which deals with the study of X-ray emission from celestial objects. *X-ray microscope, X-ray microscopic analysis, which uses
electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. ...

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 welding, 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 Vincent van Gogh, van Gogh. *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 NYPD X-ray vans, domestic police departments use X-rays for inspecting the interior of trucks. *X-ray art and fine art photography, artistic use of X-rays, for example the works by Stane Jagodič *X-ray hair removal, a method popular in the 1920s but now banned by the FDA. *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

While generally considered invisible to the human eye, in special circumstances X-rays can be visible. Brandes, in an experiment a short time after Wilhelm Röntgen, 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 Ionization or ionisation is the process by which an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday ...
of the air molecules if the intensity of the X-ray beam is high enough. The beamline from the wiggler (synchrotron), wiggler at th
ID11
at the European Synchrotron Radiation Facility is one example of such high intensity.


Units of measure and exposure

The measure of X-rays ionization, ionizing ability is called the exposure: * The coulomb per kilogram (C/kg) is the Systeme International, 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 (unit), 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 = . 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 electric charge, charge generated. This measure of energy absorbed is called the absorbed dose: * The gray (unit), 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 (unit), 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 (unit), 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 (radiation), effective dose. For X-rays the "equivalent dose" is numerically equal to a Gray (unit), Gray (Gy). 1 Sv = 1 Gy. For the "effective dose" of X-rays, it is usually not equal to the Gray (Gy).


See also

* 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 welding


References


External links

* * * *
Röntgen’s discovery of X-rays (English translation)
{{DEFAULTSORT:X-Ray X-rays, Electromagnetic spectrum IARC Group 1 carcinogens Ionizing radiation Medical physics Radiography Wilhelm Röntgen 1895 in science 1895 in Germany