He named it X -radiation to signify an unknown type of radiation. 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” in 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. In 1889 Ukrainian -born Ivan Plus, 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.
It was formed on the basis of the electromagnetic theory of light. In 1894 Nikola Tesla noticed damaged film in his lab that seemed to be associated with Crookes tube experiments and began investigating this radiant energy of “invisible” kinds.
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. They are still referred to as such in many languages, including German, Hungarian, Ukrainian, Danish, Polish, Bulgarian, Swedish, Finnish, Estonian, Turkish, Russian, Latvian, 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. Röntgen discovered their medical use when he made a picture of his wife's hand on a photographic plate formed due to X -rays.
Röntgen's biographer Otto Glasses 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.
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 1897Röntgen 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).
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. In early 1896, several weeks after Röntgen's discovery, Ivan Jovanovich Sakharov irradiated frogs and insects with X -rays, concluding that the rays “not only photograph, but also affect the living function”.
This was a result of Multi'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 Lang ill, a local photographer also interested in Röntgen's work.
Röntgen used a screen coated with barium platinocyanide. On February 5, 1896, live imaging devices were developed by both Italian scientist Enrico Salving (his “cystoscope”) and Professor McGee of Princeton University (his “Seascape”), both using barium platinocyanide.
In February 1896, Professor John Daniel and Dr. William Lowland 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.
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. The plates may have a small addition of fluorescent salt to reduce exposure times.
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 which 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.
Chandra's image of the galaxy cluster Bell 2125 reveals a complex of several massive multimillion-degree-Celsius gas clouds in the process of merging. 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.
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.
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. There is no consensus for a definition distinguishing between X -rays and gamma rays.
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 symbolAttenuation 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). 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.
At higher energies, Compton scattering dominates. 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 key photon energy where Compton scattering takes over. 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.
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.
This process produces an emission spectrum of X -rays at a few discrete frequencies, sometimes referred to as spectral lines. The Km line usually has greater intensity than the Km one and is more desirable in diffraction experiments.
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. The frequency of bremsstrahlung is limited by the energy of incident electrons.
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. X -rays can also be produced by fast protons or other positive ions.
For high energies, the production cross-section is proportional to Z 1 2 Z 2 4, where Z 1 refers to the atomic number of the ion, Z 2 refers to that of the target atom. An overview of these cross-sections is given in the same reference.
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 key 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 key 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.
Since Röntgen's discovery that X -rays can identify bone structures, X -rays have been used for medical imaging. Up to 2010, five billion medical imaging examinations had been conducted worldwide.
Bones contain much 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.
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 projection 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 technique purportedly negates projection errors associated with evaluating implant position from plain radiographs.
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 , 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 dominated 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 dominated contrast outlining the blood vessels.
Abdominal radiograph of a pregnant woman, a procedure that should be performed only after proper assessment of benefit versus riskDiagnostic 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.
This is compared to the roughly 40% chance of a US citizen developing cancer during their lifetime. 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.
Medical X -rays are a significant source of man-made radiation exposure. In 1987, they accounted for 58% of exposure from man-made sources in the United States.
Since man-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.
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).
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.
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.
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.
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. 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. For X -rays it is equal to the rad, or, in other words, 10 millijoules of energy deposited per kilogram.
For X -rays the “equivalent dose” is numerically equal to a Gray (GY). For the “effective dose” of X -rays, it is usually not equal to the Gray (GY).
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