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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:.
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 kV and thus the highest energies of the X-ray photons range from roughly 20 keV to keV.
Both of these X-ray production processes are inefficient, with only about one percent of the electrical energy used by the tube converted into X-rays, and thus most of the electric power consumed by the tube is released as waste heat. When producing a usable flux of X-rays, the X-ray tube must be designed to dissipate the excess heat. A specialized source of X-rays which is becoming widely used in research is synchrotron radiation , which is generated by particle accelerators.
Its unique features are X-ray outputs many orders of magnitude greater than those of X-ray tubes, wide X-ray spectra, excellent collimation , and linear polarization. Short nanosecond bursts of X-rays peaking at 15 keV in energy may be reliably produced by peeling pressure-sensitive adhesive tape from its backing in a moderate vacuum. This is likely to be the result of recombination of electrical charges produced by triboelectric charging.
The intensity of X-ray triboluminescence is sufficient for it to be used as a source for X-ray imaging. 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. 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.
X-ray detectors vary in shape and function depending on their purpose. Imaging detectors such as those used for radiography were originally based on photographic plates and later photographic film , but are now mostly replaced by various digital detector types such as image plates and flat panel detectors.
For radiation protection direct exposure hazard is often evaluated using ionization chambers , while dosimeters are used to measure the radiation dose a person has been exposed to. X-ray spectra can be measured either by energy dispersive or wavelength dispersive spectrometers.
For X-ray diffraction applications, such as X-ray crystallography , hybrid photon counting detectors are widely used. Projectional radiography is the practice of producing two-dimensional images using X-ray radiation. Bones contain a high concentration of calcium , which, due to its relatively high atomic number , absorbs X-rays efficiently.
This reduces the amount of X-rays reaching the detector in the shadow of the bones, making them clearly visible on the radiograph. The lungs and trapped gas also show up clearly because of lower absorption compared to tissue, while differences between tissue types are harder to see. Projectional radiographs are useful in the detection of pathology of the skeletal system as well as for detecting some disease processes in soft tissue.
Some notable examples are the very common chest X-ray , which can be used to identify lung diseases such as pneumonia , lung cancer , or pulmonary edema , and the abdominal x-ray , which can detect bowel or intestinal obstruction , free air from visceral perforations , and free fluid in ascites.
X-rays may also be used to detect pathology such as gallstones which are rarely radiopaque or kidney stones which are often but not always visible. Traditional plain X-rays are less useful in the imaging of soft tissues such as the brain or muscle.
One area where projectional radiographs are used extensively is in evaluating how an orthopedic implant , such as a knee, hip or shoulder replacement, is situated in the body with respect to the surrounding bone.
This can be assessed in two dimensions from plain radiographs, or it can be assessed in three dimensions if a technique called '2D to 3D registration' is used. This technique purportedly negates projection errors associated with evaluating implant position from plain radiographs.
Dental radiography is commonly used in the diagnoses of common oral problems, such as cavities. In medical diagnostic applications, the low energy soft X-rays are unwanted, since they are totally absorbed by the body, increasing the radiation dose without contributing to the image.
Hence, a thin metal sheet, often of aluminium , called an X-ray filter , is usually placed over the window of the X-ray tube, absorbing the low energy part in the spectrum.
This is called hardening the beam since it shifts the center of the spectrum towards higher energy or harder X-rays. To generate an image of the cardiovascular system , including the arteries and veins angiography an initial image is taken of the anatomical region of interest.
A second image is then taken of the same region after an iodinated contrast agent has been injected into the blood vessels within this area. These two images are then digitally subtracted, leaving an image of only the iodinated contrast outlining the blood vessels. The radiologist or surgeon then compares the image obtained to normal anatomical images to determine whether there is any damage or blockage of the vessel.
Computed tomography CT scanning is a medical imaging modality where tomographic images or slices of specific areas of the body are obtained from a large series of two-dimensional X-ray images taken in different directions. Fluoroscopy is an imaging technique commonly used by physicians or radiation therapists to obtain real-time moving images of the internal structures of a patient through the use of a fluoroscope. In its simplest form, a fluoroscope consists of an X-ray source and a fluorescent screen, between which a patient is placed.
However, modern fluoroscopes couple the screen to an X-ray image intensifier and CCD video camera allowing the images to be recorded and played on a monitor.
This method may use a contrast material. Examples include cardiac catheterization to examine for coronary artery blockages and barium swallow to examine for esophageal disorders and swallowing disorders. The use of X-rays as a treatment is known as radiation therapy and is largely used for the management including palliation of cancer ; it requires higher radiation doses than those received for imaging alone.
X-rays beams are used for treating skin cancers using lower energy X-ray beams while higher energy beams are used for treating cancers within the body such as brain, lung, prostate, and breast.
Diagnostic X-rays primarily from CT scans due to the large dose used increase the risk of developmental problems and cancer in those exposed. 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. 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.
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, to 1 per 10, 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. Medical X-rays are a significant source of human-made radiation exposure. By , however, medical procedures in the United States were contributing much more ionizing radiation than was the case in the early s.
In , medical exposure constituted nearly half of the total radiation exposure of the U. The increase is traceable to the growth in the use of medical imaging procedures, in particular computed tomography CT , and to the growth in the use of nuclear medicine. Dosage due to dental X-rays varies significantly depending on the procedure and the technology film or digital.
Depending on the procedure and the technology, a single dental X-ray of a human results in an exposure of 0. 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 along with other techniques [] are being researched as potential alternatives to X-rays for imaging applications. While generally considered invisible to the human eye, in special circumstances X-rays can be visible. Later he realized that the tube which had created the effect was the only one powerful enough to make the glow plainly visible and the experiment was thereafter readily repeatable. The knowledge that X-rays are actually faintly visible to the dark-adapted naked eye has largely been forgotten today; this is probably due to the desire not to repeat what would now be seen as a recklessly dangerous and potentially harmful experiment with ionizing radiation.
It is not known what exact mechanism in the eye produces the visibility: it could be due to conventional detection excitation of rhodopsin molecules in the retina , direct excitation of retinal nerve cells, or secondary detection via, for instance, X-ray induction of phosphorescence in the eyeball with conventional retinal detection of the secondarily produced visible light.
Though X-rays are otherwise invisible, it is possible to see the ionization of the air molecules if the intensity of the X-ray beam is high enough. The beamline from the wiggler at the ID11 at the European Synchrotron Radiation Facility is one example of such high intensity. The measure of X-rays ionizing ability is called the exposure:.
However, the effect of ionizing radiation on matter especially living tissue is more closely related to the amount of energy deposited into them rather than the charge generated.
This measure of energy absorbed is called the absorbed dose :. The equivalent dose is the measure of the biological effect of radiation on human tissue.
For X-rays it is equal to the absorbed dose. From Wikipedia, the free encyclopedia. Form of short-wavelength electromagnetic radiation. This article is about the nature, production, and uses of the radiation. For the method of imaging, see Radiography. For the medical specialty, see Radiology. For other meanings, see X-ray disambiguation.
Not to be confused with X-wave or X-band. Main article: X-ray detector. This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Main article: Projectional radiography. Main article: CT scan. Main article: Fluoroscopy. Science Mission Directorate. Squire's Fundamentals of Radiology.
Harvard University Press. ISBN Oxford English Dictionary Online ed. Oxford University Press. Subscription or participating institution membership required.
Nature Precedings. Philosophical Transactions of the Royal Society. Royal Society of London. The Discharge of Electricity through Gasses. Mayo Clinic Proceedings. Mayo Foundation for Medical Education and Research. PMID Archived from the original on Retrieved July Hydroenergy and Its Energy Potential.
Pinnacle Technology. Patent , , "Incandescent Electric Light". Patent , "System of Electric Lighting". These differed from other X-ray tubes in having no target electrode and worked with the output of a Tesla coil. Bibcode : Natur.. Stockholm: The Nobel Foundation. Retrieved 24 November Roentgen and the discovery of x-rays". Textbook of Radiology. Archived from the original on 11 May Retrieved 5 May Norman Publishing.
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Media History. S2CID Canadian Journal of Communication. Literature and Medicine. Birmingham City Council. Archived from the original on September 28, Radiation Biophysics. Nova Publishers.
Yale Centre for British Art. K American Journal of Roentgenology. April 10, Bibcode : Sci Pelican Publishing. Understanding Ionizing Radiation and Protection. Dentomaxillofacial Radiology. PMC Database with images. Jacob Fleischman in the entry for Elizabeth Aschheim. Retrieved Archived from the original on March 30, Archived from the original on Aquariums and fishkeeping.
Takashi Amano Herbert R. Dennerle Drs. Forage fish. Anchovies herring Ilisha mackerel small menhaden sardine shad sprats. Capelin goldband fusilier halfbeak smelt krill squid small. Leuciscinae dace shiner. Carp small killifish mosquitofish herrings river herring alewives sucker.
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Views Read Edit View history. As the right whale swims, a front gap between the two rows of baleen plates lets the water in together with the prey, while the baleens filter out the water. All baleen whales except the gray whale feed near the water surface, rarely diving deeper than m ft or for extended periods.
Gray whales live in shallow waters feeding primarily on bottom-living organisms such as amphipods. Bivalves are aquatic molluscs which have two-part shells. Typically both shells or valves are symmetrical along the hinge line. The class has 30, species , including scallops , clams , oysters and mussels.
Most bivalves are filter feeders although some have taken up scavenging and predation , extracting organic matter from the sea in which they live.
Nephridia , the shellfish version of kidneys , remove the waste material. Buried bivalves feed by extending a siphon to the surface. For example, oysters draw water in over their gills through the beating of cilia. Suspended food phytoplankton , zooplankton , algae and other water-borne nutrients and particles are trapped in the mucus of a gill, and from there are transported to the mouth, where they are eaten, digested and expelled as feces or pseudofeces.
Each oyster filters up to five litres of water per hour. Scientists believe that the Chesapeake Bay 's once-flourishing oyster population historically filtered the estuary's entire water volume of excess nutrients every three or four days. Today that process would take almost a year, [11] and sediment, nutrients, and algae can cause problems in local waters. Oysters filter these pollutants, [12] and either eat them or shape them into small packets that are deposited on the bottom where they are harmless.
Bivalve shellfish recycle nutrients that enter waterways from human and agricultural sources. Nutrient bioextraction is "an environmental management strategy by which nutrients are removed from an aquatic ecosystem through the harvest of enhanced biological production, including the aquaculture of suspension-feeding shellfish or algae". For example, the average harvested mussel contains: 0. In Sweden, environmental agencies utilize mussel farming as a management tool in improving water quality conditions, where mussel bioextraction efforts have been evaluated and shown to be a highly effective source of fertilizer and animal feed [15] In the U.
Bivalve are also largely used as bioindicators to monitor the health of an aquatic environment, either fresh- or seawater. Their population status or structure, physiology, behaviour, [17] or their content of certain elements or compounds can reveal the contamination status of any aquatic ecosystem. They are useful as they are sessile, which means they are closely representative of the environment where they are sampled or placed caging , and they breathe water all the time, exposing their gills and internal tissues: bioaccumulation.
One of the most famous projects in that field is the Mussel Watch Programme in America, but today they are used worldwide for that purpose ecotoxicology. Sponges have no true circulatory system ; instead, they create a water current which is used for circulation. Dissolved gases are brought to cells and enter the cells via simple diffusion. Metabolic wastes are also transferred to the water through diffusion.
Sponges pump remarkable amounts of water. Leuconia , for example, is a small leuconoid sponge about 10 cm tall and 1 cm in diameter. It is estimated that water enters through more than 80, incurrent canals at a speed of 6 cm per minute. However, because Leuconia has more than 2 million flagellated chambers whose combined diameter is much greater than that of the canals, water flow through chambers slows to 3.
Water is expelled through a single osculum at a velocity of about 8. The moon jellyfish has a grid of fibres which are slowly pulled through the water. The motion is so slow that copepods cannot sense it and do not react with an escape response.
An undulating live Aurelia in the Baltic Sea showing the grid in action. Higher magnification showing a prey item, probably a copepod. The prey is then drawn to the body by contracting the fibres in a corkscrew fashion image taken with an ecoSCOPE. Other filter-feeding cnidarians include sea pens , sea fans , plumose anemones , and Xenia. Tunicates , such as ascidians , salps and sea squirts , are chordates which form a sister group to the vertebrates.
Nearly all tunicates are suspension feeders , capturing planktonic particles by filtering sea water through their bodies. Water is drawn into the body through the inhalant buccal siphon by the action of cilia lining the gill slits. The filtered water is then expelled through a separate exhalant siphon. To obtain enough food, a typical tunicate needs to process about one body-volume of water per second. Flamingos filter-feed on brine shrimp. Their oddly shaped beaks are specially adapted to separate mud and silt from the food they eat, and are uniquely used upside-down.
The filtering of food items is assisted by hairy structures called lamellae which line the mandibles , and the large rough-surfaced tongue. Prions are specialised petrels with filter-feeding habits. Their name comes from their saw-like jaw edges, used to scope out small planktionic animals. The extinct swan Annakacygna is speculated to be a filter-feeder due to its bill proportions being similar to those of shoveler ducks. It is unique in being a large, flightless marine animal, unlike the smaller still volant flamingos and prions.
Traditionally, Ctenochasmatoidea as a group has been listed as filter-feeders, due to their long, multiple slender teeth, clearly well adapted to trap prey.
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