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| An '''X-ray tube''' is a [[vacuum tube]] that produces [[X-ray]]s. They are used in [[X-ray generator|X-ray machine]]s. X-rays are part of the [[electromagnetic spectrum]], an [[ionizing radiation]] with wavelengths shorter than [[ultraviolet]] light. X-ray tubes evolved from experimental [[Crookes tube]]s with which X-rays were first discovered in the late 19th century, by [[Wilhelm Röntgen]] and the availability of this controllable source of X-rays created the field of [[radiography]], the imaging of opaque objects with penetrating [[radiation]]. X-ray tubes are also used in [[CAT scan]]ners, airport luggage scanners, [[X-ray crystallography]], and for industrial inspection.
| | Many people have this habit of doing all the stuff by themselves, regardless of how critical or simple they are! These individuals won't let others interfere inside their affairs. While this stance might work in additional areas of lifetime, it is actually really not the best way to respond whenever you want to fix a Windows registry. There are some jobs such as removing spywares, virus also as obsolete registry entries, that are best left to expert softwares. In this short article I may tell we why it is very important to fix Windows registry NOW!<br><br>We can reformat your computer to create it run quicker. This usually reset your computer to whenever we initially utilized it. Always remember to back up all files and programs before carrying this out because this usually remove a files from a database. Remember before you do this you want all of the motorists plus installation files plus this ought to be a last resort should you are trying to find slow computer tips.<br><br>Registry cleaning is important because the registry could get crowded and messy when it is actually left unchecked. False entries send the running system lookin for files plus directories which have lengthy ago been deleted. This takes time plus uses valuable resources. So, a slowdown inevitably happens. It is especially noticeable when you multitask.<br><br>Registry cleaners have been designed for one purpose - to clean out the 'registry'. This is the central database which Windows relies on to function. Without this database, Windows wouldn't even exist. It's so important, that the computer is continually adding and updating the files inside it, even if you're browsing the Internet (like now). This is ideal, yet the problems occur whenever a few of those files become corrupt or lost. This occurs a lot, plus it takes a advantageous tool to fix it.<br><br>Besides, should you could get a [http://bestregistrycleanerfix.com/tune-up-utilities tuneup utilities 2014] that could work for we effectively and instantly, then why not? There is one such program, RegCure which is good plus complete. It has qualities which different cleaners never have. It is the most recommended registry cleaner today.<br><br>The initial thing you need to do is to reinstall any program which shows the error. It's typical for various computers to have certain programs that require this DLL to show the error when we try and load it up. If you see a specific program show the error, we must first uninstall that program, restart a PC plus then resinstall the program again. This could replace the damaged ac1st16.dll file and cure the error.<br><br>Maybe we are asking why these windows XP error messages appear. Well, for you to be able to know the fix, we must initially recognize where those errors come from. There is this software called registry. A registry is software that stores everything on a PC from a general configuration, setting, info, plus logs of activities from installing to UN-installing, saving to deleting, plus a lot more alterations you do in a program pass through it plus gets 'tagged' plus saved as a easy file for healing reasons. Imagine it because a big recorder, a registrar, of all your records in your PC.<br><br>All of these issues is easily solved by the clean registry. Installing our registry cleaner can allow we to utilize your PC without worries behind. You usually capable to use you system without being scared which it's going to crash inside the middle. Our registry cleaner may fix a host of mistakes on the PC, identifying missing, invalid or corrupt settings in a registry. |
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| [[Image:Coolidge xray tube.jpg|thumb|400px|Coolidge X-ray tube, from around 1917. The heated cathode is on the left, and the anode is right. The X-rays are emitted downwards.]]
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| ==Types==
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| === Rotating anode tube ===
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| [[Image:Xraytubeinhousing commons.png|thumb|300px|Simplified rotating anode tube schematic {{unordered list|A: Anode< |C: cathode |T: Anode target |W: X-ray window}}]]
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| [[File:Rotating anode x-ray tube (labeled).jpg|thumb|typical rotating anode X-ray tube]]
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| By thinning the tube, the anode can then be rotated by [[electromagnetic induction]] from a series of [[stator]] windings outside the evacuated tube.
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| Because the entire anode assembly has to be contained within the evacuated tube, heat removal is a serious problem, further exacerbated by the higher power rating available. Direct cooling by [[Heat conduction|conduction]] or [[convection]], as in the Coolidge tube, is difficult. In most tubes, the anode is suspended on ball bearings with silver powder lubrication which provide almost negligible cooling by conduction.
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| A recent development has been liquid [[gallium]] lubricated [[fluid bearing|fluid dynamic bearings]] which can withstand very high temperatures without contaminating the tube vacuum. The large bearing contact surface and metal lubricant provide an effective method for conduction of heat from the anode.
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| The anode must be constructed of high temperature materials. The focal spot temperature can reach {{convert|2,500|C}} during an exposure, and the anode assembly can reach {{convert|1,000|C}} following a series of large exposures. Typical materials are a tungsten-rhenium target on a molybdenum core, backed with graphite. The [[rhenium]] makes the [[tungsten]] more ductile and resistant to wear from the impact of the electron beams. The [[molybdenum]] conducts heat from the target. The [[graphite]] provides thermal storage for the anode, and minimizes the rotating mass of the anode.
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| Increasing demand for high-performance [[Computed tomography]] (CT) scanning and [[angiography]] systems has driven development of very high performance medical X-ray tubes. Contemporary CT tubes have power ratings of up to 100 kW and anode heat capacity of 6 MJ, yet retain an effective focal spot area of less than 1 mm<sup>2</sup>.
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| === Microfocus X-ray tubes ===
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| Some X-ray examinations (such as, e.g., [[Nondestructive testing|non-destructive testing]] and [[Microtomography|3-D microtomography]]) need very high-resolution images and do therefore require X-ray tubes that can generate very small focal spot sizes, typically below 50 µm in diameter. These tubes are called microfocus X-ray tubes.
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| There are two basic types of microfocus X-ray tubes: solid-anode tubes and metal-jet-anode tubes.
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| '''Solid-anode microfocus X-ray tubes''' are in principle very similar to the Coolidge tube, but with the important distinction that care has been taken to be able to focus the electron beam into a very small spot on the anode. Many microfocus X-ray sources operate with focus spots in the range 5-20 µm, but in the extreme cases spots smaller than 1 µm may be produced.
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| The major drawback of solid-anode microfocus X-ray tubes is the very low power they operate at. In order to avoid melting of the anode the electron-beam power density must be below a maximum value. This value is somewhere in the range 0.4-0.8 W/µm depending on the anode material.<ref>D. E. Grider, A Wright, and P. K. Ausburn (1986), “Electron beam melting in microfocus x-ray tubes”, J. Phys. D: Appl. Phys. 19: 2281-2292</ref> This means that a solid-anode microfocus source with a 10 µm electron-beam focus can operate at a power in the range 4-8 W.
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| In '''metal-jet-anode microfocus X-ray tubes''' the solid metal anode is replaced with a jet of liquid metal, which acts as the electron-beam target. The advantage of the metal-jet anode is that the maximum electron-beam power density is significantly increased. Values in the range 3-6 W/µm have been reported for different anode materials (gallium and tin).<ref>M. Otendal, T. Tuohimaa, U. Vogt, and H. M. Hertz (2008), “A 9 keV electron-impact liquid-gallium-jet x-ray source”, Rev. Sci. Instrum. 79: 016102</ref><ref>T. Tuohimaa, M. Otendal, and H. M. Hertz (2007), “Phase-contrast x-ray imaging with a liquid-metal-jet-anode microfocus source”, Appl. Phys. Lett. 91: 074104</ref> In the case with a 10 µm electron-beam focus a metal-jet-anode microfocus X-ray source may operate at 30-60 W.
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| The major benefit of the increased power density level for the metal-jet X-ray tube is the possibility to operate with a smaller focal spot, say 5 µm, to increase image resolution and at the same time acquire the image faster, since the power is higher (15-30 W) than for solid-anode tubes with 10 µm focal spots.
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| ==Physics==
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| [[Image:TubeSpectrum.jpg|thumb|300px|right| Spectrum of the X-rays emitted by an X-ray tube with a [[rhodium]] target, operated at 60 [[kilovolt|kV]]. The smooth, continuous curve is due to ''[[bremsstrahlung]]'', and the spikes are [[Energy-dispersive X-ray spectroscopy|characteristic K lines]] for rhodium atoms.]]
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| As with any vacuum tube, there is a [[cathode]], which emits electrons into the vacuum and an [[anode]] to collect the electrons, thus establishing a flow of electrical current, known as the [[charged particle beam|beam]], through the tube. A high [[voltage]] power source, for example 30 to 150 [[kilovolt]]s (kV), is connected across cathode and anode to accelerate the electrons. The [[X-ray]] spectrum depends on the anode material and the accelerating voltage.<ref>[http://www.bruker-axs.de/fileadmin/user_upload/xrfintro/sec1_3.html Diagram of continuum and characteristic lines]</ref>
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| In many applications, the current flow (typically in the range 1 [[milliamp|mA]] to 1 [[ampere|A]]) is able to be pulsed on for between about 1 [[millisecond|ms]] to 1 s. This enables consistent doses of X-rays, and taking snapshots of motion. Until the late 1980s, X-ray generators were merely high-voltage, AC to DC variable power supplies. In the late 1980s a different method of control was emerging, called high speed switching. This followed the electronics technology of switching power supplies (aka [[switch mode power supply]]), and allowed for more accurate control of the X-ray unit, higher quality results, and reduced X-ray exposures.
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| Electrons from the cathode collide with the anode material, usually [[tungsten]], [[molybdenum]] or [[copper]], and accelerate other electrons, ions and nuclei within the anode material. About 1% of the energy generated is emitted/radiated, usually perpendicular to the path of the electron beam, as X-rays. The rest of the energy is released as heat. Over time, tungsten will be deposited from the target onto the interior surface of the tube, including the glass surface. This will slowly darken the tube and was thought to degrade the quality of the X-ray beam, but research has suggested there is no effect.<ref>{{citation |title=cf., Half-Value-Layer Increase Owing to Tungsten Buildup in the X-ray Tube: Fact or Fiction |author=John G. Stears, Joel P. Felmlee, and Joel E. Gray |journal=Radiology |volume=160 |issue=3 |pages=837–838 |date=September 1986}}</ref> Eventually, the tungsten deposit may become sufficiently conductive that at high enough voltages, arcing occurs. The arc will jump from the cathode to the tungsten deposit, and then to the anode. This arcing causes an effect called "[[crazing]]" on the interior glass of the X-ray window. As time goes on, the tube becomes unstable even at lower voltages, and must be replaced. At this point, the tube assembly (also called the "tube head") is removed from the X-ray system, and replaced with a new tube assembly. The old tube assembly is shipped to a company that reloads it with a new X-ray tube.
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| The X-ray photon-generating effect is generally called the [[Bremsstrahlung]] effect, a contraction of the German ''bremsen'' for braking, and ''strahlung'' for [[radiation]].
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| The range of photonic energies emitted by the system can be adjusted by changing the applied voltage, and installing aluminum filters of varying thicknesses. Aluminum filters are installed in the path of the X-ray beam to remove "soft" (non-penetrating) radiation. The number of emitted X-ray photons, or dose, are adjusted by controlling the current flow and exposure time.
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| Simply put, the high voltage controls X-ray penetration, and thus the contrast of the image. The tube current and exposure time affect the dose and therefore the darkness of the image.
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| ===Heat unit===
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| In [[radiography]], in particular in [[radiology]], a ''heat unit'' is a usual unit derived from the [[Joule]] and measuring the quantity of [[heat]] in a device, in particular the thermal energy that an X-ray tube must be able to support and dissipate during and after an exam.
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| Historically, this unit comes from the need to express a quantity of energy whatever the [[waveform]] of the electrical source power ([[Direct current|direct]] or pulsating). The heat produced in these devices is (in Joule) :
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| :<math>E_\mathrm{heat} = V_\mathrm{eff} I_\mathrm{eff} \; t </math>
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| In [[radiography]] voltage is usually expressed in <math>\mathrm{kV_p}</math> (thousands of volts [[Peak-to-peak#Peak-to-peak amplitude|peak]]), the effective current in mA and the time in seconds:
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| :<math>E_\mathrm{heat} = w \times \mathrm{kV_p} \times \mathrm{mA} \times t</math>
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| w being the waveform ratio. With a full-wave rectification of a [[sine wave]] it equals <math>\frac{1}{\sqrt{2}} \approx 0.707</math>, thus the practical unit:
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| :1 HU = 0.707 J or
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| :1.4 HU = 1 J <ref>Perry Sprawls, Ph.D. [http://www.sprawls.org/ppmi2/XRAYHEAT/ X-Ray Tube Heating and Cooling], from ''The web-based edition of The Physical Principles of Medical Imaging'', 2nd Ed.</ref>
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| ==History==
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| === Crookes tube ===
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| [[Image:Cosser Crookes xray tube.jpg|thumb|400px|Crookes X-ray tube from early 1900s. The cathode is on the right, the anode is in the center with attached heat sink at left. The electrode at the 10 o'clock position is the anticathode. The device at top is a 'softener' used to regulate the gas pressure.]]
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| Historically, X-rays were discovered radiating from experimental [[discharge tube]]s called [[Crookes tube]]s invented by British physicist [[William Crookes]] and others. As the medical and other uses of X-rays became apparent, workshops began to manufacture specialized Crookes tubes to produce X-rays. These were the first X-ray tubes. These first generation ''[[cold cathode]]'' or ''Crookes'' X-ray tubes were used until the 1920s.
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| Crookes tubes generated the electrons needed to create X-rays by [[ionization]] of the residual air in the tube, instead of a heated [[hot cathode|filament]], so they were partially but not completely [[vacuum|evacuated]]. They consisted of a [[glass]] bulb with around 10<sup>−6</sup> to 5×10<sup>−8</sup> [[atmospheric pressure]] of [[air]] (0.1 to 0.005 [[Pascal (unit)|Pa]]). An [[aluminum]] [[cathode]] plate at one end of the tube created a beam of electrons, which struck a [[platinum]] [[anode]] target at the center generating X-rays. The anode surface was angled so that the X-rays would radiate through the side of the tube. The cathode was concave so that the electrons were focused on a small (~1 mm) spot on the anode, approximating a [[point source]] of X-rays, which resulted in sharper images. The tube had a third electrode, an anticathode connected to the anode. It improved the X-ray output, but the method by which it achieved this is not understood. A more common arrangement used a cupped plate anticathode (similar in construction to the cathode) in line with the anode such that the anode was between the cathode and the anticathode.
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| To operate, a [[Direct current|DC]] voltage of a few [[kilovolt]]s to as much as 100 kV was applied between the anodes and the cathode, usually generated by an [[induction coil]], or for larger tubes, an [[electrostatic machine]]. This created and then accelerated a small number of [[ion]]s from the low pressure gas in the tube. These struck further gas [[atom]]s, knocking electrons off them, creating more positive ions in a chain reaction. All the positive ions were attracted to the cathode. When they struck it, they knocked electrons out of the metal, which were accelerated along with the electrons knocked from the gas atoms toward the anode target. When these high speed electrons struck the atoms of the anode, they created X-rays by one of two processes, either ''[[Bremsstrahlung]]'' or ''[[X-ray fluorescence]]''.
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| Crookes tubes were unreliable. As time passed, the residual air would be absorbed by the walls of the tube, reducing the pressure. This increased the voltage across the tube, generating 'harder' X-rays, until eventually the tube stopped working. To prevent this, 'softener' devices were used (see picture). A small tube attached to the side of the main tube contained a mica sleeve or chemical that released a small amount of gas when heated, restoring the correct pressure.
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| The glass envelope of the tube would blacken in use due to the X-rays affecting its structure.
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| === Coolidge tube ===
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| [[Image:WaterCooledXrayTube.svg|thumb|300px|Coolidge side-window tube (scheme) {{unordered list|C: filament/cathode (-) |A: anode (+) |W<sub>in</sub> and W<sub>out</sub>: water inlet and outlet of the cooling device}}]]
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| [[File:Fixed anode x-ray tube.jpg|thumb|typical fixed-anode X-ray tube]]
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| The [[Crookes tube]] was improved by [[William David Coolidge|William Coolidge]] in 1913. The '''Coolidge tube''', also called '''hot cathode tube''', is the most widely used. It works with a very good quality vacuum (about 10<sup>−4</sup> Pa, or 10<sup>−6</sup> Torr).
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| In the Coolidge tube, the electrons are produced by [[thermionic emission|thermionic effect]] from a [[tungsten]] [[Electrical filament|filament]] heated by an electric current. The filament is the cathode of the tube. The high voltage potential is between the cathode and the anode, the electrons are thus [[acceleration|accelerated]], and then hit the anode.
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| There are two designs: end-window tubes and side-window tubes.
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| End window tubes usually have "transmission target" which is thin enough to allow X-rays to pass through the target (X-rays are emitted in the same direction as the electrons are moving.)
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| In one common type of end-window tube, the filament is around the anode ("annular" or ring-shaped), the electrons have a curved path.(half of a toroid)
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| What is special about side-window tubes is:
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| * An [[Electrostatic Lens]] to focus the beam onto a very small spot on the anode
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| * The anode is specially designed to dissipate the heat and wear resulting from this intense focused barrage of electrons. Some anodes are:
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| ** Mechanically spun to increase the area heated by the beam.(Medical "rotating anode")
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| ** Cooled by circulating coolant. (indirectly on most rotating anodes)
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| * The anode is precisely angled at 1-20 degrees off perpendicular to the electron current so as to allow escape of some of the X-ray photons which are emitted essentially perpendicular to the direction of the electron current.
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| * The anode is usually made out of tungsten or molybdenum.
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| * The tube has a window designed for escape of the generated X-ray photons.
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| The power of a Coolidge tube usually ranges from 0.1 to 18 [[kilowatt|kW]].
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| == Hazards of X-ray production from vacuum tubes ==
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| [[Image:hvtubes.jpg|thumb|300px|Two high Voltage rectifier tubes capable of producing X-rays]]
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| Any [[vacuum tube]] operating at several thousand volts or more can produce X-rays as an unwanted byproduct, raising safety issues.<ref>{{cite web|title=We want you to know about television radiation|year=2006|publisher=Center for Devices and Radiological Health, US FDA|url=http://www.fda.gov/cdrh/consumer/TVRad.html|accessdate=2007-12-24}} {{Dead link|date=September 2010|bot=H3llBot}}</ref><ref>{{cite web|last=Pickering|first=Martin|title=An informal history of X-ray protection|publisher=sci.electronics.repair FAQ|url=http://repairfaq.ece.drexel.edu/samnew/tvfaq/tvaihxray.htm|accessdate=2007-12-24}}</ref> The higher the voltage, the more penetrating the resulting radiation and the more the hazard. Color televisions and computer [[cathode ray tube|CRT]] displays operate at {{nowrap|30-40 [[kilovolt]]s,}} making them the main concern among household appliances. Historically, concern has focused less on the [[cathode ray tube]], since its thick glass envelope is impregnated with several pounds of lead for shielding, than on high voltage (HV) [[rectifier]] and [[voltage regulator]] tubes inside. In the late 1960s it was found that a failure in the HV supply circuit of some [[General Electric]] TVs could leave excessive voltages on the regulator tube, causing it to emit X-rays.{{citation needed|date=March 2011}} The models were recalled and the ensuing scandal caused the US agency responsible for regulating this hazard, the [[Center for Devices and Radiological Health]] of the [[Food and Drug Administration]] (FDA), to require that all TVs include circuits to prevent excessive voltages in the event of failure.{{citation needed|date=March 2011}} This hazard was eliminated with the advent of all [[solid state (electronics)|solid state]] TVs, which have no tubes beside the CRT. Since 1969 the FDA has limited TV X-ray emission to 0.5 mR ([[milliroentgen]]) per hour.
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| == See also ==
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| {{Commons_category|X-ray tubes}}
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| * [[Computed axial tomography]]
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| * [[Electron beam tomography]]
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| * [[Angiography]]
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| * [[Coronary angiography]]
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| * [[Synchrotron radiation]]
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| * [[X-ray fluorescence]]
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| * [[X-ray generator]]
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| ==Patents==
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| * [[William David Coolidge|Coolidge]], {{US patent|1211092}}, "''X-ray tube''"
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| * [[Irving Langmuir|Langmuir]], {{US patent|1251388}}, "''Method of and apparatus for controlling X-ray tubes''
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| * Coolidge, {{US patent|1917099}}, "''X-ray tube''"
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| * Coolidge, {{US patent|1946312}}, "''X-ray tube''"
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| ==References==
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| <references />
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| ==External links==
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| *[http://www.rtstudents.com/x-rays/xray-tube.htm X-ray Tube] - A Radiograph of an X-ray Tube
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| *[http://www.crtsite.com/page5.html The Cathode Ray Tube site]
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| *[http://www.nyssrs.org NY State Society of Radiologic Sciences]
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| *[http://www.xraylamp.webd.pl/?sLang=en Collection of X-ray tubes] by Grzegorz Jezierski of Poland
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| *[http://www.excillum.com/ Excillum AB, a manufacturer of metal-jet-anode microfocus x-ray tubes]
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| [[Category:Radiology]]
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| [[Category:X-ray instrumentation|Tube]]
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| [[Category:Particle accelerators]]
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| [[Category:German inventions]]
| |
Many people have this habit of doing all the stuff by themselves, regardless of how critical or simple they are! These individuals won't let others interfere inside their affairs. While this stance might work in additional areas of lifetime, it is actually really not the best way to respond whenever you want to fix a Windows registry. There are some jobs such as removing spywares, virus also as obsolete registry entries, that are best left to expert softwares. In this short article I may tell we why it is very important to fix Windows registry NOW!
We can reformat your computer to create it run quicker. This usually reset your computer to whenever we initially utilized it. Always remember to back up all files and programs before carrying this out because this usually remove a files from a database. Remember before you do this you want all of the motorists plus installation files plus this ought to be a last resort should you are trying to find slow computer tips.
Registry cleaning is important because the registry could get crowded and messy when it is actually left unchecked. False entries send the running system lookin for files plus directories which have lengthy ago been deleted. This takes time plus uses valuable resources. So, a slowdown inevitably happens. It is especially noticeable when you multitask.
Registry cleaners have been designed for one purpose - to clean out the 'registry'. This is the central database which Windows relies on to function. Without this database, Windows wouldn't even exist. It's so important, that the computer is continually adding and updating the files inside it, even if you're browsing the Internet (like now). This is ideal, yet the problems occur whenever a few of those files become corrupt or lost. This occurs a lot, plus it takes a advantageous tool to fix it.
Besides, should you could get a tuneup utilities 2014 that could work for we effectively and instantly, then why not? There is one such program, RegCure which is good plus complete. It has qualities which different cleaners never have. It is the most recommended registry cleaner today.
The initial thing you need to do is to reinstall any program which shows the error. It's typical for various computers to have certain programs that require this DLL to show the error when we try and load it up. If you see a specific program show the error, we must first uninstall that program, restart a PC plus then resinstall the program again. This could replace the damaged ac1st16.dll file and cure the error.
Maybe we are asking why these windows XP error messages appear. Well, for you to be able to know the fix, we must initially recognize where those errors come from. There is this software called registry. A registry is software that stores everything on a PC from a general configuration, setting, info, plus logs of activities from installing to UN-installing, saving to deleting, plus a lot more alterations you do in a program pass through it plus gets 'tagged' plus saved as a easy file for healing reasons. Imagine it because a big recorder, a registrar, of all your records in your PC.
All of these issues is easily solved by the clean registry. Installing our registry cleaner can allow we to utilize your PC without worries behind. You usually capable to use you system without being scared which it's going to crash inside the middle. Our registry cleaner may fix a host of mistakes on the PC, identifying missing, invalid or corrupt settings in a registry.