X-ray tube - Wikipedia

An X-ray tube is a vacuum tube that converts electrical input power into X-rays. ... The availability of this controllable source of X-rays created the field of ... X-raytube FromWikipedia,thefreeencyclopedia Jumptonavigation Jumptosearch AnX-raytubeisavacuumtubethatconvertselectricalinputpowerintoX-rays.[1]TheavailabilityofthiscontrollablesourceofX-rayscreatedthefieldofradiography,theimagingofpartlyopaqueobjectswithpenetratingradiation.Incontrasttoothersourcesofionizingradiation,X-raysareonlyproducedaslongastheX-raytubeisenergized.X-raytubesarealsousedinCTscanners,airportluggagescanners,X-raycrystallography,materialandstructureanalysis,andforindustrialinspection. Increasingdemandforhigh-performanceComputedtomography(CT)scanningandangiographysystemshasdrivendevelopmentofveryhighperformancemedicalX-raytubes. CoolidgeX-raytube,fromaround1917.Theheatedcathodeisontheleft,andtheanodeisright.TheX-raysareemitteddownwards. Contents 1History 2Physics 2.1HeatReleased 3Types 3.1Crookestube(coldcathodetube) 3.2Coolidgetube(hotcathodetube) 3.3Rotatinganodetube 3.4MicrofocusX-raytube 4HazardsofX-rayproductionfromvacuumtubes 5Seealso 6Patents 7References 8Externallinks History[edit] X-raytubesevolvedfromexperimentalCrookestubeswithwhichX-rayswerefirstdiscoveredonNovember8,1895,bytheGermanphysicistWilhelmConradRöntgen.ThesefirstgenerationcoldcathodeorCrookesX-raytubeswereuseduntilthe1920s.TheCrookestubewasimprovedbyWilliamCoolidgein1913.[2]TheCoolidgetube,alsocalledhotcathodetube,isthemostwidelyused.Itworkswithaverygoodqualityvacuum(about10−4Pa,or10−6Torr).[citationneeded] Untilthelate1980s,X-raygeneratorsweremerelyhigh-voltage,ACtoDCvariablepowersupplies.Inthelate1980sadifferentmethodofcontrolwasemerging,calledhighspeedswitching.Thisfollowedtheelectronicstechnologyofswitchingpowersupplies(akaswitchmodepowersupply),andallowedformoreaccuratecontroloftheX-rayunit,higherqualityresults,andreducedX-rayexposures.[citationneeded] Physics[edit] SpectrumoftheX-raysemittedbyanX-raytubewitharhodiumtarget,operatedat60kV.Thesmooth,continuouscurveisduetobremsstrahlung,andthespikesarecharacteristicKlinesforrhodiumatoms. Aswithanyvacuumtube,thereisacathode,whichemitselectronsintothevacuumandananodetocollecttheelectrons,thusestablishingaflowofelectricalcurrent,knownasthebeam,throughthetube.Ahighvoltagepowersource,forexample30to150kilovolts(kV),calledthetubevoltage,isconnectedacrosscathodeandanodetoacceleratetheelectrons.TheX-rayspectrumdependsontheanodematerialandtheacceleratingvoltage.[3] Electronsfromthecathodecollidewiththeanodematerial,usuallytungsten,molybdenumorcopper,andaccelerateotherelectrons,ionsandnucleiwithintheanodematerial.About1%oftheenergygeneratedisemitted/radiated,usuallyperpendiculartothepathoftheelectronbeam,asX-rays.Therestoftheenergyisreleasedasheat.Overtime,tungstenwillbedepositedfromthetargetontotheinteriorsurfaceofthetube,includingtheglasssurface.ThiswillslowlydarkenthetubeandwasthoughttodegradethequalityoftheX-raybeam.Vaporizedtungstencondensesontheinsideoftheenvelopeoverthe"window"andthusactsasanadditionalfilteranddecreasesthetubesabilitytoradiateheat.[4]Eventually,thetungstendepositmaybecomesufficientlyconductivethatathighenoughvoltages,arcingoccurs.Thearcwilljumpfromthecathodetothetungstendeposit,andthentotheanode.Thisarcingcausesaneffectcalled"crazing"ontheinteriorglassoftheX-raywindow.Astimegoeson,thetubebecomesunstableevenatlowervoltages,andmustbereplaced.Atthispoint,thetubeassembly(alsocalledthe"tubehead")isremovedfromtheX-raysystem,andreplacedwithanewtubeassembly.TheoldtubeassemblyisshippedtoacompanythatreloadsitwithanewX-raytube. TheX-rayphoton-generatingeffectisgenerallycalledthebremsstrahlungeffect,acontractionoftheGermanbremsenmeaningtobrake,andStrahlungmeaningradiation. Therangeofphotonicenergiesemittedbythesystemcanbeadjustedbychangingtheappliedvoltage,andinstallingaluminumfiltersofvaryingthicknesses.AluminumfiltersareinstalledinthepathoftheX-raybeamtoremove"soft"(non-penetrating)radiation.ThenumberofemittedX-rayphotons,ordose,areadjustedbycontrollingthecurrentflowandexposuretime. HeatReleased[edit] Heatisproducedinthefocalspotoftheanode.Sinceasmallfraction(lessthanorequalto1%)ofelectronenergyisconvertedtoX-rays,itcanbeignoredinheatcalculations.[5] Thequantityofheatproduced(inJoule)inthefocalspotisgivenby : E h e a t = w V p I t {\displaystyleE_{\mathrm{heat}}=w\mathrm{V_{p}}\mathrm{I}\mathrm{t}} w {\displaystylew} beingthewaveformfactor V p {\displaystyle\mathrm{V_{p}}} =peakACvoltage(inVolts) I {\displaystyle\mathrm{I}} =tubecurrent(inmiliAmperes) t {\displaystyle\mathrm{t}} =exposuretime(inseconds) HeatUnit(HU)wasusedinthepastasanalternativetoJoule.Itisaconvenientunitwhenasingle-phasepowersourceisconnectedtotheX-raytube.[6]Withafull-waverectificationofasinewave, w {\displaystylew} = 1 2 ≈ 0.707 {\displaystyle{\frac{1}{\sqrt{2}}}\approx0.707} ,thustheheatunit: 1HU=0.707J 1.4HU=1J[7] Types[edit] Crookestube(coldcathodetube)[edit] CrookesX-raytubefromearly1900s.Thecathodeisontheright,theanodeisinthecenterwithattachedheatsinkatleft.Theelectrodeatthe10o'clockpositionistheanticathode.Thedeviceattopisa'softener'usedtoregulatethegaspressure. CrookestubesgeneratedtheelectronsneededtocreateX-raysbyionizationoftheresidualairinthetube,insteadofaheatedfilament,sotheywerepartiallybutnotcompletelyevacuated.Theyconsistedofaglassbulbwitharound10−6to5×10−8atmosphericpressureofair(0.1to0.005Pa).Theyhadanaluminumcathodeplateatoneendofthetube,andaplatinumanodetargetattheotherend.TheanodesurfacewasangledsothattheX-rayswouldradiatethroughthesideofthetube.Thecathodewasconcavesothattheelectronswerefocusedonasmall(~1 mm)spotontheanode,approximatingapointsourceofX-rays,whichresultedinsharperimages.Thetubehadathirdelectrode,ananticathodeconnectedtotheanode.ItimprovedtheX-rayoutput,butthemethodbywhichitachievedthisisnotunderstood.Amorecommonarrangementusedacopperplateanticathode(similarinconstructiontothecathode)inlinewiththeanodesuchthattheanodewasbetweenthecathodeandtheanticathode. Tooperate,aDCvoltageofafewkilovoltstoasmuchas100kVwasappliedbetweentheanodesandthecathode,usuallygeneratedbyaninductioncoil,orforlargertubes,anelectrostaticmachine. Crookestubeswereunreliable.Astimepassed,theresidualairwouldbeabsorbedbythewallsofthetube,reducingthepressure.Thisincreasedthevoltageacrossthetube,generating'harder'X-rays,untileventuallythetubestoppedworking.Topreventthis,'softener'deviceswereused(seepicture).Asmalltubeattachedtothesideofthemaintubecontainedamicasleeveorchemicalthatreleasedasmallamountofgaswhenheated,restoringthecorrectpressure. TheglassenvelopeofthetubewouldblackeninuseduetotheX-raysaffectingitsstructure. Coolidgetube(hotcathodetube)[edit] Coolidgeside-windowtube(scheme)C:filament/cathode(-)A:anode(+)WinandWout:waterinletandoutletofthecoolingdevice IntheCoolidgetube,theelectronsareproducedbythermioniceffectfromatungstenfilamentheatedbyanelectriccurrent.Thefilamentisthecathodeofthetube.Thehighvoltagepotentialisbetweenthecathodeandtheanode,theelectronsarethusaccelerated,andthenhittheanode. Therearetwodesigns:end-windowtubesandside-windowtubes.Endwindowtubesusuallyhave"transmissiontarget"whichisthinenoughtoallowX-raystopassthroughthetarget(X-raysareemittedinthesamedirectionastheelectronsaremoving.)Inonecommontypeofend-windowtube,thefilamentisaroundtheanode("annular"orring-shaped),theelectronshaveacurvedpath(halfofatoroid). Whatisspecialaboutside-windowtubesisanelectrostaticlensisusedtofocusthebeamontoaverysmallspotontheanode.Theanodeisspeciallydesignedtodissipatetheheatandwearresultingfromthisintensefocusedbarrageofelectrons.Theanodeispreciselyangledat1-20degreesoffperpendiculartotheelectroncurrentsoastoallowtheescapeofsomeoftheX-rayphotonswhichareemittedperpendiculartothedirectionoftheelectroncurrent.Theanodeisusuallymadeoutoftungstenormolybdenum.ThetubehasawindowdesignedforescapeofthegeneratedX-rayphotons. ThepowerofaCoolidgetubeusuallyrangesfrom0.1to18kW. Rotatinganodetube[edit] SimplifiedrotatinganodetubeschematicA:AnodeC:cathodeT:AnodetargetW:X-raywindow typicalrotatinganodeX-raytube Aconsiderableamountofheatisgeneratedinthefocalspot(theareawherethebeamofelectronscomingfromthecathodestriketo)ofastationaryanode.Rather,arotatinganodeletstheelectronbeamsweepalargerareaoftheanode,thusredeemingtheadvantageofahigherintensityofemittedradiation,alongwithreduceddamagetoanodecomparedtoitsstationarystate.[8] Thefocalspottemperaturecanreach2,500 °C(4,530 °F)duringanexposure,andtheanodeassemblycanreach1,000 °C(1,830 °F)followingaseriesoflargeexposures.Typicalanodesareatungsten-rheniumtargetonamolybdenumcore,backedwithgraphite.Therheniummakesthetungstenmoreductileandresistanttowearfromtheimpactoftheelectronbeams.Themolybdenumconductsheatfromthetarget.Thegraphiteprovidesthermalstoragefortheanode,andminimizestherotatingmassoftheanode. MicrofocusX-raytube[edit] SomeX-rayexaminations(suchas,e.g.,non-destructivetestingand3-Dmicrotomography)needveryhigh-resolutionimagesandthereforerequireX-raytubesthatcangenerateverysmallfocalspotsizes,typicallybelow50 μmindiameter.ThesetubesarecalledmicrofocusX-raytubes. TherearetwobasictypesofmicrofocusX-raytubes:solid-anodetubesandmetal-jet-anodetubes. Solid-anodemicrofocusX-raytubesareinprincipleverysimilartotheCoolidgetube,butwiththeimportantdistinctionthatcarehasbeentakentobeabletofocustheelectronbeamintoaverysmallspotontheanode.ManymicrofocusX-raysourcesoperatewithfocusspotsintherange5-20 μm,butintheextremecasesspotssmallerthan1 μmmaybeproduced. Themajordrawbackofsolid-anodemicrofocusX-raytubesistheverylowpowertheyoperateat.Inordertoavoidmeltingoftheanodetheelectron-beampowerdensitymustbebelowamaximumvalue.Thisvalueissomewhereintherange0.4-0.8W/μmdependingontheanodematerial.[9]Thismeansthatasolid-anodemicrofocussourcewitha10 μmelectron-beamfocuscanoperateatapowerintherange4-8W. Inmetal-jet-anodemicrofocusX-raytubesthesolidmetalanodeisreplacedwithajetofliquidmetal,whichactsastheelectron-beamtarget.Theadvantageofthemetal-jetanodeisthatthemaximumelectron-beampowerdensityissignificantlyincreased.Valuesintherange3-6W/μmhavebeenreportedfordifferentanodematerials(galliumandtin).[10][11]Inthecasewitha10 μmelectron-beamfocusametal-jet-anodemicrofocusX-raysourcemayoperateat30-60W. Themajorbenefitoftheincreasedpowerdensitylevelforthemetal-jetX-raytubeisthepossibilitytooperatewithasmallerfocalspot,say5 μm,toincreaseimageresolutionandatthesametimeacquiretheimagefaster,sincethepowerishigher(15-30W)thanforsolid-anodetubeswith10 μmfocalspots. HazardsofX-rayproductionfromvacuumtubes[edit] TwohighVoltagerectifiertubescapableofproducingX-rays AnyvacuumtubeoperatingatseveralthousandvoltsormorecanproduceX-raysasanunwantedbyproduct,raisingsafetyissues.[12][13]Thehigherthevoltage,themorepenetratingtheresultingradiationandthemorethehazard.CRTdisplays,oncecommonincolortelevisionsandcomputerdisplays,operateat3-40kilovoltsdependingonsize,[14]makingthemthemainconcernamonghouseholdappliances.Historically,concernhasfocusedlessonthecathoderaytube,sinceitsthickglassenvelopeisimpregnatedwithseveralpoundsofleadforshielding,thanonhighvoltage(HV)rectifierandvoltageregulatortubesinsideearlierTVs.Inthelate1960sitwasfoundthatafailureintheHVsupplycircuitofsomeGeneralElectricTVscouldleaveexcessivevoltagesontheregulatortube,causingittoemitX-rays.ThemodelswererecalledandtheensuingscandalcausedtheUSagencyresponsibleforregulatingthishazard,theCenterforDevicesandRadiologicalHealthoftheFoodandDrugAdministration(FDA),torequirethatallTVsincludecircuitstopreventexcessivevoltagesintheeventoffailure.[15]Thehazardassociatedwithexcessivevoltageswaseliminatedwiththeadventofall-solid-stateTVs,whichhavenotubesotherthantheCRT.Since1969,theFDAhaslimitedTVX-rayemissionto0.5mR(milliroentgen)perhour.WiththeswitchfromCRTstootherscreentechnologiesstartinginthe1990s,therearenovacuumtubescapableofemittingX-raysatall. Seealso[edit] WikimediaCommonshasmediarelatedtoX-raytubes. Electronbeamtomography Coronaryangiography Synchrotronradiation X-rayfluorescence X-raygenerator glass-to-metal-seal Patents[edit] Coolidge,U.S.Patent1,211,092,"X-raytube" Langmuir,U.S.Patent1,251,388,"MethodofandapparatusforcontrollingX-raytubes Coolidge,U.S.Patent1,917,099,"X-raytube" Coolidge,U.S.Patent1,946,312,"X-raytube" References[edit] ^Behling,Rolf(2015).ModernDiagnosticX-RaySources,Technology,Manufacturing,Reliability.BocaRaton,FL,USA:TaylorandFrancis,CRCPress.ISBN 9781482241327. ^Coolidge,U.S.Patent1,203,495.PrioritydateMay9,1913. ^DiagramofcontinuumandcharacteristiclinesArchivedFebruary23,2008,attheWaybackMachine ^JohnG.Stears;JoelP.Felmlee;JoelE.Gray(September1986),"cf.,Half-Value-LayerIncreaseOwingtoTungstenBuildupintheX-rayTube:FactorFiction",Radiology,160(3):837–838,doi:10.1148/radiology.160.3.3737925,PMID 3737925 ^"X-RayTubeHeatingandCooling". ^"X-RayTubeHeatingandCooling". ^PerrySprawls,Ph.D.X-RayTubeHeatingandCooling,fromTheweb-basededitionofThePhysicalPrinciplesofMedicalImaging,2ndEd. ^"X-raytube". ^D.E.Grider,AWright,andP.K.Ausburn(1986),"Electronbeammeltinginmicrofocusx-raytubes",J.Phys.D:Appl.Phys.19:2281-2292 ^M.Otendal,T.Tuohimaa,U.Vogt,andH.M.Hertz(2008),"A9keVelectron-impactliquid-gallium-jetx-raysource",Rev.Sci.Instrum.79:016102 ^T.Tuohimaa,M.Otendal,andH.M.Hertz(2007),"Phase-contrastx-rayimagingwithaliquid-metal-jet-anodemicrofocussource",Appl.Phys.Lett.91:074104 ^"Wewantyoutoknowabouttelevisionradiation".CenterforDevicesandRadiologicalHealth,USFDA.2006.ArchivedfromtheoriginalonDecember18,2007.Retrieved2007-12-24. ^Pickering,Martin."AninformalhistoryofX-rayprotection".sci.electronics.repairFAQ.Retrieved2007-12-24. ^Hong,Michelle."VoltageofaTelevisionPictureTube".Retrieved11August2016. ^Murray,Susan(2018-09-23)."WhenTelevisionsWereRadioactive".TheAtlantic.Retrieved2020-12-11. Externallinks[edit] X-rayTube-ARadiographofanX-rayTube TheCathodeRayTubesite NYStateSocietyofRadiologicSciences CollectionofX-raytubesbyGrzegorzJezierskiofPoland ExcillumAB,amanufacturerofmetal-jet-anodemicrofocusx-raytubes exampleofhowX-raytubeswork. AuthoritycontrolGeneral IntegratedAuthorityFile(Germany) Nationallibraries UnitedStates Other MicrosoftAcademic Retrievedfrom"https://en.wikipedia.org/w/index.php?title=X-ray_tube&oldid=1057242275" Categories:EnglishinventionsRadiologyX-rayinstrumentationParticleacceleratorsHiddencategories:WebarchivetemplatewaybacklinksAllarticleswithunsourcedstatementsArticleswithunsourcedstatementsfromMay2019CommonscategorylinkisonWikidataArticleswithGNDidentifiersArticleswithLCCNidentifiersArticleswithMAidentifiers Navigationmenu Personaltools NotloggedinTalkContributionsCreateaccountLogin Namespaces ArticleTalk Variants expanded collapsed Views ReadEditViewhistory More expanded collapsed Search Navigation MainpageContentsCurrenteventsRandomarticleAboutWikipediaContactusDonate Contribute HelpLearntoeditCommunityportalRecentchangesUploadfile Tools WhatlinkshereRelatedchangesUploadfileSpecialpagesPermanentlinkPageinformationCitethispageWikidataitem Print/export DownloadasPDFPrintableversion Inotherprojects WikimediaCommons Languages العربيةCatalàČeštinaDeutschEestiEspañolEsperantoفارسیFrançais한국어हिन्दीHrvatskiItalianoעבריתҚазақшаLatinaLatviešuMagyarNederlands日本語NorskbokmålNorsknynorskਪੰਜਾਬੀPolskiPortuguêsRomânăРусскийSrpskohrvatski/српскохрватскиSuomiSvenskaதமிழ்УкраїнськаTiếngViệt中文 Editlinks