2023学年完整公开课版BOOK8-Unit3Inventorsandinventions

X-ray

AnX-raypicture(radiograph),takenbyWilhelmRöntgenin1896,ofAlbertvonKölliker'shand

X-rays(orRöntgenrays)areaformofelectromagneticradiationwithawavelengthintherangeof10tonanometers,correspondingtofrequenciesintherange30PHzto30EHz.X-raysareprimarilyusedfordiagnosticradiographyandcrystallography.X-raysareaformofionizingradiationandassuchcanbedangerous.InmanylanguagesitiscalledRöntgenradiationafteroneofthefirstinvestigatorsoftheX-rays,WilhelmConradRöntgen.

Unitofmeasureandexposure

Theremisthetraditionalunitofexposuretoionizingradiationforhumans.TheSIcounterpartistheSievert(Sv).OneSievertisequalto100rem.Becausetheremisarelativelylargeunit,typicalexposureismeasuredinmillirem(mrem),oronethousandthofarem.

TheaveragepersonlivingintheUnitedStatesisexposedtoapproximately150mremannuallyfrombackgroundsourcesalone.

ReporteddosageduetodentalX-raysseemstovarysignificantly.Dependingonthesource,atypicaldentalX-rayofahumanresultsinanexposureofperhaps,3,40,300,orasmanyas900mrems.

Physics

X-raysareatypeofelectromagneticradiationwithwavelengthsofaround10-10meters.WhenmedicalX-raysarebeingproduced,athinmetallicsheetisplacedbetweentheemitterandthetarget,effectivelyfilteringoutthelowerenergy(soft)X-rays.ThisisoftenplacedclosetothewindowoftheX-raytube.TheresultantX-rayissaidtobehard.SoftX-raysoverlaptherangeofextremeultraviolet.ThefrequencyofhardX-raysishigherthanthatofsoftX-rays,andthewavelengthisshorter.HardX-raysoverlaptherangeof"long"-wavelength(lowerenergy)gammarays,howeverthedistinctionbetweenthetwotermsdependsonthesourceoftheradiation,notitswavelength;X-rayphotonsaregeneratedbyenergeticelectronprocesses,gammaraysbytransitionswithinatomicnuclei.

X-rayK-seriesspectrallinewavelengths(nm)forsomecommontargetmaterials.

Target

Kβ₁

Kβ₂

Kα₁

Kα₂

Fe

Ni

Cu

Zr

Me

ThebasicproductionofX-raysisbyacceleratingelectronsinordertocollidewithametaltarget.(Inmedicalapplications,thisisusuallytungstenoramorecrackresistantalloyofrhenium(5%)andtungsten(95%),butsometimesmolybdenumformorespecialisedapplications,suchaswhensoftX-raysareneededasinmammography.Incrystallography,acoppertargetismostcommon,withcobaltoftenbeingusedwhenfluorescencefromironcontentinthesamplemightotherwisepresentaproblem).HeretheelectronssuddenlydecelerateuponcollidingwiththemetaltargetandifenoughenergyiscontainedwithintheelectronitisabletoknockoutanelectronfromtheinnershellofthemetalatomandasaresultelectronsfromhigherenergylevelsthenfillupthevacancyandX-rayphotonsareemitted.Thisprocessisextremelyinefficient(~%)andthustoproducereasonablefluxofX-raysplentyofenergyhastobewastedintoheatwhichhastoberemoved.

Thespectrallinesgenerateddependsonthetarget(anode)elementusedandthusarecalledcharacteristiclines.UsuallythesearetransitionsfromuppershellsintoKshell(calledKlines),intoLshell(calledLlines)andsoon.ThereisalsoacontinuumBremsstrahlungradiationgivenoffbytheelectronsastheyarescatteredbythestrongelectricfieldnearthehigh-Z(protonnumber)nuclei.

X-rayscandetectcancer,cysts,andtumors.Duetotheirshortwavelength,inmedicalapplicationsX-raysactmorelikeaparticlethanawave.Thisisincontrasttotheirapplicationincrystallography,wheretheirwave-likenatureismostimportant.

Nowadays,formany(non-medical)applications,X-rayproductionisachievedbysynchrotrons(seesynchrotronlight).

TocreateabloodorarteryX-ray,alsocalleddigitalangiography,iodineisinjectedintotheveinsandadigitizedimageiscreated.Then,asecondimageisestablishedofonlythepartsoftheX-rayedsectionwithoutiodine.Thefirstimageissubtractedthenafinalimageisproducedcontainingboththefirstandsecondimagestogether.Lastly,theresultsareprinted.Thedoctororsurgeonthencomparestheresultsoftheangiographytoaperfectangiographystructuretoseeifthereareanymalfunctions.

TotakeanX-rayofthebones,noiodizationisrequired.ShortX-raypulsesareshotthroughabodyatfirst.Next,thebonesabsorbthemostwavesbecausetheyaremoredenseandcontainCawhichabsorbsstrongerthanthecarbon,oxygen,andnitrogenatomsofsofttissue(duetomoreelectronsinCaatom).

Detectors

Photographicplate

ThedetectionofX-raysisbasedonvariousmethods.Themostcommonlyknownmethodareaphotographicplate,X-rayfilminacassette,andrareearthscreens.

Aphotographicplateorfilmisusedinhospitalstoproduceimagesoftheinternalorgansandbonesofapatient.Theyarealsousedinindustrialradiographyprocesses.SincephotographicplatesaresensitivetoX-rays,theyprovideaconvenientandeasymeansofrecordingtheimage.X-rayfilmisusuallyprovidedaspre-loadedpapercartridgeswiththefilminsidealightproofpaperenvelope.Anadditionalpapercoatedinathinlayerofleadisoftenincludedincontactwiththephotographicfilm.Theleadreflectsthex-raysbackthroughthephotofilmthusmoreorlessdoublingthesensitivityoftheassembly.Thusthephotographicfilmhastobeusedtherightwayround,andismarkedassuch.Theemulsionisfrequentlycoatedonbothsidesofthefilmorplateinordertoincreasethesensitivityfurther.

ThepartofthepatienttobeX-rayedisplacedbetweentheX-raysourceandthephotographicreceptortoproducewhatisashadowofalltheinternalstructureofthatparticularpartofthebodybeingX-rayed.TheX-raysareblockedbydensetissuessuchasboneandpassthroughsofttissues.ThoseareaswheretheX-raysstrikethephotographicreceptorturnblackwhenitisdeveloped.SowheretheX-rayspassthrough"soft"partsofthebodysuchasorgans,muscle,andskin,theplateorfilmturnsblack.Contrastcompoundscontainingbariumoriodine,whichareradiopaque,canbeinjectedinthearteryofaparticularorgan,orgivenintravenously.ThecontrastcompoundsessentiallyblocktheX-raysandhencethecirculationoftheorgancanbemorereadilyseen.Manyyearsagothoriumwasusedasacontrastmedium(Thorotrast)—thiscausedmanypeopletobeinjuredorevendiefromtheeffectsoftheradiationfromthethorium.

PhotographicplatesarelosingfavourinmanyX-rayfacilitiesbecauseofthenecessitytohaveprocessingfacilitiesreadilytohand,andbecausethephotographicplatesthemselves,plustheprocessingchemicalsarerelativelyexpensiveconsumables.

PhotostimulablePhosphors(PSPs)

AnincreasinglycommonmethodofdetectingX-raysistheuseofPhotostimulableLuminescence(PSL),pioneeredbyFujiinthe1980s.InmodernhospitalsaPSPplateisusedinplaceofthephotographicplate.AftertheplateisX-rayed,excitedelectronsinthephosphormaterialremain'trapped'in'colourcentres'inthecrystallatticeuntilstimulatedbyalaserbeampassedovertheplatesurface.Thelightgivenoffduringlaserstimulationiscollectedbyaphotomultipliertubeandtheresultingsignalisconvertedintoadigitalimagebycomputertechnology,whichgivesthisprocessitscommonname,computedradiography(alsoreferredtoasdigitalradiography).ThePSPplatecanbeusedoverandoveragain,andexistingx-rayequipmentrequiresnomodificationtousethem.

Geigercounter

Initially,mostcommondetectionmethodswerebasedontheionizationofgases,asintheGeiger-Müllercounter:asealedvolume,usuallyacylinder,withapolymerorthinmetalwindowcontainsagas,andawire,andahighvoltageisappliedbetweenthecylinder(cathode)andthewire(anode).WhenanX-rayphotonentersthecylinder,itionizesthegasandformsionsandelectrons.Electronsacceleratetowardtheanode,intheprocesscausingfurtherionizationalongtheirtrajectory.Thisprocess,knownasanavalanche,isdetectedasasuddenflowofcurrent,calleda"count"or"event".

Ultimately,theelectronsformavirtualcathodearoundtheanodewiredrasticallyreducingtheelectricfieldintheouterportionsofthetube.Thishaltsthecollisionalionizationsandlimitsfurthergrowthofavalanches.Asaresult,all"counts"onaGeigercounterarethesamesizeanditcangivenoindicationastotheparticleenergyoftheradiation,unliketheproportionalcounter.TheintensityoftheradiationismeasurablebytheGeigercounterasthecounting-rateofthesystem.

Inordertogainenergyspectruminformationadiffractingcrystalmaybeusedtofirstseparatethedifferentphotons,themethodiscalledwavelengthdispersiveX-rayspectroscopy(WDXorWDS).Position-sensitivedetectorsareoftenusedinconjunctionwithdispersiveelements.Otherdetectionequipmentmaybeusedwhichareinherentlyenergy-resolving,suchastheaforementionedproportionalcounters.Ineithercase,useofsuitablepulse-processing(MCA)equipmentallowsdigitalspectratobecreatedforlateranalysis.

Formanyapplications,countersarenotsealedbutareconstantlyfedwithpurifiedgas(thusreducingproblemsofcontaminationorgasaging).Thesearecalled"flowcounter".

Scintillators

Somematerialssuchassodiumiodide(NaI)can"convert"anX-rayphotontoavisiblephoton;anelectronicdetectorcanbebuiltbyaddingaphotomultiplier.Thesedetectorsarecalled"scintillators",filmscreensor"scintillationcounters".ThemainadvantageofusingtheseisthatanadequateimagecanbeobtainedwhilesubjectingthepatienttoamuchlowerdoseofX-rays.

Imageintensification

X-rayduringCholecystectomy

X-raysarealsousedin"real-time"proceduressuchasangiographyorcontraststudiesoftheholloworgans.bariumenemaofthesmallorlargeintestine)usingfluoroscopyacquiredusinganX-rayimageintensifier.Angioplasty,medicalinterventionsofthearterialsystem,relyheavilyonX-ray-sensitivecontrasttoidentifypotentiallytreatablelesions.

Directsemiconductordetectors

Sincethe1970s,newsemiconductordetectorshavebeendeveloped(siliconorgermaniumdopedwithlithium,Si(Li)orGe(Li)).X-rayphotonsareconvertedtoelectron-holepairsinthesemiconductorandarecollectedtodetecttheX-rays.Whenthetemperatureislowenough(thedetectoriscooledbyPeltiereffectorevencoolerliquidnitrogen),itispossibletodirectlydeterminetheX-rayenergyspectrum;thismethodiscalledenergydispersiveX-rayspectroscopy(EDXorEDS);itisoftenusedinsmallX-rayfluorescencespectrometers.Thesedetectorsaresometimescalled"solidstatedetectors".Cadmiumtelluride(CdTe)anditsalloywithzinc,cadmiumzinctelluridedetectorshaveanincreasedsensitivity,whichallowslowerdosesofX-raystobeused.

Practicalapplicationinmedicalimagingdidn'tstarttakingplaceuntilthe1990s.CurrentlyamorphousseleniumisusedincommerciallargeareaflatpanelX-raydetectorsformammographyandchestradiography.Currentresearchanddevelopmentisfocussedaroundpixeldetectors,suchasCERN'senergyresolvingMedipixdetector.

Note:Astandardsemiconductordiode,suchasa1N4007,willproduceasmallamountofcurrentwhenplacedinanX-raybeam.AtestdeviceonceusedbyMedicalImagingServicepersonnelwasasmallprojectboxthatcontainedseveraldiodesofthistypeinseries,whichcouldbeconnectedtoanoscilloscopeasaquickdiagnostic.

Silicondriftdetectors(SDDs),producedbyconventionalsemiconductorfabrication,nowprovideacost-effectiveandhighresolvingpowerradiationmeasurement.UnlikeconventionalX-raydetectors,suchasSi(Li)s,theydonotneedtobecooledwithliquidnitrogen.

Scintillatorplussemiconductordetectors(indirectdetection)

WiththeadventoflargesemiconductorarraydetectorsithasbecomepossibletodesigndetectorsystemsusingascintillatorscreentoconvertfromX-raystovisiblelightwhichisthenconvertedtoelectricalsignalsinanarraydetector.IndirectFlatPanelDetectors(FPDs)areinwidespreadusetodayinmedical,dental,veterinaryandindustrialapplications.AcommonformofthesedetectorsisbasedonamorphoussiliconTFT/photodiodearrays.

ThearraytechnologyisavariantontheamorphoussiliconTFTarraysusedinmanyflatpaneldisplays,liketheonesincomputerlaptops.Thearrayconsistsofasheetofglasscoveredwithathinlayerofsiliconthatisinanamorphousordisorderedstate.Atamicroscopicscale,thesiliconhasbeenimprintedwithmillionsoftransistorsarrangedinahighlyorderedarray,likethegridonasheetofgraphpaper.Eachofthesethinfilmtransistors(TFTs)areattachedtoalight-absorbingphotodiodemakingupanindividualpixel(pictureelement).Photonsstrikingthephotodiodeareconvertedintotwocarriersofelectricalcharge,calledelectron-holepairs.Sincethenumberofchargecarriersproducedwillvarywiththeintensityofincominglightphotons,anelectricalpatterniscreatedthatcanbeswiftlyconvertedtoavoltageandthenadigitalsignal,whichisinterpretedbyacomputertoproduceadigitalimage.Althoughsiliconhasoutstandingelectronicproperties,itisnotaparticularlygoodabsorberofX-rayphotons.Forthisreason,X-raysfirstimpingeuponscintillatorsmadefromeg.gadoliniumoxysulfideorcesiumiodide.ThescintillatorabsorbstheX-raysandconvertsthemintovisiblelightphotonsthatthenpassontothephotodiodearray.

Visibilitytothehumaneye

Whilegenerallyconsideredinvisibletothehumaneye,inspecialcircumstancesX-rayscanbevisible.Brandes,inanexperimentashorttimeafterRöntgen'slandmark1895paper,reportedafterdarkadaptationandplacinghiseyeclosetoanX-raytube,seeingafaint"blue-gray"glowwhichseemedtooriginatewithintheeyeitself.Uponhearingthis,Röntgenreviewedhisrecordbooksandfoundhetoohadseentheeffect.WhenplacinganX-raytubeontheoppositesideofawoodendoorRöntgenhadnotedthesameblueglow,seemingtoemanatefromtheeyeitself,butthoughthisobservationstobespuriousbecauseheonlysawtheeffectwhenheusedonetypeoftube.Laterherealizedthatthetubewhichhadcreatedtheeffectwastheonlyonepowerfulenoughtomaketheglowplainlyvisibleandtheexperimentwasthereafterreadilyrepeatable.TheknowledgethatX-raysareactuallyfaintlyvisibletothedark-adaptednakedeyehaslargelybeenforgottentoday;thisisprobablyduetothedesirenottorepeatwhatwouldnowbeseenasarecklesslydangerousandharmfulexperimentwithionizingradiation.Itisnotknownwhatexactmechanismintheeyeproducesthevisibility:itcouldbeduetoconventionaldetection(excitationofrhodopsinmoleculesintheretina),directexcitationofretinalnervecells,orsecondarydetectionvia,forinstance,X-rayinductionofphosphorescenceintheeyeballwithconventionalretinaldetectionofthesecondarilyproducedvisiblelight.

IftheintensityofanX-raybeamishighenough,theionizationoftheairwillmakethebeamvisiblewithawhiteglow.

Medicaluses

X-RayImageofamaleskull

SinceRöntgen'sdiscoverythatX-rayscanidentifybonystructures,X-rayshavebeendevelopedfortheiruseinmedicalimaging.Radiologyisaspecializedfieldofmedicine.Radiographersemployradiographyandothertechniquesfordiagnosticimaging.Indeed,thisisprobablythemostcommonuseofX-raytechnology.

X-raysareespeciallyusefulinthedetectionofpathologyoftheskeletalsystem,butarealsousefulfordetectingsomediseaseprocessesinsofttissue.SomenotableexamplesaretheverycommonchestX-ray,whichcanbeusedtoidentifylungdiseasessuchaspneumonia,lungcancerorpulmonaryedema,andtheabdominalX-ray,whichcandetectileus(blockageoftheintestine),freeair(fromvisceralperforations)andfreefluid(inascites).Insomecases,theuseofX-raysisdebatable,suchasgallstones(whicharerarelyradiopaque)orkidneystones(whichareoftenvisible,butnotalways).Also,traditionalplainX-raysposeverylittleuseintheimagingofsofttissuessuchasthebrainormuscle.Imagingalternativesforsofttissuesarecomputedaxialtomography(CATorCTscanning),magneticresonanceimaging(MRI)orultrasound.Since2005,X-raysarelistedasacarcinogenbytheU.S.government.

Radiotherapy,acurativemedicalintervention,nowusedalmostexclusivelyforcancer,employshigherenergiesofradiation.

TheefficiencyofX-raytubesislessthan2%.Mostoftheenergyisusedtoheatuptheanode.

Otheruses

OthernotableusesofX-raysinclude

X-raycrystallographyinwhichthepatternproducedbythediffractionofX-raysthroughthecloselyspacedlatticeofatomsinacrystalisrecordedandthenanalyzedtorevealthenatureofthatlattice(mostnotablyusedbyWatsonandCricktodiscoverthedoublehelixstructureofDNA).

X-rayastronomy,whichisanobservationalbranchofastronomy,whichdealswiththestudyofX-rayemissionfromcelestialobjects.

X-raymicroscopicanalysis,whichuseselectromagneticradiationinthesoftX-raybandtoproduceimagesofverysmallobjects.

X-rayfluorescence,atechniqueinwhichX-raysaregeneratedwithinaspecimenanddetected.TheoutgoingenergyoftheX-raycanbeusedtoidentifythecompositionofthesample.

PaintingsareoftenX-rayedtorevealtheunderdrawingandpentimentioralterationsinthecourseofpainting,orbylaterrestorers.ManypigmentssuchasleadwhiteshowwellinX-rayphotographs.

History

AmongtheimportantearlyresearchersinX-rayswereProfessorIvanPulyui,SirWilliamCrookes,JohannWilhelmHittorf,EugenGoldstein,HeinrichHertz,PhilippLenard,HermannvonHelmholtz,NikolaTesla,ThomasEdison,CharlesGloverBarkla,MaxvonLaue,andWilhelmConradRöntgen.

JohannHittorf

PhysicistJohannHittorf(1824-1914)observedtubeswithenergyraysextendingfromanegativeelectrode.Theseraysproducedafluorescencewhentheyhittheglasswallsofthetubes.In1876theeffectwasnamed"cathoderays"byEugenGoldstein,andtodayareknowntobestreamsofelectrons.Later,EnglishphysicistWilliamCrookesinvestigatedtheeffectsofelectriccurrentsingasesatlowpressure,andconstructedwhatiscalledtheCrookestube.Itisaglasscylindermostly(butnotcompletely)evacuated,containingelectrodesfordischargesofahighvoltageelectriccurrent.Hefound,whenheplacedunexposedphotographicplatesnearthetube,thatsomeofthemwereflawedbyshadows,thoughhedidnotinvestigatethiseffect.Crookesalsonotedthathiscathoderayscausedtheglasswallsofhistubetoglowadullbluecolour.Crookesfailedtorealisethatitwasn'tactuallythecathoderaysthatcausedtheblueglow,butthelowlevelx-raysproducedwhenthecathoderaysstrucktheglass.

IvanPulyui

AsaresultofexperimentsintowhathecalledcoldlightIvanPulyuiisreputedtohavedevelopedanX-rayemittingdeviceasearlyas1881.HereputedlyfirstdemonstratedanX-rayphotographofa13-year-oldboy'sbrokenarmandanX-rayphotographofhisdaughter'shandwithapinlyingunderit.ThedevicebecameknownasthePulyuilampandwasmass-producedforaperiod.Reputedly,PulyuipersonallypresentedonetoWilhelmConradRöntgenwhowentontobecreditedasthemajordeveloperofthetechnology.Pulyuipublishedhisresultsinascientificpaper,LuminousElectricalMatterandtheFourthStateofMatterintheNotesoftheAustrianImperialAcademyofSciences(1880-1883),butexpressedhisideasinanobscuremannerusingobsoleteterminology.PulyuididgainsomerecognitionwhentheworkwastranslatedandpublishedasabookbytheRoyalSocietyintheUK.Pulyuimademanyotherdiscoveriesaswell.HeisparticularlynotedforinventingadevicefordeterminingthemechanicalequivalentofheatthatwasexhibitedattheExpositionUniverselle,Paris,1878.PulyuialsoparticipatedinopeningofseveralpowerplantsinAustria-Hungary.

NikolaTesla

InApril1887,NikolaTeslabegantoinvestigateX-raysusinghighvoltagesandtubesofhisowndesign,aswellasCrookestubes.Fromhistechnicalpublications,itisindicatedthatheinventedanddevelopedaspecialsingle-electrodeX-raytube,whichdifferedfromotherX-raytubesinhavingnotargetelectrode.TheprinciplebehindTesla'sdeviceisnowadayscalledtheBremsstrahlungprocess,inwhichahigh-energysecondaryX-rayemissionisproducedwhenchargedparticles(suchaselectrons)passthroughmatter.By1892,Teslaperformedseveralsuchexperiments,buthedidnotcategorizetheemissionsaswhatwerelatercalledX-rays.Teslageneralizedthephenomenonasradiantenergyof"invisible"kinds.Teslastatedthefactsofhismethodsconcerningvariousexperimentsinhis1897X-raylecturebeforetheNewYorkAcademyofSciences.Alsointhislecture,TeslastatedthemethodofconstructionandsafeoperationofX-rayequipment.HisX-rayexperimentationbyvacuumhighfieldemissionsalsoledhimtoalertthescientificcommunitytothebiologicalhazardsassociatedwithX-rayexposure.

FernandoSanford

X-rayswerefirstgeneratedanddetectedbyFernandoSanford(1854-1948),thefoundationProfessorofPhysicsatStanfordUniversity,in1891.From1886to1888hehadstudiedintheHermannHelmholtzlaboratoryinBerlin,wherehebecamefamiliarwiththecathoderaysgeneratedinvacuumtubeswhenavoltagewasappliedacrossseparateelectrodes,aspreviouslystudiedbyHeinrichHertzandPhilippLenard.HisletterofJanuary6,1893(describinghisdiscoveryas"electricphotography")toThePhysicalReviewwasdulypublishedandanarticleentitledWithoutLensorLight,PhotographsTakenWithPlateandObjectinDarknessappearedintheSanFranciscoExaminer.

Hertz

In1892,HeinrichHertzbeganexperimentinganddemonstratedthatcathoderayscouldpenetrateverythinmetalfoil(suchasaluminium).PhilippLenard,astudentofHeinrichHertz,furtherresearchedthiseffect.HedevelopedaversionofthecathodetubeandstudiedthepenetrationbyX-raysofvariousmaterials.PhilippLenard,though,didnotrealizethathewasproducingX-rays.HermannvonHelmholtzformulatedmathematicalequationsforX-rays.HepostulatedadispersiontheorybeforeRöntgenmadehisdiscoveryandannouncement.Itwasformedonthebasisoftheelectromagnetictheoryoflight(Wiedmann'sAnnalen,Vol.XLVIII).However,hedidnotworkwithactualX-rays.

Röntgen

OnNovember81895,WilhelmConradRöntgen,aGermanphysicsprofessor,beganobservingandfurtherdocumentingX-rayswhileexperimentingwithvacuumtubes.Röntgen,onDecember28,1895,wroteapreliminaryreport"Onanewkindofray:Apreliminarycommunication".HesubmittedittotheWürzburg'sPhysical-MedicalSocietyjournal.ThiswasthefirstformalandpublicrecognitionofthecategorizationofX-rays.Röntgenreferredtotheradiationas"X",toindicatethatitwasanunknowntypeofradiation.Thenamestuck,although(overRöntgen'sgreatobjections),manyofhiscolleaguessuggestedcallingthemRöntgenrays.Theyarestillreferredtoassuchinmanylanguages.RöntgenreceivedthefirstNobelPrizeinPhysicsforhisdiscovery.

Röntgenwasworkingonaprimitivecathoderaygeneratorthatwasprojectedthroughaglasspartiallyevacuatedtube.Suddenlyhenoticedafaintgreenlightagainstthewall.Theoddthinghehadnoticed,wasthatthelightfromthecathoderaygeneratorwastravelingthroughabunchofthematerialsinitsway(paper,wood,andbooks).Hethenstartedtoputvariousobjectsinfrontofthegenerator,andashewasdoingthis,henoticedthattheoutlineofthebonesfromhishandweredisplayedonthewall.Röntgensaidhedidnotknowwhattothinkandkeptexperimenting.Twomonthsafterhisinitialdiscovery,hepublishedhispapertranslated"OnaNewKindofRadiation"andgaveademonstrationin1896.

Rontgendiscovereditsmedicalusewhenhesawapictureofhiswife'shandonaphotographicplateformedduetoX-rays.Hiswife'shand'sphotographwasthefirsteverphotographofahumanbodypartusingX-rays.

Edison

DiagramofawatercooledX-raytube.(simplified/outdated)

In1895,ThomasEdisoninvestigatedmaterials'abilitytofluorescewhenexposedtoX-rays,andfoundthatcalciumtungstatewasthemosteffectivesubstance.AroundMarch1896,thefluoroscopehedevelopedbecamethestandardformedicalX-rayexaminations.Nevertheless,EdisondroppedX-rayresearcharound1903afterthedeathofClarenceMadisonDally,oneofhisglassblowers.DallyhadahabitoftestingX-raytubesonhishands,andacquiredacancerinthemsotenaciousthatbotharmswereamputatedinafutileattempttosavehislife.

The20thcenturyandbeyond

Priortothe20thcenturyandforashortwhileafter,x-raysweregeneratedincoldcathodetubes.Thesetubeshadtocontainasmallquantityofgas(invariablyair)asacurrentwillnotflowinsuchatubeiftheyarefully