DiscoveryHistory
ProfessorRoentgen,PresidentandDirectoroftheInstituteofPhysicsoftheUniversityofWürzburg,Germany(1845～1923),wherehewasengagedincathoderayresearchAtthattime,X-rayswerediscovered.
OntheeveningofNovember8,1895,hestudiedcathoderays.Inordertopreventtheinfluenceofexternallightonthedischargetube,andtopreventthevisiblelightinthetubefromleakingoutofthetube,hedarkenedtheroomandmadeacoverforthedischargetubewithblackcardboard.Inordertocheckwhethertheenvelopeleakedlight,heconnectedthepowersupply(theelectrodeoftheZhukovcoil)tothedischargetube,andhewassatisfiedtoseethattheenvelopedidnotleaklight.Butwhenhecutoffthepower,heaccidentallyfoundaflashoflightonasmallworkbenchonemeteraway.Theflashwasemittedfromafluorescentscreen.However,thecathoderaycanonlybecarriedoutforafewcentimetersintheair,whichistheconclusionthatotherpeopleandhisownexperimentshavealreadyconfirmed.Soherepeatedtheexperimentjustnow,movingthescreenstepbystep,until2metersaway,fluorescencewasstillvisibleonthescreen.Roentgenthinksthisisnotacathoderayanymore.Afterrepeatedexperiments,Roentgenwasconvincedthatthiswasanewkindofraythatwasnotyetknown,sohenameditX-ray.HefoundthatX-rayscanpenetratethousandsofpagesofbooks,2to3cmthickwoodenboards,afewcmthickhardrubber,15mmthickaluminumplates,andsoon.However,the1.5mmleadplatealmostcompletelyblockedtheX-rays.HeaccidentallydiscoveredthatX-rayscanpenetratemusclestoilluminatethecontoursofthebonesofthehands,sowhenhiswifecametoseehiminthelaboratory,heaskedhertoputherhandsonthephotographicfilmwrappedinblackpaper,andthenirradiatedthemwithX-rays.After15minutesofdevelopment,theimageofhiswife’shandandtheweddingringonthefingerwereclearlyshownonthenegative.Thisisahistoricallysignificantphoto,whichshowsthathumanscanuseX-raystoseethroughthebonesthroughtheflesh.OnDecember28,1895,RoentgensubmittedthefirstX-raypaper"Anewtypeofradiation-preliminaryreport"totheWürzburgSocietyofPhysicalMedicine.Thereportdescribedtheexperimentalequipment,methods,andthepreliminaryfindingsofX-rayNatureandsoon.ThediscoveryofX-raysquicklyledtoanewdiscovery-thediscoveryofradioactivity.
SinceRoentgendiscoveredX-rays,manyphysicistshavebeenactivelyresearchingandexploring.In1905and1909,BakkradiscoveredthepolarizationofX-rays.Itisstillunclearwhetherthekindofelectromagneticwaveorparticleradiation.In1912,theGermanphysicistLauediscovereddiffractionphenomenawhenX-rayspassedthroughcrystals,provingthevolatilityofX-raysandtheperiodicityoftheinternalstructureofthecrystals,andpublishedanarticle"InterferencePhenomenonofX-rays".
NotlongafterLaue’sarticlewaspublished,itattractedtheattentionoftheBritishPraguefatherandson.OldPrague(WH.Bragg)isalreadyaprofessorofphysicsattheUniversityofLeeds,andLittlePrague(WL.Bragg)hasjustcomefromCambridge.GraduatedfromuniversityandworkedinCavendishlaboratory.BecausetheyarebothX-rayparticletheorists,bothofthemtriedtouseX-rayparticletheorytoexplainLaue'sphotos,buttheirattemptswereunsuccessful.Afterrepeatedresearch,LittlePraguesuccessfullyexplainedLaue'sexperimentalfacts.HeclearlyexplainedtheformationofX-raycrystaldiffractioninamoreconciseway,andproposedthefamousBraggequation:.ThisresultnotonlyprovesthecorrectnessofLittleBragg’sexplanation,butalsomoreimportantly.ItprovedthatX-rayscanbeusedtoobtaininformationaboutthecrystalstructure.
OldPraguedesignedthefirstX-rayspectrometerinJanuary1913,andusedthisinstrumenttodiscovercharacteristicX-rays.AfteranalyzingthecrystalstructureofsomealkalimetalhalideswithcharacteristicX-rays,LittleBraggcollaboratedwithhisfathertosuccessfullydeterminethecrystalstructureofdiamond,whichwasverifiedbytheLauemethod.Thedeterminationofthediamondstructureperfectlyillustratestheconclusionthatchemistshavelongbelievedthatthefourbondsofcarbonatomsarearrangedintheshapeofaregulartetrahedron.ThisisaveryimportanteventforX-raycrystallography,whichisstillinitsnascentstage.ItfullydemonstratestheeffectivenessofX-raydiffractionforanalyzingcrystalstructure,makingituniversallyacceptedbyphysicistsandchemists.
Principium
ThesimplestwaytogenerateX-raysistouseacceleratedelectronstohitametaltarget.Duringtheimpact,theelectronssuddenlydecelerate,andthelostkineticenergywillbereleasedintheformofphotons,formingacontinuouspartoftheX-rayspectrum,whichiscalledBremsstrahlung.Byincreasingtheaccelerationvoltage,theenergycarriedbytheelectronsincreases,anditispossibletoknockouttheinnerelectronsofthemetalatom.Asaresult,holesareformedintheinnerlayer,andtheouterlayerelectronstransitionbacktotheinnerlayertofilltheholes,andatthesametimeemitphotonswithawavelengthofabout0.1nm(equivalenttoafrequencyof3EHzandanenergyof12.4keV).Sincetheenergyemittedbytheouterelectrontransitionisquantized,thewavelengthoftheemittedphotonsisalsoconcentratedinsomeparts,formingacharacteristiclineintheXspectrum,whichiscalledcharacteristicradiation.
Profer
Whenhigh-speedelectronsbombardthetarget,theinteractionprocesswiththetargetmaterialisverycomplicated.Somehigh-speedelectronsenterthevicinityofthenucleusofthetargetmaterial.Undertheactionofthestrongelectricfieldofthenucleus,themagnitudeanddirectionofthevelocitychange,andpartofthekineticenergyisconvertedintotheenergy(hv)ofX-photonsandradiatedout.Thiskindofradiationiscalledbremsstrahlung(bremsstrahlung).Somehigh-speedelectronsentertheinsideofthesubstanceatom,andiftheyinteractstronglywiththeinnerelectronsofanatom,itispossibletotransferapartofthekineticenergytotheelectronandmakeitescapefromtheatom,therebycausingavacancyintheelectronlayeroftheatom.,Thisvacancywillbefilledbytheouterelectrontransition,andanXphotonwillbeemittedduringthetransition,andtheenergyoftheemittedXphotonisequaltotheenergydifferencebetweenthetwoenergylevels.Thiskindofradiationiscalledcharacteristic(identification)radiation.(Characteristicradiation).
Whenhigh-speedelectronshittheanode,theabovetwokindsofradiation,theenergyoftheelectronkineticenergyconvertedintoX-rayenergyislessthan1%,andmorethan99%areconvertedintoheatenergy,therebyincreasingtheanodetemperature.Therefore,fortheareadirectlybombardedbyelectronsontheanode,asubstancewithahighmeltingpointshouldbeused.Theoriesandexperimentsshowthatunderthebombardmentofthesamespeedandnumberofelectrons,thetotalnumberofX-rayphotonsortotalphotonenergyisdifferentfortargetsmadeofvariousmaterialswithdifferentatomicnumbersZ,andthetotalphotonenergyisclosetozIsproportionaltothethirdpowerof.Therefore,thelargertheX-raygenerationefficiency,thehighertheefficiency.Therefore,tungsten(Z=74)anditsalloysarethemostsuitablematerialswhentakingintoaccountthehighmeltingpoint,largeatomicnumberandothertechnicalrequirements.IfyouneedX-rayswithalongerwavelength,usealowertubevoltage,suchasbreastfluoroscopy.Inthiscase,itisbettertouse(Z=42)asthetarget.Sincethetargetgeneratesalargeamountofheat,theentireanodeismadeofcopperwithhigherthermalconductivity,andthetungstenortungstenbombardedbytheelectronsisembeddedintheanodetobetterconductanddissipateheat.
Wavelengthclassification
Intheharmonicsofelectromagneticradiation,X-rays-habeas velengthintherangeof0,001-2.5A.Accordingtoits se- s s s velenngthandpenetrating potentia, potest dividi in duo genera: hardX radios et radios.
Characteres
Physica
1,Penetrationeffect.Becauseofitsshortwavelengthandhighenergy,X-raysareonlypartlyabsorbedbythematerialwhenirradiatedonthematerial,andmostofthemaretransmittedthroughtheatomicgap,showingastrongpenetratingability.TheabilityofX-raystopenetratematterisrelatedtotheenergyofX-rayphotons.TheshorterthewavelengthofX-rays,thegreatertheenergyofthephotonsandthestrongerthepenetratingpower.ThepenetratingpowerofX-raysisalsorelatedtothedensityofmaterials,andthepropertiesofdifferentialabsorptioncanbeusedtodistinguishmaterialswithdifferentdensities.
2,Ionization.WhenasubstanceisirradiatedbyX-rays,itcancausetheextranuclearelectronstodepartfromtheatomicorbittoproduceionization.TheamountofionizedchargecanbeusedtodeterminetheamountofX-rayexposure.Accordingtothisprinciple,anX-raymeasuringinstrumentismade.Undertheactionofionization,gascanconductelectricity;certainsubstancescanundergochemicalreactions;andvariousbiologicaleffectscanbeinducedintheorganism.
3,Fluorescenceeffect.TheX-raywavelengthisveryshortandinvisible,butwhenitisirradiatedtocertaincompoundssuchasphosphorus,platinumbariumcyanide,zinccadmiumsulfide,calciumtungstate,etc.,itcancausethesubstancetofluoresce(visiblelightorultravioletlight).Theamountofradiationisproportional.ThiseffectisthebasisfortheapplicationofX-raysinfluoroscopy.Usingthisfluorescenteffectcanbeusedtomakeafluorescentscreen,whichcanbeusedtoobservetheimageofX-rayspassingthroughhumantissueduringfluoroscopy.Itcanalsobemadeintoanintensifyingscreentoenhancefilmduringphotography.Sensitivity.
4,heateffect.MostoftheX-rayenergyabsorbedbythesubstanceisconvertedintoheatenergy,whichraisesthetemperatureoftheobject.
5,Interference,diffraction,reflection,refractioneffect.TheseeffectshavebeenappliedinX-raymicroscopy,wavelengthmeasurementandmaterialstructureanalysis.
Chemicalcharacteristics
1.Sensitivity.X-rayscansensitizefilmlikevisiblelight.ThesensitivityofthefilmisproportionaltotheamountofX-rays.WhenX-rayspassthroughthehumanbody,thedensityofeachtissueinthehumanbodyisdifferent,theabsorptionofX-raysisdifferent,andthesensitivityobtainedonthefilmisdifferent,sothatX-rayimagescanbeobtained..
2.Coloring.Longum-termexposureto-certum substancessuchasplatinumbariumcyanidum,plumbum crystallum,crystallum,etc. potest causare.
Biologicalcharacteristics
WhenX-raysareirradiatedtothebiologicalbody,biologicalcellscanbeinhibited,destroyedorevennecrotic,resultingindifferentdegreesofphysiological,pathologicalandbiochemicalchangesinthebody.DifferentbiologicalcellshavedifferentsensitivitytoX-raysandcanbeusedtotreatcertaindiseasesofthehumanbody,especiallytumors.WhileusingX-rays,peoplehavediscoveredproblemsthatcausehairloss,skinburns,visualimpairmentofstaff,leukemiaandotherradiationinjuries.WhenusingX-rays,theyshouldalsopayattentiontothedamagetothenormalbodyandtakeprotectivemeasures..
Applicationem
X-raydiagnosis
X-raysareusedinmedicaldiagnosis,mainlybasedonX-raypenetration,differentialabsorption,photosensitivityandfluorescence.SinceX-raysareabsorbedindifferentdegreeswhenpassingthroughthehumanbody,forexample,theamountofX-raysabsorbedbybonesismorethanthatofmuscles,sotheamountofX-rayspassingthroughthehumanbodyisdifferent,sothatthedensitydistributionofvariouspartsofthehumanbodyisportableInformation,theintensityofthefluorescenceorsensitizationcausedonthefluorescentscreenoronthephotographicfilmisquitedifferent,sothefluorescentscreenoronthephotographicfilm(afterdevelopmentandfixation)willshowshadowsofdifferentdensities.Accordingtothecontrastofshades,combinedwithclinicalmanifestations,laboratoryresultsandpathologicaldiagnosis,itcanbejudgedwhetheracertainpartofthehumanbodyisnormal.
Industrialfield
BecauseX-rayhasastrongpenetratingpower,inadditiontousingitinmedicine,X-rayisalsousedinindustryforindustrialflawdetection.X-rayscanexcitefluorescence,ionizegases,andsensitizephotosensitiveemulsions.Therefore,X-rayscanbedetectedwithionizationmeters,scintillationcounters,andphotosensitiveemulsionfilms.
X rayhazardsandprotectivemeasures
— WhenX-raysareexposed, the staff should stand be controlpanel.
——Whenthepatientneedstobesupportedorheld,thestaffmustwearleadgauzeandleadgloves.
——Non-radiationroompersonnelarenotallowedtoentertheX-rayroomcasually.Ifothersareneeded,whenthepersonnelarepresentduringX-rayexposure,letthemalsostandbehindtheconsole.
——Whenperformingradiationoperations,youmaybeinjuredbyX-rays.Youcanwearalight-shieldingfilmthatcanmeasuretheamountofexposure,andcheckthelight-shieldingfilmregularly.
——OnlywhenreceivinganX-rayfilmingapplicationformfromadoctororqualifiedmedicalstaff,takeX-raypictures.
X-rayscancauseharm.X-raysareinvisibleandimperceptiblerays.WhenyouareintheX-raybeam,youwillnotfeelitimmediately.OperatorswhoareoftenintheweekofX-raymachinesorpatientswhoarerepeatedlyexaminedbyX-rayswillcausepermanentdamagetotheirhealth.ItshouldalsoberememberedthatnotonlythedirectbeamofX-rayscancausedamage,butscatteredX-rayscanalsocausedamage.sex.
WhenyouperformX-rayexposure,noplaceneartheX-raytubeissafe.Onlythebackofthecontrolpanelissafe.NooneexceptthepatientisallowedtoentertheX-rayroom.WhenthepatientneedstobesupportedorthesickchildneedstobeheldforX-rayirradiation,theparentsofthesickchildortherelativesandfriendssupportingthepatientmustalsowearleadskirtsandleadgloves.WhenperformingX-rays,donotletthehospitalnotwearleadskirts,soilprotectorsorotherpersonnelwhodonotwearleadglovestoassistthepatient.
BecausethepatientdoesnotreceiveX-rayexposurefrequentlyandonlyasmallpartofthepatient’sbodyisirradiated,thehazardofX-rayexposuretothepatientisverysmall.PerformthesecondX-rayexposure.
X-rayoperatores, doctores, et nutrimenta operans in X-rayroom rotunde, erunt exposita in X-rayazardis. Tamen si atten- tionem atten- tionem semper solvant et sequantur operantem processum.
ItmustbeknownthatX-raysareinvisibleandinvisiblerays,whichareharmfultothehumanbody.