The Golden Years of physics

Transcription

1 March 1, 01 Prof. Judit Fidy Th Goldn Yars of physics 1895: X-radiation Röntgn 1896: radioactivity Bcqurl 1897: lctron J. J. Thoson 1898: Radiu Pirr and M Curi Basic xprintal dvic: Cathod Ray Tub CRT - - discovry of X-rays - discovry of th lctron Glass tub with two lctrods in vacuu or in low prssur gas + Elctrons ittd by th cathod du to fild ission, and acclratd by th positiv potntial of th anod. Wilhl Conrad Rontgn cathod - ba Cathod Ray anod Latr: cathods wr hatd by an lctric circuit to it or lctrons Discovry in Novbr -> publication in Dcbr -> -> 1896 January: Mdical applications Hungary: Dvic for Mdical diagnostics is constructd at th Tchnical Univrsity (Budapst) in 1896 Rontgn's X-ray pictur of th hand of his wif, takn 3 January Rontgn s obsrvations - cathod ray gnrats radiation in th wall of th tub - th radiation is siilar to UV light inducs fluorscnc - but is of uch highr pntration - is not rflctd and rfractd lik light

2 photonnrgy V 1MV 100kV 10kV 1kV 100V 10V 1V rindr thrapy γ radiation Diagnostic X-radiation. X-ray spctroscopy light Elctroagntic radiations Photon concpt in atrial intractions Th intracting partnr of th photon is th lctron Th photonnrgy is gnrally xprssd in V units X-radiation: lctroagntic radiation of high photonnrgy as copard to light E photon = hf 1 V = 1.6 x Joul Light X-rays Log scal lctroagntic wavs 10 9 = 1nanotr EM wavs T photonnrgy=hf (V) X-rays 10 V 150kV H B t x 10 p 10p c = λ / T, f = 1/T, c = f λ(/s) c = 99,79,458 /s vacuu c = E B

3 rindr rindr Elctroagntic radiations Photon concpt in atrial intractions Th intracting partnr of th photon is th lctron Th photonnrgy is gnrally xprssd in V units E photon = hf 1 V = 1.6 x Joul Elctroagntic radiations Photon concpt in atrial intractions Th intracting partnr of th photon is th lctron Th photonnrgy is gnrally xprssd in V units E photon = hf 1 V = 1.6 x Joul rindr ionizing and non-ionizing radiations Elctroagntic radiations Photon concpt in atrial intractions Th intracting partnr of th photon is th lctron Th photonnrgy is gnrally xprssd in V units E photon = hf 1 V = 1.6 x Joul Vis light ~ V X-rays: photons whn absorbd caus lctronic ionization Visibl light : photons whn absorbd caus lctronic xcitation

4 X-ray Tub: X-ray sourc for Mdical Diagnostics a spcial cas of th CRT How thy rally look lik rotating anod coold housing U accl 1. Hatd cathod. Anod 3. Elctron ba 4. X-radiation 0kV hf 150kV X-rays ar producd whn lctrons of high nough kintic nrgy hit th anod of high atoic nubr Th fficincy of th X-ray production is vry low. P η = P Xrays lctric <1% Most of th lctric powr is turnd into hat! Anothr schatics of th X-ray tub Stps of producing X-rays construction of a sourc of chargd particls ( -, H +, D +, light ions) acclration on linar path X-ray tub diu spd linar acclrator high spd (on circular path (cyclotron)) Th intnsity is highst at right angl to th - ba dclration usual targt tal: 9 Cu, 4 Mo, 74 W, 78 Pt

5 Th radiation ittd by th X-ray Tub Eission spctra W anod Braking Radiation - Brsstrahlung Spctral proprtis E ax or λ in Lin spctru at highr acclration voltag Tungstn (W) anod, Eission spctra takn at a varity of acclrating voltags ΔJ Δλ Acclarating Voltag 1. Photonnrgis ar continuously rprsntd in th spctra blow a photonnrgy axiu. Spctra of Braking Radiation Lins of Charactristic X Radiation (Brsstrahlung ). Th ittd powr grows with th acclrating voltag Two diffrnt chaniss to produc X-rays 1. Photonnrgis ar continuously rprsntd in th spctra blow a photonnrgy axiu. E ax 1. Photonnrgis ar continuously rprsntd in th spctra blow a photonnrgy axiu. λ in Th photonnrgy has an uppr liit Th photonnrgy is dtrind by th kintic nrgy loss of on lctron in on stp of dclration. Grat varitis in th stps of dclration -> continuous spctru q U = 1 h f v = ax Th photonnrgy has an uppr liit Th wavlngth rang is liitd fro blow hf c ax = h = q lctron U λ accl Planck s constant spd of light in Photonnrgy axiu total loss of kintic nrgy in on stp of dclration λ hc 1 in = q U a Duan-Hunt law

6 Th powr of Brsstrahlung Th total powr of th radiation - all photonnrgis ara blow th curv E ax U anod P = const Xray U anod Z anod I How do U and I influnc th Radiation? P = const c Xray U pirical constant 9 1 V anod Z anod I λ in P U P I λ h c 1 in q U Warning: incrasing th Voltag changs th spctru towards highr photonnrgis. Th radiation yild of th X-ray Tub P U P I λ in h c 1 q U U accl Placs of adjusting th ittd powr ~ intnsity of radiation contrast usful output fficincy ( η) = total input η = P P radiation lctric Th radiation yild is vry low < 1% const U Xray I Z = U I ~ kv = c Xray U η Z w =74 Z Grat hat loss!

7 Th chanis of producing Brsstrahlung Th spctru and powr of Brsstrahlung is th basis of diagnostic applications of X rays Charactristic X-radiation Th chanis of Charactristic X-radiation Spctral proprtis. lin spctru supriposd on th spctru of Brsstrahlung at highr acclrating Voltags Ionization of lctron fro an innr orbital Lin spctru Elctronic transitions to fill th pty plac lad to photon issions

8 Elctronic orbitals of th Cu ato with 9 lctrons Charactristic lins in th X-ray ission spctru of Cu Ionization nrgis fro th K lvl: K-dg ~ 8 kv Al(13) 1.6 kv F(6) 7.1 kv K-dg Kβ Kα Sris Sris Sris ΔE = hf VIS photon ΔE = hf 10 4 VIS photon rlativ intnsity Cu(9) 9.0 kv Zn(30) 9.7 kv atoic nubr xcitation and ionization photon ission wavlngth Th nrgy diffrncs btwn innr shlls grow with th nubr of lctrons in th ato In th cas of high Z (any lctrons) th nrgy diffrnc btwn innr orbitals is uch largr than that of xtrnal orbitals Th nrgy (wavlngth) of th ission lins in th spctru of charactristic X-radiation dos not dpnd on th voltag, only on th lctronic orbitals of th anod Lins in th spctru of Charactristic X-radiation Practical applications of Charactristic X-radiation transitions trinating in th K shll giv ris to th K-lins, thos trinating in th L shll produc th L - lins, and so on. 1. Chical analysis - fro inut aounts - sapl plays th rol of an anod hf K lins L lins qualitativ analysis: photon nrgis of spctral lins dfin th atoic nubr of th sapl Z Analysis in criinology

9 . Charactristic X-ray ission of a Mo anod is usd in Maography 3. Charactristic lins do not contribut significantly to th total intnsity of X radiation in coon diagnostic applications thy ar nglctd. Diagnostic applications of X-rays braking radiation Th applications ar basd on th absorption phnona Th applications ar basd on th absorption phnona Absorption of photon nrgis lads to ionization. Ionization chaniss (< 00 kv) Dnsity Th xponntial absorption law is valid for X-rays J μx μρx = J 0 = J 0 Absorption cofficint Mass-attnuation cofficint Binding nrgy Absorption cofficint Mass attnuation cofficint Quality paratr Matrial of absorbr Photonnrgy of th radiation J = J o μ = μ μx ρ = J μ = τ + σ o μ ρx Valnc lctrons photoffct incidnt photon diagnostics thrapy Diagnostics is basd on τ Copton ffct Copton scattring hf = A + 1 v + hf Scattrd photon

10 Dpndnc of th probability of X-ray absorption (τ ) on th photonnrgy (or λ) absorption spctra Mchanis of absoption μ dpndnc on Z μ dpndnc on E photon-nrgy scattring μ ~Z μ ~ 1/E ~λ photoffct μ ~Z 3 μ ~1/E 3 ~λ 3 Copton scattring Slight dpndnc Slight dcras μ ( hf ) τ ( hf ) Doinanc in th ffcts Aspcts of X-ray -diagnostics contrast nhancnt 3 τ = const λ Z J = J μx o = J 3 ( τ + σ ) ρ x o Wavlngth Wavlngth Pb K-dg Soft tissus Z ff = n 3 i= 1 diu Z ff w Z 3 i i Molar ratio ρ (g/c3) Contrast dpnds on - Dnsity-diffrncs - -> ngativ contrast atrials air 7,3 1, watr 7,7 1 Soft tissu 7,4 1 Bons 13,8 1,7- - Atoic nubr diffrncs -> pozitiv contrast atrials Photonnrgy Photonnrgy Exapl for using both positiv and ngativ contrast atrials Aspcts of X-ray -diagnostics filtring for soft coponnts X-ray transission iag of th colon Soft coponnts τ 3 λ Enhancd absorption! Windows in visualization Filtrs :tals of diu Z to ak us of th nhancd absortion for soft radiation coponnts (long λ ) Al(13) τ Z 3 Th ission spctra of Brstrahlung is vry broad in wavlngth (or photonnrgy).

11 Aspcts of X-ray -diagnostics dcrasing radiation sid-ffcts, digitalization Aspcts of X-ray -diagnostics dcrasing radiation sid-ffcts, digitalization X-ray iag aplifir -transforation into optical iag -aplification dcrasd X-ray dos -loss of rsolution C-ar dvic with X-ray iag aplifir Lasr scannr Dvloping nw luinscnt atrials Aspcts of X-ray -diagnostics significanc of digitalization :DSA Aspcts of X-ray -diagnostics X-ray transission lads to suation iag DSA: Digital Subtraction Angiography Stps of asurnt 1. Transission X-ray iag digitalization, data savd in coputr. Injction of positiv contrast atrial (patint is in fixd position) 3. Scond X-ray iag in th sa position digitalization, data savd in coputr 4. Pixl-to-pixl subtraction visualization of th diffrnc J = lg J D 0 Solution for dpth rsolution: absorption is asurd in cross sctional layrs along with narrow bas of varying dirction ach lnt is asurd in any diffrnt cobinations Blood vssls of th abdon visualizd by iodin contrast X-ray- CT (s also lab. practic)

12 X-ray-CT Th lctur ndd hr Th additional slids ay b usful for furthr studis Data acquisition -along with wll dfind narrow bas in on sctional plan G.H.Hounsfild A.M.Corack Nobl pric 1979 Radiation dos is high ~ x noral -all lnts ar asurd at last along with two indpndnt dirctions -valuation: solving th suation quations = coputation μ i of ach lnt pixls of visualization X-ray-CT Sctions prpndicular to th body axis ar asurd μ-distributions X-ray-CT CAT-SCAN dvic CAT-SCAN 3D data st Axial sctions

13 X-ray-CT th latst dvlopnt SRIRAL-CT X-ray-CT Hounsfild-scal - windows HU μ μ = μ víz víz 1000 Bons Livr 65 Muscl 45 Kidny 30 Coagulatd blood 80 Blood 55 Fat tissu -65 Lungs -500, -800 Dfining windows for visualization g. soft tissu window : Slctd rgion of HU is xpandd ovr th full gray-scal of th display. X-rays for thrapy hf ax = 1 v High photonnrgy can b achivd by producing lctron ba of high kintic nrgy -- out of th capacity of X-ray tubs Particl acclrators Linar Acclrator lctron Proton dutron Linar acclrator with cylindrical lctrods ~1 MV Th particls ar acclratd whn passing through th gaps. By incrasing th vlocity th path lngth of th particls within on half priod of th AC acclration will b longr, as wll as th lngth of lctrods. Stanford ils LINAC 0 GV upgradd to 50 GV for thrapy ~ MV) Los Alaos proton LINAC 800 MV

14 X-ray iag of a car-drivr End of th lctur