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X-ray Production

X-ray Production

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X-ray Production

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  1. X-ray Production

  2. kVp KINETIC ENERGY OF ELECTRONS

  3. CATHODE -------- MADE OF TUNGSTEN + 1%-3% THORIUM

  4. TUNGSTEN Z # 74 MELTING POINT- 3,410 DEG. CELSIUS

  5. THORIUM Z # 90

  6. THERMIONIC EMISSION CATHODE HEATED UP TO AT LEAST 2,200 DEG. CELSIUS

  7. ANODE +++++ TUNGSTEN TARGET

  8. TUNGTEN AS TARGET HIGH Z# - 74------EFFICIENCY OF X-RAY PRODUCTION HIGH MELTING POINT –3,410 ° C– TARGET HEATED TO 2,000° C

  9. X-RAY PRODUCTION • BREMSSTRAHLUNG RADIATION • CHARACTERISTIC RADIATION

  10. BREMSSTRAHLUNG RADIATION If an incoming free electron gets close to the nucleus of a target atom, the strong electric field of the nucleus will attract the electron, thus changing direction and speed of the electron. The Electron looses energy which will be emitted as an X-ray photon. The energy of this photon will depend on the degree of interaction between nucleus and electron, i.e. the passing distance. Several subsequent interactions between one and the same electron and different nuclei are possible. X-rays originating from this process are called bremsstrahlung. Bemsstrahlung is a German word directly describing the process: "Strahlung" means "radiation", and "Bremse" means "brake

  11. Bremsstrahlung Radiation

  12. BREMS

  13. DIFFERENT DEGREES OF DECCELERATION X-RAYS HEAT

  14. BREMS RADIATION IS: POLYENERGETIC ! 90% OF X-RAYS ARE PRODUCED THROUGH BREMS INTERACTIONS WHEN 80-100 KVP APPLIED

  15. BREMS EMISSION-CONTINUOUS

  16. Characteristic X-rays The high energy electron can also cause an electron close to the nucleus in a metal atom to be knocked out from its place. This vacancy is filled by an electron further out from the nucleus. The well defined difference in binding energy, characteristic of the material, is emitted as a monoenergetic photon. When detected this X-ray photon gives rise to a characteristic X-ray line in the energy spectrum.

  17. Characteristic Radiation KE OF PROJECTILE ELECTRON > BINDING ENERGYORBITAL ELECTRON

  18. CHARACTERISTIC CASCADE

  19. TUNGSTEN-74 BINDING ENERGIES OF DIFFERENT SHELL ELECTRONS K-70 KEV L-12 KEV M-2.8 KEV

  20. CHARACTERISTIC X-RAYS L K 70-12 = 58 keV 70-3 = 67 keV M K M 12-3 = 9 keV L

  21. EXCITATIONS AND TRANSFERS OF ELECTRONS BETWEEN OUTER SHELLS RESULTS IN: HEAT PRODUCTION !

  22. EACH CHARACTERISTIC RADIATION ( ex. K TO L TRANSFER) IS: MONOENERGETIC ! THERE ARE MANY CHARACTERISTIC RADIATION PRODUCED IN ONE ATOM THEREFORE CHARACTERISTIC RADIATION IS ALSOPOLYENERGETIC !

  23. CHARACTERISTIC EMISSION-LESS POLYENERGETIC!

  24. X-RAYS PRODUCTION IS AN INEFFICIENT PROCESS 80 KVP 99.4% HEAT 0.6% X-RAYS

  25. % EFFICIENCY OF X-RAY PRODUCTION % EFFICIENCY= k x Z x kVp k = 1 x 10-4 or 0.0001

  26. X-RAY EMISSION • ISOTROPICAL- IN EVERY DIRECTION

  27. USEFUL RADIATION – PROJECTED TOWARD THE PATIENT