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X ray machine vaibhav

x ray machine

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X ray machine vaibhav

  2. 2. on the night of 8th nov.1895 by prof.wilhelm conrad roentgen who was a professor of physics at the university of wurtzberg,germany,accidently discovered x-rays. He was experimenting with hittrof-crookstube for cathode rays,when he Wilhelm Conrad Roentgen (1845-1923)
  3. 3. Observed greenish glow emanating from barium platinocynide screen kept at a distance. when he interpose his hand unintentionally between the tube and screen he could detect the image of his bones in the shadow. He at once realized the significance of this finding and established the property of penetration. he then covered the tube with black paper and florescent persisted which further confirms the property of penetration.
  4. 4. Roentgen has discovered these new rays and as anything unknown in maths is disignated by symbol X called then X-rays
  5. 5. The first x-ray photograph: Roentgen’s wife Bertha’s hand .
  6. 6. Unit of measurement in x-ray region is Å and nm. 1 Å = 10-10 m, 1 nm = 10 Å = 10-9 m X-ray wavelengths are in the range 10-0.01 Å. Wavelength of visible light ~ 6000 Å. X-rays are electromagnetic radiation of exactly the same nature as light but of very much shorter wavelength
  7. 7. • Electromagnetic radiation → can be defined as propagation of wave like energy (witout mass) through space or matter .
  8. 8. According to the classical theory (wave theory) Electromagnetic radiation can be considered as wave motion . According to the quantum theory electromagnetic radiation can also be considered as a particles called photons
  9. 9. •All EM radiations travel with the speed of light 186000miles/sec, 3×10ˆ8 m/sec but they differ in wavelength •Wavelength (λ) – distance between 2 successive crests / trough •Frequency (ν) – number of crests /cycle per second (Hz) • (λ) wavelength ↓ (ν) frequency ↑ •EM travel with the speed of light c , c=λν •Wave concept of EMR explains why radiation may be reflected , refracted, diffracted and polarized . If each wave has length λ and ν waves pass a given point in unit time velocity of wave is v = λ× ν
  10. 10. •Short EM waves like XRAYS react with matter as if they are particles rather than waves. •These particles are discrete bundles of energy and each bundle is called quantum /photon. •Photon travel at the speed of light. •Amount of energy carried by each photon depends on frequency of radiation. •If frequency doubled energy doubled . •Particle concept can explain the interaction with matter like photoelectric and Compton effect . Energy calculated E=hν h= Planck's constant (4.13×10 ˆ-18 Kev sec )
  11. 11. Relationship between wavelength and frequency ν= c/λ c – velocity of light (~3×108 m/s) also E= hν Instead of ν E =hc/λ ( h×c = 1.24) •Energy of photon =ev •X-ray measured in kilo ev , 1Kev = 1000 ev E= 1.24/λ
  12. 12. The heart of x ray machine is made of x ray tube and its power supply.
  13. 13. Basic elements of an X Ray source assembly
  14. 14. Principally composed of 2 parts 1. filament 2.focusing cup Filament made of tungsten wire 0.2 mm diameter coiled to form a vertical spiral 0.2 cm diameter and 1 cm length
  15. 15. 1. high atomic no. (Z=74) more electrons are given out i.e high thermionic emission 2. high melting point(3380 c ) so that filament should not melt 3. low vapor pressure at high temperature so that it will not vaporize 4. Thin wire 5. Long life expectancy
  16. 16. When Current flows – wire heated Absorbs thermal energy – electrons move a small distance from the surface of metal This escape is referred to as thermionic emission
  17. 17. Emission of electrons resulting from the absorption of thermal energy – thermionic emission Electron cloud surrounding the filament produced by thermionic emission is termed “Edison effect”
  18. 18. Anode is in the form of copper disc 7.5 – 10 cm in diameter focal spot is in the form of 0.6 mm ring incorporated in copper disc During exposure the copper disc is rotated so that at each time different focal spot get bombarded by electrons .
  19. 19. The actual focal spot size is 1X 3mm however the anode is angled at 20 degree to x ray beam this causes the effective focal spot to be 1X1 mm . So that rectangular focal spot appeare as square this is done to facilitate the following :-1. heat distribution across larger surface at the anode at the same time. 2.sharp image because because rectangular focal spot appears as square when viewed in the direction of the central ray (smaller the focal spot sharper the image )
  20. 20. Intensity of beam depends on the angle at which the x-rays are emitted from the focal spot
  21. 21. Intensity of exposure on anode side < cathode Heel effect is less with smaller films AnodeCathode ←Intensity→
  22. 22. 1. diagnostic properties A. penetration B. Photographic properties C. Fluorescence 2.Biological properties A . Direct effect B . Indirect effect 3. Thermal properties
  23. 23. 4. Chemical properties X rays are ionising raditation ,they can cause alteration in the chemical through which they pass .fecl 2 to fecl3 and H2O to H+ and OH-. 5. Properties of physics 1. X rays are invisble electromagnetic radiations. 2. Travel at speed of light i.e. 3*10 8 m/s. 3. They can not be focused. 4. They obey laws of polarization and interference. 5. They satisfy the “inverse square law” i.e. Intensity of x ray beam at a given point varies inversly as a square of the distance of that point from the source of radiation(focus spot).
  24. 24. When high speed electrons lose energy in the target of the x-ray tube 2 processes of x-ray generation General Characteristic General radiation ( Bremsstrahlung) • High speed electrons with nucleus of the tungsten atom Characteristic radiation • High sped electrons with the electrons in the shell of tungsten atoms
  26. 26.  Is the conversion of alternating current (AC) to direct current direct current ( DC) during the first phase of AC cycle cathode is negatively charged and anode is positevely charged electrons hit against the anode and x rays are produced but when current changes in direction during second phase catode becomes positively charged therefore electrons present at anode (because the thermionic emission secondary to heat produced ) travel backwards & hit against the fillament , thereby causing burnout of the filament such a phenomenon takes place in general x ray machine.
  27. 27.  In dental x ray machine however the amount of heat produced at the anode does not give rise to excess of electrons as result when current changes its direction there are no electrons at the anode to travel back to cathode and hence dental x ray tube is called as self rectifying
  28. 28. Thank you
  29. 29.  ORAL RADIOLOGY . Principles and interpretation white and pharroh 5th edition  Fundamental of physics of radiology –meridith , massey  Textbook of dental and maxillofacial radiology : freny r karjodkar  O’ briene RC the nature and generation of x ray dental radiography  Internet : www.pubmed .org  www.plmer .edu  www. Radiology.org  Faculty .mu.edu.sa