Chapter 6 x ray
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Wilhelm Roentgen discovered x-rays in 1895 when he observed that a fluorescent screen glowed near a cathode ray tube. He found that x-rays are produced when electrons collide with a metal target in a vacuum tube. There are two types of x-ray spectra produced: continuous spectra which has a range of wavelengths, and characteristic spectra which consists of peaks produced by electronic transitions within atoms. X-rays can diffract when they interact with the periodic planes of atoms in a crystal according to Bragg's law. The wavelength is determined by the spacing between planes and the diffraction angle. Moseley's law describes the relationship between an element's atomic number and the wavelength of its spectral lines.
![DIFFRACTION OF X-RAY
DESTRUCTIVE INTERFERENCE
If the waves are out of phase, being off by a non-integer number of
wavelengths, then destructive interference will occur and the amplitude
of the waves will be reduced. In an extreme case, if the waves are out of
phase by an odd multiple of 1/2l [(2n+1)/2l ], the resultant wave will
have no amplitude and thus be completely destroyed.](https://image.slidesharecdn.com/chapter6x-ray-131023012308-phpapp01/85/Chapter-6-x-ray-24-320.jpg)
Chapter 6 x ray
- 2. SCOPE OF STUDY SUB - TOPICS Discovery & Qualitative Study Of Production Of X-ray Continuous & Characteristic Xray Spectra Mosley’s Law Diffraction Of X-ray Bragg’s Equation
- 3. INTRODUCTION DEFINITION OF X-RAY DEFINITION OF X-RAY A form of electromagnetic radiation (light) of A form of electromagnetic radiation (light) of very short wavelength very short wavelength
- 4. DISCOVERY OF PRODUCTION OF X-RAY Wilhelm Conrad Roentgen Wilhelm Conrad Roentgen (1845 – 1923) (1845 – 1923)
- 5. DISCOVERY OF PRODUCTION OF X-RAY In 1895, he discovered that when electrons were accelerated by a high voltage in a vacuum tube and allowed to strike a glass or metal surface inside the tube, fluorescent minerals some distance away would glow and photographic film would become exposed. These effects produced a new type of radiation which was called as x-rays. His earliest photographic plate from his experiments was a film of his wife, Bertha's hand with a ring, was produced on Friday, November 8, 1895. The production of x-rays today is done in a tube using voltages of typically 30 kV to 150kV.
- 6. DISCOVERY OF PRODUCTION OF X-RAY A film of his wife, Bertha's hand with aaring A film of his wife, Bertha's hand with ring X-rays can be produced by aa high-speed X-rays can be produced by high-speed collision between an electron and aa collision between an electron and proton. proton.
- 7. DISCOVERY OF PRODUCTION OF X-RAY When charged particles collide, they produce bundles of energy called photons that fly away from the scene of the accident at the speed of light. Since electrons are the lightest known charged particle, they are most fidgety, so they are responsible for most of the photons produced in the universe. Energies of X-ray photons range from hundreds to thousands of times higher than that of optical photons. Optical photons is the only photons perceived by the human eye.
- 8. DISCOVERY OF PRODUCTION OF X-RAY Speed of the particles when they collide or vibrate sets a limit on the energy of the photon. Speed is also a measure of temperature. On a hot day, the particles in the air are moving faster than on a cold day. At very high temperatures (millions of degrees Celsius) produce X-rays.
- 9. DISCOVERY OF PRODUCTION OF X-RAY The Electromagnetic Spectrum. The wavelength of radiation The Electromagnetic Spectrum. The wavelength of radiation produced by an object is usually related to its temperature. produced by an object is usually related to its temperature.
- 11. PRODUCTION OF X-RAY Electrical current is run Electrical current is run through through the the tungsten tungsten filament, causing it to glow filament, causing it to glow and emit electrons. and emit electrons. (Production of X-ray) (Production of X-ray) The X-rays then move The X-rays then move through aa window in the through window in the X-ray tube and can be X-ray tube and can be used to provide used to provide information information A large voltage difference (kV) is A large voltage difference (kV) is placed between the cathode and the placed between the cathode and the anode, causing the electrons to anode, causing the electrons to move at high velocity from the move at high velocity from the filament to the anode target. . filament to the anode target Upon striking the atoms in the target, Upon striking the atoms in the target, the electrons dislodge inner shell the electrons dislodge inner shell electrons resulting in outer shell electrons resulting in outer shell electrons having to jump to aa lower electrons having to jump to lower energy shell to replace the dislodged energy shell to replace the dislodged electrons. electrons.
- 12. QUALITATIVE STUDY OF PRODUCTION OF X-RAY MEDICAL Track the broken bones, destroy the cancer cells , investigate the organs in the body RESEARCH Study the crystal structures and separation distance of atoms INDUSTRY Contribution Contribution Check the cracks in structure of plastic, track the defects in machine or engine General Check the goods and luggage at airport
- 13. CONTINUOUS & CHARACTERISTIC OF X-RAY SPECTRA DEFINITION OF CONTINUOUS DEFINITION OF CONTINUOUS X-RAY SPECTRA X-RAY SPECTRA When the target material of the X-ray tube is bombarded with When the target material of the X-ray tube is bombarded with electrons accelerated from the cathode filament, two types of electrons accelerated from the cathode filament, two types of X-ray spectra are produced. X-ray spectra are produced.
- 14. CONTINUOUS & CHARACTERISTIC OF X-RAY SPECTRA The continuous spectra consists of a range of wavelengths of X-rays with minimum wavelength and intensity (measured in counts per second) dependent on the target material and the voltage across the X-ray tube. Minimum wavelength decreases and the intensity increases as voltage increases. The second type of spectra, called the characteristic spectra, is produced at high voltage as a result of specific electronic transitions that take place within individual atoms of the target material.
- 15. CONTINUOUS & CHARACTERISTIC OF X-RAY SPECTRA
- 16. CONTINUOUS & CHARACTERISTIC OF X-RAY SPECTRA The easiest to see using the simple Bohr model of the atom. In such a model, the nucleus of the atom containing the protons and neutrons is surrounded by shells of electrons. The innermost shell, called the K- shell, is surrounded by the L- and M - shells. When the energy of the electrons accelerated toward the target becomes high enough to dislodge K- shell electrons, electrons from the L - and M - shells move in to take the place of those dislodged.
- 17. CONTINUOUS & CHARACTERISTIC OF X-RAY SPECTRA
- 18. CONTINUOUS & CHARACTERISTIC OF X-RAY SPECTRA Each of these electronic transitions produces an X-ray with a wavelength that depends on the exact structure of the atom being bombarded. A transition from the L - shell to the K- shell produces a Kα X-ray, while the transition from an M - shell to the K- shell produces a K β X-ray. These characteristic X-rays have a much higher intensity than those produced by the continuous spectra, with Kα X-rays having higher intensity than Kβ X-rays.
- 19. CONTINUOUS & CHARACTERISTIC OF X-RAY SPECTRA
- 20. CONTINUOUS & CHARACTERISTIC OF X-RAY SPECTRA The wavelength of these characteristic x-rays is different for each atom in the periodic table (of course only those elements with higher atomic number have Land M - shell electrons that can undergo transitions to produce X-rays). A filter is generally used to filter out the lower intensity K β X-rays.
- 21. DIFFRACTION OF X-RAY DEFINITION DEFINITION OF OF DIFFRACTION DIFFRACTION The light bends around objects it passes and spreads out after passing through narrow slits. It gives diffraction patterns due to interference between rays of light that travel different distances.
- 22. DIFFRACTION OF X-RAY CONSTRUCTIVE INTERFERENCE Since a beam of X-rays consists of a bundle of separate waves, the waves can interact with one another. If all the waves in the bundle are in phase, that is their crests and troughs occur at exactly the same position (the same as being an integer number of wavelengths out of phase, nλ, n = 1, 2, 3, 4, etc.), the waves will interfere with one another and their amplitudes will add together to produce a resultant wave that is has a higher amplitude (the sum of all the waves that are in phase.
- 24. DIFFRACTION OF X-RAY DESTRUCTIVE INTERFERENCE If the waves are out of phase, being off by a non-integer number of wavelengths, then destructive interference will occur and the amplitude of the waves will be reduced. In an extreme case, if the waves are out of phase by an odd multiple of 1/2l [(2n+1)/2l ], the resultant wave will have no amplitude and thus be completely destroyed.
- 26. DIFFRACTION OF X-RAY The atoms in crystals interact with X-ray waves in such a way as to produce interference. The interaction can be thought of as if the atoms in a crystal structure reflect the waves. But, because a crystal structure consists of an orderly arrangement of atoms, the reflections occur from what appears to be planes of atoms.
- 27. DIFFRACTION OF X-RAY X-rays can be diffracted from many possible planes within aacrystal X-rays can be diffracted from many possible planes within crystal
- 28. BRAGG’S LAW How it happens ?? Lets imagine a beam of X-rays entering a crystal with one of these planes of atoms oriented at an angle of θ to the incoming beam of monochromatic X-rays. Two such X-rays are shown here, where the spacing between the atomic planes occurs over the distance, d. Ray 1 reflects off of the upper atomic plane at an angle θ equal to its angle of incidence. Similarly, Ray 2 reflects off the lower atomic plane at the same angle θ.
- 29. BRAGG’S LAW
- 30. BRAGG’S LAW While Ray 2 is in the crystal, however, it travels a distance of 2a farther than Ray 1. If this distance 2a is equal to an integral number of wavelengths (nλ), then Rays 1 and 2 will be in phase on their exit from the crystal and constructive interference will occur.
- 31. BRAGG’S LAW How to prove ?? If the distance 2a is not an integral number of wavelengths, then destructive interference will occur and the waves will not be as strong as when they entered the crystal. Thus, the condition for constructive interference to occur is nλ = 2a nλ = 2a
- 32. BRAGG’S LAW But from trigonometry, we can figure out what the distance 2a is in terms of the spacing, d, between the atomic planes. a = d sin θ a = d sin θ or 2a = 2 d sin θ or 2a = 2 d sin θ nλ = 2d sin θ nλ = 2d sin θ Bragg's Law Bragg's Law
- 33. BRAGG’S LAW
- 34. MOSELEY’S LAW Henry Moseley Henry Moseley (1887–1915) (1887–1915)
- 35. MOSELEY’S LAW Moseley's Law describes the relationship Moseley's Law describes the relationship between atomic number and wavelength of a between atomic number and wavelength of a spectral line spectral line
- 36. MOSELEY’S LAW The constant σ (sigma) is equal to 1 for the K-lines and 7.4 for the more shielded L-lines. For energy this expression is approximately equivalent to
- 37. MOSELEY’S LAW
- 38. MOSELEY’S LAW
- 39. ~~ THE END ~~ “ Life is a succession of lessons, which must be lived to be understood” ~Ralph Wardo Emerson~
Editor's Notes
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