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Interaction of Electromagnetic Radiation with Matter

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Interaction of Electromagnetic Radiation with Matter

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    1. Interaction of Electromagnetic Radiation with Matter N E 162 – Lecture 5 Chapter 8 of Text book Jasmina Vujic

    2. Electromagnetic Radiation Its Nature and Properties: Dual Nature Wave properties: ???m??????1/s???c (m/s) = ?? Particle Properties: m = 0, E = h?, p = E/c = h?/c = h/? h?= 6.63 x 10-34 J s Photons = Neutral cannot steadily lose E as they penetrate matter can travel some distance d before interacting with any atom Photon can be absorbed - and it disappears, Photon can scatter, changing its direction w/ or w/o E-loss

    3. Electromagnetic spectrum

    4. Interaction of Photons with Matter Photoelectric Effect Compton Scattering Pair Production Photonuclear Reactions In addition, there are two processes with very small energy transfer: Thomson (elastic) scattering on a ‘free’ electron, redirection of low energy photon without change in energy Raleigh (coherent) scattering results from combined (coherent) action of an atom as a whole.

    5. Photoelectric Effect Photoelectron is detected whenever a ‘metal’ is illuminated by light of a frequency ??which is greater than a critical threshold frequency, irrespective of the intensity of light. This is in direct conflict with prediction based on the wave nature of light (if light is classical wave: the electron should absorb E continuously and at any intensity, it should be just a matter of time until electron has sufficient E to escape. Thus there should be no threshold frequency). Photoelectric effect could be explained if one assumed that the E carried by the incoming light came in discrete amounts. This amount only depends of ? and not on the intensity I =Einstein in 1905 ->Nobel Prize in 1921

    6. Photoelectric Effect

    7. Compton Scattering

    8. Compton Scattering ? = 00, h?’max = h?, Tmin = 0 T= 1800, h?’min = h?????? h??mc2) Tmax = h????h?’=2?h?????mc2/h??

    9. The Klein-Nishina Formula for differential scattering cross section Per electron and per atom

    10. The Klein-Nishina Formula coefficients Differential Klein-Nishina energy-transfer cross section: Differential Klein-Nishina energy-scattering cross section: The total Compton attenuation coefficient:

    11. Pair Production

    12. Photonuclear Reactions (?,n),(?,p), (?,2n), (?,?), (?,f) etc. These are the threshold reactions - photon must have enough energy to overcome the binding energy of the ejected nucleon. Need at least several MeV of photon energy. 206Pb(?,n)205Pb, Emin = 8 MeV

    13. Total linear attenuation coefficient Total mass attenuation coefficient

    14. Total mass energy transfer coefficient g takes into account the Bremsstrahlung contribution by the electrons freed in each process

    16. Photon attenuation

    17. Photon with Attenuation

    18. Photon fluence for monoenergetic beam

    19. Half-Value layer

    20. Point Source

    21. Tables of X-Ray Mass Attenuation Coefficients http://physics.nist.gov/PhysRefData/XrayMassCoef/cover.html Tables of X-Ray Mass Attenuation Coefficients and Mass Energy-Absorption Coefficients from 1 keV to 20 MeV for Elements Z = 1 to 92and 48 Additional Substances of Dosimetric Interest* J. H. Hubbell+ and S. M. Seltzer Ionizing Radiation Division, Physics Laboratory National Institute of Standards and Technology Gaithersburg, MD 20899

    22. Tables of X-Ray Mass Attenuation and Mass Energy Absorption Coefficients Abstract: Tables and graphs of the photon mass attenuation coefficient ??? and the mass energy-absorption coefficient ?en/? are presented for all of the elements Z = 1 to 92, and for 48 compounds and mixtures of radiological interest. The tables cover energies of the photon (x-ray, gamma ray, bremsstrahlung) from 1 keV to 20 MeV. The ??? values are taken from the current photon interaction database at the National Institute of Standards and Technology, and the ?en/? values are based on the new calculations by Seltzer described in Radiation Research 136, 147 (1993). These tables of ??? and ?en/? replace and extend the tables given by Hubbell in the International Journal of Applied Radiation and Isotopes 33, 1269 (1982).

    23. http://physics.nist.gov/PhysRefData/XrayMassCoef/ElemTab/z08.html

    24. http://physics.nist.gov/PhysRefData/XrayMassCoef/ElemTab/z19.html

    25. http://physics.nist.gov/PhysRefData/XrayMassCoef/ElemTab/z82.html

    26. http://physics.nist.gov/PhysRefData/XrayMassCoef/ComTab/bone.html

    27. Bone, Cortical (ICRU-44) - Composition Z/A = 0.51478 I (eV)=112.0 ?=1.920E+00 (g/cm3) I - mean excitation energy H-1: 0.034000 C-6: 0.155000 N-7: 0.042000 O-8: 0.435000 Na-11: 0.001000 Mg-12: 0.002000 P-15: 0.103000 S-16: 0.003000 Ca-20: 0.225000

    28. http://physics.nist.gov/PhysRefData/XrayMassCoef/ComTab/tissue.html

    29. Tissue, Soft (ICRU Four-Component) Z/A = 0.54975 I(eV)=74.9 ? = 1.000E+00 (g/cm3) 1: 0.101174 6: 0.111000 7: 0.026000 8: 0.761826

    30. http://physics.nist.gov/PhysRefData/XrayMassCoef/ComTab/water.html

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