Interaction of radiation with Matter - Dr. Vandana
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Interaction of radiation with Matter - Dr. Vandana
- 1. Presented By: Dr. Vandana, Dept. of Radiotherapy CSMMU, Lucknow
- 6. Ionizing ionizes [strips electrons from] atoms Non-Ionizing many other modes of interaction Electro Magnetic Spectrum (EMR)
- 12. Process Definition Attenuation Removal of radiation from the beam by the matter. Attenuation may occur due to scattering and absorption Absorption The taking up of the energy from the beam by the irradiated material. It is absorbed energy, which is important in producing the radiobiological effects in material or soft tissues. Scattering refers to a change in the direction of the photons and its contributes to both attenuation and absorption Transmission Any photon, which does not suffer the above processes is transmitted.
- 13. Photon High Speed Electrons
- 22. Material Density (g/cm 3 ) Atomic Number Number of Electrons per Gram Hydrogen 0.0000899 1 6.00 × 10 23 Carbon 2.25 6 3.01 × 10 23 Oxygen 0.001429 8 3.01 × 10 23 Aluminum 2.7 13 2.90 × 10 23 Copper 8.9 29 2.75 × 10 23 Lead 11.3 82 2.38 × 10 23 Effective Atomic Number Fat 0.916 5.92 3.48 × 10 23 Muscle 1.00 7.42 3.36 × 10 23 Water 1.00 7.42 3.34 × 10 23 Air 0.001293 7.64 3.01 × 10 23 Bone 1.85 13.8 3.00 × 10 23 Data from Johns HE, Cunningham JR. The physics of radiology. 3rd ed. Springfield, IL: Charles C Thomas, 1969.
- 31. Photon Energy (MeV) Relative Number of Interactions (%) P.E. ( τ / ρ ) Compton ( σ / ρ ) Pair Prod. ( π / ρ ) 0.01 95 5 0 0.026 50 50 0 0.060 7 93 0 0.150 0 100 0 4.00 0 94 6 10.00 0 77 23 24.00 0 50 50 100.00 0 16 84 Data from Johns HE, Cunningham JR. The physics of radiology. 3rd ed. Springfield, IL: Charles C Thomas, 1969.
- 32. Figure: Plot of total mass attenuation coefficient ( μ / ρ ) as a function of photon energy for lead and water. (from Johns HE, Cunningham JR. The physics of radiology, 3rd ed.) Energy Range Dominant Effects Up to 50KeV PE (Photo Electric) effect is important 60 KeV - 90 KeV Both PE & Compton effect 200 KeV - 4 MeV Compton effect Beyond 20 MeV Pair Production
- 33. Radiation type Direction Recoil electrons Travels forward, angle not more than 90°. Photoelectrons and electron pairs Travels forward Characteristic and annihilation radiation Isotropic i.e. equally in all directions Coherent scattered photons Isotropic Compton scatter photons In forward direction, small angle of scattering, lesser scattering for greater incident energy
- 47. Any Questions?
Editor's Notes
- In passing through matter, the intensity of the radiation is reduced (attenuation), both because some radiation energy is taken Up by material (absorption) and some is deflected from its original path to travel in a new direction (scattering). It should be noted that any effect of radiation on matter depends on how much energy that matter receives (absorbs) from the beam
- In passing through matter, the intensity of the radiation is reduced (attenuation), both because some radiation energy is taken Up by material (absorption) and some is deflected from its original path to travel in a new direction (scattering). It should be noted that any effect of radiation on matter depends on how much energy that matter receives (absorbs) from the beam
- So if we focus on the left hand side of the diagram, we can see two thin layers of the absorbant material, the First layer will decrease the intensity of the incident beam to half of its original value, which gets further reduced to its 1/4 th by the next layer of the material. Hence if we closely observe this behavior, each extra layer is reducing the intensity of the beam by its half. In this way, the beam is never completely attenuated and at all time there are chances of some residual radiation. This is of importance as this may affect the dose of the radiation in radio therapy.
- The wavelength change depends neither on the material being irradiated nor on the radiation energy, but only upon the angle through which the radiation is scattered.
- Explain the pair production, its uses (effects) in radio therapy, roles in radio therapy of compton effect, absorption, scattering, attenuation, photo electric.