interaction of radiation with matter
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Interaction of Radiation with Matter. Topics . Radiation intensity Attenuation Linear attenuation coefficient Differential absorption Half-value layer Transmission Fraction X-ray Interaction Mechanism. Radiation Intensity. - PowerPoint PPT PresentationTRANSCRIPT
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Interaction of Radiation with Matter
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Topics Radiation intensityAttenuation Linear attenuation coefficientDifferential absorption Half-value layerTransmission FractionX-ray Interaction Mechanism
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Radiation IntensityThe intensity of radiation is defined as the rate of emitted energy from unit surface area through unit solid angle.
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AttenuationThe total reduction in the number of x-rays remaining in an x-ray beam after penetration through a given thickness of tissue.
Attenuation is the product of absorption and scattering.
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Linear Attenuation CoefficientThe attenuation coefficient is a quantity that characterizes how easily a material or medium can be penetrated by a beam of light, sound, particles, or other energy or matter.
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Differential Absorption
The difference in x-ray interaction.
Increases as the kVp is reduced.
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Differential absorption and attenuation of the x-ray beam depend on the following factors:The atomic number (Z) of the atoms in tissue.
The mass density of the atoms in tissue.
The x-ray energy.
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Half Value Layer (HVL)The Thickness of an absorber needed to reduce the intensity of the x-ray beam into half of its original value.
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X-ray Interaction MechanismCoherent ScatteringCompton ScatteringPhotoelectric EffectPair ProductionPhotodisintegration
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Coherent ScatteringEnergies below approximately 10 keV.
Sometimes called classical scattering or Thompson scattering, Rayleigh Scattering.
No ionization.
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Coherent Scattering
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Coherent scattering
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Compton EffectIn the Compton effect, the incident x-ray interacts with an outer shell electron and ejects it from the atom, thereby ionizing the atom. The ejected electron is called a Compton electron or a secondary electron.
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Compton EffectThe probability of the Compton effect is inversely proportional to x-ray energy (1/E) and independent of atomic number.
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Compton Effect
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Compton Effect
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Photoelectric EffectInteracts with inner shell electrons
X-rays are absorbed
The electron removed from an atom is called photoelectron.
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Photoelectric EffectThe probability if the photoelectric effect is inversely proportional to the third power of the x-ray energy (1/E)3.
The probability of photoelectric effect is directly proportional to the third power of the atomic number of the absorbing material (Z3).
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Photoelectric Effect
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Photoelectric Effect
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Atomic Number and K-shell Electron binding energy of radiologically important elements
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Effective Atomic Number of Materials Important to Radiologic Science
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Pair ProductionIncident electron interacts with the nuclear field.
The interaction between the x-ray and the nuclear field causes the x-ray to disappear, and in its place, two electrons appear, one positively charged (positron) and one negatively charged (electron).
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Pair Production
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Pair ProductionOccurs above 1.02 MeV
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PhotodisintegrationOccurs with x-ray energies above 10 MeV.
The nucleus is raised to an excited state and instantly emits a nucleon or other nuclear fragment.
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Photodisintegration
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Photodisintegration
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