Week 3a Chapter 10 & 11 X-ray Production and Emission 79

Week 3a Chapter 10 & 11 X-ray Production and...

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Chapter 10 X-ray Production & Chapter 11 X-ray Emissions Electron- Anode Interaction Imagine the energy needed to propel electron from 0 to half the speed of light in one to three centimeters. The electrons that travel from the cathode to the anode are called projectile electrons.
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X-ray Production Electron- Anode Interaction When they strike the heavy metal atoms of the anode they interact with the atoms and transfer their kinetic energy to the target. These interactions happen at a very small depth of penetration into the target.
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Electron Interaction with Target The electrons interact with either the orbital electrons or nucleus of the target atoms. Interaction with the outer shell electrons produce heat
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Electron Interaction with Target There is no ionization but there is excitation. More than 99% of the kinetic energy of the projectile electron is converted to thermal energy.
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Electron Interaction with Target The production of heat increases directly with tube current. Through the diagnostic range, heat production increases directly with the increase of kVp.
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X-ray Efficiency The efficiency of x-ray production is independent of the tube current. Regardless of what mA setting is used, the x-ray production remains constant. The efficiency increases with the increasing projectile electron energy. At 60 keV only 0.5% of the energy is converted to x-rays, at 20 MeV, it is 70%.
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Characteristic Radiation When the projectile electron interacts with an inner shell electron of the target atom rather than with the outer shell electron, Characteristic X- radiation can be produced.
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Characteristic Radiation The interaction is sufficiently violent to Ionize the target atom by removing a K shell electron. A outer shell electron falls down to replace the lost electron.
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Characteristic Radiation The translation from outer shell electron to fill the hole in the K shell is accompanied by the emission of an x-ray photon. The K shell has an average energy of 69 keV.
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Characteristic Radiation Only the K- characteristic x-rays are useful and contribute greatly to diagnostic radiographs.
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Characteristic Radiation Characteristic x- rays are produced by transitions of orbital electrons from the outer shell to the inner shell and is characteristic of the target element.
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Bremsstrahlung Radiation Heat and Characteristic x-rays are the product of interaction with the electrons of the target atom. There is a third type of interaction.
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Bremsstrahlung Radiation The projectile electron can also interact with the nucleus of the target atom. The nucleus has a strong positive charge. The projectile electron misses all if the orbital electrons.
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Bremsstrahlung Radiation And comes close to the nucleus.
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