Chapter10XrayProduction[第10章透视生产和](80)

• For tungsten you can have one of 15 energies .
Discrete X-ray Spectrum
• There are 15 energies
• There are 5 vertical line representing K xrays.
• 4 representing L xrays.
Characteristic Radiation
• Characteristic xrays are produced by transitions of orbital electrons from the outer shell to the inner shell and is characteristic of the target element.
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.
Characteristic Radiation
• Only the Kcharacteristic x-rays are useful and contribute greatly to diagnostic radiographs.
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.
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.
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.
Bremsstrahlung Radiation
• And comes close to the nucleus.
• The strong positive charge of the nucleus causes it to slow, lose kinetic energy and change direction.
• Remaining represent lower energy outer shell electrons.
Discrete X-ray Spectrum
• K x-rays are the only characteristic x-rays of tungsten that have sufficient energy to be of value in radiography.
• Characteristic X-ray require 70 kVp or higher. Based upon the energy of the kshell electron.
• Bremsstrahlung X-rays can be produced at any projectile electron energy. In diagnostic radiography most of the x-rays are bremsstrahlung x-rays.
Characteristic Radiation
• When the projectile electron interacts with an inner shell electron of the target atom rather than with the outer shell electron, Characteristic Xradiation can be produced.
• Bremsstrahlung is a German word for braking.
• This energy of x-ray is dependent upon the amount of kinetic energy in the interaction.
Bremsstrahlung Radiation
• Interaction with the outer shell electrons produce heat
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.
Continuous X-ray Spectrum
• The Bremsstrahlung x-ray energies range from zero to a peak and back to zero.
• This is referred to as the Continuous X-ray Spectrum.
Continuous X-ray Spectrum
• The majority of the useful x-rays are in the continuous spectrum.
– These interactions happen at a very small depth of penetration into the target.
Electron Interaction with Target
• The electrons interact with either the orbital electrons or nucleus of the target atoms.
Chapter 10 X-ray Production & Chapter 11 X-ray Emissions
• Electron- Anode Interaction
– ImagBiblioteka ne 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.
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.
X-ray Emission Spectrum
• If a relative number of x-ray photons were plotted as a function of their energies we can analyze the x-ray emission spectrum.
Discrete X-ray Spectrum
• Characteristic x-rays have a precisely fixed or discrete energies.
• These energies are characteristic of the differences between electron binding energies of a particular element.
• This is different from Characteristic X-ray that have a specified energy.
• Low energy Bremsstrahlung x-ray result from slight interaction with the nucleus.
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.
• Understanding the x-ray emission spectra is key to understanding how changes in kVp, mA, time and filtration affects the optical density and contrast of the radiograph.