Linear attenuation and absorption coefficients
What does the mass attenuation coefficient provides us with?
A means for comparing the stopping power of materials independent of the materials state.
What is the mass attenuation coefficient dependent on?
The medium and the photon energy
What is linear attenuation?
- Describes the probability of an event happening (Compton scattering or photoelectric absorption)
What affect does energy have on the linear scatter coefficient?
As energy increase the linear scatter coefficient decreases High energy radiation is therefore less scattered
What affect does photon energy have on the total beam energy?
As photon energy increases the energy gained by the electron increases which then increases the proportion of the beam energy taken by the electron For example: 30KeV photon retains 97% of its energy whereas 100KeV photon retains 91% of its energy.
What affect does photon energy have have on the linear attenuation coefficient?
As photon energy increases the linear attenuation increase
What are the two important processes involving diagnostic energies?
Photoelectric absorption Compton scattering
What does each of the important attenuation processes involving diagnostic energies provide?
Photoelectric absorption: Shows attenuation and complete absorption Compton scattering: Produces attenuation and partial absorption
What is the mass energy absorption coefficient?
It is the average fraction of kinetic energy of secondary charged particle (electrons) produced in photoelectric and compton interactions and lost in radiative processes (Bremsstrahlung)
How do you calculate mass attenuation coefficients?
Linear attenuation coefficient / density of the material
What is the linear scatter coefficient?
Part of the linear attenuation coefficient that accounts to Compton scattering which results in beam attenuation and energy loss
What is the linear absorption coefficient?
Part of the linear attenuation coefficient which accounts for absorption by photoelectric effect This is always less then the total attenuation of the photon beam which includes scatter.
What is the mass energy transfer coefficient used for?
Relates the energy Fluence to kerma
What does the linear attenuation coefficient depend on?
The absorbers atomic number and density. The photons energy.
What does the mass attenuation coefficient depend on?
The absorbers atomic number but independent of it density.
What is the mass energy transfer coefficient?
The energy transferred from the incident photons to the charged particles (electrons) of the absorber
What is the mass attenuation coefficient?
The fraction of the radiation removed from the beam of unit cross sectional area in a medium of unit mass The probability of an interaction of an x-ray quantum and a medium containing N atoms per unit volume which is proportional to density
What is the linear attenuation coefficient?
The fractional reduction in the intensity of the beam per unit thickness of the medium.
What is the total attenuation of the beam?
The sum of photoelectric absorption Compton scattering
What is the mass energy absorption coefficient used for?
Used to relate exposure to absorbed dose.