Interactions of Photons with Matter Flashcards
(8 cards)
What is HVL?
The thickness of an absorber that decreases the transmitted beam to half it’s initial intensity
HVL = ln2/LAC
What is the unit of cross-section?
Barn (=10^-28m^2)
What is the linear attenuation coefficient?
The probability per unit length for interaction
Determines the amount of x-rays removed from the beam over distance x
Responsible for contrast in an image
Function of the material (density and Z) and energy of the incident photons
As energy, density and Z increase, LAC increases
Total LAC is the sum of LAC due to photoelectric, Compton, Rayleigh
What is the mass attenuation coefficient?
The attenuation coefficient accounting for the density of the material
MAC = LAC/density
What is penetration power?
The average distance travelled before an interaction
What properties affect the cross-section for photoelectric effect interactions? Where do they originate?
Z, E and rho
High Z = more electrons = more likely to interact
High E = faster = less likely to interact
What is the cross-section?
The probability of interaction (likelihood of an interaction occurring)
What property that effects the photoelectric absorption is important in radiation protection?
Z - increase Z = increase cross section of pe, more photons absorbed, therefore more shielded from radiation because less get through (more are absorbed)
