X-Ray Interactions with Matter PDF

X-ray Interactions with Matter RADT 1010 - Pass through - absorb Scatter - compton Loading… Rehmenent Attenuation don't memorize but understand Reduction in intensity of a beam of radiation as it traverses matter by either: Remna...

X-ray Interactions with Matter RADT 1010 - Pass through - absorb Scatter - compton Loading… Rehmenent Attenuation don't memorize but understand Reduction in intensity of a beam of radiation as it traverses matter by either: Remnant radiation scatter or absorption Scatter Change in direction of an x-ray photon due to an interaction with the medium with or without a Loading… - may lose may not lose loss of energy of the photon energy , ignore (could be scatter) - Absorption Transfer of energy from radiation to the medium; after transfer it is present in the medium initially as kinetic - energy of electrons Within Patient body ~ Five Basic Interactions: Photoelectric absorption* - most impact Coherent scattering* low energy Compton scattering* - most impact Pair production* high energy Photodisintegration* high energy * Photons either interact and change direction, or are absorbed  Photoelectric Effect o Absorption – total photon energy transferred o No scatter o Photon interacts with inner shell electron  X-ray energy going in Atom - kicked out transfers energy Incoming photon knocks out k shell electron; it is totally absorbed. electron L shell orbital electron ‘jumping orbitals’ and filling in K shell. Produces characteristic radiation when ‘jumping orbitals’.  Dropping down to be filled Loading… M shell orbital electron ‘jumping orbitals’ and filling in L shell. Produces characteristic radiation when ‘jumping orbitals’.  End Products of PE: 1. Photoelectron (negative ion absorbed in 1-2 mm of tissue (is 2. Characteristic radiation or secondary radiation – Low E and absorbed locally except for iodine and barium 3. Positive ion (the atom) (the atom is ionized)  happening Probability of PE # increases when the atomic increases o Increases as atomic number increases – roughly to the third power of the atomic number - PE ~ Z3 z = atomic Number o More likely when the photon energy and the binding energy are nearly the same - PE ~ 1 if binding is more , not enough to be absorbed E3 o Results in high contrast images and high patient dose  Compton Effect (known as scatter o Scatter o Photon interacts with outer shell electron  wave length mean in changed X-ray lost9 Scattered going in energy and interacting Photoelectric electron Illustration of high and low energy incoming x ray photons and angle of deflections. Note the higher energy x ray photon stays closer to its original path more energy doesn't change direction as much  End Products of CE: 1. Recoil or compton electron 2. Scattered photon 3. Positive ion (the atom)  Probability of CE # atomic o Independent of Z - - more likely to happen with higher z o Number of reactions decrease as photon energy increases - CE ~ 1 E o Results in low contrast images (bad) = lots of greys Scatter Nothing good about scatter !  Energy of the Scattered Photon o Depends upon the initial energy of the photon o Depends upon the angle of deflection o The larger the angle, the less energy the scattered photon has -greater angle lessenerg o t  As kV increases… * high kn low" contrast o PE decreases o CE increases - Scatter Scatter Less absorption, more scatter produced  Scatter Possible ~ Leakage - absorption X-ray Interactions with Matter Video Next class…