Photon Interactions Flashcards
What is the energy level for coherent interaction
< 10 Kev
Coherent interaction is dependent on what?
High Z
Photoelectric effect is dependent on?
Z^3 / E^3
What is the energy level for photoelectric
60-90 Kev
what is Compton dependent on?
Independent of z #, depends on elector density
What energy level does Compton happen at?
25 Kev - 10mev
What energy does pair production happen at?
> 1.02 MeV
Pair production is dependent on?
Z^2
Coherent occurs at -??
Low energy & high Z
Interaction when a photon passes near an electron & sets it into a oscillation.
Coherent
The electron then gives Off the same energy at the same frequency as the incident photon.
Coherent scatter
Interaction where a photon passes near an e- and sets it into an oscillation.
Coherent scatter
Photon Interaction with an inner electron & ejects one the of orbital elections
Photoelectric effect
Interaction where a photon interacts with a inner electron & emits an electron & can produce characteristic xrays or auger electron
Photoelectric effect
With photoelectric effect as photon energy increases what happens to ejected electron
Less of refraction angle
What would be the probability of photoelectric effect when transitioning from a tungsten target to a molybdenum target
Molybdenum^3 / tungsten^3 ( decrease as target Z decreases )
An incoming photon hits an outer orbital electron & not all energy is transferred. This results in an ejected electron and a weaker photon.
Compton effect
Interaction where binding energy is less than incoming energy of photon
Compton effect
Electron density decreases slowly with
Increase in atomic number
Compton effect is dependent on
Electron density
Dominate interaction for rad therapy?
Compton effect
Compton effect: radiation that scattered at right angle energy?
0.511 meV
Compton effect: radiation scattered at 180° (backscatter) energy
O.255 meV
An incoming photon interaction with the nucleus & gives up all its energy in creating a position and a negatron -
Pair production
Threshold for pair production
1.02 meV
Likelyhood of pair production increases with
Z ^2
Nucleus absorbs a high energy photon (>10 MeV)
Photodisintegration
Energy causes nucleus to eject a particle, therefore changing its nucleon #
Photodisintegration
Quantity of Matter per unit volume (kg/m^3)
mass density
When mAS is doubled there is
Twice the probability of interaction as there are twice as many electrons
U/p shows us
Mass attenuation coefficient for photoelectric Compton and pair production combined
Total kinetic energy of all particles is the same before & after collision
Elastic collision
Some kinetic energy is lost to excitation, ionization or bremsstrahlung
Inelastic collision
Follow a zig-zag path as they are easily scattered due to low mass
Light charged particles: electRons / positRons
Follow a straight path, energy lost per unit path length is proportional to square of charge & inversely proportional to velocity
Heavy charged particles: protons, alpha particles - heavy nuclei
Electrons interact w matter similar to
Heavy particles, but they scatter much more & change direction more
Electrons lose energy by______&_________?
Collisional & radiative means
Electron interacts w/ another electron in matter
Collisional
Electron interacts with/ a positively changed nucleus in matter
Radiative
Stopping power of election
2mev/cm ( loses 2 meV per cm - 10 meV can only penetrate 5 cm )
Best absorbers for Neutron interactions
Hydrogenous materials (not high Z material )
Biological effects of radiation result primarily in damage to DNA
Direct radiation
Measure of the rate at which energy is transferred from ionizing radiation to soft tissue,
Linear energy transfer (let)
Radiation interacts w other atoms to produce free radicals that then do the damage to critical targets
Indirect acton
Atom or molecule that has an unimpaired orbital electron in the outer shell
Free radical
