Exam Review 9/4 PPT4 Flashcards
the process of an atom acquiring a positive
or negative charge
ionization
___ ionization - occurs when a particle (charged) such as an electron, proton or alpha particle collides with matter to produce a charged particle.
direct
___ ionization - occurs when an uncharged particle or radiation such as a photon or neutron liberate a directly ionizing particle when they interact with matter.
indirectly
the number of photons that pass through an
imaginary cross section of a sphere
fluence
the fluence per unit time
Fluence rate or flux density
Compton is dominant in the diagnostic or therapy energy range?
Therapy
Photelectric is dominant in the diagnostic or therapy energy range?
Diagnostic
What interaction occurs at Low photon Energy and High Z?
Coherent scatter (aka classical/Rayleigh)
Coherent scatter only occurs at energies ___
less than 10 KeV
the probability of what interaction increases by Z^3 and decreases by E^3?
Photoeltric Effect
What interaction is this? The photon interacts with an atom and ejects on of the orbital electrons. The photon gives 100% of its energy to the ejected electron.
Photelectric
in the ___ (type of interaction), a domino effect may then occur with the discrete energies being emitted and even giving off Auger electrons
photoelectric effect
in the photelectric effect, a domino effect may then occur with ___ being emitted and even giving off ___
discrete energies (characteristic x-ray), Auger electrons
Which of the following interactions could result in an Auger e-, scattered photon, ejected e-, etc
…
Which of the following interactions could result in an Auger e-, scattered photon, ejected e-, etc
..
Which of the following interactions could result in an Auger e-, scattered photon, ejected e-, etc
..
Compton occurs at what energies?
25KeV to 10MeV
What interaction is this? An incoming photon hits an outer orbital electron & not all energy is transferred. This results in an ejected electron and a weaker photon.
Compton
In the ___ the binding energy of the e- must be __ than the energy of the __
compton effect, e-, photon
interaction that is independent of Z
compton
Compton side scatter (right angle - 90 degrees) energy:
.511 MeV
Compton backscatter (180 degrees) energy:
.255MeV
Compton: If you increase E, angular dependence is ___, so photon scatter is also more ___
more forward-peaked, forward
What does this image show?
If you increase E, angular dependence is more forward-peaked, so photon scatter is also more forward
What does this graph show?
As energy increases, bone and tissue absorption become the same - poor contrast (why MV images are poor quality)
What interaction is this?
An incoming photon interacts with the nucleus and gives up all of its
energy in creating a positron and negatron
Pair production
Pair production probability increases with __.
Z^2
Pair production energy threshold:
1.02 MeV
Positron loses energy and combines with a free electron to give rise to two annihilation photons with .511MeV each.
Annihilation reaction
When ____ (type of interaction) occurs, it can recombine to form an annihilation reaction.
pair production
Reaction that occurs when a nucleus absorbs a high-energy photon and a particle is ejected from the nucleus
Photodisintegration
Photodisintegration energy threshold
> 10 MeV
y, n reaction occurs at what energy?
> 10 MV
y, n reaction occurs where ?
gantry head
y, n reaction causes?
unwanted neutron production (contamination)
y, n reaction is more common in what materials?
high Z
Elastic or inelastic collision?
Total kinetic energy of all particles is the same before and after collision
elastic
Elastic or inelastic collision?
some kinetic energy is lost and becomes excited or ionized
inelastic
Describe what is happening in the graph
For a small energy range, water is a better attenuator than lead
Compton is independent of Z
“Dose deposited increases very slowly at first, then very sharply near the end
of the range before dropping to almost zero value” describes?
Bragg Peak
kinetic energy loss per unit path-length
stopping power
stopping power formula
MeV/cm or 2Mev/cm
Biologic effects of radiation result primarily in damage to ___
DNA
atoms of the target become ionized or excited and lead t events resulting in biologic change
direct action
radiation interacts with other atoms to produce free radicals that then do the damage to critical target
indirect action (usually water)
measure of the rate at which energy is transferred from ionizing radiation to soft tissue
LET (linear energy transfer)
Coherent scatter
photoelectric
photoelectric
Coherent Scatter
Compton
Compton
Compton
Pair production
Pair production to annihilation reaction:
Positron loses energy and combines with a free electron to give rise to two annihilation photons with .511M
photodisintegration
Fluence rate or flux density
fluence per unit time
