Review Exam 1 Flashcards
Mode of decay when high n/p+ ratio
B-
Mode of decay when too many neutrons
B-
Mode of decay when too many p+
Beta +/Positron emission
Most likely mode of decay for heavier elements
Alpha
Mode of decay for PET
Positron Emission
Mode of decay that can result in characteristic or Auger e-
Electron capture
Isotope
same # of p+, diff # neutrons
Isotone
Same # of neutrons, diff # p+
Isobar
Same # nucleons (both), diff p+
Formula for # of e- in a shell
2n^2
speed of light
3 x 10^8
The penetrability of the beam is the definition of?
Expressed by what 2 concepts?
Beam quality.
HVL or kVp
The # of photons
Quantity
Space charge effect
Space-charge effect creates a cloud of electrons caused by the electrons repelling each other, rather than the free flow of electrons. Can cause reduced beam output.
Positive side of x-ray tube
anode
negative side of x-ray tube
Cathode
What does cathode do?
Has tungsten filament that emits e- when heated (thermionic emission occurs here)
What does anode do?
Contains tungsten target; electrons hit target to produce x-rays.
Contains tungsten target; electrons hit target to produce x-rays.
Anode
Has tungsten filament that emits e- when heated (thermionic emission occurs here)
Cathode
3 reasons tungsten is chosen for the target?
- High Z (high production efficiency)
- High melting point
- Dissipates heat (prevents overheating)??
Explain anode-heel effect
The heel attenuates more electrons, so intensity on the heel side is decreased. The greater the target angle, the greater the attenuation of the beam.
Avg energy of ployenergetic beam is?
1/3 max photon energy
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.
Indirect ionization
Atoms of the target become ionized or excited
Direct action
Radiation interacts with other atoms to produce free radicals that then do the damage to critical targets.
Indirect action
Interaction dominant in tx range?
Compton
Interaction dominant in dx range?
Photoelectric
Probability of brems:
Z^2
Z of tungsten
74
Beam flatness is measured where?
10 cm depth in water, but only middle 80% of beam bc of penumbra.
Beam flatness is?
of photons
Beam flatness is quantity or quality?
Quantity
How does filtration affect the quality of the beam?
it hardens the beam
How does filtration affect the quantity of the beam?
Reduces it by 4x (to 1/4)
What does beam flatness look like deeper than 10 cm?
middle hump
What does beam flatness look like more shallow than 10 cm?
lateral horns
Linac Part: changes direction of horizontal beam to vertical
Bending Magnet
Linac Part: copper “pipe” held under high vacuum to remove air molecules, where e- are accelerated
Waveguide
Energy range for Grenz:
10-20kVp
Energy range for Contact therapy:
40-50kVp
Energy range for Superficial
50-150kVp
Energy range for orthovoltage
150-500kVp
Energy range for supervoltge
500kVp – 1MV
What is the input electron energy from the electron gun?
50 keV
Photon interaction most likely with High Z:
Coherent
Photoelectric Z and/or E:
Z^3/E^3
Pair production Z and/or E:
Z^2
Comp Z and/or E:
Ind of Z, depends on e-density
Coherent energy range:
<10KeV
Photelectric energy range:
60-90 KeV
Compton energy range:
25 KeV – 10 MeV
Pair production energy range:
> 1.02 MeV
Pneumonic for photon interaction:
CoPhoComPair
Coherent - inner or outer shell e-?
outer
Photelectric - inner or outer shell e-?
inner
Compton - inner or outer shell e-?
outer
Pair Production - inner or outer shell e-?
inner
What happens to penumbra if you increase SSD?
it increases
Klystron vs magnetron:
Cheaper
Shorter lifespan
Magnetron
Klystron vs magnetron:
Higher energy
More stable
More expensive
Klystron
Klystron vs magnetron:
More common in high energy Linacs
Klystron
What linear accelerator component sets the dose rate?
Modulator
What components in the linear accelerator treatment head change between electron and photon mode? Photon mode
Target and flattening filter is in the carousel when it is in photon mode.
What components in the linear accelerator treatment head change between electron and photon mode? Electron mode
Target is removed and scattering foil is put in
Klystron vs magnetron - which one amplifies microwaves?
Klystron
Klystron vs magnetron - which one generates microwaves?
magnetron
What machine component injects pulsed electrons to waveguide?
Electron gun