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
Variation of dose in comparison to CAX dose at depth of 10cm is the definition for?
Flatness
The amount of time to deliver 1 cGy, with a 10x10 cm FS, to a specified depth (usually DMAX), at a distance of 100cm away is the definition of?
MU
The photon interacts with an atom and ejects on of the (inner) orbital electrons. The photon gives 100% of its energy to the ejected electron.
Photoelectric Effect
Auger and characteristic x-rays can occur with which photon interaction?
Photelectric
An incoming photon hits an outer orbital electron & not all energy is transferred. This results in an ejected electron and a weaker photon.
Compton
Annihilation reaction can happen after?
Pair production
An incoming photon interacts with the nucleus and gives up all of its energy in creating a positron and negatron.
Pair production
Modes of decay: Combination of two lighter nuclei
Nuclear Fusion
Modes of decay: Nucleus splits into two
Nuclear Fission
1 J/kg = ___ Rads = ___ Gy
100, 1
1 Gy = ___ cGy
100
1cGy = ___ rad = ___ Gy
1, 0.01
A photon passes near an electron and sets it into an oscillation. The oscillating e- then re-radiates the energy at the same frequency as
the incident photon.
Coherent scatter
MU: The amount of time to deliver ___, with a __ FS, to a specified depth (usually ___), at a distance of ___ away is the definition of?
1 cGy, 10x10 cm, DMAX, 100cm
What is meant by “good geometry”?
Put the detector where no scatter will be measured.
To measure beam flatness, all points must be within __?
3%
A voltage rectifier does what?
Prevents backflow (e- can only go in one direction)
When the beam goes through the mirror it is what type of filtration?
Inherent
Describe the difference in HVLs for monoenergitc beams vs polyenergetic beams:
Why?
Monoenergetic - all HVLs are the same thickness
Polyenergetic - Each subsequent HVL will be thicker due to beam hardening
How do you calculate the binding energy for the L or M-shell?
E = E (k-shell) - E (L or M-shell)
How does kVp affect output?
squared relationship
How mA or mAs affect output?
Directly proportional relationship
What does a flattening filter do to the avg energy of the beam? Why?
Increases it due to beam hardening
Flattening filter filters out __ photons?
low energy
Brems produces a monoenergetic or polyenergetic beam?
polyenergetic
Characteristic produces a monoenergetic or polyenergetic beam?
monoenergetic
Why doesn’t this graph start out at 0?
The beam has been hardened, so all low energy photons have been filtered out already.
Calculate the avg energy of this graph.
150keV x 1/3 = 50 keV
Explain what the peaks are.
Characteristic x-ray of different atoms that are emitted that occur when the electron drops from one orbital to the other after an e- has been ejected from that orbital.
The energy will always be the same for the same atom. The energy is “characteristic” of each atom.
A high speed electron passes near a
nucleus and is deflected from its pass after being acted upon by Coulomb forces. They lose energy, slow down and propagates the
energy through space.
Brems
“braking radiation”
Brems
Brems or Characteristic: Part or all of the electron’s energy may be given off
Brems
Electron can engage in multiple ___ interactions
Bremsstrahlung
Brems or Characteristic?
Brems
Brems or Characteristic: Direction of beam depends on energy.
Breams
The higher the energy of a brems beam, the ___ (direction) beam is.
more forward
Probability of brems varies with __ of the __.
Z^2, target
What determines the energy of the Brem beam?
How close it gets to nucleus and how much it makes it change its path
Brems or Characteristic?
Brems
An electron interacts with an atom by ejecting an orbital electron which leaves the atom ionized.
Characteristic
Describe how a characteristic x-ray occurs: (4 steps)
- An electron interacts with an atom by ejecting an orbital electron which leaves the atom ionized.
- A vacancy is created and an outer orbital electron will fall down to a
closer orbital - When an electron moves down there is an energy potential, which results in x-rays.
- Energy potential between orbital levels result in discrete (monoenergetic) energies
Characteristic is also called?
Fluoroscence
Characteristic
Electron capture and ___ are competing processes?
Beta +
Characteristic is favored in the __ Z range, while Auger is favored in __.
high, low
Which is more likely to occur, a characteristic x-ray or an Auger e-?
Characteristic
A is
Atomic mass #, # of nucleons
Z is
Atomic #, # of p+
Are photons directly or indirectly ionizing?
Indirectly
…
Fluence
…
Fluence rate or flux density
Which interaction independent of Z?
Compton
Identify the mode of decay:
Alpha
Identify the mode of decay:
B-
Identify the mode of decay:
B+ or positron emission
Identify the mode of decay:
E- capture
Identify the mode of decay: helium nucleus
Alpha
Identify the mode of decay: 2 protons, 2 neutrons, no electrons
Alpha
Identify the mode of decay:
Excess neutrons (high n/p) ratio, and it must be reduced. Done by emitting an electron.
B-
Identify the mode of decay:
neutron to proton
B-
Identify the mode of decay:
proton to neutron
B+ or e- capture
Identify the mode of decay:
Deficiency in neutrons
B+
Identify the mode of decay:
low n/p ratio
B+
Identify the mode of decay:
Orbital electron gets captured by nucleus and combines with a proton, transforming into a neutron
E- capture
Identify the mode of decay:
Alternative to positron decay; unstable nuclei deficient of neutrons seeks to increase n/p ratio.
E- capture
Identify the mode of decay:
Characteristic x-ray or Auger e- can be emitted
E- capture
Pair production can lead to ___.
An annihilation reaction.
Explain the relationship between Atomic #, n/p+ ratio and stability for heavy nuclei:
For heavy nuclei (atomic # > 20), stable nuclei have a n/p+ ratio of 1.4 to 1 (1.4 neutrons to 1 proton)
Explain this graph
For heavy nuclei (atomic # > 20), stable nuclei have a n/p+ ratio of 1.4 to 1 (1.4 neutrons to 1 proton)
Explain the relationship between Atomic #, n/p+ ratio and stability for lighter nuclei:
1:1 n/p+ ratio is stable for an atomic # < 20
When looking at an equation where decay is taking place, what defines the mode of decay?
The particle that is emitted from the reaction
What is the mean life formula?
Ta = 1.44 (T1/2)
What is the parent and the daughter?
The parent is the original and the daughter is what the parent decays into.
What nuclear reaction is used when making radioactive isotopes? (2 names)
alpha, p+
fusion
What nuclear reaction is this?
alpha, proton
What particle is this?
Deuteron
Nuclear reaction that occurs when high Z nuclei are bombarded by neutrons. After absorbing the neutrons, it splits into nuclei of lower Z, as well as more neutrons.
Fission
Fission
What are the scales used for each graph?
Left - linear
Right - logarithmic
What is the decay constant (definition)?
Portion of atoms decaying per unit time
B-
B+
proton
neutron
Alpha
e- and positron rest mass
9.11 x 10^-31
E- rest energy
0.511 MeV
rest mass for p+ and neutron
1.675 x 10^-27
deuteron rest mass
3.34 x 10^-27
alpha rest mass
6.65 x 10^-27 (approx. double deuteron)
charge?
-1
charge?
+1
charge?
+1
charge?
0
charge?
+1
charge?
+2
The process by which an unstable nucleus/atom attempts to become stable. This results in emitting radiation (usually a particle) and the transformation of the unstable atom into a different more stable atom.
Radioactive decay
What linac component is shown?
Klystron
What linac component is shown?
Magnetron
What linac component is shown?
Klystron
Explain this graph.
Air KERMA is higher in the buildup region. Absorbed dose is higher after the buildup region due to also measuring backscatter.
2 modes of decay that are competing processes:
B+ and electron capture
