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ABR Part III > Radiation Interactions > Flashcards

Radiation Interactions Flashcards

1
Q

What is the energy of a scattered photon after undergoing a Compton Scatter event?

A

E’ = E0/(1+E0/0.511*(1-cos(theta)))

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2
Q

What is the maximum allowable exposure for an unbadged worker?

A

Same as the public, TEDE = 1 mSv/year

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3
Q

What is the energy of a photon given its wavelength?

A

E= hc/lambda

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4
Q

What is Planck’s constant?

A

4.1357 eV/s

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5
Q

How many Bq per Ci?

A

1 Ci = 3.7E10 Bq

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6
Q

How densely ionizing are alpha particles? (i.e., how many ion pairs per mm?)

A

5000 ion pairs/mm

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7
Q

What is an air kerma strength U?

A

1 micro-Gy*m^2/h

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8
Q

How does the probability of a photoelectric interaction relate to Z of the absorber and E of the photon?

A

Z^3/E^3

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9
Q

What is the conversion between J and eV?

A

1.6E-19 J/eV

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10
Q

How do you calculate the effective Z of a mixture?

A

x = 2.94, Zeff = rootx( f1Z1^x + f2Z2^x + fn*Zn^x) where f1, f2, and fn are the fraction of protons contributed to the mixture by each component.

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11
Q

How does the probability of pair production vary with Z of the absorber?

A

Z*ln(E) with a minimum E threshold of 1.022 MeV

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12
Q

How does the rate of energy loss to bremsstrahlung interactions vary with E and Z?

A

E*Z^2

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13
Q

How does the rate of electron energy loss to collisional interactions vary with E and Z?

A

E/Z

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14
Q

How does the relative probability of radiation losses compared to collisional losses vary with E and Z? (efficiency of the target)

A

Srad/Scol ~ EZ9E-10

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15
Q

How do you convert 1 R to 1 C/kg?

A

1R = 2.58E-4 C/kg

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16
Q

What is the W of air?

A

34 eV/ion pair

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17
Q

What is the rest mass energy of a proton?

A

938 MeV

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18
Q

What is the rest mass energy of an electron?

19
Q

How do you calculate electron density?

20
Q

What is Na?

A

6.022E23 atoms/mole

21
Q

How much does a 6 MV beam get attenuated per cm of water?

A

3%/cm (note this is attenuation only, need to add inverse square on top of this.

22
Q

How are TAR and TMR related?

A

TMR = TAR/BSF

23
Q

How much more sensitive is a diode than an ion chamber?

A

20,000 more times

24
Q

How do you calculate optical density for film?

A

OD = log(I0/I)

25
Q

What is required for transient equilibrium?

A

T1/2 of the daughter must be shorter than T1/2 of the parent, but not insanely so

26
Q

What is required for secular equilibrium?

A

T1/2 of the daughter must be much, much shorter than T1/2 of the parent

27
Q

Draw the gas amplification curve

28
Q

What is exposure?

A

measure if ionization by photons in air - charge produced in air when all electrons liberated by photons in mass dm of air are completely stopped in air.

29
Q

How would you convert dose to air to dose to water?

A

Multiply by the ratio of mass attenuation coefficients

30
Q

Why is electronic equilibrium (CPE) important?

A

Because it is a requirement of cavity theory - allows us to measure dose in cavities that aren’t large enough for all ions to be completely stopped and collected in the cavity.

31
Q

What are some common types of tough water?

A

solid water, plastic water, slab phantom, virtual water

32
Q

How would you get a correction factor for solid water?

A

Take a measurement under the same conditions, and same depth, with the same chamber in water and in the phantom and your correction factor is the reading in water/reading in phantom

33
Q

How equivalent are solid water phantoms to water?

A

around +/- 1% different
Readings in phantom are hot for photons (phantom > water) and cold for electrons (phantom < water)

34
Q

What would be an ideal phantom?

A

One that gives you the same readings as water for all:
-modalities
-energies
-depths

35
Q

What checks would I do for a new slab phantom?

A
  • physical dimensions
  • physical density
  • CT it to make sure it’s homogeneous
  • radiological equivalence with water (either vs water or another slab phantom that has been previously validated)
  • measure and save conversion factors - may vary with modality and energy
36
Q

How do you validate the response of your detector/electrometer combinations?

A

strontium well - beta emitter with a half life of like 30 years and you can stick your chamber in there and expect your response by just accounting for the decay

37
Q

What is the accuracy of TLD?

38
Q

What is the accuracy of OSLD?

39
Q

What is a pro of OSLD?

A

it’s non-destructive readout so can be read out multiple times

40
Q

What is a big con of OSLD?

A

stronger energy dependence compared to TLD

41
Q

Draw a photomultiplier tube

42
Q

How accurate is TLD/OSLD?

43
Q

What device do we use for daily proton and photon QA?

A

daily QA3 - 5 ion chambers for flatness/symmetry/energy, 12 diodes for light/rad field coincidence

44
Q

What is our TrueBeam EPID resolution?

ABR Part III (13 decks)

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