Radiation Interactions Flashcards by Lydia Morrison

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

E’ = E0/(1+E0/0.511*(1-cos(theta)))

How well did you know this?

Not at all

Perfectly

What is the maximum allowable exposure for an unbadged worker?

Same as the public, TEDE = 1 mSv/year

How well did you know this?

Not at all

Perfectly

What is the energy of a photon given its wavelength?

E= hc/lambda

How well did you know this?

Not at all

Perfectly

What is Planck’s constant?

4.1357 eV/s

How well did you know this?

Not at all

Perfectly

How many Bq per Ci?

1 Ci = 3.7E10 Bq

How well did you know this?

Not at all

Perfectly

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

5000 ion pairs/mm

How well did you know this?

Not at all

Perfectly

What is an air kerma strength U?

1 micro-Gy*m^2/h

How well did you know this?

Not at all

Perfectly

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

Z^3/E^3

How well did you know this?

Not at all

Perfectly

What is the conversion between J and eV?

1.6E-19 J/eV

How well did you know this?

Not at all

Perfectly

How do you calculate the effective Z of a mixture?

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.

How well did you know this?

Not at all

Perfectly

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

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

How well did you know this?

Not at all

Perfectly

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

E*Z^2

How well did you know this?

Not at all

Perfectly

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

E/Z

How well did you know this?

Not at all

Perfectly

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

Srad/Scol ~ EZ9E-10

How well did you know this?

Not at all

Perfectly

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

1R = 2.58E-4 C/kg

How well did you know this?

Not at all

Perfectly

What is the W of air?

34 eV/ion pair

How well did you know this?

Not at all

Perfectly

What is the rest mass energy of a proton?

938 MeV

How well did you know this?

Not at all

Perfectly

What is the rest mass energy of an electron?

0.511 MeV

How do you calculate electron density?

Na*Z/A

What is Na?

6.022E23 atoms/mole

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

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

How are TAR and TMR related?

TMR = TAR/BSF

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

20,000 more times

How do you calculate optical density for film?

OD = log(I0/I)

What is required for transient equilibrium?

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

What is required for secular equilibrium?

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

Draw the gas amplification curve

What is exposure?

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.

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

Multiply by the ratio of mass attenuation coefficients

Why is electronic equilibrium (CPE) important?

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.

What are some common types of tough water?

solid water, plastic water, slab phantom, virtual water

How would you get a correction factor for solid water?

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

How equivalent are solid water phantoms to water?

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

What would be an ideal phantom?

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

What checks would I do for a new slab phantom?

- 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

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

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

What is the accuracy of TLD?

~2%

What is the accuracy of OSLD?

~3%

What is a pro of OSLD?

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

What is a big con of OSLD?

stronger energy dependence compared to TLD

Draw a photomultiplier tube

How accurate is TLD/OSLD?

~3%

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

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

What is our TrueBeam EPID resolution?

~0.5 mm