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Chamber Fluence effects: Pfl 
  • In-scattering
  • Obliquity
  • Not required for parallel-plate
Gradient Effects: Pgr
  • Errors in reading if a gradient is observed over the diameter of a cylindrical chamber
  • Not exhibited in parallel-plate
Recombination Effects: Pion
Account for ion recombination before collected by detector.
Polarity Effects: Ppol
  • Compton Current
  • Extracameral Current
  • More severe in electron beams than photon beams
Wall corrections: Pwall
Accounts for ionization effects occuring within the chamber wall if the wall is a different material than phantom.
Central Electrode Corrections: Pcel
Accounts for ionization effects occuring within the central electrode.
List all six chamber correction factors
  • Pfl
  • Pion
  • Pgr
  • Ppol
  • Pwall
  • Pcel
Work function of dry air, Wair/e
33.97 J/C
Geometric Efficiency, εf
εf = Ω / 4π
Intrinsic Efficiency, εi
εi = number of counts / number of incident particles
Minimum Detectable Activity, MDA
MDA = LLD / (εi * εf * t)
Lower Limit of Detection, LLD
LLD = 4.66σβ + 3
Standard Deviation, σμ
σμ = √μ
Type I error
False Positive
Type II error
False Negative
What is the probability of being within one STDev of the average in a Poisson distribution?
What is the probability of being within two STDevs of the average in a Poisson distribution?
What is the probability of being within three STDevs of the average in a Poisson distribution?
How much energy is required to create one ion pair in dry air?
Optical Density formula
OD = log(Io/It)

  • Io = Nominal light signal
  • It = Light signal transmitted through film 
When using radiochromic film, how long must you wait before reading, and why?
24 hours due to continuing reactions
What is the band gap (ionization energy) for a diode?
n-type semiconductor pentavalent is an example of what?
electron donor
p-type semiconductor trivalent is an example of what?
electron acceptor ("hole")
List advantages of using a diode
  • Can be made very small
  • Can directly measure %DD for electrons since the stopping power varies similar to water with energy
List disadvantages of using a diode
  • Sensitivity degrades with radiation damage
  • Temperature dependance (0.5% per °C)
  • Angular dependance
  • Field size dependance
  • Requires frequent recalibration
  • Strong energy dependance
List advantages of using an ion chamber
  • Good energy independance (40kV - 50MV)
  • Accurate to 1% with proper care
List disadvantages of using an ion chamber
  • Some dose rate dependance
  • Large size
By how much does 1 Gy raise water temperature, in °C?
2.39e-4 °C
List advantages and disadvantages of using a calorimeter

  • Absolute measurement (no calibration required)
  • Accurate to within 0.5%

  • Delicate and impractical for routine use 
What is a REM ball?
A Bonner sphere of diameter 10-12" that may be used to directly measure dose equivalent without knowing dose spectrum
How many ferric ions are produced per 100eV in Fricke dosimetry?
15.7 ferric ions per 100eV
Calculate the cumulative activity for a radioactive source
Acum = A/λ = 1.443*T1/2
Calculate the mean life of a radioactive source
τ = 1/λ = 1.443 * T1/2
Under what conditions does transient equilibrium occur?
T1/2,p >~ T1/2,d
Under what conditions does secular equilibrium occur?
T1/2,p >> T1/2,d
Under what decay conditions does equilibrium never occur?
T1/2,d > T1/2,p
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