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Rad 520 Physics > Calibration of Dose Output/ Radiation measurements > Flashcards

Calibration of Dose Output/ Radiation measurements Flashcards

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1
Q

Exposure is a measurement in ____

A

air

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2
Q

What are the stipulations for exposure?

A

Only under 3MeV
Only measured in air

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3
Q

The quantity of radiation for all types of ionizing radiation, (charged and uncharged), all materials and all energies

A

Absorbed dose

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4
Q

SI unit for absorbed dose

A

Gray

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5
Q

Traditional unit for absorbed dose

A

Rads

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6
Q

the biological effect of radiation depends on the dose and also type of radiation

A

Dose equivalent (H)

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7
Q

Used to assess risk from radiation and not radiation prescriptions?

A

Dose equivalent (H)

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8
Q

Traditional unit for (H)

A

rem

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9
Q

SI unit for (H)

A

Sievert (SV)

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10
Q

Quality Factor (Q)

A

accounts for how different radiation types affect cells differently

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11
Q

Unit of Q

A

Unitless

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12
Q

Q is similar to using___

A

RBE

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13
Q

Quality factor for xrays, gamma rays and electrons

A

1

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14
Q

Quality factor for neutrons, energy < 10keV

A

5

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15
Q

Quality factor for protons

A

2 or 1.1

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16
Q

Quality factor for alpha particles

A

20

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17
Q

the ratio of the dose of 250 kVp xrays to produce a specified biological effect to the dose of the given radiation to produce the same effect

A

RBE

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18
Q

when a volume is irradiated by photons, energy is given to charged particles by such photons

A

Collisional Kerma

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19
Q

The energy given to irradiation volume is ______ to energy given to charged particles

A

equal

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20
Q

???Kerma is _____ in the buildup region compared to absorbed dose

A

higher

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21
Q

After dmax, what happens to absorbed dose compared to kerma

A

it is higher than kerma

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22
Q

Deeper the buildup region

A

the greater the skin sparing

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23
Q

Look up redmaxing effect

A
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24
Q

F med (F factor) converts?

A

Roentgen to Rad (exposure to dose)

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25
Q

What is the mean energy required to produce an ion pair in dry air (constant for all electron energies)

A

W= 33.97 eV/ionpair

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26
Q

D=X * W/e

A

33.97 J/C * 2.58 x 10^-4 c/kgR = 0.876 rad/R

27
Q

Transmission factor in air

A

AQE

28
Q

Factor to take dose in air to dose in other media

A

Dair = 0.876 * X * A

29
Q

The energy loss by electrons per unit path length of a material

A

stopping power

30
Q

Two types of stopping power

A

Collisional and radiative

31
Q

Limitations in calculations from absorbed dose from exposure

A

derived from exposure in air
only valid for photons <3MeV

32
Q

Ratio for the number of photons or particles passing through a cross sectional area of a sphere

A

Fluence

33
Q

Units of fluence

A

1/cm^2 or cm^-2

34
Q

the ratio of radiant energy passing through a sphere of cross-sectional area

A

fluence energy

35
Q

Photons in a fluence can be

A

monoenergetic or polyenergetic

36
Q

How to find energy fluence

A

Take the number of photons x the keV of each and add together
i.e (photons/cm^2 * keV) + (photons/cm^2 * keV)

37
Q

KERMA

A

Kinetic energy released in Matter per unit mass

38
Q

energy transfer via radiative photons (bremsstrahlung (g))

A

Radiative KERMA

39
Q

collisions between photons and charged particles results in electrons which dissipate energy via collisions leading to ionization and excitation

A

Collisional KERMA

40
Q

KERMA units

A

Gy

40
Q

Kerma is defined

A

in any medium and indirectly ionizing radiation (Photons and neutrons)

41
Q

occurs when the number and energy of charged particles (electrons) are equal entering and exiting the measurement volume

A

Charged particle equilibrium (CPE)

42
Q

CPE is used to measure

A

Exposure (ion chambers)

43
Q

measure the charged produced in air volum by the electrons liberated by a photon beam

A

ion chamber (plus electrometer)

44
Q

Electonmeter has what type of voltage

A

bias

45
Q

pros of bias voltage

A

-keeps ions from recombining and not being read by ion chamber

46
Q

what is bias voltage

A

no ground and it isn’t held at a neutral voltage

47
Q

what are free air ion chambers used for

A

primary devices that check clinical devices

48
Q

A free air ion chamber is

A

an open system to the outside air

49
Q

combined before can be read by collecting device/ charge created by never collected

A

Ion Recombination

50
Q

Desirable ion chamber characteristics

A
  • minimal variation in sensitivity or exposure calibration factor over wide energy range
  • minimal dependence with direction of incident radiation
    -minimal stem leakage
    -minimal ion recombination
    -should be calibrated against a primary standare
51
Q

Cons of free-ion chambers

A

-air density changes, temp, pressure and humdity
-Ion recombination
-air attenuation of photons
-secondary chamber chambers calibrated against free air chamber use expousre calibraion factors

52
Q

Thimble chamber has what surrounding it

A

solid air shell; material made with equivalent Z as air

53
Q

Wall on thimble chamber has to be as thick as what?

A

as thick as max electron range, may need buildup cap for higher energies

54
Q

What must a thimble chamber have to measure exposure

A

-Have a defined cavity volume
-be air equivalent
-wall thickness to provide electronic equilibrium

55
Q

Thimble chamber must be calibrated at

A

a national lab that uses a FAC

56
Q

Not really in practice now, example is victoreen R meter

A

Condenser chamber

57
Q

Farmer chamber measures

A

photon exposure in the therapeutic energy range

58
Q

Farmer chamber wall is

A

pure graphite (tissue equivalent)

59
Q

Central electrode of farmer chamber

A

Pure aluminum

60
Q

Farmer chamber insulator is

A

polytricholorfluoroethylene

61
Q

Collection volume of farmer chamber

A

0.6cm^3

62
Q

Farmer chamber has ____ electrodes

A

Three

63
Q

Bias voltage volts

A

300

Rad 520 Physics (5 decks)

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