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Dosimetry > Useful Things to Memorize (Midterm) > Flashcards

Useful Things to Memorize (Midterm) Flashcards

1
Q

What is the mass of a proton, relative to an electron?

A

1836x

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2
Q

What’s the maximum angle of scattering for a large projectile relative to small target?

A

0.03 degrees

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3
Q

Maximum angle of scattering for two equal masses?

A

90 degrees

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4
Q

Maximum angle of scattering for a projectile much smaller than target.

A

180 degrees

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5
Q

What is the maximum energy lost to an electron by a proton

A

0.22% (4/1836)

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6
Q

Is the energy deposit of an electron with a large target big or small?

A

Very small

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7
Q

What make up the vast majority of interactions? Hard or Soft?

A

Soft

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8
Q

Angle between scatterings of two equal masses?

A

90 degrees

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9
Q

When is the only time that a charged particle has a magnetic field strength comparable to its electric field strength?

A

At relativistic speeds

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10
Q

Maximum kinetic energy of a photoelectron

A

hf - W

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11
Q

Total energy of a particle in special relativity

A

(gamma)mc^2 E = T + RestEnergy

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12
Q

Approximate rest energy of an Electron, Proton and Neutron

A

Electron - 0.511 MeV Proton - 938.3 MeV (say 1000) Neutron - 939.6 MeV (say 1000)

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13
Q

What is binding energy proportional to

A

Proportional to Z^2 Inversely proportional to n^2

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14
Q

How does an Auger electron form

A

A vacancy exists in a low shell An electron from an upper shell drops down to fill vacancy This releases energy, which excites an upper shell electron and ejects it

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15
Q

Low Z atoms fill K-shell vacancies primarily by ________ High Z atoms fill K-shell vacancies primarily by ___________

A

Auger Electron Emission Characteristic Radiation

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16
Q

What is the fluorescent yield for vacacnies higher than the L-Shell

A

Practically zero

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17
Q

Relation between hard angle of a sphere to area

A

= dA/r^2

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18
Q

For a flat faced detector, the hard angle is equal to what?

A

Area of detector/r^2

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19
Q

Equation for beam fluence of parallel beam

A

N/A where N is average number of particles

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20
Q

Fluence relation by the inverse square law

A

F1/F2 = r2^2/r1^2

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21
Q

What is the interaction cross section of the coulomb force

A

Infinite

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22
Q

What does the Probability of an interaction depend on?

A

number of tar/cc Interaction cross section dx or, (cross section)(N)/dA or Nint/N

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23
Q

What does the number of interactions rely on?

A

(n_targets/cc)(cross section)(Fluence)(dA)(dx)

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24
Q

What are the 3 types of interactions of a charged particle with an atomic electron?

A

Inelastic Scattering Inelastic Radiative scattering Electron capture

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25
Q

What is the approximate radius of an atom?

A

Bohr radius, 0.53 * 10^-8 cm

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26
Q

What is the differential cross section proportional to?

A

Z1^2 and Z2^2

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27
Q

What is the approximate total cross section for elastic p-p scattering

A

10^-19 cm^2

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28
Q

What is the approximate magnitude of the proton scattering by a heavy nucleus?

A

10^-19 cm^2

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29
Q

What is the primary mechanism by which projectile charged particles lose radiative energy?

A

Brensstrahlung Radiation

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30
Q

What approximation is made when a fast moving charged particle interacts with a charged target

A

Straight trajectory approximation

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31
Q

What is the classical interaction cross section with an electron proportional to?

A

Proportional to Z1^2 Inversley proportional to (beta)^2

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32
Q

At relativistic speeds, what is the approximate cross section of interactions with an electron? What about at non relativistic speeds?

A

10^-19 cm^2/e for relativistic 10^-16 cm^2/e for non relativistic

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33
Q

Why are small energy losses much more dominant?

A

Because they occur for large impact parameters. Large impact parameters have correspondingly large cross sections.

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34
Q

About how much smaller is collision stopping power with a nucleus relative than with an electron?

A

About 1000x smaller. So normally it is negligible, especially for heavy projectiles

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35
Q

True or false. For all charged particles, nuclei collision stopping power should be taken into account.

A

False. It’s negligible for all charged particles. Of course for a more accurate result, use it anyway if u have a table. But otherwise don’t bother.

36
Q

What are the impact parameters for Hard and Soft collisions.

A

Hard - small parameters Soft - larger parameters (This is why the VAST majority of interactions are soft)

37
Q

True or false. A proton will lose a substantial amount of its energy to an electron in a hard collision.

A

False. At most, it’s still only 0.22%. That FAR exceeds the BE of the electron usually, but its still nothing substantial to the proton.

38
Q

True or false. In a soft collision, energy transferring to electron is so small that BE and Excitations can’t be ignored.

A

True

39
Q

True or false. Atomic electrons can still be considered free is a soft collision.

A

False. These interactions are inelastic

40
Q

What is collision stopping power proportional to?

A

Proportional to Z1^2 Inversely proportional to (beta)^2

41
Q

Remember these graphs

A
42
Q

Why do projectiles usually not experience full interactions with the nucleus?

A

Due to shielding around the nucleus. You need to approach a distance between nucleus and K-shall orbital to not experience shielding.

43
Q

What is radiation yield defined as

A

(average energy lost to radiation)/(total beginning energy)

ONLY when projectile is brought to rest

44
Q

What is the general rule of thumb for electrons in water.

A

Above 0.5 MeV, you can approximate that electrons lose about 2 MeV/cm in water

45
Q

Remember this image of stopping powers for electrons in Water

A
46
Q

True or false. Heavy particles have much less range straggling than electrons because they deviate from a straight line significantly less.

A

True

47
Q

Just remember:

Energy is lost ONLY to electrons. These interactions determine the path length

Energy is NOT lost to the nucleus, BUT interactions with nucleus change directions, and therefore the range

A
48
Q

Difference between Rcsda and Rmax

A

Rcsda = Path length = range assuming NO nuclear scattering

Rmax = range with FEWEST nuclear scattering

49
Q

Ratio between Rmax/Rcsda for high Z atoms

A

0.5

50
Q

Units of dose

A

Gray = J/kg

51
Q

If the medium is thin, how much energy on average is lost to electrons?

A

SceP = Scet

52
Q

What method must be used to calculate energy lost in a thick medium

A

Residual Range Method

53
Q

Difference between slow and fast primary/secondary electrons

A

Slow - set in motion from soft collisions. Have almost no range. Get absorbef on site locally

Fast - Delta-rays. Energetic enough to leave interaction site. May possibly escape medium

54
Q

True or False, Brems radiation is absorbed in mass.

A

FALSE! It escapes. When calculating Eabs for dose, you do NOT include radiation energy

55
Q

What types of energy contribute to dose in dm

A

ONLY COLLISION ENERGY! Nothing else!

56
Q

At what depth that CPE-delta begin at for heavy particle beams?

A

At a depth greater than Rcsda for the most energetic possible secondary electrons

For electron beams, it’s impossible to predict.

57
Q

Dose of a beam to a material

A

D = (ScedxNparticles)/(mass traversed through)

58
Q

TEmax = Delta = energy of electrons that have an Rcsda less than the thickness of a material. Those will NOT leave

A

Then use that number and restrictive stopping power into dose equation

59
Q

Dose around some point for a thin medium

A

(fluence)(Sce/rho)

60
Q

Dose at any point

A

(fluence)(Sce/rho)for T at x

(this only applies for heavy particles due to very small straggling)

61
Q

Roughly where does the bragg peak occur

A

At a depth = Rcsda

62
Q

Roughly how much larger is dose at bragg peak than at surface?

A

5-10x larger

63
Q

Why is fluence of a heavy beam even for the most part then drop very heavily at the end?

A

Due to electron capture

64
Q

What is the naming convention for primary and secondary electrons

A

Primary electron is ALWAYS the higher of the two energies. By this sense Tlost mas = T/2

65
Q

Remember these diagrams of electron beams

A
66
Q

Dose at any point x can be calculated by using ___________. This is ALWAYS valid

A

(fluence)(restrictive stopping power)

67
Q

In general,

σcp int ____ σphoton int

A

>>

68
Q

Compton found that a scattered wave generally has ______ wavelength

A

longer

69
Q

Classical wave theory says that scattered waves are formed from

A

Charged particles oscillating due to Electric field from incoming EMR. The scattered wave has f = original wave

70
Q

For compton scattering

Low hf lose _____ % of their E

High hf lose ______ % of their E

A

small

CAN LOSE large

71
Q

When can electrons be considered free?

A

When Etr >> BE

72
Q

For a low hf, electron can’t be considered free. Instead we get two other interactions which are,

A

Rayleigh Scattering

PE effect

73
Q

Rayleigh scattering mechanism

A

Atomic electrons vibrate with same frequency as incoming wave

They radiate a scattered wave with that energy

Then they relax

There’s no excitation or ionization

TtrR = 0

74
Q

Mechanism of PE Effect

A

Absorption interaction

Atom absorbs photon, photoelectron is ejected

Vacancy exists in atom and needs to be filled

(nucleus also recoils, but very slightly, energy is negligible)

Vacancy is filled either through Auger electrons or characteristic x-rays

75
Q

Energy of a photo electron

A

Tpe = hf - BE

76
Q

Energy transferred to atom in PE Effect

A

Ttr = Tpe + TAuger e

77
Q

Approximately how many electrons/g are there for

Hydrogen

2 <= Z <= 20

Z > 20

A

NA

NA/2

<= NA/2

78
Q

Approximately what percent of e-e interactions have very small energy loss?

A

90%

79
Q

How come SC/rho for high Z is < low Z

A

Because as Z increases, I also increases and so does the delta correction factor. In addition, ne/g decreases

80
Q

Why do heavy charged particles lose essentially no energy to Bremmstrahlung radiation? (and thus SR = 0) for heavy charged particles.

A

Because the energy loss depends 1/m2

This is why electrons lose energy, but not charged particles.

81
Q

What is radiative stopping power proportional to?

A

Ztar2 and Eprof

82
Q

What is orbital velocity dependent on?

A

Zeff/n

83
Q

What is orbital radius dependent on?

A

a0n2/Zeff

84
Q

Radius of an approximated nucleus sphere

A

(1.2E-13)A1/3

85
Q

Quick approach to find mean free path length?

A

Recall: MFPL is the dx at which Pint = 1. Solve from there.

86
Q

Hard angle of a sphere

A

4π

87
Q

Regardless of photon energy, a photon scattered in a compton scatter has energy of approximately ____ for 90 degree scatters, and ____ for back scatters.

A
  1. 5 MeV
  2. 25 MeV

Dosimetry (1 decks)

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