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MRSC 2501 > Interactions with Matter > Flashcards

Interactions with Matter Flashcards

1
Q

What us the atomic number?

A

Z

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2
Q

What is the Z number

A

Atomic number. Number of protons (and e- in a stable atom).

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3
Q

Describe the energy state of electrons in the K shell

A

LOWEST energy state

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4
Q

which Shell typically has the highest EB?

A

K

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5
Q

How to calculate the number of electrons in a shell?

A

2n squared.

n = the shell

k=1, L=2, M=3 etc.

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6
Q

Which electrons determine the chemical properties of an atom?

A

Valence shell.

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7
Q

EB equation

A

F = 1/d squared.

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8
Q

Atomic emmisions = e- moving from shell levels. producing what?

A

Chara or Auger.

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9
Q

What is EB determined by

A

Z no. (Protons)

Distance

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10
Q

What is anotehr name for chara radiaiton?

A

Photon emission

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11
Q

What is de-excitation?

A

High shell e- filling a lower vacancy.

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12
Q

What is the fluorescent yield in the human body?

A

<10%

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13
Q

What is flourescent yield ?

A

P% that electron excitation will cause chara and not auger.

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14
Q

Do higher Z number materials have a higher or lower FY?

A

Higher.

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15
Q

What is the equation for Auger electron?

A

Auger E = E1-E2-E3

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16
Q

What bombards the atom during chara interection?

A

e-

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17
Q

What happens to incident electron and the ‘hit’ electron during PE
interection?

A

Incident : diverted

hit e-: EJECTED as PHOTOELECTRON and absorbed.

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18
Q

What is produced during ionisation?

A

An Ion pair

positive ion and negative electron.

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19
Q

What can also be produced during secondary ionisations?

A

Delta ray.

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20
Q

What causes an electron to slow down during bremms?

A

Electric force of positive nucleus.

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21
Q

What can the E of bremms equal?

A

0 and max E of incident electron.

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22
Q

Why is majority of bremms filtered out?

A

its of low E and only really increases dose.

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23
Q

What does intensity mean in nuclear physics?

A

E of beam.

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24
Q

How do charged particles typically interact?

A

by ionisation and excitation

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25
Q

Bremms less likely with alpha particles why?

A

They have more mass than e-

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26
Q

What factors effect range?

A 
E
Mass (of particle, less the more range)
Charge (less charge more range)
Density of medium (lead has more particles and is dense, more particles mean more chance of interactions and less range).
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27
Q

Will more E increase or decrease LET?

A

Decrease

28
Q

As range decrease will LET increase or decrease?

A

Increase

29
Q

What units does NM typically work in?

A

KEV

30
Q

Alpha particle typical E in air?

A

MEV

31
Q

What is units for LET?

A

KeV/mm

32
Q

An X-ray tube operating at a peak voltage of E, is equivalent to a
monoenergetic beam of?

A

E/3

33
Q

If an X-ray tube was running at 120kVp what is its equivalent keV? and why?

A

40 keV.

E/3

120/3 = 40

34
Q

What is attenuation?

A

Attenuation is the overall reduction in the

number of photons as it passes through matter

35
Q

In what 2 ways can photons be attenuated?

A

Absorption and scattering.

36
Q

What is Attenuation dependent on?

A

Thickness of material
Z no. of material
E of incident photon.

37
Q

What effects linera attenuation coefficient?

A

X ray E - reduces coefficient as E increases.

Z and density of material : increases coeffecient as these factors increase.

38
Q

Does a higher linear attenuation coefficient value indicate less or more attenuation?

A

More.

39
Q

What is the half value layer?

A

The Half Value Thickness (HVT) is the thickness of
absorber needed to reduce the incident radiation
intensity by a factor of two.

40
Q

What energies does coherent occur at and what is the P% of it occuring?

A

<200keV and 5%

41
Q

What occurs in coherent?

A

incident E is equal to e- means a photon of same incident E is emitted and scattered.

42
Q

The removal of an e- during PE effect causes what?

A

an e- to fill vacancy and therefore cause Auger or chara (more likely due to higher Z of medical materials).

43
Q

What happens to the incident e- during PE effect?

A

its ABSORBED and a photoelectron is emitted.

44
Q

Where does PE effect typically occur?

A

Inner shell e-

45
Q

When is PE most likely to occur?

A

when photon E is only SLIGHTLY HIGHER than EB.

46
Q

Why is there a decreased chance of PE if energy is too high?

A

Less chance photon will interact with an e-

47
Q

Why is PE important for x-rays?

A

need ABSORPTION for image detail but as E increases its less predominant e.g. CXR energies have increased compton effect , hence why a grid is needed.

48
Q

Why are aluminium and rare earth materials used as filters?

A

Al - removes low E photons (reduces patient dose)

Rare earth materials - remove high E photons (to reduce compton effect).

49
Q

Does a higher Z number increase or decrease chance of PE effect?

A

Increase it as more e- to interact with.

(Z)cubed.

50
Q

Tissues differ in atomic number, which result in differences in
absorption between tissues, this is called …?

A

differential absorption

51
Q

does bone absorb more or less radiation than soft tissue?

A

more.

52
Q

at what E does compton typically occur between?

A

30keV-30MeV

53
Q

What shell does compton typically occur in?

A

Outer

54
Q

What does compton typically interact with?

A

a free electron (low BE)

55
Q

Does absorption or scattering occur with compton?

A

both

56
Q

What is importnant about comton in a radiobiolgical sense?

A

The absorober becomes a SECONDARY RADIATION SOURCE

57
Q

what 3 things can occur with a scattered xray?

A

Leave patient
undergo further comton scattering
be absorbed through PE effect.

58
Q

at what energy does comton typically plateu at?

A

1.02 MeV

59
Q

Why is Z number not a factor with compton effect?

A

The EB is low so Proton count isnt as important.

ELECTRON DENSTIY HOWEVER IS IMPORTANT.

60
Q

Why are Higher E scatter xrays with less of scattering angle less favoruble in DR?

A

reduces image quality.

61
Q

why does comtpn plateu at around 1.02 MeV??

A

Pair Production becomes more predominant.

62
Q

Will pair production occur at 1 MEV? Justify answer

A

No. It only occurs at energies in excess of 1.02 MEV

63
Q

Describe process of Pair production

A

incident photon (gamma)

atom NUCLEUS

Positron and e- emitted. (0.511) x2 MEV

64
Q

What are the factors affecting Pair production

A

Photon E (increase will increase P% of pair production)

Z no. (increase will increase P% of pair production).
More protons increase electric field.

65
Q

Equation for P% of pair production

A

P% of PP = (E - 1.02)Z

66
Q

What modality is based on pair production

A

PET in Nuke med

MRSC 2501 (3 decks)

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