Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

physics > Interaction Processes > Flashcards

Interaction Processes Flashcards

You may prefer our related Brainscape-certified flashcards:
Physics 101 flashcards AP® Physics flashcards
1
Q

what is absorption

A

transfer to a medium

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what is scatter?

A

radiation which travels in a different direction compared to the primary beam

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what is TMAC

A

Total Mass Attenuation Coefficient
a fraction of the x-ray beam is removed, enabling comparison between the materials
it is independent within the material density

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what are the interaction processes?

A
  • Photoelectric absorption
  • Compton scatter
  • Elastic scattering
  • Pair production

With each interaction it has its own MAC

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Explain TMAC?

A
  • it is used to avoid TLAC
  • divide TLAC by density
  • u
  • p
  • value given for a medium which is independent of the density medium
  • TMAC = TLAC/ density
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Describe the process of elastic scattering?

A

photon collides with an electron within an atom, as it has no energy the electron can’t be released, so the photon rebounds in a different direction, causing scattering, with the atom recoiling.
There is NO energy transfer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

State the scatter/ absorption for ES

A
  • forward scatter
  • ONLY SCATTER NO ABSORPTION
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

where is ES found

A

at low energies

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Describe the process of PEA?

A

it is when the BE is equal to the photon energy (or a tiny bit greater), all the energy if transferred to the electron. The electron is ejected from an atom (photoelectron has its own KE). This has ionised an atom with a vacancy, the vacancy is filled (characteristic radiation)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what is the x-ray production process within PEA?

A

characteristic radiation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what happens within PEA if all energy is given up by the photon?

A

it no longer exists

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What does PEA depend on?

A

ENERGY DEPENDENT (large energy difference will cause it to be transparent, e will remain in the orbital)
number of protons, as it links with the number of energy levels/ electron shells. The photon must have the same or tiny but greater energy than the outer electron. The photon is absorbed by the inner electron

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

State the scatter/ absorption for PEA?

A

NO SCATTER, ONLY ABSORPTION

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

describe PEA in soft tissue?

A

low proton number = low IE
- low energy photons via CR, quickly absorbed
- increase in internal energy and temp increase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

describe PEA in high Z

A
  • most likely interaction
  • low BE
  • electron ejected from inner shell
  • CR
  • dependent on Z
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what is the by product of photoionisation?

A

photoelectrons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what is the relation with PEA and Z

A

PEA is directly proportional to Z^3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is PEA used in?

A

mammography

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

what is attentuation

A

absorption + scatter

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

what is the density in white regions

A

high density

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

what is the density in dark regions

A

low density, less absorption

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

what is the total dose

A

absorption of primary beam + absorption of scatter

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

is the energy in a secondary beam higher or lower than a primary

A

lower

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

what type of beam does PEA occur at

A

low energy beams

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What happens if the x-ray photon energy is too low

A

there is no PEA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

what happens in PEA if the energy is above the BE

A

PEA is reduced, incidence decreases as energy increases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

when does absorption occur

A

at high Z

28
Q

what happens when the photon energy increases

A

the likelihood of ionisation reduces until the next threshold is reached and an electron can be ejected at that level. A gradual fall leads to a sudden increase in PEA likelihood as photon energy increases until final IE is reached. Further increases results in a final decrease in PEA incidence.

29
Q

are soft photons good or bad

A

bad

30
Q

when does absorption energies occur?

A

when the attenuation suddenly increases, with the photon energy = BE
This is dependent on Z

31
Q

describe the relation with PEMAC?

A

PEMAC is inversely proportional to PE^3
small increase in PE produces a large decrease in PEA

32
Q

describe absorption edges

A
  • interaction with the M shell: x-ray photon = BE M-shell
  • PEA occurs
  • when photon energy> BE, PEA falls
  • until the energy = BE of L, then PEA occurs causing a peak in PEA
  • when energy > BE of L, PEA falls
  • until photon energy = BE of K then PEA occurs
33
Q

when does an absorption edge occur?

A

PE = BE

34
Q

why are absorption edges useful?

A

in detectors, contrast agents and planning

35
Q

does bone have a high or low Z

A

high, more likely to be absorbed

36
Q

state the relation with PEA and TMAC

A

PEA is part of TMAC
PEMAC is part of TMAC
PEMAC = t/ p (density)
t= PEA

37
Q

how does a high Z link with attenuation

A

they have more energies that a proton can react with, increasing the chances for a photon to remove an electron. A slight change in proton number causes a large change in beam intensity

38
Q

state the equation for PEMAC & Z

A

PEMAC directly proportional to Z^3

39
Q

state the equation for PEA and photon energy

A

PEA is inversely proportional to photon energy cubed

40
Q

what happens when there is a high Z

A

PEA is high

41
Q

what is the relationship between CS and energy

A

CS is inversely proportional to energy

42
Q

what is CS proportional to

A

electron density (dependent on density) greater electron density, greater CS

independent of Z

43
Q

what is uptake like with CS

A

fairly even with all tissues

44
Q

what direction of scatter is most common with CS

A

forward

45
Q

what is the Compton recoil electron?

A

the ejected electron may ionise other atoms before coming to rest

46
Q

what happens when PE increases?

A

CS decreases as photons are less likely to be defected off the path. Less CS occurs

47
Q

what happens to the photon in CS once it collides?

A

the photon changes direction, causing scattering, the loss of energy depends on the scattering angle

48
Q

what is the greatest loss in energy angle?

A

180

49
Q

describe the CS process?

A
  • the x-ray photon energy> BE (much greater)
  • photon transfers KE to the electron
50
Q

describe the scattering with CS

A

when the beam energy is high then forward scatter occurs, as less energy is transferred to the electron. It does occur in all directions up to 100 keV
Above 100 KeV CS decreases
Forward direction- over 1 MeV

51
Q

describe the relation with CEMAC

A

CEMAC = sigma (CS)/ p(density ) which is proportional to electron density/ energy

52
Q

describe the process of PP

A
  • high energy photons interact with the nuclear coulomb field producing a negatron and positron pair
  • this energy is converted into the rest mass and KE of negatron and positron
  • the mass of the positron and negatron is converted into two photons - ANNIHILATION ENERGY
53
Q

What is the energy of the positron and negatron for PP

A

1.02 MeV

54
Q

What is the photon energy within the PP

A

0.51 MeV each

55
Q

what happens when Z increases in PP

A

PP increases, more photons create a stronger columb field which chances of interaction increasing

56
Q

what is PP proportional to?

A

Z and E

57
Q

what is TMAC?

A

sum of all individual mass coefficients

58
Q

which interaction processes are energy dependent?

A

CS and PEA

59
Q

Is PEMAC less important with higher energy

A

yes

60
Q

Is CEMAC less important with higher energy

A

no

61
Q

what is the highest energy used in RT

A

PPMAC

62
Q

what happens to the dosimeter readings as attenuating materials increase in thickness

A

it reduces

63
Q

how is an exponential curve created

A

X-ray tube -> attenuating medium -> radiation measuring device

Aluminium is 0.5mm thick (each)
1. first recording is with no Al
2. from then onwards add 0.5 mm each time recording the reading and thickness

64
Q

what is the total linear attenuation coefficient

A

quantity related to attenuating properties of medium, different materials have different values

65
Q

do larger atoms have a greater chance of attenuation or lower

A

greater chance

66
Q

does more or less electrons increase attenuation chances

A

more

67
Q

what is the exponential constant

A

2.72

physics (25 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions