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FRCR Physics > Radiation Physics > Flashcards

Radiation Physics Flashcards

1
Q

What is the valence shell concerned with?

A

It is concerned with the chemical, thermal, optical and electrical properties of the element.

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2
Q

What is the relative mass, charge of alpha particle?

A

Relative mass of 4 and relative charge of +2

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3
Q

What is the binding energy?

A

This is the energy expended in completely removing the electron from the atom against the attractive force of the positive nucleus
This is expressed in eV.

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4
Q

What does the binding energy depend on?q

A

Depends on the shell- Ek>EL> Em

And on the element, increasing as the atomic no increases,

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5
Q

What is an excited atom?

A

This is when an electron is raised from one shell to another further out. This involves the expenditure of energy, therefore the atom has more energy than normal.

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6
Q

T/F

The photons travel in a straight line

A

True

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7
Q

T/F?

The wavelength and frequency are proportional to each other.

A

False
They are inversely proportional
Wavelength x frequency = constant

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8
Q 
Radio waves
Microwaves
Infrared
Visible light
Ultraviolet
X and gamma rays
A

In the order of increasing photon energy, increasing frequency and decreasing wavelength

Photon energy is proportional to frequency

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9
Q

T/F?

Photon energy is proportional to frequency

A

True

The constant of proportionality is called the Planck’s constant- h

E= hf

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10
Q

What is the relationship between the intensity and amplitude?

A

Intensity is proportional to the square of amplitude

I = a2*

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11
Q

how are x-rays produced?

A

these are produced when fast moving e are suddenly stopped by impact on a metal target.
The kinetic energy is converted into 1% x ray and 99% heat.

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12
Q

describe the anatomy of an X-ray tube;

A

its ade up of:

  • -ve catode, incorporates a fine tungsten coil or filament
  • +ve anode, incorporates a smooth flat metal target, usually of tungsten
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13
Q

explain the process of electron production in X-ray tube.

A

the filament is heated by passing an electrical current through it to a temp at which it is white hot.
this causes e to be emitted by the process of thermionic emission.
they get attracted by the positive anode. because of vacuum they bombard the target with high velocity

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14
Q

the min and max photon energy in bremst are influenced by what?

A

the min is affected by the filtration added and the max depends only on the KV

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15
Q

the most common photon energy is typically between ….. and ….. of the kv

A

1/3 and 1/2

the effective energy is greater between 50-60% of the max

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16
Q

in the range of 60-120 kv the intensity of the emitted x ray is proportional to ……. x…….. the exact exponent being dependent on the filtration.

A

kv*2 x mA

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17
Q

define the efficiency of x ray production;

A

this is the ratio of x ray output to electrical power supplied.
this increases with the kv.
the efficiency is also greater the higher the atomic number of the target.

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18
Q

what is the effect of increasing kv on effective energies and the ∑ no of x ray photons?

A

increasing the kv increases the maximum and effective energies and the total number of x ray photons.

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19
Q

what is the effect of increasing mA on the shape of the spectrum or the characteristic radiation?

A

increasing the mA has no effect on the shape of the spectrum

it increases the output of both bremss and characteristic radiation.

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20
Q

what is the effect of changing he target to one of the lower atomic number?

A

it reduces the output of bremss but otherwise does not affect its spectrum unless the filtration is also changed. the photon energy of the characteristic lines will be less.

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21
Q

compare the x ray produced by the 3 phase vs single phase generators;

A

a three phase generator produces more x ray and at higher energies than those produced by the single phase pulsating potential generator when operated at the same values of kv and mA.

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22
Q

what are the three possible fates of individual photons?

A

transmission
absorption
scatter

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23
Q

x ray absorption and scattering processes are……..processes

A

stochastic, governed by law of chance.

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24
Q

the x ray image is formed by……… photons.

what sort of photons represent attenuation by the matter.

A

the x ray image is formed by the transmitted photons.

those that are absorbed or scattered represent attenuation by matter.

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25
Q

define attenuation;

A

this is the fact that there are fewer photons in the emerging beam than in the beam entering the material.

absorbed + scattered = attenuated photons.

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26
Q

define HVL

A

this is the thickness of the material that reduces the intensity of the narrow beam to half its original value.
The HVL is a measure of the penetrating power or the effective energy of the beam

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27
Q

what is the relationship between the HVL and the LAC

A

LAC = 0.693/HVL

ie LAC is inversely proportional to HVL

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28
Q

what does LAC measure?

A

it measures the probability of that a photon interacts (ie absorbed or scattered) per unit length of the path it travels in a specified material.

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29
Q

T/F?

The LAC applies only to narrow mono-energetic beam

A

true

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30
Q

T/F?

The HVL can be used for beams that are not monoenergetic but applies only to narrow beams.

A

true

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31
Q

what could cause the HVL to decrease and LAC to increase?

A

the density of the material increases
the atomic number increases
the photon energy of the radiation decreases

eg Pb is more effective than Al at absorbing x rays because of its higher density and atomic number

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32
Q

what is mass attenuation coefficient?

A

MAC = LAC/ density

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33
Q

what does the MAC depend on?

A

it depends only on the atomic number of the material and the photon energy.

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34
Q

T/F?

MAC depends on density

A

false
MAC is independent of the density.
it only depends on the atomic number and photon energy.

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35
Q

what is the typical HVL value for a typical diagnostic beam in tissue/ bone and lead?

A

tissue - 30 mm
bone - 12 mm
lead- 0.15 mm

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36
Q

what is beam hardeing?

A

as the beam penetrates the material it becomes more homogenous
the proportion of higher energy photons in the beam increases, this process is known as beam hardening.The average energy of the photon increases , the beam becomes harder and more penetrating.

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37
Q

T/F?

the second HVL which reduces the beam intensity from 50 to 25% is greater than the first HVL which reduces it from 100 to 50%

A

true

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38
Q

name the three interaction process between x rays and matter;

A
  1. interaction with a loosely bound or free electron - Compton effect/ inelastic/ non coherent scattering
  2. interactions with inner shell or bound electrons - photoelectric absorption photon is totally absorbed.
  3. interactions with a bound electron- elastic scatter
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39
Q

what is the angle of scatter ø?

A

this is the angle between the scattered ray and the incident ray.
PHOTONS may be scattered in ALL directions
ELECTRONS are projected sideways and forward direction.

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40
Q

what is the effect of greater the angle of scatter on the range of the recoil electron?

A

the greater the angle of scatter= the greater the energy and range of the recoil electron = the greater the loss of energy ( and increase of wavelength) of the scattered photon

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41
Q

what is the effect of scatter angle on the photon energy. Please compare back/side/forward

A

the backscattered photon, ø =180, is less energetic and is softer than a side scattered photon when ø = 90, which in turn is softer than a forward scattered photon ø = 0

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42
Q

what is the effect of having a high initial photon energy?

A

The higher the initial photon energy, the greater the remaining photon energy of the scattered radiation and the more penetrating it is
also, the greater the energy that is carried off by the recoil electron and the greater its range.

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43
Q

when is the softening effect of compton is greatest?

A

with large scattering angles as well as with high energy x rays.

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44
Q

the probability that the compton process will occur is proportional to what?

A

it is proportional to physical density of the material
and to electron density

It is independent of the atomic number
~ 1/E

45
Q

T/F?

the compton process is dependent on te atomic number

A

false

it is independent

46
Q

T/F?
The compton LAC ~ density/ E
and is independent of Z

A

true

47
Q

the mass attenuation coefficient for the Compton effect is the same within … in air, tissue, bone, contrast and lead.

A

10%

*** in the diagnostic energy range no more than 20% of the energy is absorbed, the rest being scattered.

48
Q

in low Z material such as tissue , the characteristic radiation has very …… energy

A

low

it is absorbed immediately with ejection of Auger electron
photoelectric absorption in such material is complete absorption.

49
Q

the characteristic rays from barium and iodine may be sufficiently energetic to leave the patient.
in this respect, they act like ……..scattered rays.

A

Compton scattered rays

50
Q

when is photoelectric absorption more likely to happen?

A

the more tightly the e is bound to the atom and the nearer the photon energy is to its binding energy , the more likely photoelectric absorption is to happen- so long as the photon energy is greater than the binding energy-

51
Q

the chance of photoelectric absorption increases with…

A

it increases as the atomic number of the material increases
it is also proportional to the density of the material

~density x Z3/E3

52
Q

what is the effective atomic number?

A

this is the weighted average of the atomic numbers of the constituent element.

ie cube root of weighted sum of the cubes of the atomic number of the constituent

53
Q

T/F?

the compton and photoelectric interactions depend on the lecular confugurations.

A

false

it depends on the effective atomic number.

54
Q

T/F?

the higher the atomic number he greater is the Ek and the greater is the photon energy at which the edge occurs

A

true

55
Q

what is the us of absorption edge?

A

it is important in choosing materials for x ray beam filters , contrast media, and imaging phosphors

56
Q

T/F?

the compton coefficient is dependent on Z

A

false

it is independent of the Z and little affected by E

57
Q

where would the photoelectric absorption predominates?

A

photoelectric absorption is more important in high Z material and low energy photons.

58
Q

what is the photon energy at which the two processes (compton and ph.e.) are equally important in tissue, that

A

30 kev for air, water, and tissue
50 kev for Al and bone
300 kev for iodine and barium
500 kev for lead

59
Q

what is the predominant process for air, water, and soft tissue?

A

Comptton

60
Q

compton process is the predominant process for what?

A

for air, water and soft tissue

61
Q

the photoelectric process is the predominant process for what?

A

for contrast media, lead and material used in film, screen, and other imaging devices.

62
Q

what process is used inbone?

A

both are important inbone.

63
Q

what is an elastic scatter/ Rayleigh scatter/ classical scatter?

A

the photon bounces off an e that is firmly bound to its parent atom.
it occurs if the photon energy is less than the binding energy of the e and with diminishng probability at increased energies.

No ionisation, no secondary electron.
little sig in radiology

64
Q

secondary radiation refers to ……

A

compton scattered radiation.

65
Q

when travelling through air the electron loses an average of ….. ev per ion pair formed.

A

34 ev

66
Q

T/F?

the range is proportional to the density of the material

A

false

its inversely proportional

67
Q

T/F?

Both beta and alpha particles are charged particles and are directly ionising.

A

true

68
Q

T/F?

x and gamma rays are directly ionising.

A

false

they are indirectly ionising, through their secondary electrons.

69
Q

T/F?

neutrons ionise tissue indirectly through collisions with hydrogen nuclei.

A

true

70
Q

what is the purpose of filtration?

A

to remove lower energy photons before they reach the skin.

71
Q

what is added/additional filtration?

A

a uniform flat sheet of metal usually Al is placed bwn the X-ray tube and the patient.

72
Q

what attenuation process is used in additional filtration?

A

photoelectric absorption

73
Q

how would you minimise inherent filtration?

A

a tube with a window of beryllium (Z = 4) instead of glass is used.

74
Q

define inherent filtration.

A

filtering within the target and by the window of tube housing, he insulating oil, and the glass insert. the combined effect of these component is expressed as thickness of Al, usu 1mm, and its called inherent filtration.

75
Q

what is the total filtration?what is it usually?

A

∑ inherent + added filtration

at least 2.5 mm Al

76
Q

what are the characteristics of a good filter?

A

the atomic number should be sufficiently high so that the photoelectric absorption predominates.

77
Q

what would happen to filtration if filter material’s atomic number is too high?

A

filter might actually soften the beam.

78
Q

name couple of good / adequate filter material;

A

Al- Z =13, Ek= 1.6 KeV
copper- Z = 29 with added filter thickness in the range of 0.1-0.3 mm

Cu is more efficient but it produces 9 kev characteristic x rays. these must be absorbed by a backing filter of Al on the patient’s side of the compound filter.

79
Q

what is the problem wit copper?

A

it produces 9 kev characteristic x rays. these must be absorbed by a backing filter of Al on the patient’s side of the compound filter.

80
Q

what is the effect of filtration?

A

a filter attenuates the lower energy x rays more in proportion to higher energy x rays.
it therefore increases the penetrating power- HVL- of the beam at the cost of reducing its intensity.
ir reduces the skin dose with no effect on the image.

81
Q

what is the effect of increasing filteration:

A
  1. causes the continuous x ray spectrum to shrink and move to the right.
  2. it increases the minimum and effective photon energies but does not affect the max photon energy.
  3. It reduces the area of spectrum and the total output of x rays.
  4. it increases the exit dose : entry dose ratio or film dose : skin dose ratio
82
Q

T/F?

above a certain thickness, there is no gain from increasing the filtration

A

true

as the output is reduced with little improvement in the patient dose or HVL.

83
Q

where would you use K edge filters?

A

mammography

84
Q

what is K edge filters? what do they filter?

A

they remove both high and low energy x rays but they are transparent to energies just below the k edge

85
Q

what is a wedge filter?

A

a shaped filter may be attached to the tbe to make the exposure across the film more uniform and compensate for the large difference in transmission .

86
Q

define absorbed dose;

A

this is the energy that is deposited per unit mass of the stated material in joules /kg

SI unit = Gray, Gy
1Gy = 1 J/Kg

87
Q

rad was the old SI unit for absorbed dose. What is 1 rad in Gy?

A

1 Gy = 100 rad

88
Q

what is kerma measured in?

A

Gray

89
Q

what is the differece between absorbed dose and kerma?

A

kerma is the energy transferred per unit mass, whereas absorbed dose is the energy deposited by secondary electrons.

for diagnostic radiology, they can be used interchangably.

90
Q

what does the exposure apply to?

A

it applies to x and gamma rays only.

kerma also applies to neutrons.

91
Q

what process predominates in :

  • muscle
  • compact bone
A
  • muscle : compton process

- compact bone: photoelectric

92
Q

what measures the ionisation chamber?

A

electrometer

93
Q

go through ionisation chamber on p 17/18/19

A

..

94
Q

what would DAP use?

A

they use an ionisation chamber mounted on the collimator of the X-ray tube.

95
Q

how do we measure the radiation dose?

A

lithium fluoride thermoluminescence dosimeters used for both personal dosimetry and patient dosimetry.

  • the photographic effect in silver bromide used in film badge.
  • photoconductivity in silicon diodes to be used in direct reading electronic personal dosimeter and dosimeters used for quality assurance
96
Q

films and diodes use …….atomic number. so that factors to correct their reading to air kerma are dependent on the energy spectrum.

to provide meaningful results , they are used with…… so that their readings are correctly interpreted.

A

high

filters.

97
Q

what is the relationship between intensity and Kv and mA?

A

Intensity∞ kv2*
intensity ∞ mA
inversely proportional to square of distance F from a point source.

Air kerma rate ∞ kv2* x mA / F2*

98
Q

fine qualty

A

this is the term used to describe the penetrating power of an x ray beam.

99
Q

T/F

the greater the HVL, the greater the effective energy

A

true

100
Q

what is the effect of increasing Kv on HVL?
effect of constant vs pulsating potential on HVL?
effect of filtration on HVL
effect of mA or exposure on HVL

A

HVL increases :
-as the applied kv is incresed
- for constant potential than pulsating potential.
- as the filtration increases
HVL unaffected by mA or exposure and distance from the target.

101
Q

define luminescence;

A

this is the process in which a material absorbs energy from an external source and re emits that energy in the form of visible light.
a property that has luminescent properties are described as phosphors.

102
Q

what are the two types of luminenscence?

A

2 types:

  1. fluorescence , this is the emission of light following energy iput
  2. hosphorescence- which describes delayed light emission referred to as afterglow.
103
Q

go through thermoluminescent on p 20a

A

..

104
Q

a material that has luminescent properties is described as ….

A

phosphor

105
Q

what is a scintillants

A

these are crystalline materials with luminescent properties that are used for detection of gamma radiation.

106
Q

thermoluminescent vs photostimulable

A

thermoluminescent : light is emitted following heating of irradiated material
Photostimulable : light is emitted when the irradiated phosphor is exposed to light.
either process can be used for measurement of radiation dose.

107
Q

the intensity of light emitted from a phosphor is proportional to the energy absorbed from x ray or gamma ray which in itself is proportional to intensity of the beam itself.

A

true

108
Q

define excitation

A

this is the process that results in electron being raised from the valence into the conduction band

109
Q

What is a nucleon?

A

Protons and neutronsw

FRCR Physics (9 decks)

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