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3. Radiology > 3.1 - Physics Basics > Flashcards

3.1 - Physics Basics Flashcards

1
Q

What are radiographs created by?

A

X-ray photons that are projected through and object and then interact with the receptor on other side to form an image

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2
Q

What is black in radiographs?

A

Air

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3
Q

What is a lighter colour in radiographs?

A

dense enamel

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4
Q

What colour is amalgam in radiographs?

A

WHite

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5
Q

What colour is skin of cheek?

A

Darker image - like gingival

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6
Q

What to radiographs allow us to do?

A

Aid diagnosis, planning and monitoring

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7
Q

What are x-rays?

A

Type of EM radiation

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8
Q

What is electromagnetic radiation?

A

Flow of energy from one point to another and is created by simultaneously varying electric and magnetic fields

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9
Q

Describe properties of x-rays?

A

No mass
No charge
Travels at speed of light
Can travel in a vacuum

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10
Q

What is the electromagnetic spectrum?

A

Spectrum of all the types of EM radiation and they all have different properties depending on energy wavelength and freq

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11
Q

What does a shorter wavelength equal?

A

Higher frequency and higher energy

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12
Q

What does a longer wavelength equal?

A

lower frequency

lower energy

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13
Q

What is a wavelength

A

When top of wave moves up and down once

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14
Q

What is frequency?

A

How many times the wave shape repeats per unit time and is measured in hertz

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15
Q

What is freq measured in?

A

Hertz

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16
Q

What does one hertz equal?

A

One cycle per second

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17
Q

What is wavelength?

A

The distance over which the wave shape repeats itself and is in m

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18
Q

What is speed?

A

Freq x wavelength

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19
Q

What is speed of all EM radiation?

A

3x10 power 8

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20
Q

What happens as wavelength decreases?

A

Freq increases

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21
Q

What are photons?

A

Packets of energy that are measured in electron volts

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22
Q

What are photons measured in?

A

Electron volts (eV)

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23
Q

What are the types of x-rays?

A

Hard xray s

soft x-rays

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24
Q

What are hard x-rays?

A

higher energy x-rays that can penetrate human tissues and are used in medical imaging

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25
Q

What are soft x-rays?

A

Nit useful to medical imaging and are lower energy and easily absorbed

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26
Q

What are the properties of x-rays?

A

EM radiation - no mass no charge, travels at speed of light, can travel in a vacuum

man made

not detectable by human sense

causes ionisation

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27
Q

What is ionisation?

A

Displacement of electrons from atoms/molecules

28
Q

How are x-rays produced?

A

Electrons are fired at atoms at very high speeds and on collision the kinetic energy of these electrons is is converted to electromagnetic radiation and heat - the photons are then aimed at the patient

29
Q

What are atoms made of?

A

Protons - pos mass 1

Neutrons - 0 - mass 1

Electrons - neg - mass 0

30
Q

What is the charge of nucleus?

A

Positive as composed of p and n

31
Q

What is the atomic number?

A

Number of protons

32
Q

What is mass number?

A

Number of protons and neutrons

33
Q

What charge is atom in ground state?

A

Neutral

34
Q

What do the number of electrons = when neutral?

A

No of protons

35
Q

What happens during ionisation?

A

Adding or removal of electrons to an atom (adding - neg and removing - pos)

36
Q

Where do electrons go?

A

They spin around the atom in shells - k l m n o shells

37
Q

What shell is filled first?

A

Inner shell

38
Q

Describe electron shells

A

k - 2
l - 8
m -18
n - 32

39
Q

How do we work out how many electrons a shell can have?

A

2n squared

40
Q

How are outer electrons held in shells?

A

They are held by electrostatic force

41
Q

What is electrostatic force?

A

Neg charge of electrons held in by positive charge of protons

42
Q

What is needed to remove electron from its shell?

A

Specific amount of energy to overcome attraction to positive nucleus

43
Q

What is binding energy?

A

This is the additional energy required to exceed electrostatic force

44
Q

When is electrostatic force greatest?

A

When electron is closer to nucleus

45
Q

What does the energy required to move an electron to a more outer shell away from nucleus equal?

A

The difference in binding energy of the two shells

46
Q

What happens if an electron drops to an inner shell?

A

Energy is released in form of x-ray photons if enough energy

47
Q

How much energy is required to move electron from K shell to L shell in tungsten?

binding energy of k shell - 69.6
binding energy of l shell - 10.2

A

69.6-10.2 = 59.4

48
Q

What is the dental x-ray unit composed of?

A

Tube head

Collimator

Positioning arm

Control Panel

Circuitry

49
Q

What is current?

A

The flow of an electric charge usually by movement of electrons

50
Q

What units is current in?

A

Amps (A)

51
Q

What directions of current are there?

A

Direct current

Alternating current

52
Q

What is DC?

A

Direct current is when current flows in one direction

53
Q

What is AC?

A

when current flow repeatedly reverses direction over and over again

54
Q

What does x-ray production require?

A

Unidirectional current - x-ray units provided by mains AC electricty so we have to use generators to modify AC so it mimics constant DC§

55
Q

What is rectification?

A

This is when AC IS MODIFIED BY GENERATOR TO MIMIC CONSTANT DC

56
Q

What is voltage?

A

Difference in electrical potential between 2 points in electrical field and is in volts

57
Q

What volatge do dental x-ray units need?

A

2 different voltages

one as high as 10s of thousands of volts

one as low as 10 volts

58
Q

What are transformers?

A

used to alter the voltage and current from one circuit to another

59
Q

What transformers do X-ray tubes have?

A

there are two different ones

step up transformer going from mains to x-ray tube

step down transformer from mains to filament

60
Q

What does a step up transformer do?

A

Increases potential difference across X-ray tube as is 60,000 to 70000 volts (60-7keV)

61
Q

What does a step down transformer do?

A

It decreases the potential difference across filament and is around 10v and 10 amps

62
Q

What is a filament?

A

The filament is the source of electrons (cathode) in x-ray tubes.

63
Q

What is x-ray beam made up of?

A

Millions of x-ray photons directed in same general direction

64
Q

What directions do photons travel in?

A

Straight line but diverge from source (not parallel)

65
Q

What happens to dose of x-rays as you increase distance from x-ray source?

A

if close to the source then full intensity beam but further away some photons pass straight by and around

66
Q

What is inverse square law?

A

if you double the distance you quarter the dose

3. Radiology (12 decks)

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