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Radiology > Basic Physics > Flashcards

Basic Physics Flashcards

1
Q

X-rays are a form of what kind of radiation?

A

Electromagnetic radiation

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2
Q

The flow of energy from electromagnetic radiation is created by what? What is it represented by?

A

Simultaneously varying electrical and magnetic fields Represented as a sine wave

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3
Q

What are the properties of electromagnetic radiation? (4)

A
  • no mass
  • no charge
  • Always travels at the ‘speed of light’ (3x108 ms-1 = 671 million mph)
  • Can travel in a vaccum
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4
Q

Describe the EM spectrum (3 main points).

A
  • consists of all the diff types of EM radiation
  • Each type has diff properties depening on its energy/wavelength/frequency
  • 7 main groups
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5
Q

What are the 7 EM groups?

A
  • gamma ray
  • X-ray
  • Ultraviolet
  • Visible light
  • Infrared
  • Microwave
  • Radio
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6
Q

Describe gamma rays in terms of wavelength, frequency and energy.

A

Shorter wavelength, higher frequency and higher energy

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7
Q

What is the wavelength?

A

How ‘big’ one cycle is

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8
Q

What is the frequency of a wave? What is it measured in?

A

How many times the wave’s shape repeats per unit time

Hertz (Hz) [one hertz = one cycle per sec]

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9
Q

Speed = frequecny x wavelength

BUT EM radiation speed is constant (3x108ms-1)

What does this mean for the relationship between frequency and wavelength in EM radiation?

A

If frequency increases then wavelength must decrease (and vis versa)

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10
Q

photons and mocement of enery etc

A
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11
Q

What are the 2 types of X-rays you get?

A
  • Hard x-rays
  • Soft x-rays
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12
Q

Describe hard x-rays.

A

Higher energies and are able to penetrate human tissues

(mediacal imaging mainly uses these types of x-rays)

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13
Q

Descibe soft X-rays.

A

Lower energies and easily absorbed

NOTE: dont want soft x-rays if want radiographs as you need some x-rays to reach the receptors

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14
Q

What are the basic properties of X-rays? (4)

A
  • form of EM radiation (no mass, no charge, very fast, can travel in a vaccum)
  • undetectable to human senses (contrasts with visible light)
  • Man-made
  • Cause ionisation (displacement of electrons from atoms/molecules)
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15
Q

How are x-rays and gamma rays similar?

A

They are identical except that gamma rays ocur naturally and X-rays are man-made

Gamma rays also generally have higher energies

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16
Q

Describe the basic production of X-rays.

A
  • Electrons fired at atoms at very high speed
  • On collision, the kinetic energy of these electrons is converted to electromagnetic radiation (ideally X-rays) and heat is produced as a side-effect
  • The X-ray phoons are aimed at a subject
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17
Q

What is the basic structure of an atom?

A
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18
Q

Describe neutrons, protons and electrons. (charge, mass, location)

A
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19
Q

What is the overall charge of the nucleus?

A

Positive

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20
Q

What dictates the atomic number and mass number of an element?

A

AN = number of protons

Mass number = protons + neutrons

21
Q

The number of electrons determines what in an atom?

A

Its chemical properties

22
Q

What is the innermost electron shell?

A

K (then it foes L, M, N, O etc.)

23
Q

How do you figure out the max no. of electrons a shell can hold?

A

max. no. = 2n2 (n=shell number)
e. g. L shell = 2x22 = 8 electrons

Max no.’s for first shell’s go (2, 8, 18, 32)

24
Q

Orbiting electrons are held within their shells by what?

A

Electrostatic force

(-ve charge of electrons attracted to overall +ve charge of nucleus)

25
Q

To remove an electron from its shell, a specific amount of energy is required to overcome the electrostatic force. What is this energy called?

A

Binding energy (additional energy required to exceed electrostatic force)

26
Q

The energy required to move anelectron to a more outer shell requires what energy?

A

The difference between the 2 binding energies of the shells

27
Q

If an electron drops to a more inner shell, what energy is required?

A

none - the difference in the 2 binding energies is released

Can be released in the form of heat or x-rays (if sufficient energy)

28
Q

What are the main components of a dental X-ray unit?

A

Tubehead

Collimator

Positioning arm

Control panel

Circuitry

29
Q

What is the definiion of a current?

A

Flow of electric charge, usually by the movement of electrons

30
Q

What are currents measured in? Describe this measurement.

A

Amps

Measure of how much charge flows past a point per second

31
Q

Currents can also be defined by their direction. What are these 2 categories? Describe them.

A

Direct current (DC) = constant unidirectional flow e.g. batteries

Alternating current (AC) = flow repeatedly reverses direction

32
Q

When it comes to powering machienary, does it matter what direction a current is flowing in?

A

No - as long as it is flowing

33
Q
A
34
Q

X-ray production requires what kind of current? (direction)

A

Unidirectional current

35
Q

X-ray production requires a unidirectional current BUT x-ray units are powered by mains electricity (AC - alternating currents). How is this problem resolved? What is the process called?

A

X-ray units have generators which modify the alternatig current so that it mimics a constant directional current

Process called rectification

36
Q

What is the voltage?

A

Difference in electrical potential beween 2 points in a n electrical fiels

Related to how forcefully a charge will be pushed through an electrical field

NOTE: potential differenece is the same as voltage and the unit for voltage is volt

37
Q

Describe the electrical supply to an X-ray unit in the UK mentioning the current and volts.

A

From mains supply:

  • alternating current (less than or equal to 13 amps) [need DC but fixed by rectification)
  • 220-240 volts
38
Q

What voltages does an X-ray machiene need?

A

2 diff voltages:

  • one as high as 10s of thousands of volts
  • one as low as around 10 volts

(mains supply only gives a voltage of 220-240 volts)

39
Q

How is the problem of volatge (mains supply not sufficient) for the X-ray machines resolved?

A

Transformers alter the voltage (and current) from one circuit to another

40
Q

What transformers are found in the X-ray unit?

A

2 diff ones:

  • Step-up transformer for the X-ray tube
  • Step-down transformer for the filament
41
Q

Describe the step-up transformer.

A

increases potential difference across x-ray tube

Usually 60,000-70,000 volts (60-70kV)

Current reduced to milliamps (mA)

42
Q

Describe the step-down transformer.

A

decrease potential difference across filament

approx 10 volts

approc 10 amps

43
Q

What are x-ray beams made up of?

A

Millions of x-ray photons directed in the same general direction

44
Q

Describe how the photons in X-ray beams move/travel?

A

Effectively travel in straight lines but diverge from the X-ray source (dont travel in parallel)

45
Q

What is the x-ray beam inensity defined as?

READ PIC AND UNDERSTAND

A

The quantitiy of photon energy passing through a cross-sectional area of the beam per unit time

Increase in number and/or energy of phtons = increase in intensity

46
Q

The dose from the X-ray decreases with what?

A

Distance from the x-ray

47
Q

What is the inverse square law that describes intensity of x-ray beam at a point?

A
48
Q
A

answer = 0.25 grays

49
Q

What is the difference between other types of ionising radiation and x-rays?

A

others produced by radioactive decay of unstable atoms unlike x-rays which are directly man-made

Radiology (12 decks)

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