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Year 3 Radiography > Production and properties of X rays > Flashcards

Production and properties of X rays Flashcards

1
Q

atomic mass unit

A

1/12 mass of carbon atom

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2
Q

mass of proton, neutron and electron

A

proton and neutron= 1amu

electron= 1/1840

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3
Q

structure of an atom

A

nucleus of protons and neutrons

electrons in orbit around nucleus

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4
Q

what is Z

A

proton number

and electron number

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5
Q

what is A

A

atomic number. number of protons and neutrons in nucleus

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6
Q

define excitation

A

moving electron inner ā€“> outer shell to excite the atom (move to higher energy level)

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7
Q

define ionisation

A

complete removal (or addition) of an electron from an atom, causing it to gain or lose charge

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8
Q

what is binding energy

A

attraction between -ve e- and +ve protons (nucleus)

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9
Q

where is binding energy greatest

A

K shell (greater for electrons closer to nucleus)

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10
Q

what is a photon

A

packet of X ray energy, equivalent to a quantum of energy

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11
Q

what kind of radiation is x rays

A

electromagnetic radiation, ionising

high frequency, short wavlength

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12
Q

what is the biggest source of ionising radiation

A

radon (gas released from soil/rocks)

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13
Q

what % of ionising radiation is artificial

A

13%

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14
Q

name the other type of ionising radiation

A

gamma rays

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15
Q

wavelength and freq of x rays/ gamma rays

A

short wavelength

high freq

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16
Q

how fast do x rays travel in a vacuum

A

speed of light

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17
Q

range of x ray wavelengths

A

0.01-0.05nm

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18
Q

x rays obey the inverse square law. what is this

A

intensity of radiation reduces to 1/4 when distance from source is doubled

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19
Q

why must x ray production be in a vacuum

A

otherwise atoms of air would be in the way of electron movement

20
Q

3 steps to produce x rays

A
  1. produce lots of electrons
  2. accelerate them to very high energy
  3. smash them in to target
21
Q

main components of tube head and their function

A
  • glass x ray tube (filament, copper block, target)
  • step up transformer (high voltage to accelerate electrons)
  • step down transformer (low voltage to heat filament
  • lead casing (to stop x rays escaping)
  • oil (conduct heat away from insert)
  • aluminium filtration (removes unwanted low energy electrons)
  • collimator
  • beam indicating device
22
Q

what direction do electrons flow?

A

negative (cathode) to positive (anode)

23
Q

how are electrons produced

A

thermionic emission from heating the filament at the cathode

24
Q

what is tube current?

A

the amount of electron flow

25
Q

how to increase tube current

A

increase heating of filament

26
Q

how are electrons accelerated to anode

A

high potential difference

27
Q

what happens when the electrons reach the anode

A

hit a small target area, stop moving (lose energy)

energy lost as heat (99%) or x rays (1%)

28
Q

how is the heat removed

A

copper block and surrounding oil

29
Q

why is the tungsten used for the target

A
  • high melting point (not affected by heat from electrons)

- high atomic number (74) so lots of interaction for electrons

30
Q

what happens to produce a) heat-producing reaction

b) x ray producing reaction

A

a) heat-producing reaction: incoming electron hits an outer-shell tungsten electron
b) x ray producing reaction: incoming electron avoids outer shell tungsten electrons and comes very close to tungsten nucleus. the electron-nucleus attraction causes the electrons to lose energy as x rays. the further round the nucleus the electrons are deflected, the higher energy the photons

31
Q

tube current value for dental radiographs

A

7-10mA

32
Q

kV value for dental radiographs

A

60-70kVp

33
Q

why is high kV used?

A

less dose to patient because electrons more accelerated, more likely to reach nucleus

34
Q

function of kV

A
  • determines quality of X ray beam ie energy of photons
  • determines penetrating power of photons
  • affects film contrast
35
Q

function mA and time

A

determine quantity of x ray photon

affects degree of blackening of film (optical density)

36
Q

name 2 methods of x ray production

A

Bremsstrahlung radiation

characteristic radiation

37
Q

describe Bremsstrahlung radiation

A

incoming electron penetrates outer electron shells and passes close to nucleus of tungsten atom
this is slowed down and reflected by nucleus with large loss of energy emitted in the form of x rays

38
Q

what is maximum potential energy

A

enough energy given to moving electron so that it fully stops at the target nucleus

39
Q

what is filtration

A

removal of low-energy photons produced when bombarding electrons are only partly deflected. they have little penetrating power so are not useful

40
Q

describe and explain spectrum produced by Bremsstrahlung radiation

A

continuous. incoming electrons slowed down/ deflected to varying degrees

41
Q

describe characteristic radiation

A

incoming electron collides with inner shell tungsten electron, displacing it to outer shell (excitation) or displacing it from atom (ionisation). an outside electron jumps down to fill gap. this decrease in energy causes x ray production

42
Q

describe pattern of x ray production in characteristic radiation

A

always the same amount of x ray produced (hence characteristic) because same amount of energy lost when electrons move rings Lā€“>K on the tungsten atom

43
Q

what electrons are useful for diagnosis and why

A

K shell elctrons because they have the highest binding energy

44
Q

what kV is needed to displace K shell electron to produce x ray?

A

69.5kV

45
Q

what is
k alpha
k beta

A

k alpha: L to K electron movement

k beta: M to K electron movement

46
Q

what type of radiography uses filtration?

A

both

Year 3 Radiography (9 decks)

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