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Yr 3 - Radiology > Production of xrays > Flashcards

Production of xrays Flashcards

1
Q

What is the history of X-rays?

A

1895 discovered by roentgen
1896 walkhoff takes first dental X-ray (25 min exposure)
1890s Rollins introduces collimation and filtration
1950s Extraoral imaging technique invented in finland
Now approx 18 million dental X-rays taken per year in UK

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2
Q

What is the charge of a proton?

A

+1

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3
Q

What is the Mass (amu) of a proton?

A

1

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4
Q

What is the charge of a neutron?

A

0

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5
Q

What is the mass (amu) of a neutron?

A

1

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6
Q

What is the charge of an electron?

A

-1

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7
Q

What is the mass (amu) of an electron?

A

1/1840

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8
Q

What does amu stand for?

A

Atomic mass unit

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9
Q

What is an atomic mass unit (amu)?

A

1/12 mass of a Carrbon 12 atom

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10
Q

What is the atomic number?

And which letter is it represented by?

A

The number of protons in the nucleus

z

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11
Q

What is the relationship between the number of protons and electrons orbiting the nucleus?

A

The same number of each!

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12
Q

What does the number of protons/electrons determine?

A

The chemical properties of the atom

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13
Q

What is the charge of an atom?

A

It is electrically neutral

Nucleus +1 and electrons -1 and same no. of each

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14
Q

How are electrons limited?

A

To certain orbits or shells

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15
Q

What are the letters used to show the electron shell?

A

K, L, M, N, O, P

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16
Q

Each electron shell has a fixed energy, what is the difference in energy for a shell that is closer to the nucleus?

A

The closer the shell to the nucleus the lower the energy - needs less energy to hold it in place like sitting on centre of roundabout

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17
Q

What is ionisation?

A

The removal of an ion (or more) from an atom

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18
Q

What is excitation?

A

The movement of an ion to another energy shell (of higher energy)

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19
Q

How many electrons does each shell have?

A

They each have a max number i.e. 2, 8, 18

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20
Q

How do +ve and -ve charges interact?

A

Opposite charges attract

like charges repel

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21
Q

What is binding energy?

A

The work needed to overcome the attraction of an electron to the nucleus and remove electron from an atom

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22
Q

Which shell has the greatest binding energy?

A 
k shell (closest to nucleus)
= outer shells its smaller as electron is further away from the nucleus = less attraction
23
Q

What does ionisation create?

A

An ion pair

24
Q

What is an ion pair?

A

+ve and -ve ion = produced simultaneously by the addition of sufficient energy to a neutral atom/molecule to cause it to dissociate into oppositely charged fragments

25
Q

What are X-rays?

A

A form of ionising radiation that sits on the electromagnetic spectrum at the high energy end with gamma rays

26
Q

What is each X-ray?

A

A photon (a packet of energy/quantum of energy)

27
Q

How many photons are X-ray beams used in dentistry made up from?

A

Millions!!

28
Q

What are the properties of X-rays?

A
  • Invisible and weightless
  • Travel in straight lines
  • Travel at the speed of light (in a vacuum)
  • Range of frequencies and wavelengths 0.01- 0.05nm (different properties)
  • Penetrating
  • Ionising
  • Follows the inverse square law
29
Q

What is the inverse square law?

A

When distance from source is doubled, intensity of radiation is 1/4

30
Q

Essentially what is a radiograph?

A

A shadow of the body based on the electron densities of materials and how much a tissue absorbs the radiation

31
Q

How are X-rays produced?

A
  1. Produce lots of electrons
  2. Accelerate them to very high energy
  3. Smash them into a target
32
Q

How are electrons accelerated to a v. high energy?

A

Using a high potential difference (kV) between negative and positive

33
Q

What material is the target usually made of?

A

Tungsten

34
Q

Why does the tungsten target need special features?

A

Gets very hot and needs to not melt and be destroyed

35
Q

How does the smashing of electrons into the target produce X-rays?

A

Rapid deceleration of electrons = interactions with the anode (loss of energy)

36
Q

What are the different components of an X-ray tube head?

A
  • Glass x-ray tube (filament, copper block and target)
  • Step up transformer
  • Step down transformer
  • Lead casing
  • Oil
  • Aluminium filtration
  • Collimator
  • Beam indicating device
37
Q

What is the role of the step up transformer?

A

Increases the voltage to accelerate electrons from cathode to anode

38
Q

What s the role of the step down transformer?

A

Decreases the voltage heat the filament (cathode) where the electrons come from

39
Q

What is the role of the lead casing?

A

Contains X-rays (only use those coming out in the right direction)

40
Q

What is the role of the oil?

A

To conduct heat away from the insert (glass X-ray tube)

41
Q

What is the role of the aluminium filtration?

A

Filters out low energy X-rays (decrease exposure)

42
Q

What is the role of the collimator?

A

Shape the beam = only covers the area we need to on the patient

43
Q

What is thermionic emission?

A

electrons produced by filament heating (cathode mA)

44
Q

What does the extent of filament heating control?

A

The amount of electrons produce

and here the current flowing between the cathode and anode (tube current in mA)

45
Q

What properties of tungsten make it ideal as a target?

A
  • High melting point (won’t melt over lifetime of insert)

- High atomic number (74) = lots of atomic electrons for electrons from filament to interact with and produce X-rays

46
Q

What does the energy lost during smashing against target get transferred into?

A

99% Heat

1% X-rays

47
Q

How is the heat produced in smashing removed?

A

Copper Block

Surrounding Oil

48
Q

Why are heat producing collisions most common?

A

There are many outer shell tungsten electrons which can interact and each electron can have many heat producing collisions

49
Q

What are the three variables of X-ray sets?

A

kV
mA
Time

50
Q

What does the kV of an X-ray set determine?

A

QUALITY of x-ray beam (energy of photons = penetrating power)
Affects film contrast

51
Q

What does the mA & time of an X-ray set determine?

A

QUANTITY of x-ray photons

Affects degree of blackening of film (optical density)

52
Q

What are the two methods of X-ray production?

A
  1. Bremsstrahlung radiation

2. Characteristic radiation

53
Q

What is bremsstrahlung radiation?

A

Where an incoming electron penetrates the outer electron shells and passes close to the nucleus of tungsten atoms -> almost goes into orbit around nucleus

= slows down -> loss of energy -> electromagnetic wave/ X-ray),
= small interaction with nucleus = small deviation (produces weak x-ray only -> most common = filtered out & deviates to varying degrees = continuous spectrum of x-ray photon energies)
= all energy in electron can be produced i.e. electron can slow down enough it stops

54
Q

What is characteristic radiation?

A

Where incoming electrons collide with inner shell electrons displacing it into outer shell/ ejecting it from atom = huge loss of energy (higher energy level electrons jump down to fill the gap = produces X-ray photon… k alpha = L->K, K beta = M->K less frequent but bigger)

=always the same energy between specific shells = predictable
n.b. only electrons from k shell are of diagnostic importance
=bombarding high speed electrons need energy >69.5kV to displace a K shell electron and produce a characteristic line on the spectrum (energy of electron is directly related to the kV - potential difference across the x-ray tube)

Yr 3 - Radiology (9 decks)

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