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RAD > RAD03-2002 How are X-Rays produced? > Flashcards

RAD03-2002 How are X-Rays produced? Flashcards

1
Q

What is the main part of the X-ray unit called?

A

Tubehead

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2
Q

What is within the tubehead the produces the x-rays themselves?

A

Glass x-ray tube

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3
Q

What is the cathode?

A

At one end of the glass tube there is a coil of wire called the filament

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4
Q

What is the anode?

A

At the other end of the glass tube there is a target made of tungsten set into a block of copper

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5
Q

What is the entire X-ray tube surrounded by?

A

Oil

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6
Q

What unit is within the tube head?

A

Step up transformer

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7
Q

What part of the tube head is in contact with the patients face?

A

Spacer cone

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8
Q

What is the function of the step-up transformer?

A

To step up the mains voltage to 60,000 to 70,000

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9
Q

What is the function of the surrounding oil?

A

Removes heat that is produced during x-ray production

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10
Q

What is the function of the spacer cone?

A

Indicates the direction of the beam and sets the ideal distance of the X-ray tube’s target to the skin of the patient’s face

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11
Q

What is the density off any substance described as?

A

Atomic number (z)

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12
Q

What is the atomic number

A

Number of protons

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13
Q

What occurs the glass x ray tube during x-ray exposure?

A

As electric current flows through the filament and heats up
The electrons from the tungsten atoms are boiled off and released, and a cloud of electrons forms around the end of the filament
60k voltage is provided from the step up transformed, which allows the electrons to travel across the gap to the tungsten target

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14
Q

What happens to the heat produced?

A

Conducted away down the big copper block

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15
Q

What are the implications of some photons leaving the target in other directions?

A

Must never hold the tubehead because your hand could be directly irradiated by leaked radiation

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16
Q

What happens when the accelerated electron approaches tungsten?

A

The electron passes near the nucleus and is attracted towards and deflected and slowed in its path

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17
Q

What are the effects of the electron slowing down as is it deflected in tungsten?

A

The electron loses some of its energy, which is converted into an x-ray photon and emitted

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18
Q

How does the proximity of the electron to the nucleus affect the defection?

A

The closer the electron is to the nucleus, the larger the deflection therefore will be a stronger and longer X-ray

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19
Q

What type of spectrum does the deflection of the accelerated electron result in?

A

Continuous spectrum

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20
Q

Which energy photons are more dangerous for the patient?

A

Low energy

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21
Q

What is the overall energy of the photon determined by?

A

The energy of the incoming electrons which is determined by the size of the voltage

22
Q

How does the size of the voltage affect the energy of the electron?

A

The bigger the voltage, the greater the energy given to the electron

23
Q

How does the number of low energy photons differ from high energy photons?

A

There are very many low energy photons whilst relatively few high energy photons

24
Q

What is Emax?

A

The maximum energy any one photon can have

25
Q

What is the Emax for a 60kV machine?

A

60,000 volts

26
Q

How does a higher kV affect the number of photons?

A

A higher kV produces more photons

27
Q

What is an alternative method X-rays can be produced?

A

X-ray producing collision

28
Q

How are x-rays produced via x-ray producing collisions?

A

The incoming electron passes into the atom of tungsten and interacts with one of the orbiting electrons
The electron is knocked out of the atom and the incoming electron is deflected in its path and leaves the atom
The displacement of an inner shell electron means the atom is unstable so an electron from the adjacent shell drops to fill the gap
As one electron drops to the next shell, it is dropping from one energy to another, so energy is emitted in the form of an x-ray photon.
There will be a similar cascade of electrons to fill the void, again energy being released as a photon
Eventually a free electron is captured and the atom is returned to it stable state

29
Q

What type of spectrum is formed as a result of rearrangement of the electrons?

A

Characteristic

30
Q

Why is rearrangement of electron known as characteristic spectrum?

A

The electrons are only of specific energy levels thats are specific to the size of the gap

31
Q

When will photons from the characteristic spectrum be formed?

A

When the voltage is 70kV or more

As lower kV do not give the incoming electrons enough energy to knock out an inner shell electron from tungsten atom

32
Q

How are lowest energy photons removed from the beam before hitting the patient?

A

Passing the beam through an aluminium sheet, which absorbs and filters out lowest energy photons that are most harmful

33
Q

What is the recommenced thickness for aluminium?

A
  1. 5mm for x-ray units operating at less than 70kv

2. 5mm for x-rays operating at more than 70kV

34
Q

What are the 3 main controls on the control panel?

A

kV
milli amperage (mA)
Time

35
Q

What controls are fixed in dental sets?

A

kV an mA is fixed and you cannot alter it

But time can change

36
Q

What does kV determine?

A

The energy of the photon and hence their penetrating power

Affects the film contrast

37
Q

What does a lower kV mean in terms of contrast?

A

Lower kV shows bigger contrast with less shades of grey

The difference between black and white is more obvious

38
Q

Why is a higher kV more ideal for patients?

A

More photons penetrate hence less absorption

39
Q

What has happened in grey areas of an x-ray image?

A

Some photons have passed through and hit the film and there is scattering of photons

40
Q

What has happened in white areas of the x-ray image?

A

Photons have been stopped by a filling

41
Q

What has happened in black areas of an x-ray image?

A

All photons have passed through and hit the film

42
Q

What do mA and time determine?

A

Determines quantity of electrons leaving tube hence quantity of photons

43
Q

How does increased photons affect the x-ray image?

A

Leads to increased blackening and over exposure

44
Q

What does an over-exposed look like?

A

Too dark

45
Q

How is rectification achieved?

A

Via either half wave pulses where X-ray fire only on positive waves
Or single phase full wave rectification where negative is flipped to positive

46
Q

Why are X-rays firing only only positive waves very inefficient?

A

Longer exposure and X-ray fires from 0 on every new pulse

47
Q

What type of current is recommended?

A

DC but it is expensive

48
Q

What is FSD?

A

The distance form focal spot on the target to the end of the spacer cone that touches the patients head

49
Q

What is the effect of a long FSD?

A

Smaller beam hence patient has less irration

50
Q

What FSD is recommended?

A

200mm

51
Q

What is the collimator?

A

The device that restricts beam size

RAD (7 decks)

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