Production of X-rays Flashcards

1
Q

What are the main components of an x-ray tube? (5)

A
Tubehead
Collimator
Positioning arms
Control Panel
Circuitry
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2
Q

Describe the 9 components of the tubehead.

A
  1. Glass x-ray tube containing - filament, copper block and target
  2. Step-up transformer - high kV across x-ray tube
  3. Step-down transformer - low filament mA
  4. Glass may be leaded with lead-free window
  5. Lead shield to minimise radiation leakage
  6. Oil to facilitate heat removal
  7. Aluminium filter removes low energy, (soft) damaging x-ray photons
  8. Collimator to restrict the size and shape of the beam
  9. Beam-indicating device (BID) or spacer “cone” - may be part of the collimator
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3
Q

To produce x-rays, a small electric current is passed through a filament, what is the current?

A

8-10 mA

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4
Q

What does the small current used to produce x-rays need to be passed through?

A

A step-down transformer

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5
Q

What happens to the filament during the production of x-rays?

A

The filament is heated by current due to the excitation of electrons within the wire.

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6
Q

During the production of x-rays, the electrons from the outer shells are lost, what happens to these ‘free’ electrons?

A

They surround the filament in an electron cloud.

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7
Q

During the production of x-rays, what happens between the cathode and anode?

A

A large potential difference (SI) is applied.

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8
Q

What does the step-up transformer do?

A

It changes 240 volts to 50-90 kV

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9
Q

What does the focusing cup do?

A

Focusing cup points electrons towards target/focal spot of anode.

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10
Q

What happens to electrons as the current is flowing through the filament?

A

The -vely charged electrons are attracted to the +vely charged anode, they are pulled across by the high voltage kV between the cathode and anode, electrons have high energy and are fast moving.

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11
Q

How do electrons then cause the production of x-rays?

A

Electrons hit the target and come to a sudden stop, losing energy, the energy is converted to 99% heat and 1% X-rays.

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12
Q

What happens to the heat produced when electrons hit the target?

A

The heat is absorbed by the copper and dissipated into the surrounding oil.

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13
Q

What happens to the x-rays produced by the electrons hitting the target?

A

The x-rays radiate in all directions, most are absorbed by the leaded glass and the target directs x-rays towards the unleaded window so a beam of radiation is emitted.

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14
Q

What are the two types of x-ray spectra?

A
  1. The continuous spectrum and 2. The Characteristic spectrum.
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15
Q

Describe the continuous spectrum.

A

Bremsstrahlung or breaking radiation, has a wide range of photon energies.

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16
Q

Describe the characteristic spectrum.

A

Depends on the material used in the anode, emitted by loss of electrons from the K and L shells.

17
Q

What are the properties of x-rays? (11)

A
  1. Travel in straight lines in free space
  2. X-Ray photons form a divergent beam
  3. Can travel through a vacuum
  4. Can penetrate matter
  5. Can be absorbed
  6. Can be scattered
  7. Not detectable by human senses
  8. Produce a latent image on film emulsion
  9. Cause ionisation
  10. Can cause biological damage
  11. Cause certain salts to fluoresce and emit light
18
Q

Definition of Scattering

A

Random change in direction after hitting something.

19
Q

Definition of Absorbtion

A

Deposition of energy in tissues.

20
Q

Definition of Intensity

A

Number of x-ray photons in a defined area of the beam.

21
Q

Definition of Attenuation

A

Reduction in intesity of beam due to scattering and absorption.

22
Q

Definition of Ionisation

A

Removal of electron from neutral atom to give -ve (electrons) and +ive (atom) ions.

23
Q

Definition of Penetration

A

The ability of photons to pass through or into tissues/materials.

24
Q

What are the four possible interactions of the x-ray beam?

A

Completely Scattered = with no loss of energy
Absorbed = with total loss of energy
Scattered = with some absorption and loss of energy
Transmitted unchanged

25
Q

What are the four possible interactions of x-rays at atomic level?

A

Rayleigh (unmodified) scattering = pure scatter
Photoelectric effect = pure absorption
Compton effect = absorption and scatter
Pair production = pure absorption

26
Q

Explain the Photoelectric effect.

A

Incoming x-ray interacts with the K electron, the electron is ejected with much energy and the PHOTOELECTRON undergoes further interactions.
The x-ray photon has lost all energy and disappears.
The inner shell vacancy is filled by the outer shell, excess energy is emitted as light or low energy x-ray.
Free electron is captured and there is then atomic stability and a neutral state.

27
Q

Explain the Compton effect.

A

An incoming x-ray photon interacts with loosely bound, outer shell electron which is then ejected with some energy from x-ray.
The compton recoil electron can cause ionisation.
The remaining photon energy is scattered, may undergo further Compton reactions or Photoelectric reactions. They escape tissues into the clinical environment.