Radiation Safety Flashcards

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1
Q

What are the 2 forms of x-ray production?

A

Bremsstrahlung
Characteristic

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2
Q

With the aid of a diagram describe bremsstrahlung

A

Electron deflected by atomic nucleus
Continuous x-rays

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3
Q

With the aid of a diagram describe characteristic X-ray production

A

Inner shell electron scattered
Outer shell electron fills vacancy
Releases X-ray with characteristic energy

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4
Q

Draw and describe a typical X-ray spectrum

A

Low energy limited by self absorption
Intensity depends on square of kV
Characteristic lines
Max energy is generating voltage

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5
Q

What proportion of a clinical beam is bremsstrahlung?

A

90% bremsstrahlung
10% characteristic

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6
Q

Define stochastic and deterministic effects

A

Stochastic - probability of effect proportional to dose
No threshold

Deterministic - no effect below a threshold dose
Above threshold severity of effect increases with dose

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7
Q

Define effective dose

A

Sum ( tissue weighting factor x equivalent dose )

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8
Q

Define equivalent dose

A

Absorbed dose x radiation weighting factor

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9
Q

How is surface dose calculated from radiographic factors?

A

Surface dose = tube output x inverse square factor x back scatter factor x mAs

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10
Q

Describe the components of a X-ray generator

A

Cathode- source of electrons
Focusing cup - ensures electrons hit focal spot
Kilovoltage - accelerates electrons
Anode - converts electrons to X-rays
Anode is tungsten - high melting point
Rotating anode for cooling
Vacuum
Steel housing with lead lining

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11
Q

What is the heel effect?

A

Variation in X-ray intensity across field due to self absorption in the target

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12
Q

How can the beam be visualised?

A

Light beam diaphragm to visualise size and path

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13
Q

Name the 3 interaction types

A

Transmission - forms image
Scattered - staff dose
Absorbed - patient dose

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14
Q

Define attenuation

A

Number of photons removed from the beam

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15
Q

Define absorption

A

Taking up of energy from the beam by the irradiated material

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16
Q

Define mass attenuation coefficient

A

Linear attenuation coefficient / density

17
Q

Define KERMA

A

Kinetic energy release per unit mass
Gy
The energy transferred from the beam to the electrons at a specific point

18
Q

What assumptions are required for air KERMA to equal dose to air?

A

Negligible re-irradiation (bremsstrahlung)
Short electron range

19
Q

Define absorbed dose

A

Energy absorbed in mass

20
Q

Define exposure

A

Sum of all the charges / mass of air in volume

21
Q

Name the 4 interaction processes

A

Photoelectric effect
Compton scattering
Rayleigh scattering
Pair production