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IRMER Exam > Radiation Physics > Flashcards

Radiation Physics Flashcards

1
Q

What is a photon?

A

Packet of energy - single particle of light or x-ray

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2
Q

What are x-ray beams made from?

A

Photons

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3
Q

What is relationship between electrons and photons?

A

Input of a photon causes an electron to transition to higher energy orbit

Transition of electron to lower energy orbit = loss of energy = photon emitted

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4
Q

What particles are released from radioactive decay?

A

Alpha and beta partciles

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5
Q

What are alpha particles?

A

Unstable nucleus which can emit 2 photos and 2 neutrons

The emitted particle identically helium nucleus has charge of +2

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6
Q

Why is alpha particles so ionising?

A

Relatively high mass and charge

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7
Q

What stops alpha particles?

A

10mm air or less mm matter

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8
Q

What are beta particles?

A

Unstable nucleus ejects electron by internal conversion

Emitted particle has charge of -1

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9
Q

What is more ionising alpha or beta?

A

Beta particles

Stopped by few mm Al

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10
Q

What is a gamma ray?

A

Excited nucleus can emit gamma ray to return to ground state

Emitted g-ray has no charge

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11
Q

How ionising are gamma rays?

A

Less ionising but very penetrating

Few mm Pb required

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12
Q

Difference between g-rays and x-rays?

A

Same - different manner of production

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13
Q

How are x-rays produced?

A

Accelerating e- towards metal target

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14
Q

Why are x-rays less damaging a/b particles?

A

No charge and they travel of the steep of light

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15
Q

How are diagnostic X-ray tubes efficient?

A

Creating x-ray = lot of heat

Anode absorbs electrons and has high melting point

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16
Q

What is Bremsstrahlung - breaking radiation?

A

Rapid deceleration of e- passing close to target nucleus = photons given off
Creates lots of low energy photons

17
Q

What is attenuation?

A

Max photon energy is set by peak tube voltage, kVp

Interaction of orbital electrons = heat

18
Q

X-ray beams are polyenergetic what does this mean?

A

Have a spectrum of energies - lower energy components are preferentially absorbed

19
Q

What is filtration?

A

Low energy photons no use in imaging as weakly penetrating - but still contribute to patient dose

Remove these low energy photons w/ metal on output ports

20
Q

What filtration is used?

A

Legal requirement in all diagnostic X-ray tubes - 1.5mm Al

21
Q

What is Compton effect?

A

Scattering of x-ray causing fogging film

22
Q

How to optimise contrast? - what is disadvantage of this?

A

Most tissues are of similar dentistry - low kV optimise contrast
Transmission increase w/ Kv = lower pt dose - need to compromise between contrast and dose

23
Q

How can beam quality be increased?

A

Increasing kV or using more filtration

24
Q

What dose doubling mA do?

A

Doubles dose

Number of photons directly proportional to tube current

IRMER Exam (8 decks)

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