Photon Interaction Mechanisms 2 Flashcards

You may prefer our related Brainscape-certified flashcards:
1
Q

What is Compton scattering?

A

Incident photon inelastically scatters an outer free electron (recoil electron) and photon of lower energy is scattered from atom

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What did Compton find?

A

Incident photons scattered off graphite target leads to an increased wavelength at increased angles

Tested at low intensity to dismiss chance of being a Doppler shift

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What happens in elastic photon scattering?

A

Photon changes direction on interaction without losing energy

(creates noise and spread of dose)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is Thompson scattering?

A

γ + e- -> γ

incident γ interacts with an oscillating atomic electron and emission of photon with same wavelength (change direction but no net effect)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is Rayleigh scattering?

A

Incident γ interacts with whole atom causing bound electrons to vibrate and emission of photon with same wavelength (occurs in forward direction)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the equation of the attenuation coefficient for elastic scatter?

A

Φ ∝ Z^2 / E

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

When does elastic scatter occur?

A

More at lower energies and high Z materials

(no contribution to absorption as no energy lost)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the energy of the recoil electron?

A

It shares its energy with photon (they travel in opposite directions)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Why is Compton scattering different to other types of scattering?

A

it is inelastic / incoherent

it is ionising

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the atomic Compton scatter attenuation coefficient σ?

A

A measure of the chance of a Compton scatter interaction

σ ∝ Z/E

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What does σ depend on?

A

High enough electron density (enough outer shell electrons)

Being more dominant than PE effect (as they happen around same energy but PE occurs first)

Z

E

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is Compton shift?

A

Change in wavelength (or energy) of incident photon after a Compton scatter

(energy and momentum must be conserved)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the de Broglie wavelength equation?

A

p = h / λ = hv / c

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the recoil electron energy?

A

T = E_i - E_f

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

How does the scatter angle change the energy of scatted photon?

A

Greater the scatter angle (up to 180 degrees), the greater the loss of energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

When does the highest possible energy loss occur?

A

In back scatter

17
Q

When does Compton scattering occur?

A

At mid to high energies in higher Z materials

(at lower atomic numbers more dominant as PE is weaker)

(dominant at 100keV - 10MeV)

18
Q

Which process is dominant at low photon energies?

A

Photoelectric effect

19
Q

Which process is dominant at very high photon energies?

A

Pair Production

20
Q

What happens at lower energy levels (up to 80keV)?

A

Low transmission (high skin dose)

Good contrast (PE effect)

21
Q

What happens at mid energy levels (80keV - 120 keV)?

A

Acceptable signal and contrast

Compton effect

X-ray imaging

CT imaging

22
Q

What happens at higher energy levels (120keV - 1MeV)?

A

High signal

Reduced contrast

Reduced image quality

High doses

23
Q

As multiple types of interaction can happen simultaneously to different photons in the beam, how do we know where each one deposits its energy?

A

Depends on the secondary interactions of each process