Nuclear

Question 1

Describe the process of the production of X-rays

Answer 1

Produced when fast moving electrons are stopped in either a single event (converting the whole energy of the electron into an X-ray photon) or in multiple events releasing Bremsstrahlung (breaking radiation).

Question 2

What is the equation which describes the intensity of mono-energetic photons as they pass through an absorber of thickness x.

Answer 2

I = I0e^-ux

Question 3

What are the four mechanism through which EM radiation interact with matter

Answer 3

Elastic Scattering 
Compton effect (inelastic Scattering)
Photoelectric effect (Absorption)
Pair Production (Absorption)
All four mechanisms contribute to attenuation and the sum of all four gives the attenuation coefficient.

Question 4

Describe Elastic scattering

Answer 4

The incoming photon deflects from an electron but loses no energy. Not particularly important as it only contributes significantly to attenuation at very low photon energies.

Question 5

Describe Compton Scattering (inelastic scattering)

Answer 5

Incident photon interacts with an orbital electron, transfers some of its energy into the electron (recoil electron) and is scattered away at an angle.

Question 6

What happens to the scattered photon in Compton scattering and what is its significance

Answer 6

It can be in any direction and is important as it significantly affects the resolution of the imaging systems. By transferring a large proportion of energy to the recoil electron this can ionise an atom.

Question 7

Describe the photoelectric affect and the significance

Answer 7

incident photon is completely absorbed in a single interaction and a bound electron is ejected from the atom (causing ionisation). This causes the electron shell to have a vancency which is filled by an electron from another shell and thus emits an X - ray photon.

Question 8

Describe Absorption - Pair Production

Answer 8

If the incident photon has energy greater than 1.022 MeV when passing a nucleus, then an electron-positron pair can be created. The difference between the photon energy and the rest mass energy is given equally to the electron and positron as kinetic energy. Mass creation.