X-ray production

Question 1

How are xrays produced

Answer 1

1. Filament electrically heated and a cloud of electrons are produced around it (cathode)
2. High voltage causes electrons to accelerate towards the anode and bombard the target (focussing device aims electron at focal spot)
3. Energy is lost by electrons either by heat (99%) or X-rays
4. Heat is removed by copper and oil
5. X-rays are emitted in all directions but only those emitted through the small window leave the tubehead

Continous or characteristic spectrum

Question 2

Describe the continous spectrum

Answer 2

1. The incoming electrons passes close to the target nucleus and this causes it to be slowed down and deflected
2. The lost kinetic energy is released as photons
3. Energy of the photon can be anything between 0 and the maximum kV

Question 3

Describe the characteristic spectrum

Answer 3

1. The incoming electron collides with an inner shell electron and either displaces it into a peripheral shell (excitation) or removes it completely (ionisation)
2. Following the ionization/excitation of the tungsten atoms by the bombarding electrons, the orbiting tungsten electrons rearrange themselves to return to neutral or ground states
3. This involves the electron jumping from one energy level to another, resulting in emission of X-ray photons with specific energy

Question 4

What are the differnet ways xrays can interact

Answer 4

1. Occurs in the patients
2. Xray photons interact with atom in tissues
3. This leads to attenuation of the xray beam (attenuation is defined as a reduction in the number of photons within the beam due to absorption and scatter

Question 5

Describe the photo electric effect

Answer 5

1. Incoming photon interacts with inner shell electron of tissue atom
2. This inner shell electron is ejected with energy into the tissues and will undergo further interactions
3. Xray photon disappears having deposited all of its energy (pure absorption)
4. Vacancy is filled by outershell electron and cascade starts with atomic stability and is achieved by capture of a free electron shell and cascade starts until atomic stability is achieved by capture of a free electron to return the atom to its neutral state

Question 6

Describe the compton effect

Answer 6

1. Incoming xray photon interacts with outer electron of atom
2. Outershell electron is ejected with some energy loss of incoming photon but not all
3. Remainer of incoming photon energy is deflected or scattered from original path as a scattered photon