Topic 4: x-rays Flashcards
How is the number of e- released in an exposure determined?
By selected mA
How are the total number of X-rays produced in an exposure calculated?
mAs = mA x T
- mA = e- current
- T = time exposure in seconds
KE acquired by e- measured in?
- Selected kV
3 types of interactions of e- + atoms
1) Incoming e- + outer shell e- of target atom
2) Incoming e- + inner shell e-
3) Incoming e- + nuclei
How far away is e- from surface of target when interactions occur?
0.5mm
Describe the interactions with tungsten atoms
- Most e- are in the outer orbital = incoming e- need small amount of energy to interact
- Small amount of energy = EM radiation = electrostatic repulsion BUT too small to produce X-rays
- All energy released = heat
2 process X-ray produced in X-ray tube
1) Characteristic radiation
2) Bremsstrahlung
Describe characteristic radiation
1) Excitation: sufficient energy given to bound e- = raise to next orbital
2) Ionisation: binding energy of orbital e- is overcome + released from atom
Describe excitation
- e- removal = temporary = returns to original position
- Gives out photon = energy = gained by e- in raising itself to new shell
Describe ionisation
- Released e- = delta ray = carries KE donated during interaction
- Delta ray = goes to interact with other atoms until all KE lost
- Ionization can only occur = if KE incoming e- =/> specific binding energy of orbital bound e-
- Ionisation of K shell = leaves vacancy = e- from shell further from nucleus drops to K shell
- Releases X-ray = value = difference in binding energies between shells
- If L shell to K shell = K-alpha emission
- If M shell to K shell = K-beta emission
3 variables of energy bands
1) Atom type = atomic number
2) Shell from which e- ejected
3) Shell from which replacement e- comes
Describe Bremsstrahlung
- When electrically charged particle + large KE = deflected by second charged mass
- Deflection = change in momentum for incoming e- = gives emission of photon of EM radiation
- Loss of energy = incoming e- slow down
- Amount of KE given to X-ray photon from incoming e- = determined by how close e- passes to nucleus
