Radiation Safety Flashcards
What are the 2 forms of x-ray production?
Bremsstrahlung
Characteristic
With the aid of a diagram describe bremsstrahlung
Electron deflected by atomic nucleus
Continuous x-rays
With the aid of a diagram describe characteristic X-ray production
Inner shell electron scattered
Outer shell electron fills vacancy
Releases X-ray with characteristic energy
Draw and describe a typical X-ray spectrum
Low energy limited by self absorption
Intensity depends on square of kV
Characteristic lines
Max energy is generating voltage
What proportion of a clinical beam is bremsstrahlung?
90% bremsstrahlung
10% characteristic
Define stochastic and deterministic effects
Stochastic - probability of effect proportional to dose
No threshold
Deterministic - no effect below a threshold dose
Above threshold severity of effect increases with dose
Define effective dose
Sum ( tissue weighting factor x equivalent dose )
Define equivalent dose
Absorbed dose x radiation weighting factor
How is surface dose calculated from radiographic factors?
Surface dose = tube output x inverse square factor x back scatter factor x mAs
Describe the components of a X-ray generator
Cathode- source of electrons
Focusing cup - ensures electrons hit focal spot
Kilovoltage - accelerates electrons
Anode - converts electrons to X-rays
Anode is tungsten - high melting point
Rotating anode for cooling
Vacuum
Steel housing with lead lining
What is the heel effect?
Variation in X-ray intensity across field due to self absorption in the target
How can the beam be visualised?
Light beam diaphragm to visualise size and path
Name the 3 interaction types
Transmission - forms image
Scattered - staff dose
Absorbed - patient dose
Define attenuation
Number of photons removed from the beam
Define absorption
Taking up of energy from the beam by the irradiated material
