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
Define mass attenuation coefficient
Linear attenuation coefficient / density
Define KERMA
Kinetic energy release per unit mass
Gy
The energy transferred from the beam to the electrons at a specific point
What assumptions are required for air KERMA to equal dose to air?
Negligible re-irradiation (bremsstrahlung)
Short electron range
Define absorbed dose
Energy absorbed in mass
Define exposure
Sum of all the charges / mass of air in volume
Name the 4 interaction processes
Photoelectric effect
Compton scattering
Rayleigh scattering
Pair production
