lec 5 radiation measurements
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15 Terms
The amount of radioactive material is called the _______ of the material
Activity
What is Exposure? What is it measured in?
The amount of charge created by gamma and x-rays in a volume of air. It is measured in Roentgen (R)/unit of time (Hr)
What is Absorbed Dose? What is it measured in?
The energy absorbed per unit mass. Measured in Gray, which is 1 J/kg.
What is the conversion for Roentgen to Rad?
1 R = 0.95 rad
What are radiation weighting factors? What are they measured in?
A way to account for the fact that high-LET radiation is higher risk.
Measured in Sv or rem
What is the conversion for Sv to rem?
1 Sv = 100 rem
Which particles are considered high LET radiation?
Alpha particles and protons
Which particles are considered low LET radiation?
Electrons and photons (bc they cause low electrons to be emitted, but they themselves do not have an LET)
What is relative biological effectiveness?
Essentially, how powerful is this type of radiation at causing biological damage?
What is effective dose? What is it measured in?
Different organs respond differently to radiation, so the effective dose accounts for this by assigning tissue weighting factors.
It is measured in Sv and rem.
What is the inverse square law when considering distance and its effect on dose rate?
Doubling your distance from a source will decrease your dose rate by a factor of four.
Look at inverse square law and try to solve this equation:
If the exposure rate from a patient is 5 mR/hr at 1 foot (30 cm), what is the exposure rate at 1 meter (100 cm)?
Good luck!
What is the specific Gamma Ray Constant? What is the equation?
The exposure or dose rate created per unit activity at a specific distance for a specific isotope.
X= AΓ/d^2
What type of source are patients usually treated like and why?
They are usually treated as line sources because the radioactivity will distribute roughly evenly shortly after injection.
Another explanation for a line source if you need it
Instead of all the radiation coming from one tiny point, it comes from along the whole length of the source because the radioactivity is spread out along that line.