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32 Cards in this Set

  • Front
  • Back
Exposure refers to what kind of radiation?
Electromagnetic radiation (x-ray and gamma only)
Equations dealing with exposure are done assuming a certain geometry of the source called a
point source geometry.
When we say that we have a point source geometry we are saying that the radiation source is _______relative to you at the distance we are describing.
small
Point source geometry assumes that we have a _______ radiation field, and therefore an equal distribution of radiation
spherical
What are two ways to convert activity to exposure rate (aka, rate of exposure)
Gamma constant

x = 6CE
If we know the gamma constant for 99mTc is
0.7 R• cm2/mCi • hr and
the activity is 100 mCi and the distance is 1 foot, calculate the exposure

now calculate it in mR
0.078 R/hr

7.8 mR/hr
If you need to determine the exposure rate, but you don’t have access to the gamma constant whatX is a way to calculate the exposure rate quickly
X = 6CE
Using the X = 6CE equation, what must you remember about the units
the units are always written in R/hr at a distance of 1 foot
With the X = 6CE formula, what does the C stand for, what does the E stand for?
C = number of curies
E = energy in MeV
With the _____ equation we can only end up with R/hr at a distance of 1 foot, so we would have to do further calculations to detrermine any distance other than 1 foot. With the ______ we could use any distance we wanted,
X = 6CE

gamma constant
We have 100 mCi of 99mTc (100 mCi of tecnesiun 99m) with an energy of 140 keV. Claculate the exposure
0.084 R/hr at a distance of 1 foot
Say we have 100 mCi of cesium 137 at a distance of 1 meter with an energy of 622 Mev and a gamma constant of 3.3 R x cm^2 / mCi x hr. Calculate the exposure
0.033 R/hr
You have 100 mCi of cesium 137 at a distance of 1 meter with an energy of 622 Mev, calculate the exposure?
0.036 R/hr
If you have 10 R/hr at a distance of 1 ft. What is the exposure at 1 meter?
.9 R/hr
With the inverse square law, if you double the radius (distance) the exposure factor goes down by how much?
2^2 or 4
With the inverse square law, if we triple the radius (distance) the exposure factor goes down by a factor of how much?
3^2 or 9
With the inverse square law, if we quadruple the radius (distance) our exposure factor goes down by a factor of how much?
4^2 or 16
Alpha particles are very large and have a double charge. They have a finite range in the medium they are traveling through, but are very easily shielded. If they are so easily shielded, then why do they have a quality factor of 20?
Because they are high LET radiation. They have a high energy deposition per unit path length.
Electromagnetic radiation is shielded probabilistically. There is a certain probability of shielding a certain percentage of the beam. If you have a statistically significant number of photons you can say if we put X amount of lead between you and the source I will be able to shield what that fraction is. How do we determine that fraction?
I = Io e^-μx
Describe what each component of this formula is I = Io e^-μx
Io = original exposure rate
μ = 0.693/HVL
x = thickness of the shield
When we shield, we try to get the exposure rate to what?
Certain regulatory specifications. we are incapable of getting the exposure rate to 0
Say we have and original intensity of 100 mR/hr, a half value layer of 1.2 mm, and a shield of3.6mm. What is the intensity?
I = 12.5 R/hr
Calculate the HVL if Io = 100 mR / hr
I = 20 mR / hr
Shield = 3.6 mm
HVL = 1.55 mm
Where does the leakage radiation come from?
The tube head
Room shielding can be made of either lead or concrete. Needs to go ____ up the wall. If using lead there needs to be a ____ inch overlap.
7 ft ½ inch overlap
Workload is measured in ______
Milliampers per minute
In dealing with workload, what two things do we take into consideration?
We look at the weeks work and the current that are going to be used
This basically figures out how many minutes of current you will be using in 1 week.
Workload
The use factor describes what?
Which wall the tube is pointed at. Wall behind bucky is high, while the other walls will be less
This describes what is on the other side of each of the walls in a room involving radioactive procedures.
Occupancy Factors(this includes the floor and ceiling)
Hallway occupancy factor is probably about _____ Patient waiting area occupancy factor is
.25 or 25%
1 or 100%
When a physicist goes to check a room to make sure the construction met the design, what radioactive source do they use?
Technesium