Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
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
|