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LET & Shielding
X-ray Tube
Activity Math
Half-Lives
Reactor & Purity
100
Alpha, then beta, then gamma (lowest LET)
Which has the highest LET in tissue: 400 keV alpha, 400 keV beta, or 400 keV gamma?
100
Heat (only ~1% becomes x-rays)
Most electron energy striking the anode becomes this.
100
1 disintegration per second
Define 1 Bq.
100
The radionuclide / nucleus
Physical half-life is a property of this, not of the patient.
100
U-235
Natural uranium is mostly U-238. Enrichment increases this isotope.
200
LET increases; range decreases
Same kinetic energy: as size and charge of a particle increase, LET does this and range does this.
200
Bremsstrahlung
The continuous x-ray spectrum is produced by this process.
200
3 mCi
Convert 1.11 x 10^8 Bq to mCi. (1 Ci = 3.7 x 10^10 Bq)
200
1/Te = 1/Tp + 1/Tb
Formula relating effective, physical, and biologic half-life.
200
Absorbing them to slow or stop the chain reaction
Control rods work by doing this to neutrons.
300
They are uncharged, so they ionize only occasionally through interactions, not continuously
Why do photons usually have lower LET than charged particles?
300
Characteristic x-rays
The discrete spikes on an x-ray spectrum are this.
300
20 mCi/ml
A vial has 180 mCi in 9 ml. What is the specific activity?
300
Shorter than both
Effective half-life is always this compared with Tp and Tb.
300
Slow them to thermal energies so fission is more likely
A moderator is used to do this to neutrons.
400
Plastic / low-Z (not lead — avoids extra bremsstrahlung)
Best first-line shield for an energetic beta emitter.
400
Quantity / number of x-rays (not max energy)
Raising mAs while holding kVp constant mainly changes this.
400
12 ml
Total activity 300 mCi. A 2 ml sample measures 50 mCi. Total volume?
400
About 28.3 mCi (t=6 h, λ=0.0866/h)
A 8-hour T1/2 tracer is 40 mCi at noon. How much remains at 6 PM?
400
Heat boils water → steam spins a turbine → generator
Reactor heat becomes electricity by this chain.
500
K-alpha 70 keV (90-20) and K-beta 85 keV (90-5). L-line 15 keV may follow
K=90 keV, L=20 keV, M=5 keV. After a K-shell vacancy, name the K-characteristic energies.
500
Remove low-energy photons that raise patient dose but do not make the image
Main reason to add aluminum filtration to the beam.
500
1.5 mCi/ml (15 mCi in 10 ml)
You draw 3 ml from 50 mCi in 10 ml and add 7 ml saline. New SA?
500
90 minutes (one half-life)
Counts fall from 80,000 to 40,000 in 90 minutes. What is T1/2?
500
Radiochemical purity. Example: 80 mCi desired form / 100 mCi total = 80%
Course definition: desired isotope in the desired chemical form, as a percent of TOTAL activity.