Ionization Chambers and Electrometers ch 6

Question 1

Ionization chambers if not sealed require their readings to be corrected for
temperature and pressure because:

A. Walls of the chamber expand and shrink with temperature
B. The collecting electrodes electrical conductivity changes
C. The volume of the air changes
D. Mass of the air in the chamber changes

Answer 1

D. Mass of the air in the chamber changes

Question 2

Thimble chambers are used to calibrate radiation beams because:

A. They are sturdy
B. They have good spatial resolution
C. They do not significantly perturb the beams
D. All of the above

Answer 2

D. All of the above

Question 3

Thimble chamber walls:

A. Are made from high Z atomic number material
B. Need be very thick
C. Are air-equivalent
D. Are made of ferromagnetic material

Answer 3

C. Are air-equivalent

Question 4

Parallel-plate ionization chambers are primarily used to measure:
A. Ionization at deeper locations in a phantom
B. Surface dose
C. Scattered radiation dose
D. Interstitial dose

Answer 4

B. Surface dose

Question 5

Which of the following is not a desirable characteristic of an ionization chamber:

A. Energy independence
B. High signal to noise ratio
C. Change in sensitivity with the direction of the incident beam
D. Reproducibility

Answer 5

C. Change in sensitivity with the direction of the incident beam

Question 6

The threshold energy for a free-air ion chamber is 3 kV
True
False

Answer 6

False

Question 7

Which of the following is NOT a chamber characteristic?
a. Minimal “stem” effect or radiation leakage
b. Minimal variation in sensitivity over a wide range of photon energies
c. Sufficient volume for degree of sensitivity needed
d. Directionality dependence

Answer 7

d. Directionality dependence