Practice Problems Dosimetry & Instrumentation ch 6&8

Question 1

The process whereby energy is transferred from a photon beam to electrons in the
medium is called:
A. Electron Capture
B. Absorption
C. Bremsstrahlung
D. Scatter

Answer 1

B. Absorption

Question 2

Match the most appropriate instrument to the procedure in each question:
I. Liquid scintillation counter
II. NaI well counter
III. Geiger-Mueller (GM) counter
IV. Thermoluminescent dosimeter (TLD)
V. Ionization chamber survey meter
A. Used to detect very small levels of radioactivity
B. Particulate contamination survey for Tc-99m or used with a wipe test to
check radioactive shipments
C. Radiation survey of a diagnostic x-ray installation
D. Personnel monitoring

Answer 2

I. Liquid scintillation counter -B.
II. NaI well counter -B.
III. Geiger-Mueller (GM) counter -A.
IV. Thermoluminescent dosimeter (TLD) -D.
V. Ionization chamber survey meter -C.

A. Used to detect very small levels of radioactivity
B. Particulate contamination survey for Tc-99m or used with a wipe test to
check radioactive shipments
C. Radiation survey of a diagnostic x-ray installation
D. Personnel monitoring

Question 3

Collecting all the negative ions produced by a beam of photons in a small volume of
air, under conditions of electronic equilibrium, is a direct measure of:
A. Dose Equivalent
B. LET
C. Absorbed Dose
D. Exposure
E. Specific Ionization

Answer 3

D. Exposure

Question 4

If the temperature is 22ºC and the pressure is 770 mm mercury, the correction to an
ionization chamber reading would be ___:
A. 1.013
B. 1.0
C. 0.994
D. 0.987
E. 0.974

Answer 4

D. 0.987

Question 5

Megavoltage photons can be detected by all of the following except:
A. An Ion Chamber
B. A Geiger Counter
C. A Diode
D. A Thermoluminescent Dosimeter (TLD)
E. A Flow Meter

Answer 5

E. A Flow Meter

Question 6

Exposure is _______.
A. The energy absorbed in a given mass of a medium
B. The air kerma of a photon beam
C. Measured in Sv
D. The ionization in a given mass of air

Answer 6

D. The ionization in a given mass of air

Question 7

Match the following units with the quantities below: (answers may be used more than
once or not at all)
I. Bq
II. Sv
III. C/kg
IV. Gy
V. J
A. Absorbed Dose
B. Activity
C. Exposure
D. Dose Equivalent

Answer 7

I. Bq - B
II. Sv - D
III. C/kg - C
IV. Gy - A
V. J - Energy
A. Absorbed Dose
B. Activity
C. Exposure
D. Dose Equivalent

Question 8

Ion chamber readings are corrected for temperature and pressure because:
A. The chamber’s calibration factor is stated at 22ºC and 760 mmHg
B. As temperature increases, the gas in the chamber expands, resulting in a
higher collected charge
C. As pressure increases, the gas in the chamber is compressed, resulting in
a lower collected charge
D. All of the above are true

Answer 8

A. The chamber’s calibration factor is stated at 22ºC and 760 mmHg

Question 9

Which of the following radiation detectors can be used to calibrate a linac photon
beam?
I. TLD chip
II. Therapy Verification Film
III. Diode
IV. Farmer Ion Chamber
A. 1, 2, 3
B. 1, 3
C. 2, 4
D. 4 only
E. All of the above

Answer 9

D. 4 only

Question 10

Factors influencing the relationship of “dose equivalent” to “absorbed dose” for
particulate radiation include:
I. Atomic Mass
II. Electric Charge
III. Kinetic Energy
IV. Linear Energy Transfer (LET)
A. 1,3
B. 2,4
C. 3,4
D. 2,3,4
E. all of the above

Answer 10

E. all of the above

Question 11

Ion-recombination can be a problem when using a:
A. Calorimeter
B. Geiger Counter
C. Ionization Chamber
D. TLD

Answer 11

C. Ionization Chamber

Question 12

An unsealed ion chamber is exposed under identical condition to the same amount of
radiation in cities A and B. It has a lower charge reading in city A than in city B because:
A. The relative humidity might be higher in city B
B. The temperature might be higher in city B
C. The pressure might be lower in city A
D. The stem effect might be more in city B
E. Background radiation could be higher in city B

Answer 12

C. The pressure might be lower in city A

Question 13

For a cylindrical ion chamber with inner radius, r, the effective point of dose
measurement in water is shifted:
A. Upstream by a distance of 2 r for electron beams
B. Upstream by a distance of r for electron beams
C. Downstream by a distance of 0.75 r for electron beams
D. Downstream by a distance of r for electron beams
E. Upstream by a distance of 0.5 r for electron beams

Answer 13

E. Upstream by a distance of 0.5 r for electron beams

Question 14

Exposure is defined for ionization produced in:
A. Water
B. Tissue
C. Air
D. Fat

Answer 14

C. Air

Question 15

One Roentgen corresponds to a charge of:
A. 3.7 x 1010 disintegrations/sec
B. 2.58 x 10-4 coulomb/kg
C. 0.03 esu of electrostatic charge
D. 1 electron volt

Answer 15

B. 2.58 x 10-4 coulomb/kg

Question 16

A free-air ionization chamber is an instrument used to measure:
A. The charge of free electrons in a radiation beam
B. Ionization produced in a well specified volume of air according to
the definition of Roentgen
C. Charge particle equilibrium
D. Number of ionization tracks produced by electrons

Answer 16

B. Ionization produced in a well specified volume of air according to
the definition of Roentgen

Question 17

The most common wall material used for the outer wall of the ionization chamber is:
A. Aluminum
B. Copper
C. Graphite or Nylon
D. Lead

Answer 17

C. Graphite or Nylon

Question 18

Calibration of an ionization chamber means it has been:
A. Exposed to radiation to stabilize
B. Compared against a national standard to establish a correction factor
C. Tested against leakage and electrical shorts
D. Made waterproof

Answer 18

B. Compared against a national standard to establish a correction factor

Question 19

An electrometer is an instrument used to measure:
A. Charge, Current
B. Voltage, Resistance
C. Capacitance
D. All of the above

Answer 19

A. Charge, Current