RAPHEX QUESTIONS AND ANSWERS SURE A+
✔✔An isotope that decreases in activity by 5% per day has an approximate half-life of
A. 1.5d
B. 5 d
C. 10 d
D. 13.5 d
E. 20 d - ✔✔D. 13.5 d. A(t) = Ao * e ^2t , where 2 = In(2)/t1/2. Therefore, at t=1 day,
A(t)=A(1 day) = 0.95Ao, and In(0.95A0 Ao) = -In(2) /41/2 x 1 day, so 0.0513 = 0.693/1/2
Or t1/2 = 13.5 days
✔✔103 (46) Pd decays to 103 (45) Rh. What is the primary mode of decay?
A. alpha decay
B. beta minus decay
C. electron capture
D. gamma emission
E. photonuclear disintegration - ✔✔C. electron capture.
✔✔The advantage of using a bowtie filter in CT imaging is
A. it absorbs low-energy x-rays
B. reduced scatter-to-primary ratio
C. reduced dose to the periphery of the patient
D. All of the above are true.
E. None of the above is true. - ✔✔D. All of the above are true.
✔✔What characteristic x-ray energies are possible for molybdenum, given energy levels
for its K, L, and M shells of 20 keV, 2.5 keV, and 0.5 keV, respectively?
A. Continuous spectrum from 0.5 keV to 20 keV
B. Continuous spectrum from 2 keV to 19.5 keV
C. 20 keV, 2.5 keV, 0.5 keV
D. 19.5 keV, 17.5 keV, 2 keV
E. 22.5 keV, 20.5 keV, 3 keV - ✔✔D. 19.5 keV, 17.5 keV, 2 keV. Characteristic x-rays
are emitted with discrete energies equal to the difference in energy levels between each
orbital electron shell.
, ✔✔After the replacement of the ionization chamber in a linac, which machine
parameters are expected
to change the most?
A. flatness
B. symmetry
C. output
D. beam profile
E. energy - ✔✔C. output. The output can change significantly after the replacement of
an ion chamber due to differences
in the amount of gas between the old and new chambers. Therefore, machine output
will need to be adjusted/recalibrated after the chamber replacement. The flatness and
the symmetry are function of the beam steering, and the beam energy is determined by
the accelerating potential and the target.
✔✔The ____ in a medical linac generates the high power and short-duration pulses to
run the electron gun and the klystron.
A. power supply
B. modulator
C. magnetron
D. wave guide
E. accelerator tube - ✔✔B. modulator
✔✔If a flattening filter designed for a 6-MV beam is accidentally applied to a 15-MV
beam, the magnitude of the horns at max will __________ and the dose rate per pulse
will ___________compared to the use of the proper 15-MV flattening filter.
A. increase; increase
B. increase; decrease
C. increase; remain the same
D. decrease; increase
E. decrease; decrease - ✔✔D. decrease; increase. As the x-ray beam energy
increases, the fluence distribution will be more forward peaked. So,
higher-energy beams need thicker flattening filters. Therefore, if a 6-MV flattening filter
is used for the 15-MV beam, the magnitude of the horns will decrease due to insufficient
attenuation along the CAX relative to off-axis points, and the dose rate will increase due
to a
decreased filter thickness.
✔✔Arrange the following MV photon and MeV electron beams in order of greatest to
least electron current in the linac accelerating cavity for the same dose rate.
A. 9 MeV, 6 MV, 15 MV
B. 9 MeV, 15 MV, 6 MV
C. 6 MV, 9 MeV, 15 MV
D. 6 MV, 15 MV, 9 MeV
✔✔An isotope that decreases in activity by 5% per day has an approximate half-life of
A. 1.5d
B. 5 d
C. 10 d
D. 13.5 d
E. 20 d - ✔✔D. 13.5 d. A(t) = Ao * e ^2t , where 2 = In(2)/t1/2. Therefore, at t=1 day,
A(t)=A(1 day) = 0.95Ao, and In(0.95A0 Ao) = -In(2) /41/2 x 1 day, so 0.0513 = 0.693/1/2
Or t1/2 = 13.5 days
✔✔103 (46) Pd decays to 103 (45) Rh. What is the primary mode of decay?
A. alpha decay
B. beta minus decay
C. electron capture
D. gamma emission
E. photonuclear disintegration - ✔✔C. electron capture.
✔✔The advantage of using a bowtie filter in CT imaging is
A. it absorbs low-energy x-rays
B. reduced scatter-to-primary ratio
C. reduced dose to the periphery of the patient
D. All of the above are true.
E. None of the above is true. - ✔✔D. All of the above are true.
✔✔What characteristic x-ray energies are possible for molybdenum, given energy levels
for its K, L, and M shells of 20 keV, 2.5 keV, and 0.5 keV, respectively?
A. Continuous spectrum from 0.5 keV to 20 keV
B. Continuous spectrum from 2 keV to 19.5 keV
C. 20 keV, 2.5 keV, 0.5 keV
D. 19.5 keV, 17.5 keV, 2 keV
E. 22.5 keV, 20.5 keV, 3 keV - ✔✔D. 19.5 keV, 17.5 keV, 2 keV. Characteristic x-rays
are emitted with discrete energies equal to the difference in energy levels between each
orbital electron shell.
, ✔✔After the replacement of the ionization chamber in a linac, which machine
parameters are expected
to change the most?
A. flatness
B. symmetry
C. output
D. beam profile
E. energy - ✔✔C. output. The output can change significantly after the replacement of
an ion chamber due to differences
in the amount of gas between the old and new chambers. Therefore, machine output
will need to be adjusted/recalibrated after the chamber replacement. The flatness and
the symmetry are function of the beam steering, and the beam energy is determined by
the accelerating potential and the target.
✔✔The ____ in a medical linac generates the high power and short-duration pulses to
run the electron gun and the klystron.
A. power supply
B. modulator
C. magnetron
D. wave guide
E. accelerator tube - ✔✔B. modulator
✔✔If a flattening filter designed for a 6-MV beam is accidentally applied to a 15-MV
beam, the magnitude of the horns at max will __________ and the dose rate per pulse
will ___________compared to the use of the proper 15-MV flattening filter.
A. increase; increase
B. increase; decrease
C. increase; remain the same
D. decrease; increase
E. decrease; decrease - ✔✔D. decrease; increase. As the x-ray beam energy
increases, the fluence distribution will be more forward peaked. So,
higher-energy beams need thicker flattening filters. Therefore, if a 6-MV flattening filter
is used for the 15-MV beam, the magnitude of the horns will decrease due to insufficient
attenuation along the CAX relative to off-axis points, and the dose rate will increase due
to a
decreased filter thickness.
✔✔Arrange the following MV photon and MeV electron beams in order of greatest to
least electron current in the linac accelerating cavity for the same dose rate.
A. 9 MeV, 6 MV, 15 MV
B. 9 MeV, 15 MV, 6 MV
C. 6 MV, 9 MeV, 15 MV
D. 6 MV, 15 MV, 9 MeV
