MEDICAL DOSIMETRY UPDATED FINAL EXAMS
ACTUAL QUESTIONS AND ANSWERS SURE A+
✔✔what is the gamma emission of the radio nuclide 192 Ir - ✔✔several gammas of
mean energy around 400 keV
✔✔what is the gamma emission of the radionuclide 222Rn - ✔✔several gammas of
mean energy around 0.8 MeV
✔✔what is the gamma emission of the radio nuclide 125 I - ✔✔mean energy 28 KeV
✔✔what is the half-life of 60 Co - ✔✔5.26 years
✔✔what is the half-life of 137 Cs - ✔✔30 years
✔✔what is the half-life of 192 Ir - ✔✔74 days
✔✔what is the half-life of 226Ra - ✔✔1626 years
✔✔what is the half-life of 125 I - ✔✔59.6 days
,✔✔The mean life of a 192 Ir source is given by - ✔✔106.5 days, use equation
1.44×T1/2
✔✔after two half lives the initial activity of a given radioisotope would have reduced to -
✔✔1/4
✔✔The mean life of a radioactive source is given by - ✔✔1.44 × T1/2
✔✔what is the SI unit of activity - ✔✔Becquerel (Bq)
✔✔one becquerel corresponds to the following number of nuclear transformations per
second - ✔✔1
✔✔1 Curie is equal to how many becquerel - ✔✔37GBq or 3.7 × 10^10
✔✔Isomeric transition is characterized by - ✔✔no change in the atomic number or mass
number
✔✔what is the SI unit to radioactivity - ✔✔Becquerel
✔✔what is the half-life of a free neutron - ✔✔12 minutes
✔✔how are x-rays produced - ✔✔by decelerating high speed electrons in a target
✔✔what is the mechanism of x-ray production in a kV x-ray unit - ✔✔The potential
difference V between cathode and anode accelerates the filament electrons
✔✔what is the mechanism of x-ray production in an accelerator unit - ✔✔electrons are
accelerated to near velocity of light, are bunched together and injected into the
microwave carrying cavities to be accelerated by the waves and their phase stable
position
✔✔what is the fraction of electron energy that is converted to x-rays - ✔✔only a small
fraction is converted to x-rays, a fraction of a percent in kV units
✔✔x-ray spectrum produced is influenced by what? - ✔✔The thickness of the target
✔✔what causes the heating up of the target - ✔✔electron absorption in the target
✔✔in a clinical accelerator, how big is the area that the electrons impinge on the target?
- ✔✔3mm diameter
,✔✔why are therapy x-ray beams used in kV only medium filtered? - ✔✔They just need
to be filtered enough to remove very low energy photons which would only increase skin
dose
✔✔for accelerator photon beams that AAPM TG-51 recommends what has the beam
quality specifier? - ✔✔PDD (10×10×10, SSD)x
✔✔the bremsstrahlung x-ray spectrum produced in the target has a_____ spectrum -
✔✔continuous
✔✔The maximum energy of the photons in the x-ray spectrum cannot exceed the
energy of the_____ - ✔✔electrons incident on the target
✔✔other than bremsstrahlung X-ray what other X-rays are produced in the target? -
✔✔characteristic
✔✔The intensity of x-ray spectrum produced by a linear accelerator is maximum along
the_____ - ✔✔central axis
✔✔The intensity of the x-ray spectrum produced by a linear accelerator decreases
considerably with ______, with respect to the central axis - ✔✔increasing angle
✔✔the kV X-ray unit used in OrthoVoltage therapy must have a target that _____ -
✔✔of a high z number and a high melting point
✔✔The output of a kilovoltage therapy unit is roughly proportional to - ✔✔(tube voltage
kV)^2
and the Z of the target
✔✔photons lose energy and small increments, thus gradually slowing down in the
medium. T or F - ✔✔false, photons either interact or they do not. They do not lose
energy continuously
✔✔what type of photons are transmitted by and have not had any interaction with the
medium traversed? - ✔✔primary photons
✔✔Megavoltage photon interactions can release electrons of _____ - ✔✔significant
energy
✔✔electrons have a _____ range in a medium - ✔✔finite
✔✔a pencil beam of electrons incident on a foil spreads into a beam of larger cross-
section due to______ - ✔✔Coulumbic interactions with nuclei of atoms
, ✔✔why aren't foils used for photon beams in the same way they are used for electron
beams? - ✔✔because photons do not lose energy in the same way electrons do and
are easily transmitted by foils
✔✔high energy electrons scatter ______ than low energy electrons - ✔✔less
✔✔high energy electrons scatter _____ in high Z materials - ✔✔more
✔✔to produce an electron-positron pair and the vicinity of a nucleus, the interacting
photon must have a minimum energy of what? - ✔✔1.02 MeV
✔✔to interact by photoelectric effect the interacting photon must have an energy -
✔✔equal to or just greater than the binding energy of the electron
✔✔to undergo a Compton effect, the energy of the interactive photon must be - ✔✔very
much larger than the electron binding energy
✔✔in the photoelectric interaction, the photon loses_____ - ✔✔All the energy
✔✔in a Compton interaction, the photon loses_____ - ✔✔part of its energy
✔✔The probability of Compton interaction - ✔✔decreases with an increase in photon
energy
✔✔as the photon energy increases, the Compton electron gets ejected in which
direction? - ✔✔more and more in the forward direction
✔✔in the mega voltage energy range the predominant interaction and patient is what? -
✔✔Compton
✔✔The probability of pair production in the interacting medium varies as____ - ✔✔Z^2
✔✔The probability of photoelectric effect in a medium roughly varies as_____ - ✔✔Z^4
✔✔is the photon energy increases, the probability of photoelectric effect roughly varies
as_____ - ✔✔1/E^3
✔✔in pair production, after expending energy for the creation of the pair, the excess
photon energy is_____ - ✔✔shared by the electron and the positron
✔✔in pair production, the positron, at the end of its range in the medium_____ - ✔✔is
annihilated resulting in two annihilation protons
ACTUAL QUESTIONS AND ANSWERS SURE A+
✔✔what is the gamma emission of the radio nuclide 192 Ir - ✔✔several gammas of
mean energy around 400 keV
✔✔what is the gamma emission of the radionuclide 222Rn - ✔✔several gammas of
mean energy around 0.8 MeV
✔✔what is the gamma emission of the radio nuclide 125 I - ✔✔mean energy 28 KeV
✔✔what is the half-life of 60 Co - ✔✔5.26 years
✔✔what is the half-life of 137 Cs - ✔✔30 years
✔✔what is the half-life of 192 Ir - ✔✔74 days
✔✔what is the half-life of 226Ra - ✔✔1626 years
✔✔what is the half-life of 125 I - ✔✔59.6 days
,✔✔The mean life of a 192 Ir source is given by - ✔✔106.5 days, use equation
1.44×T1/2
✔✔after two half lives the initial activity of a given radioisotope would have reduced to -
✔✔1/4
✔✔The mean life of a radioactive source is given by - ✔✔1.44 × T1/2
✔✔what is the SI unit of activity - ✔✔Becquerel (Bq)
✔✔one becquerel corresponds to the following number of nuclear transformations per
second - ✔✔1
✔✔1 Curie is equal to how many becquerel - ✔✔37GBq or 3.7 × 10^10
✔✔Isomeric transition is characterized by - ✔✔no change in the atomic number or mass
number
✔✔what is the SI unit to radioactivity - ✔✔Becquerel
✔✔what is the half-life of a free neutron - ✔✔12 minutes
✔✔how are x-rays produced - ✔✔by decelerating high speed electrons in a target
✔✔what is the mechanism of x-ray production in a kV x-ray unit - ✔✔The potential
difference V between cathode and anode accelerates the filament electrons
✔✔what is the mechanism of x-ray production in an accelerator unit - ✔✔electrons are
accelerated to near velocity of light, are bunched together and injected into the
microwave carrying cavities to be accelerated by the waves and their phase stable
position
✔✔what is the fraction of electron energy that is converted to x-rays - ✔✔only a small
fraction is converted to x-rays, a fraction of a percent in kV units
✔✔x-ray spectrum produced is influenced by what? - ✔✔The thickness of the target
✔✔what causes the heating up of the target - ✔✔electron absorption in the target
✔✔in a clinical accelerator, how big is the area that the electrons impinge on the target?
- ✔✔3mm diameter
,✔✔why are therapy x-ray beams used in kV only medium filtered? - ✔✔They just need
to be filtered enough to remove very low energy photons which would only increase skin
dose
✔✔for accelerator photon beams that AAPM TG-51 recommends what has the beam
quality specifier? - ✔✔PDD (10×10×10, SSD)x
✔✔the bremsstrahlung x-ray spectrum produced in the target has a_____ spectrum -
✔✔continuous
✔✔The maximum energy of the photons in the x-ray spectrum cannot exceed the
energy of the_____ - ✔✔electrons incident on the target
✔✔other than bremsstrahlung X-ray what other X-rays are produced in the target? -
✔✔characteristic
✔✔The intensity of x-ray spectrum produced by a linear accelerator is maximum along
the_____ - ✔✔central axis
✔✔The intensity of the x-ray spectrum produced by a linear accelerator decreases
considerably with ______, with respect to the central axis - ✔✔increasing angle
✔✔the kV X-ray unit used in OrthoVoltage therapy must have a target that _____ -
✔✔of a high z number and a high melting point
✔✔The output of a kilovoltage therapy unit is roughly proportional to - ✔✔(tube voltage
kV)^2
and the Z of the target
✔✔photons lose energy and small increments, thus gradually slowing down in the
medium. T or F - ✔✔false, photons either interact or they do not. They do not lose
energy continuously
✔✔what type of photons are transmitted by and have not had any interaction with the
medium traversed? - ✔✔primary photons
✔✔Megavoltage photon interactions can release electrons of _____ - ✔✔significant
energy
✔✔electrons have a _____ range in a medium - ✔✔finite
✔✔a pencil beam of electrons incident on a foil spreads into a beam of larger cross-
section due to______ - ✔✔Coulumbic interactions with nuclei of atoms
, ✔✔why aren't foils used for photon beams in the same way they are used for electron
beams? - ✔✔because photons do not lose energy in the same way electrons do and
are easily transmitted by foils
✔✔high energy electrons scatter ______ than low energy electrons - ✔✔less
✔✔high energy electrons scatter _____ in high Z materials - ✔✔more
✔✔to produce an electron-positron pair and the vicinity of a nucleus, the interacting
photon must have a minimum energy of what? - ✔✔1.02 MeV
✔✔to interact by photoelectric effect the interacting photon must have an energy -
✔✔equal to or just greater than the binding energy of the electron
✔✔to undergo a Compton effect, the energy of the interactive photon must be - ✔✔very
much larger than the electron binding energy
✔✔in the photoelectric interaction, the photon loses_____ - ✔✔All the energy
✔✔in a Compton interaction, the photon loses_____ - ✔✔part of its energy
✔✔The probability of Compton interaction - ✔✔decreases with an increase in photon
energy
✔✔as the photon energy increases, the Compton electron gets ejected in which
direction? - ✔✔more and more in the forward direction
✔✔in the mega voltage energy range the predominant interaction and patient is what? -
✔✔Compton
✔✔The probability of pair production in the interacting medium varies as____ - ✔✔Z^2
✔✔The probability of photoelectric effect in a medium roughly varies as_____ - ✔✔Z^4
✔✔is the photon energy increases, the probability of photoelectric effect roughly varies
as_____ - ✔✔1/E^3
✔✔in pair production, after expending energy for the creation of the pair, the excess
photon energy is_____ - ✔✔shared by the electron and the positron
✔✔in pair production, the positron, at the end of its range in the medium_____ - ✔✔is
annihilated resulting in two annihilation protons
