A photon beam of fluence 1.0 × 108 photon/cm2
is incident on a circular detector of radius 1
cm. If the radius of the detector is doubled to
2 cm, and the number of photons remains
constant, what is now the photon fluence
incident on the detector?
A.
B.
C.
D.
0.25 × 108 photon/cm2
0.5 × 108 photon/cm2
1.0 × 108 photon/cm2
2.0 × 108 photon/cm2
A photon beam of fluence 1.0 × 108 photon/cm2
is incident on a circular detector of radius 1
cm. If the radius of the detector is doubled to
2 cm, and the number of photons remains
constant, what is now the photon fluence
incident on the detector?
A. 0.25 × 108 photon/cm2
Fluence is defined as number of photons
per unit area. If the radius of the detector
is doubled, the area is multiplied by 4, so
the fluence decreases by a factor of 4.
For an electron with kinetic energy
of 1.0 MeV, the radiant energy is
For an electron with kinetic energy
of 1.0 MeV, the radiant energy is
A. 0.511 MeV
B. 1.0 MeV
C. 1.022 MeV
D. 1.511 MeV
B. 1.0 MeV
If 1% of the photons in a 10 keV beam are
attenuated in 1 cm of unit density material
with an inner-shell binding energy of 1 keV,
then the mass energy transfer coefficient is
If 1% of the photons in a 10 keV beam are
attenuated in 1 cm of unit density material
with an inner-shell binding energy of 1 keV,
then the mass energy transfer coefficient is
A. 0.009 cm2 g-1
B. 0.009 keV cm2 g-1
C. 0.01 cm2 g-1
D. 0.01 keV cm2 g-1
A. 0.009 cm2 g-1
The radiant energy is defined to be
the energy of a particle excluding
rest energy.
1% attenuation in 1 cm of unit density material
means the mass attenuation coefficient is 0.01
cm2 g-1, and 90% (0.9) of the energy is
transferred to charged particles, so the mass
energy transfer coefficient is 0.01 × 0.9 = 0.009
cm2 g-1
1
Suppose a 1 MeV photon interacted with gas in a
cavity, generating a 500 keV photon and a 500 keV
electron. Downstream in the cavity the 500 keV
electron interacted with a gas atom to generate a
250 keV Bremsstrahlung photon. The energy
transferred is
A. 250 keV
B. 500 keV
C. 750 keV
D. 1000 keV
Suppose a 1 MeV photon interacted with gas in a
cavity, generating a 500 keV photon and a 500 keV
electron. Downstream in the cavity the 500 keV
electron interacted with a gas atom to generate a
250 keV Bremsstrahlung photon. The energy
transferred is
B. 500 keV
The energy transferred is
the energy transferred to
the charged particle as a
result of the initial
interaction and does not
include radiative losses
by charged particles
while in the volume.
Suppose a 1 MeV electron interacted with gas in a
cavity, generating a 500 keV Bremsstrahlung
photon, resulting in 500 keV remaining energy in the
electron. The energy transferred is
Suppose a 1 MeV electron interacted with gas in a
cavity, generating a 500 keV Bremsstrahlung
photon, resulting in 500 keV remaining energy in the
electron. The energy transferred is
A. 0 keV
B. 500 keV
C. 1000 keV
A. 0 keV
Kerma is related to the energy
fluence, Ψ, by
Kerma is related to the energy
fluence, Ψ, by
A. Multiplying it by the linear attenuation
coefficient.
B. Multiplying it by the mass attenuation
coefficient.
C. Multiplying it by the mass energy
absorption coefficient.
D. Multiplying it by the mass energy transfer
coefficient.
D. Multiplying it by the mass energy transfer
coefficient.
Energy transferred is only defined for
interactions involving incident uncharged
particles.
Kerma is the expectation value of the
energy transferred and is found my
multiplying the energy fluence (radiant
energy per unit area) by the mass energy
transfer coefficient (fraction of initial
energy transferred to charged particles).
2
Suppose a 1 MeV photon interacted with gas in a
cavity, generating a 500 keV photon and a 500 keV
electron. Downstream in the cavity the 500 keV
electron interacted with a gas atom to generate a
200 keV Bremsstrahlung photon. The net energy
transferred is
Suppose a 1 MeV photon interacted with gas in a
cavity, generating a 500 keV photon and a 500 keV
electron. Downstream in the cavity the 500 keV
electron interacted with a gas atom to generate a
200 keV Bremsstrahlung photon. The net energy
transferred is
A. 200 keV
B. 300 keV
C. 500 keV
D. 750 keV
B. 300 keV
Suppose the electron in the previous question
interacted with a gas atom outside the cavity to
generate a 100 keV Bremsstrahlung photon. The
net energy transferred is now
The net energy
transferred is the energy
transferred to the
charged particle minus
the energy emitted as
radiative losses.
Suppose the electron in the previous question
interacted with a gas atom outside the cavity to
generate a 100 keV Bremsstrahlung photon. The
net energy transferred is now
A. 100 keV
B. 150 keV
C. 200 keV
D. 250 keV
C. 200 keV
In this previous example, the
difference between net energy
transferred and energy imparted is
In this previous example, the
difference between net energy
transferred and energy imparted is
A.
A.
B.
C.
D.
The net energy transferred looks at all radiative interactions of
the secondary electron whereas the energy imparted only looks
at radiative interactions that occur in the collection volume.
The net energy transferred looks at all radiative interactions of
the secondary electron whereas the energy imparted only looks
at the production of the initial secondary photon.
The net energy transferred only looks at radiative interactions of
the secondary electron that occur in the collection volume
whereas the energy imparted looks at all radiative interactions.
The net energy transferred only looks at radiative interactions of
the secondary electron that occur in the collection volume
whereas the energy imparted only looks at the production of the
initial secondary photon.
We need to subtract the
energy of the second
Bremsstrahlung photon
because in calculating
the net energy
transferred, we are not
interested where the
radiative loss event has
occurred.
The net energy transferred looks at all radiative
interactions of the secondary electron whereas the energy
imparted only looks at radiative interactions that occur in
the collection volume.
3
Suppose a 10 MeV photon interacted with gas in a
cavity, generating a positron-electron pair.
Downstream in the cavity the positron undergoes
annihilation with an electron to generate two 511
keV photons. The energy transferred is
approximately
Suppose a 10 MeV photon interacted with gas in a
cavity, generating a positron-electron pair.
Downstream in the cavity the positron undergoes
annihilation with an electron to generate two 511
keV photons. The energy transferred is
approximately
A. 0.5 MeV
B. 1 MeV
C. 9 MeV
D. 10 MeV
C. 9 MeV
Suppose a 10 MeV photon interacted with gas in a
cavity, generating a positron-electron pair.
Downstream in the cavity the positron undergoes
annihilation with an electron to generate two 511
keV photons. The net energy transferred is
approximately
Suppose a 10 MeV photon interacted with gas in a
cavity, generating a positron-electron pair.
Downstream in the cavity the positron undergoes
annihilation with an electron to generate two 511
keV photons. The net energy transferred is
approximately
A. 1 MeV
B. 8 MeV
C. 9 MeV
D. 10 MeV
C. 9 MeV
What is the difference between kerma
and collision kerma?
What is the difference between kerma
and collision kerma?
A. Depending on the size of the volume of interest,
the two can be the same.
B. Kerma describes the initial transfer of energy to
charged particles, whereas collision kerma
describes the net energy transferred to charged
particles.
C. Kerma is defined for only a monoenergetic
beams, whereas collision kerma can be defined
for a polyenergetic beam.
D. Kerma is defined for only indirectly ionizing
radiation, whereas collision kerma is defined for
only directly ionizing radiation.
B. Kerma describes the initial transfer of energy to
charged particles, whereas collision kerma
describes the net energy transferred to charged
particles.
After using approximately 1 MeV to generate the
positron-electron pair, 9 MeV is left to transfer to
kinetic energy of charged particles.
Because the annihilation photons obtained their
entire energy from the rest mass of the positron,
there are no radiative losses in this case, so the
net energy transferred is the same as the energy
transferred.
4