Ver 4.16
Chapter III
X-RAY Production
Filters
and
Half-Value Layers
Joseph F. Buono RTT
Allied Health Science
Nassau Community
1 Education Drive
Garden City, NY 11530-6793
phone: 516 - 572 - 7536 office
- 9460 Secretary
email: joseph.buono@ncc.edu
website: rtscanner.com
page setup
10×7.5
Title
Main Menu
Objectives
next by default
- X-Ray Production - electron interactions with matter
- excitation
heat
- ionization
x-ray production
- bremsstrahlung
x-ray production
- diagram of x-ray tube
- operation of x-ray tube
- graph of intensity vs. photon energy
Effect of mas, KVp, Target Material on Quality and Quantity
- milliampere second
- kilovolt potential
- target material
- x-ray distribution
- line focus
- anode heel effect
- Filters
- Half-Value Layer
- Table - ( Summary of factors that effect Quality and Quantity )
- Questions
mm
Objectives
1 - Define thermionic emission.
2 - State the reasons for using tungsten as the filament material.
3 - State the reasons for using tungsten as the target material.
4 - Define bremsstrahlung radiation.
5 - Label the parts of an x-ray tube.
6 - State the efficiency of x-ray production in the diagnostic range.
7 - Label the graph of intensity verses photon energy.
8 - State the effects of mas, voltage and target material on quality and quantity.
9 - State the three types of electron interactions with matter.
10 - Define x-ray distribution around a thin target verses electron energy.
Main Menu
Obj 1
Objectives
11 - State the difference between a reflective target and transmission target.
12 - Define line focus.
13 - Define anode heel effect.
14 - State the effect of filters on beam hardness and skin dose.
15 - Define combination filters.
16 - List the components of thoraeus filters.
17 - Define Half-Value Layers and beam hardness.
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Obj 2
Electron Interactions
Electron Interactions
Main Menu
EI 0
Electron Interactions
Three types of electron interactions with matter will be studied.
Of these, only the last two will produce x-rays.
1. excitation
2. ionization
3. bremsstrahlung
Main Menu
EI 1
Electron Interactions
1. excitation
Excitation
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Ex 0
Electron Interactions
1. excitation - this is a process were an electron in the atom receives enough
energy to move to a higher energy state within the atom
The cause of excitation in this case, is the absorption of a small amount of
energy from the incoming electron to an orbital electron in the atom.
The amount of energy absorbed by the orbital electron is
NOT enough to free it from the atom
(if it were freed from the atom it would be called ionization).
The atom is still electrically neutral, because it still
has the same number of electrons and protons.
The electron in the atom that absorbed the energy is said to be in an excited
state and will lose this excess energy in a very short period of time.
This excess energy will eventually show up as heat.
Main Menu
Ex 1
Electron Interactions
1. excitation
NOTE: In x-ray production the element of choice will turn out to be tungsten.
Therefore, an of atom tungsten will be used in the animation.
Tungsten Atom
with the K, L, & M shells
filled for this demonstration
nucleus
K
L
M
Main Menu
Ex 2
Electron Interactions
1. excitation
NOTE: In x-ray production the element of choice will turn out to be tungsten.
Therefore, an of atom tungsten will be used in the animation.
Tungsten Atom
incident electron
with kinetic energy of
200 KeV
Main Menu
Ex 3
Electron Interactions
1. excitation
NOTE: In x-ray production the element of choice will turn out to be tungsten.
Therefore, an of atom tungsten will be used in the animation.
Tungsten Atom
transfer
of energy
incident electron
with kinetic energy of
200 KeV
Main Menu
Ex 4
Electron Interactions
1. excitation
NOTE: In x-ray production the element of choice will turn out to be tungsten.
Therefore, an of atom tungsten will be used in the animation.
Tungsten Atom
electron is in a
higher energy
state
transfer
of energy
The interaction can be with any one of
the orbital electrons, but most likely
with an outer shell electron.
Main Menu
The incident electron because it
loses only a small amount of
energy to the orbital electron
will have it's path changed by a
very small angle.
The path of the incident electron
would have continued in a straight
line if it did not lose any energy by
interacting with the orbital electron.
Ex 5
Electron Interactions
1. excitation
NOTE: In x-ray production the element of choice will turn out to be tungsten.
Therefore, an of atom tungsten will be used in the animation.
Tungsten Atom
Generally an atom in an excited state
will lose this excess energy with in a
very short period of time.
Very low energy photon.
The excitation energy that is
given off by the orbital electron
will eventually be seen as heat
The incident electron because it
loses only a small amount of
energy to the orbital electron
will have it's path changed by a
very small angle.
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Ex 6
X-RAY PRODUCTION
Electron Interactions
2. Ionization
Ionization
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EI 0
Electron Interactions
2.
X-RAY PRODUCTION
Ionization - is the removal of an electron from an atom
This will give rise to the production of:
Characteristic Radiation
This is the production of x-rays by an electron filling the
vacancy of a liberated orbital electron in the target material.
If a "free" electron fills the vacancy then a characteristic photon with
an energy equal to the binding energy of that electron vacancy for
the tungsten atom.
If another orbital electron fills the vacancy it would also produce a
characteristic photon but with an energy that is equal to the difference
between the two energy levels.
One of the things that the binding energy is dependent
on is the number of protons in the nucleus.
Because all elements have different numbers of protons they
therefore have different binding energies.
"free" electrons are electrons that
are not bound to the atom
( they have zero binding energy )
Thus the characteristic radiation that would be produced will be
the signature of that element.
For tungsten the binding energy of the k inner shell is 69.5 KeV, thus the characteristic
radiation for that shell electron is 69.5 KeV if a "free" electron fills the vacancy.
Main Menu
I1
Electron Interactions
X-RAY PRODUCTION
2. Ionization
Tungsten atom
with only the K & L shells shown
the "K" shell
binding energy
is 69.5 KeV
free electrons
hole or vacancy
in K shell
incident electron
200 KeV
incident electron
with kinetic energy of
200 KeV
incident electron loses
a minimum of 69.5 KeV of energy
(binding energy of K shell)
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I2
Electron Interactions
X-RAY PRODUCTION
2. Ionization
Tungsten atom
with only the K & L shells shown
if incident electron loses 95 KeV
then
the liberated electron energy is:
if a "free" electron sees the
vacancy in the atom
then:
95 KeV - 69.5 KeV = 25.5 KeV
hole or vacancy
in K shell
25.5 KeV
incident electron
200 KeV
105 KeV
lets assume the incident electron
lost 95 KeV
then:
electron energy after collision is:
incident electron loses
a minimum of 69.5 KeV of energy
(binding energy of K shell)
200 KeV - 95 KeV = 105 KeV
Main Menu
I3
Electron Interactions
X-RAY PRODUCTION
2. Ionization
Tungsten atom
with only the K & L shells shown
characteristic radiation
of 69.5 KeV is given off
if a "free" electron sees the
vacancy in the atom
then:
25.5 KeV
incident electron
200 KeV
105 KeV
energy before
interaction
200 KeV
energy after
interaction
105.0 KeV
25.5 KeV
69.5 KeV
200.0 KeV
The energy before and after MUST be equal.
Main Menu
I4
X-RAY PRODUCTION
Electron Interactions
2. Ionization
(K and L shell transition)
Tungsten atom
with only the K & L shells shown
characteristic radiation
photon energy = K - L
shell energy levels
OR
69.5 KeV - 12.1 KeV = 57.4 KeV
characteristic radiation of
the L shell with an energy
of 12.1 KeV
"L" shell
binding energy
of 12.1 KeV
Main Menu
I5
Electron Interactions
X-RAY PRODUCTION
3. Bremsstrahlung Radiation
Bremsstrahlung Radiation
Main Menu
Bm 0
X-RAY PRODUCTION
3. Bremsstrahlung Radiation
Electron Interactions
- this is the production of x-rays from the interaction of
the incident electron with the nuclear field of an atom
In x-ray production we will take advantage of a property of nature, which is
that a moving charged particle will lose energy when it is made to change its
velocity (speed and/or direction) .
Therefore, you need a source of charged particles.
The easiest types of charged particle to produce are electrons, for every
atom has them and they are easy to liberate.
Again we will take advantage of nature, for when you heat an object to very high
temperatures you will liberate (boil off) electrons.
The higher the temperature the greater the number of electrons liberated.
Therefore you would like to have as high as temperature as possible.
Main Menu
Bm 1
X-RAY PRODUCTION
Electron Interactions
3. Bremsstrahlung Radiation
Tungsten because of it's high melting point is used as a source of electron and
this process of boiling off electrons is called thermionic emission.
Next we need a way of changing the velocity of the electrons.
One way of changing the direction and speed of a charged particle is to
place an atom, which would then be called a target, in its path and let the
electrons interact with it.
This slowing of the electrons is called bremsstrahlung interaction, which is the
German word for "braking".
Thus the radiation produced in this manner is called bremsstrahlung radiation.
Main Menu
Bm 2
X-RAY PRODUCTION
Electron Interactions
3. Bremsstrahlung Radiation
The target material chosen is again tungsten.
Tungsten is chosen for two main reasons.
First:
It has a high melting point.
this is needed because most of the electron energy is converted into heat
Second:
It also has a high atomic number that will give the nucleus a high positive charge
and therefore the electrons will more readily interact with it.
Main Menu
Bm 3
Electron Interactions
X-RAY PRODUCTION
3. Bremsstrahlung Radiation
is all known as:
white radiation
continuous radiation
braking radiation
Tungsten atom
with only the K & L shells shown
Main Menu
Bm 4
Electron Interactions
X-RAY PRODUCTION
3. Bremsstrahlung Radiation
Tungsten atom
with only the K & L shells shown
20 KeV
One of the factor that effect
the how much energy that an
electron will lose is the
distance from the nucleus.
incident electron
200 KeV
incident electron
with kinetic energy of
200 KeV
if the kinetic energy of electron
after interaction is 20 KeV
close
encounter
close encounter
high energy transfer
to photon
Then the energy of photon is:
200 KeV - 20 KeV = 180 KeV
180 KeV
Main Menu
Bm 5
Electron Interactions
X-RAY PRODUCTION
3. Bremsstrahlung Radiation
50 KeV
Tungsten atom
with only the K & L shells shown
distant encounter
low energy transfer
to photon
20 KeV
incident electron
200 KeV
distant
encounter
incident electron
with kinetic energy of
200 KeV
incident electron
200 KeV
150 KeV
close
encounter
close encounter
high energy transfer
to photon
180 KeV
Main Menu
Bm 6
Electron Interactions
X-RAY PRODUCTION
3. Bremsstrahlung Radiation
50 KeV
Tungsten atom
with only the K & L shells shown
distant encounter
low energy transfer
to photon
Next: What is the most likely distance that an
electron will interact with the nucleus.
20 KeV
Remember if the atom is enlarged to fill a
baseball stadium the nucleus would be the
size of a grain of rice in center field.
incident electron
200 KeV
distant
encounter
150 KeV
nucleus
incident electron
200 KeV
close
encounter
close encounter
high energy transfer
to photon
180 KeV
Main Menu
Bm 7
Electron Interactions
X-RAY PRODUCTION
3. Bremsstrahlung Radiation
Tungsten atom
with only the K & L shells shown
Next: What is the most likely distance that an
electron will interact with the nucleus.
Remember if the atom is enlarged to fill a
baseball stadium the nucleus would be the
size of a grain of rice in center field.
You are standing many miles ( hundreds
if not thousands of miles) away from the
stadium and shooting in the direction of
the stadium.
Imagine you are blind folded and have
a machine gun that shoots electrons.
nucleus
It does not take much imagination to realize that the
vast majority of the times the bullets are going miss
the grain of rice by very wide margins.
Thus the vast majority of the bremsstrahlung
photons that are produced will be of low energy.
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Bm 8
A simple diagram of an x-ray tube
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Xray 0
simple diagram of an x-ray tube
AC power supply
necessary circuitry to
generate as pure a DC
voltage as possible.
rectifier
-
+
KVp power out
cathode
(-)
thermionic
emission
tungsten
filament
-
Glass envelope
(to maintain vacuum)
electron flow
anode
(+)
tungsten target
thin
glass
window
+
filament power control (mas)
milliampere second
Main Menu
Xray 1
operation of an x-ray tube
rectifier
-
cathode
(-)
thermionic
emission
+
anode
(+)
electron flow
mainly bremsstrahlung radiation
plus some characteristic radiation
-
+
Only showing those photons that
emerge on the patient side of tube, all
other photons are NOT shown.
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Xray 2
operation of an x-ray tube
rectifier
NOTE:
At this energy range only about 1% of the
electron energy is converted into x-ray
production, thecathode
remainder of the energy
- ) as heat.
eventually shows( up
thermionic
emission
-
-
+
anode
(+)
electron flow
+
Main Menu
Xray 3
Graph of intensity Vs photon energy
Graph of intensity Vs photon energy
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Gph 0
Graph of intensity Vs photon energy
But first what is intensity?
Intensity can be described many different ways.
max
―
reading
One definition is to say that it is the amount of energy in the beam of radiation.
For this presentation it will be the NUMBER of photons in the beam of radiation.
number of
photon per
energy unit
0
0
photon energy
KeV
max energy photon
kVp setting
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Gph 1
Graph of intensity Vs photon energy
First will examine ideal bremsstrahlung production
max
―
reading
start by looking at a
photons with energy E1
Count the number of
photons at this energy.
number of
photon per
energy unit
Low energy
photon
E1
The number of low energy is large because
most of the interaction between the electrons
and the nuclear field is at great distances.
0
0
10 KeV
E1
which could be 10 KeV
energy photons
photon energy
KeV
max energy photon
kVp setting
Main Menu
Gph 2
Graph of intensity Vs photon energy
First will examine ideal bremsstrahlung production
NEXT look at photons with energy E2
max
―
reading
Again count the number of photons at this energy.
But the number of photons counted at this
energy value will be SIGNIFICANTLY SMALLER.
number of
photon per
energy unit
This is because the incoming electron have
to be much closer to the nucleus of the
atom to have higher energy .
0
0
10 KeV
20 KeV
E1
E2
photon energy
KeV
max energy photon
kVp setting
which could be 20 KeV
energy photons
Main Menu
Remember HIGHER energy photons are smaller
because they have smaller wavelength’s.
Gph 3
Graph of intensity Vs photon energy
First will examine ideal bremsstrahlung production
max
―
reading
This process is repeated for a number of different photon energies.
A straight line can be drawn to connect the points.
ideal bremsstrahlung production
number of
photon per
energy unit
0
0
10 KeV
20 KeV
E1
E2
photon energy
KeV
max energy photon
kVp setting
Main Menu
Gph 4
Graph of intensity Vs photon energy
First will examine ideal bremsstrahlung production
This will harden the beam of
radiation due to the filtering effects
of the target and glass housing.
max
―
reading
ideal bremsstrahlung production
This is for an ideal beam, but
a practical beam must interact
with the target material and
the glass housing.
number of
photon per
energy unit
0
0
E1
E2
photon energy
KeV
max energy photon
kVp setting
Main Menu
Gph 5
Graph of intensity Vs photon energy
First will examine ideal bremsstrahlung production
photons coming from the target
max
―
reading
ideal bremsstrahlung production
number of
photon per
energy unit
atoms in the
glass housing
First look at just Low Energy Photons
As can be seen very few low
energy photon get past the glass.
0
0
Thus having a very low intensity.
E1
E2
photon energy
KeV
max energy photon
kVp setting
Main Menu
Gph 6
Graph of intensity Vs photon energy
First will examine ideal bremsstrahlung production
max
―
reading
Next a look at higher energy photons.
This process is repeated
for a number of different
photon energies.
number of
photon per
energy unit
photons coming from the target
ideal bremsstrahlung production
Even through there are many fewer
higher energy photons more of them
get through the glass.
0
0
E1
E2
photon energy
KeV
Thus giving a higher number
max energy
photon
then the low energy
photons.
kVp setting
Main Menu
Gph 7
Graph of intensity Vs photon energy
First will examine ideal bremsstrahlung production
max
―
reading
Next draw a line that connects all the points.
This process is repeated
for a number of different
photon energies.
number of
photon per
energy unit
ideal bremsstrahlung production
This is the photon intensity
after the what is called inherent
filtration due to the target and
tube housing.
0
0
E1
E2
photon energy
KeV
max energy photon
kVp setting
Main Menu
Gph 8
Graph of intensity Vs photon energy
First will examine ideal bremsstrahlung production
characteristic radiation
(needs to be added to the radiation already there)
Contribution of characteristic radiation to total x-ray production is:
max
―
reading
At 80 KVp about 10% of total.
Increasing to about 28% at 150 KVp.
Decreasing after that and becoming negligible above 300 KVp.
ideal bremsstrahlung production
number of
photon per
energy unit
0
0
E1
E2
photon energy
KeV
max energy photon
kVp setting
Main Menu
Gph 9
Effects of
1. mas
2. KvP
3. Target Material
on
Quality and Quantity
Main Menu
0
Quality and Quantity
Main Menu
Q&A 0
Quality and Quantity
Tube 1
This one operating at:
Two
X-ray Tube
100 KVp
Tube 2
This one operating at:
200 KVp
100 KeV
200 KeV
electrons
electrons
100 KV
X-ray Beam
Ionization chamber
distance from
source 50cm
200 KV
X-ray Beam
Ionization chamber
Main Menu
Q&A 1
Quality and Quantity
Two
X-ray Tube
Tube 1
This one operating at:
100 KVp
Tube 2
This one operating at:
200 KVp
100 KeV
200 KeV
electrons
electrons
100 KV
X-ray Beam
200 KV
X-ray Beam
distance from
source 50cm
Beam 1
Beam 2
40mR/min
15mR/min
Beam 1 has a higher
intensity then Beam 2.
Thus it has a higher
Quantity but lower
Quality (penetration).
Beam 2 on the other hand has
a higher penetration then
Beam 1, therefore it has a
higher Quality but lower
Quantity (intensity).
Main Menu
Q&A 2
Quality and Quantity
Two
X-ray Tube
Tube 1
This one operating at:
100 KVp
200 KVp
100 KeV
200 KeV
electrons
electrons
100 KV
X-ray Beam
I2 = I1
d1
d2
= 40mR/min
50cm 2
100cm
= 40mR/min
1 2
2
= 10mR/min
200 KV
X-ray Beam
distance from
source 50cm
Beam 1
Beam 2
40mR/min
15mR/min
Use inverse square law
to find new intensity.
2
Tube 2
This one operating at:
distance from
source 100cm
10mR/min
This Beam 1 now measured at this new
distance has a lower intensity then
Beam 2. Thus is not it only has a lower
Quality (penetration) but also a lower
Quantity.
Main Menu
Q&A 3
milliampere second ( mas )
NOTE: the KVp will be held constant for this part.
AC power supply
rectifier
-
+
KVp power out
tungsten
filament
cathode
(-)
-
anode
(+)
tungsten target
+
Main Menu
mas 1
milliampere second ( mas )
NOTE: the KVp will be held constant for this part.
One way to control the intensity of an xray tube is to control the number of
electrons that strike the target.
AC power supply
rectifier
-
+
KVp power out
tungsten
filament
cathode
(-)
electrons
anode
(+)
tungsten target
To control the number of electrons that strike
the target you adjust the heat of the filament.
-
+
This is accomplished by controlling
the current flow through the filament.
The higher the current flow the higher the temperature
and thus more electrons that are boiled off.
Main Menu
mas 2
milliampere second ( mas )
NOTE: the KVp will be held constant for this part.
But milliampere second ( mas ) refers to the
current flow from the cathode to the anode and
NOT the current flow through filament itself.
AC power supply
rectifier
-
+
KVp power out
Let this represents a setting of 200 milliamperes for 1 sec or 200 mas
-
+
which could give rise
to 40 mR of exposure
200 ma × 1 s = 200 mas ⇒ 40 mR of exposure
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mas 3
milliampere second ( mas )
NOTE: the KVp will be held constant for this part.
AC power supply
rectifier
-
+
KVp power out
Let this represents a setting of 200 milliamperes for 1 sec or 200 mas
or the setting could have been
100 milliamperes for 2 sec or 200 mas
-
+
Again the exposure would be the same.
200 ma × 1 s = 200 mas ⇒ 40 mR of exposure
100 ma × 2 s = 200 mas ⇒ 40 mR of exposure
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mas 4
milliampere second ( mas )
NOTE: the KVp will be held constant for this part.
At this point increase the mas from 200 mas to 400 mas.
AC power supply
rectifier
-
+
KVp power out
These added electrons will generate the same energy photons as the first group of electrons.
That is true because the new electrons have the
same energy as the first electrons, therefore the
photons that are produced will also have the
same average energy.
There are now twice the number of electrons striking the target.
-
+
100 ma × 2 s = 200 mas ⇒ 40 mR of exposure
Main Menu
mas 5
milliampere second ( mas )
NOTE: the KVp will be held constant for this part.
AC power supply
rectifier
-
+
KVp power out
Therefore with an setting of 400 mas the exposure would be 80 mR.
Thus intensity (I) and mas are directly related.
-
+
I1
mas1
—— = ———
I2
mas2
100 ma × 2 s = 200 mas ⇒ 40 mR of exposure
400 mas ⇒ 80 mR of exposure
Main Menu
mas 6
milliampere second ( mas )
NOTE: the KVp will be held constant for this part.
graph of intensity vs photon energy for different mas setting
( same KVp setting )
The AC
change
in supply
tube mas results
power
in a proportional change in the
x-ray intensity at all energies.
400 mas
Intensity
rectifier
-
+
KVP power out
200 mas
0
25
50
But the photons that are
produced will have the
same average energy, thus
the QUALITY of the x-ray
beam will remain the SAME.
characteristic
radiation 75
100
Photon energy (KeV)
Thus intensity (I) and mas are directly related.
-
+
I1
mas1
—— = ———
I2
mas2
100 ma × 2 s = 200 mas ⇒ 40 mR of exposure
400 mas ⇒ 80 mR of exposure
Main Menu
mas 7
Kilo Voltage potential ( KVp ) NOTE: the mas will now be held constant for this part.
One very important way of controlling
QUALITY and Quantity of an x-ray beam
is to control the voltage of the tube.
AC power supply
rectifier
-
+
KVP power out
KVp
-
+
Main Menu
KVP 0
Kilo Voltage potential ( KVp ) NOTE: the mas will now be held constant for this part.
One very important way of controlling
QUALITY and Quantity of an x-ray beam
is to control the voltage of the tube.
AC power supply
rectifier
-
+
KVP power out
72 KVp
Let the setting be 72 KVp
-
+
which could give rise
to 50 mR of exposure at
some fixed mas setting
KVp control setting
72 KVp ⇒ 50 mR of exposure
Main Menu
KVP 1
Kilo Voltage potential ( KVp ) NOTE: the mas will now be held constant for this part.
AC power supply
At this point increase the
KVp from 72 to 82 KVp.
rectifier
-
+
KVP power out
72 KVp
82
The number of electrons striking the target is still the same (same mas setting).
But the energy of the electrons has increased ( higher KVP ).
Thus the photons that are produced will
also have a higher energy than before.
There will also be an increased in the efficiency of
converting the electron energy to photon energy.
-
+
KVp control setting
72 KVp ⇒ 50 mR of exposure
82 KVp
Main Menu
KVP 2
Kilo Voltage potential ( KVp ) NOTE: the mas will now be held constant for this part.
AC power supply
rectifier
-
+
KVP power out
82 KVp
KVp1 2
—— = ———
I2
KVp2
I1
-
+
I1 = 50 mR 82 KVp
72 KVp
= 64.8 mR
It was found that the intensity of the radiation
produced is related to the square of the voltage.
2
KVp control setting
72 KVp ⇒ 50 mR of exposure
82 KVp ⇒ 64.8 mR of exposure
Main Menu
KVP 3
Kilo Voltage potential ( KVp ) NOTE: the mas will now be held constant for this part.
graph of intensity vs photon energy for different KVp setting
( same mas setting )
82 KVp
It can be seen that the area
AC power supply
under the curve has greatly
increased by changing the
voltage from 72 to 82KVp.
Intensity
72 KVp
82 KV beam
-
72 KV beam
+
82 KVP power out
50 characteristic75
radiation
25
Thus increasing Quantity
rectifier
of the x-ray beam.
Photon energy (KeV)
The maximum intensity
has shifted to the right.
100
Also the higher energy
photons have increased by
a larger amount then the
lower energy photons.
Thus increasing the hardness
of the beam of radiation.
KVp1 2
—— = ———
I2
KVp2
I1
-
+
KVP control setting
72 KVp ⇒ 50 mR of exposure
82 KVp ⇒ 64.8 mR of exposure
Main Menu
KVP 4
Target Material ( Z )
Last way that will be examined to
control QUALITY and QUANTITY of
an x-ray beam is to look at the
target material itself.
AC power supply
rectifier
-
+
At this time take a closer look inside the target
-
+
Main Menu
TM 0
Target Material ( Z )
Main Menu
TM 1
Target Material ( Z )
The target is made
up of individual
tungsten atoms.
tungsten atoms
At this time will only be
studying bremsstrahlung
production
therefore
need to look only at the
nucleus of the atoms.
Main Menu
TM 2
Target Material ( Z )
will only examine
one atom in the
target
therefore it has a
+74 charge
the atomic number Z for
tungsten (W) is 74
Main Menu
TM 3
Target Material ( Z )
The amount of energy lost by the electron is
dependent on the strength of the nuclear field
and the distance from the nucleus.
40 KeV electron
(interaction with tungsten nucleus )
+74 charge
an electron with
90 KeV energy
interacts by
bremsstrahlung
In this example lets say that the electron
had a close encounter with the nucleus,
and therefore lost 50 KeV of energy.
50 KeV photon
(interaction with tungsten nucleus )
Main Menu
TM 4
Target Material ( Z )
Intensity
standard graph of intensity vs photon energy
tungsten Z=74
40 KeV electron
(interaction with tungsten nucleus )
25
90 KeV energy
50 characteristic75
radiation
100
Photon energy (KeV)
50 KeV photon
(interaction with tungsten nucleus )
Main Menu
TM 5
Target Material ( Z )
Again, the amount of energy lost by the electron
is dependent on the strength of the nuclear field
and the distance from the nucleus.
30 KeV electron
( interaction with gold nucleus )
NEXT:
Change the target
to gold with Z= 79
+79 charge
90 KeV energy
repeat
The distance from the nucleus and the energy
of the electron is the same as before, but the
charge on the nucleus is greater, therefore the
interaction between them is stronger. Thus the
energy lost by the electron will be greater.
40 KeV electron
( interaction with tungsten nucleus )
interacts by
bremsstrahlung
NEXT:
plot intensity vs
photon energy
60 KeV photon
( interaction with gold nucleus )
50 KeV photon
( interaction with tungsten nucleus )
Main Menu
TM 6
Target Material ( Z )
standard graph of intensity vs photon energy
As the graph indicates NOT ONLY is the intensity of the x-ray tube higher because of
the higher atom number material, but there are more higher energy photons then
lower energy photons in the beam, thus also increasing the QUALITY of the beam.
30 KeV electron
( interaction with gold nucleus )
If the atomic number is lowered
then the opposite effect is be seen.
Intensity
gold
Z=79
tungsten Z=74
125 KeV energy
40 KeV electron
( interaction with tungsten nucleus )
Some x-ray tubes use a low
atomic number material, so as
to better x-ray soft tissue.
NEXT:
plot intensity vs
photon energy
molybdenum
Z=42
25
50 characteristic75
radiation
60 KeV photon
100 with gold nucleus )
( interaction
Photon energy (KeV)
50 KeV photon
( interaction with tungsten nucleus )
Main Menu
TM 7
X-Ray Distribution
X-Ray Distribution
around a thin target
Main Menu
Dis 0
X-Ray Distribution
thin
target
Note: The x-ray intensity is the same in all directions.
electron beam
100 KV
400 KV
100 KeV
400 KeV
x-ray intensity
Note: As the electron energy is increased the
x-ray distribution starts to have an increased
intensity in the forward direction.
Main Menu
Dis 1
X-Ray Distribution
thin
target
electron beam
Note:
The increased forward direction of the distribution
become more pronounced as the energy of the
incident electron increases.
100 KV
400 KV
20 MV
4 MeV
20 MeV
4 MV
Main Menu
Dis 2
X-Ray Distribution
thin
target
electron beam
100 KV
400 KV
20 MV
electrons
target
x-rays
4 MV
Patient
target
electrons
x-rays
Patient
Because of the x-ray distribution, for low
energy x-ray production a reflective type
target is used. This is were the electrons
and the x-ray's that are utilized are both on
the same side of the target.
For high energy x-ray production a transmission
type target is used. This is were the electrons
and the x-ray's that are utilized are on opposite
sides of the target.
Main Menu
Dis 3
Line Focus
Line Focus
Main Menu
LF 0
Line Focus
Source
Point
Source
Patient
Bone
Film
Bone
Beam eye view of a portion of the film.
If the size of the source
is a point source then the
image is sharp.
LF 0.1
Line Focus
Two more point sources are
added at the ends of the
original source.
Source
Patient
Bone
Film
Bone
The size of the shaded area is
determined by a number of factors.
One of which is the source size.
Thus the problem is how to reduce the
source size and dissipate the heat that
is generated in a reasonable time so
that the patient dose not move.
LF 0.2
Line Focus
The electrons strikes the actual
target area on the anode and
some of their energy, about 1%,
is transformed into x-rays.
anode - target
focal spot
actual focal spot
Electron Flow
The remainder of the energy,
about 99%, is converted into
heat that must be dissipated
by the target.
But the larger the focal spot, the less
detail that can be seen on the x-ray film.
Thus a bigger focal spot would be needed
to allows for the accumulation of larger
amounts of heat before damage to the
tungsten target can occurs.
These two conflicting problems, the need for a large focal spot to dissipate the
heat, and the need for a small focal spot to produce good radiographic detail
were resolved in 1918 with development of the LINE FOCUS PRINCIPLE.
Main Menu
LF 1
Line Focus
anode - target
focal spot
actual focal spot
Electron Flow
The patient, which is at right angle
to the electron flow, will see what is
called the apparent focal spot.
apparent focal spot
Main Menu
This is equivalent to source size.
LF 2
Line Focus
anode - target
focal spot
actual focal spot
Electron Flow
To make the target area appear
smaller you make the angle of
the target smaller
this is the new
apparent source size
Main Menu
LF 3
Line Focus
anode - target
focal spot
actual focal spot
Electron Flow
To make the target area appear
smaller you make the angle of
the target smaller
The anode angle vary
from about 6O to 20O.
this is the new
apparent source size
There is a limit to which the
anode angle can be decreased
because of the anode heel effect.
Main Menu
LF 4
Anode Heel Effect
Anode Heel Effect
Main Menu
AH 0
Anode Heel Effect
(+) anode
(-) cathode
filament
tungsten target
central axis
- +
filament power
control (mas)
Film
NEED to graph film density VS film position
film density = dose and/or intensity
intensity
Main Menu
position
AH 1
Anode Heel Effect
(+) anode
Enlarge
(-) cathode
electron interaction
generating X-rays
electron
filament
tungsten target
- +
filament power
control (mas)
Film
film density = dose and/or intensity
intensity
Main Menu
position
AH 2
Anode Heel Effect
Film
40” SID
Film
Main Menu
AH 3
Anode Heel Effect
In the diagnostic energy range the
x-ray production is isotropic, that is,
equal in all directions.
First label each
ray in the beam.
If we assume an ideal point source.
Than the exposure would have
a circular distribution centered
on the source.
40” SID
1
2
3
4
5
6
7
100
Film
Thus the exposure at the central ray on the film (ray 4)
would normally have the highest value.
All exposure will be compared
to the central ray on the film.
Thus its value is 100%.
Main Menu
AH 4
Anode Heel Effect
But Ray 3 has less target
material to travel through.
Thus its relative
strength is greater.
As you move laterally from the central ray, in either
direction, the expectation is that the exposure
would be lower due to the inverse square law.
1
2
3
4
5
6
7
will first examine left side
40” SID
105
100
Film
Ray 3 should be little less then the center ray
because it is a little further away from the source.
Main Menu
AH 5
Anode Heel Effect
Depending on the angle of the ray,
which will determine the distance
from the source to the film,
and how much target material
is in its path will determine the
relative exposure.
1
40” SID
108
2
110
3
105
4
100
5
6
7
Film
The same reasoning would
apply to rays 1 and 2.
Main Menu
AH 6
Anode Heel Effect
1
40” SID
108
2
110
3
105
4
100
5
90
6
7
80
75
Film
The logic on the right side is the same, but
because of the greater amount of target material
in the path of the rays the exposure will be less
than the central ray exposure.
Main Menu
AH 7
Anode Heel Effect
cathode side
40” SID
1
108
2
110
3
105
4
100
5
6
90
anode side
7
80
75
Film
field size at 40 SID
Three important points are illustrated with this
example of the anode heel effect.
1 – The intensity on the anode side of the film is
significantly less than the cathode side of the tube.
2 – The anode heel effect is much less noticeable when
larger Source Image Distance is used.
3 – For the same Source Image Distance the anode heel
2
3 be less for smaller
4
effect will
field sizes.5
1
6
same field size at 40 SID
70” SID 108
110
intensity
Main Menu
105
100
cathode side
90
80
anode side
center axis
film position
AH 8
FILTERS
FILTERS
Main Menu
FL 0
first 5 low energy photons (i.e. 100 KeV of energy each)
FILTERS
second 5 high energy photons (i.e. 200 KeV of energy each)
For simplicity will examine a beam of radiation that
consist of just two different energy photons.
Remember the higher the energy of the
photons the smaller the wavelength.
Therefore, the higher energy photons will be smaller.
Main Menu
FL 1
first 5 low energy photons (i.e. 100 KeV of energy each)
FILTERS
second 5 high energy photons (i.e. 200 KeV of energy each)
unfiltered
beam
average energy = 150 KeV
Find the average energy of this unfiltered beam .
Because the number of high and low energy photons are the same:
100 KeV + 200 KeV
average energy = ——————————
2
300 KeV
= —————
2
= 150 KeV
Main Menu
FL 2
first 5 low energy photons (i.e. 100 KeV of energy each)
FILTERS
second 5 high energy photons (i.e. 200 KeV of energy each)
unfiltered
beam
average energy = 150 KeV
Intensity = 1500 KeV
Find the Intensity of this beam.
The intensity of the beam is the amount of energy in the beam.
therefore
Intensity = 5 × 100 KeV
=
500 KeV
=
1500 KeV
+
5 × 200 KeV
+
1000 KeV
Main Menu
FL 3
first 5 low energy photons (i.e. 100 KeV of energy each)
FILTERS
second 5 high energy photons (i.e. 200 KeV of energy each)
unfiltered
beam
average energy = 150 KeV
Intensity = 1500 KeV
filter
Atoms that
makeup the
filter
Main Menu
FL 4
first 5 low energy photons (i.e. 100 KeV of energy each)
FILTERS
second 5 high energy photons (i.e. 200 KeV of energy each)
unfiltered
beam
average energy = 150 KeV
Intensity = 1500 KeV
Main Menu
FL 5
first 5 low energy photons (i.e. 100 KeV of energy each)
FILTERS
second 5 high energy photons (i.e. 200 KeV of energy each)
unfiltered
beam
filtered
beam
average energy = 150 KeV
Intensity = 1500 KeV
2 low energy photons remaining
4 high energy photons remaining
average energy = 166.7 KeV
Find the average energy of the filtered beam.
average energy =
=
2 × 100 KeV
+
6
4 × 200 KeV
200 KeV
+
6
800 KeV
=
1000 KeV
6
=
166.7 KeV
Main Menu
FL 6
first 5 low energy photons (i.e. 100 KeV of energy each)
FILTERS
second 5 high energy photons (i.e. 200 KeV of energy each)
unfiltered
beam
filtered
beam
average energy = 150 KeV
Intensity = 1500 KeV
2 low energy photons remaining
4 high energy photons remaining
average energy = 166.7 KeV
Intensity = 1000 KeV
Find the Intensity of this beam.
The intensity of the beam is the amount of energy in the beam.
therefore
Intensity = 2 × 100 KeV
=
200 KeV
=
1000 KeV
+
4 × 200 KeV
+
800 KeV
Main Menu
FL 7
first 5 low energy photons (i.e. 100 KeV of energy each)
FILTERS
second 5 high energy photons (i.e. 200 KeV of energy each)
unfiltered
beam
filtered
beam
average energy = 150 KeV
Intensity = 1500 KeV
2 low energy photons remaining
4 high energy photons remaining
average energy = 166.7 KeV
Intensity = 1000 KeV
As can be seen the average energy of
the beam has increased, therefore
making the beam more penetrating.
But this came at the cost of reduced intensity,
therefore in radiation therapy the Beam On
Time must be increased to keep the dose the
same and in diagnostic radiology the mas must
be increased to keep the film density the same.
Main Menu
FL 8
FILTERS
graph of intensity vs photon energy for different filters
SAME mas and KVP settings
2mm Al
added filtration
Effect of Filters on Patient
Exposure in Diagnostic Radiology
intensity
Trout and coworkers demonstrated
the degree of patient protection
afforded by filters
4mm Al
added filtration
0
25
characteristic
radiation 75
50
photon energy (KeV)
100
Exposure to Skin for same density
film of a 18 cm thick pelvic
phantom using 60 kVp x-ray beam.
Al
Exposure Decrease in
filter
to skin exposure dose
(mm)
(mR)
(%)
None
2380
—
Increased the filtration from 2 mm Al to 4 mm Al.
0.5
1850
22
As can be seen the intensity has decreased.
1.0
1270
47
3.0
465
80
But the quality of the beam has increase.
This is because more of the low
energy photons have been removed .
and less high energy photons have been removed.
As can be seen there is a large
reduction in patient exposure
by up to 80% with a 3 mm of
aluminum filter.
Main Menu
FL 9
FILTERS
Combination filters used in Radiation Therapy
X-ray tube
graph of intensity vs photon energy for different filters
intensity
characteristic
radiation of tungsten
( 58 & 69 KeV )
next graph output
Al filter
the high energy characteristic
radiation of tungsten target will
come through the aluminum filter
and reach the patient
0
50
100
150
photon energy (KeV)
Al
first add aluminum filter
200
The lower energy characteristic radiation of
the tungsten will be effectively removed by the
inherent as well as the added filtration.
The characteristic radiation of aluminum ( 1.5 KeV ) will be effectively
removed by the intervening air molecules before reaching the patient.
Main Menu
FL 10
FILTERS
Combination filters used in Radiation Therapy
X-ray tube
graph of intensity vs photon energy for different filters
intensity
Sn
Al
Al filter
Al & Sn (tin)
combination filter
VERY IMPORTANT NOTE
the aluminum MUST be placed
closest to the patient
characteristic radiation
of Sn (tin) 29 KeV
0
50
100
150
photon energy (KeV)
200
NEXT add tin ( Sn ) filter to the aluminum filter
If the filter is placed in the wrong order, then the soft
characteristic radiation ( 29 KeV ) coming from the tin filter
would be MUCH GREATER. This is because the aluminum filter
would not be on the patient side to absorb most of the
soft characteristic radiation coming from the tin.
Main Menu
FL 11
FILTERS
Combination filters used in Radiation Therapy
X-ray tube
graph of intensity vs photon energy for different filters
intensity
Sn
Al
Al filter
Al & Sn (tin)
combination filter
But there are still some low energy photons in the
beam form the characteristic radiation of tin.
characteristic radiation
of Sn (tin) 29 KeV
0
50
100
150
photon energy (KeV)
As can be seen the intensity has decreased
considerably in the 30 to 70 KeV range.
200
To remove these low energy photons in this
energy range a copper filter is added between
the aluminum and the tin filters.
Thus the quality of the beam has increased.
Main Menu
FL 12
FILTERS
Combination filters used in Radiation Therapy
X-ray tube
intensity
graph of intensity vs photon energy for different filters
Sn
Cu
Al
Al filter
Al & Sn (tin)
combination filter
VERY IMPORTANT NOTE:
The aluminum MUST be placed
closest to the patient and the tin
closest to the x-ray tube.
characteristic radiation
of Sn (tin) 29 KeV
0
50
100
150
photon energy (KeV)
combination filter
Sn (tin)
Cu (copper)
Thoraeus filter
Al (aluminum)
200
To remove these low energy photons in this
energy range a copper filter is added between
the aluminum and the tin filters.
Main Menu
FL 13
Half Value Layers
Half Value Layers
Main Menu
HVL 0
Half Value Layers
X-ray tube
electron flow
heat filament
central
axis
ionization
chamber
Main Menu
HVL 1
Half Value Layers
X-ray tube
Description of the
x-ray beam is:
electron flow
90 KVP
The inherent filtration of this x-ray tube is
such that for a set of 90 KVP and some
mas the OUTPUT is 120 R/min.
This is the way the beam would be used.
Thus a patient would be placed in the
beam for treatment or an x-ray.
120 R/min
Main Menu
HVL 2
Half Value Layers
X-ray tube
electron flow
90 KVP
BUT just knowing the KVP of the beam
does NOT convey enough information
about the beam’s hardness.
In order to have a better knowledge of the
beams penetration they used the
Half-Value Thickness of the beam.
Depending on the beams energy either
aluminum or copper
was used.
For low energy beams (superficial)
aluminum was used.
Density is 2.70 gm/cm3
For higher energy beams (orthovoltage)
copper was used.
Density is 8.96 gm/cm3
Therefore because this beam is a
superficial unit,
aluminum will be used to describe its
hardness.
Tx Beam
120 R/min
120 R/min
Avogadro's number = 6.0221415 × 1023
Main Menu
HVL 3
Half Value Layers
X-ray tube
electron flow
90 KVP
Thus at this point turn off the beam.
Place an aluminum block in the path of the
beam that will reduce the intensity by 50%.
Example:
As a first attempt let us
try 2mm AL block.
2mm AL
Tx Beam
120 R/min
Main Menu
HVL 4
Half Value Layers
X-ray tube
electron flow
90 KVP
2mm AL
Let us add 1 more mm
of AL to the block.
1mm AL
3mm AL
The intensity was NOT reduced
by 50% thus you would need to
make the AL block thicker.
Tx Beam
120 R/min
80 R/min
60 R/min
Main Menu
HVL 5
Half Value Layers
X-ray tube
electron flow
90 KVP
If you needed a more penetrating beam then
you would need to a filter.
(Assuming you did NOT increase the KVP).
2mm AL
1mm AL
3mm AL
Thus the Half-Value Layer
for this beam is 3mm AL.
Tx Beam
120 R/min
60 R/min
Main Menu
HVL 6
Half Value Layers
X-ray tube
electron flow
90 KVP
If you needed a more penetrating beam then
you would need to a filter.
(Assuming you did NOT increase the KVP).
Let us again place an aluminum
block in the path of the beam that
will reduce the intensity by 50%.
3mm AL
Again the intensity was NOT
reduced by 50% thus you would
need to make the AL block thicker.
You will note that the
Tx Beam
intensity is lower
110 R/min
than before.
65 R/min
Main Menu
HVL 7
Half Value Layers
X-ray tube
electron flow
90 KVP
Thus the Half-Value Layer
for this beam is 4.5mm AL.
3mm AL
4.5mm AL
1.5mm AL
Again the intensity was NOT
reduced by 50% thus you would
need to make the AL block thicker.
Tx Beam
110 R/min
55 R/min
65 R/min
Main Menu
HVL 8
Half Value Layers
Graph
monoenergetic x-ray beam
Graph
polyenergetic x-ray beam
10090
10090
In a monoenergetic x-ray
beam the first HVL is the
same as the second HVL.
50
40
30
In this example 2 cm.
20
10
9
8
7
6
5
4
3
2
Thus in a monoenergetic beam adding
filters dose NOT change the hardness of
the beam, it just reduces the intensity.
1
0
2
4
6
8
absorber thickness
cm of aluminum
10
12
80
70
60
Percent Transmitted Intensity
Percent Transmitted Intensity
80
70
60
50
40
In a polyenergetic x-ray
beam the first HVL is smaller
then the second HVL.
In this example
the first HVL is 2 cm.
30
20
10
And the second
HVL is 4 cm.
9
8
7
6
5
And the third
HVL is 4.1 cm.
4
Thus
in a polyenergetic beam adding filters
3
increases the hardness of the beam, by
preferentially
absorbing the low energy
2
photons over the higher energy photons.
Again adding
the filters does
1
increases the hardness of the beam,
0
2
4
6
but at the cost of reduced intensity.
8
10
12
absorber thickness
cm of aluminum
Main Menu
HVL 9
Quality & Quantity
Summary of factors that effect Quality and Quantity
Summary of factors that
effect Quality and Quantity
Main Menu
QQ 0
Quality & Quantity
Summary of factors that effect Quality and Quantity
mAs
KVP
Z
of target
filtration
distance
Quantity
(Intensity)
(amount)
Quality
(penetration)
(hardness)
Main Menu
QQ 1
Quality & Quantity
Summary of factors that effect Quality and Quantity
total # of
electrons
mAs
Quantity
(Intensity)
(amount)
KVP
Z
of target
filtration
distance
filling in
for the
converse
Quality
(penetration)
(hardness)
mAs (milliampere second ) is the total number of electrons that strike the target
If the number of electrons that hit the target is increased then the number of photons
that are produced will also increase, therefore the intensity of the beam will increase.
Thus the change in
I1
mAs1
intensity is directly
—— = ———
proportional to the
I2
mAs2
change in mAs
Changing the number of electrons that strike the target
will not change the energy that each electron will have.
Therefore, the energy of the photons will not change,
thus the beam hardness will remain the same.
Main Menu
QQ 2
Quality & Quantity
Summary of factors that effect Quality and Quantity
total # of
electrons
mAs
KVP
Z
of target
filtration
distance
Quantity
(Intensity)
(amount)
Quality
(penetration)
(hardness)
KVP (Kilo Volt Potential ) is the driving voltage used to give the electrons their energy
Increasing the KVP will cause a
large increase in x-ray intensity.
KVP1
—— = ———
I2
KVP2
I1
2
The change in intensity
is proportional to the
square of the ratio of
the voltages.
Increasing the voltage will increase the energy of the
electrons which will in turn increase the energy of the
photons thus increasing the hardness of the beam.
In balancing kVp and mAs to produce a
constant optical density on a film there is a
rule of thumb which states that a 15% increase
in kVp is equivalent to doubling the mAs.
Main Menu
QQ 3
Quality & Quantity
Summary of factors that effect Quality and Quantity
total # of
electrons
mAs
KVP
Z
of target
filtration
distance
Quantity
(Intensity)
(amount)
Quality
(penetration)
(hardness)
Z is atomic number of target
Increasing the atomic number will
increase the strength of the nuclear
field which will cause a proportional
increase in x-ray intensity.
Because of an increase in the strength of the
nuclear field there is also an increase in the
efficiency in high-energy x-ray production as
compared to low energy x-rays. Therefore, there is
an overall increase in hardness.
Main Menu
QQ 4
Quality & Quantity
Summary of factors that effect Quality and Quantity
total # of
electrons
mAs
KVP
Z
of target
filtration
distance
Quantity
(Intensity)
(amount)
Quality
(penetration)
(hardness)
filtration: there are two types of filtration
● inherent filtration
● added filtration
inherent filtration is due to the glass housing and the
target of the x-ray tube. As the x-rays leave the target
and traverse the glass housing the low energy x-rays
are absorbed, thus hardening the beam.
The inherent filtration for a general
purpose x-ray tube is approximately
equivalent to 0.5 mm aluminum HVL.
Main Menu
QQ 5
Quality & Quantity
Summary of factors that effect Quality and Quantity
total # of
electrons
mAs
KVP
Z
of target
filtration
distance
Quantity
(Intensity)
(amount)
Quality
(penetration)
(hardness)
filtration: there are two types of filtration
● inherent filtration
● added filtration
added filtration is metal that is added
to the x-ray tube to harden the beam
as filtration is added to the x-ray tube
the beam intensity is decreased.
Main Menu
QQ 5
Quality & Quantity
Summary of factors that effect Quality and Quantity
total # of
electrons
mAs
KVP
Z
of target
filtration
distance
Quantity
(Intensity)
(amount)
Quality
(penetration)
(hardness)
distance: is the point at which the intensity is measured from the source of radiation
as distance is increased the
intensity decreases by the
inverse square law
d1
—— = ——
I2
d2
I1
2
Quality is a measure of the photon energies
in the beam of radiation. Since the energies
of the photons do not change over distance
the hardness is unaffected.
END
Main Menu
QQ 6
Questions
You must keep your own score.
Take your time with the mouse click.
Main Menu
Qa 0
1) The process of boiling off electrons is called?
- heat dissipation
b) - electron generation
c) - electron production
d) - thermionic emission
a)
Qa 1.1a
1) The process of boiling off electrons is called?
- heat dissipation
b) - electron generation
c) - electron production
d) - thermionic emission
a)
incorrect
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Qa 1.1b
1) The process of boiling off electrons is called?
- heat dissipation
b) - electron generation
c) - electron production
d) - thermionic emission
a)
“d” is correct
Qa 1.1c
2) The wire that is heated to produce the electrons is made of?
- carbon
b) - tungsten
c) - low atomic number element for heat dissipation
d) - can be any atomic number material
a)
Qa 1.2a
2) The wire that is heated to produce the electrons is made of?
- carbon
b) - tungsten
c) - low atomic number element for heat dissipation
d) - can be any atomic number material
a)
incorrect
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Qa 1.2b
2) The wire that is heated to produce the electrons is made of?
- carbon
b) - tungsten
c) - low atomic number element for heat dissipation
d) - can be any atomic number material
a)
“b” is correct
Qa
1.2c
3) What are the electron interactions that will produce x-rays?
- excitation, ionization
b) - ionization, electron equilibrium
c) - bremsstrahlung, ionization
d) - excitation, bremsstrahlung
a)
Qa 1.3a
3) What are the electron interactions that will produce x-rays?
- excitation, ionization
b) - ionization, electron equilibrium
c) - bremsstrahlung, ionization
d) - excitation, bremsstrahlung
a)
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Qa 1.3b
3) What are the electron interactions that will produce x-rays?
- excitation, ionization
b) - ionization, electron equilibrium
c) - bremsstrahlung, ionization
d) - excitation, bremsstrahlung
a)
“c” is correct
Qa 1.3c
4) The target material of an x-ray tube is chosen because of its:
a)
b)
c)
d)
- high melting point and high atomic number
- high melting point and low atomic number
- low melting point and high atomic number
- low melting point and low atomic number
Qa 1.4a
4) The target material of an x-ray tube is chosen because of its:
a)
b)
c)
d)
- high melting point and high atomic number
- high melting point and low atomic number
- low melting point and high atomic number
- low melting point and low atomic number
incorrect
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Qa 1.4b
4) The target material of an x-ray tube is chosen because of its:
a)
b)
c)
d)
- high melting point and high atomic number
- high melting point and low atomic number
- low melting point and high atomic number
- low melting point and low atomic number
“a” is correct
Qa 1.4c
5) What is efficiency of x-ray production in the diagnostic range?
- 100%
b) - 99%
c) - 1%
d) - need to know the mas setting
a)
Qa 1.5a
5) What is efficiency of x-ray production in the diagnostic range?
- 100%
b) - 99%
c) - 1%
d) - need to know the mas setting
a)
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Qa 1.5b
5) What is efficiency of x-ray production in the diagnostic range?
- 100%
b) - 99%
c) - 1%
d) - need to know the mas setting
a)
“c” is correct
Qa 1.5c
6) An x-ray tube with a setting of 150 mas has an intensity of 75 mR/sec.
What is the intensity if the mas is changed to 200 mas?
a) - 25 mR/sec
b) - 50 mR/sec
c) - 100 mR/sec
d) - 125 mR/sec
Qa 1.6a
6) An x-ray tube with a setting of 150 mas has an intensity of 75 mR/sec.
What is the intensity if the mas is changed to 200 mas?
a) - 25 mR/sec
b) - 50 mR/sec
c) - 100 mR/sec
d) - 125 mR/sec
incorrect
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Qa 1.6b
6) An x-ray tube with a setting of 150 mas has an intensity of 75 mR/sec.
What is the intensity if the mas is changed to 200 mas?
a) - 25 mR/sec
b) - 50 mR/sec
c) - 100 mR/sec
d) - 125 mR/sec
“c” is correct
Qa 1.6c
7) The x-ray intensity is greatest in what direction for a
15 MV linear accelerator:
a) - is equal in all directions
b) - at right angles to electron flow
c) - in the opposite direction of electron flow
d) - in the same direction of electron flow
Qa 1.7a
7) The x-ray intensity is greatest in what direction for a
15 MV linear accelerator:
a) - is equal in all directions
b) - at right angles to electron flow
c) - in the opposite direction of electron flow
d) - in the same direction of electron flow
incorrect
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Qa 1.7b
7) The x-ray intensity is greatest in what direction for a
15 MV linear accelerator:
a) - is equal in all directions
b) - at right angles to electron flow
c) - in the opposite direction of electron flow
d) - in the same direction of electron flow
“c” is correct
Qa 1.7c
8) The x-ray intensity is greatest in what direction for
diagnostic x-ray production?
a) - is equal in all directions
b) - at right angles to electron flow
c) - in the opposite direction of electron flow
d) - in the same direction of electron flow
Qa 1.8a
8) The x-ray intensity is greatest in what direction for
diagnostic x-ray production?
a) - is equal in all directions
b) - at right angles to electron flow
c) - in the opposite direction of electron flow
d) - in the same direction of electron flow
incorrect
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Qa 1.8b
8) The x-ray intensity is greatest in what direction for
diagnostic x-ray production?
a) - is equal in all directions
b) - at right angles to electron flow
c) - in the opposite direction of electron flow
d) - in the same direction of electron flow
“a” is correct
Qa 1.8c