Lessons in Radiography
Using the X-Ray Simulation Program
Student Booklet
Prepared by the North Central Collaboration for Education in NDT. Partial
support for this work was provided by the NSF-ATE (Advanced
Technological Education) program through grant #DUE 9602370. Opinions
expressed are those of the authors and not necessarily those of the National
Science Foundation.
Table of Contents
Introduction .......................................................................................................................... 1
Contents of this Training Packet .................................................................................. 1
Lesson One: Film Properties ................................................................................................ 2
Introduction .................................................................................................................. 2
Objectives ..................................................................................................................... 2
Log Relative Exposure Calculations.............................................................................. 4
Sensitometric Curve Calculations for AGFA Film ...................................................... 5
Simulator Exercise ....................................................................................................... 6
Laboratory Exercise ..................................................................................................... 9
Lesson Two: Kilovoltage Effect on Contrast ..................................................................... 10
Introduction ................................................................................................................ 10
Objectives ................................................................................................................... 10
Calculations ................................................................................................................ 11
Simulator Exercise ..................................................................................................... 13
Writing Assignment ................................................................................................... 15
Laboratory Exercise ................................................................................................... 16
Lesson Three: Milliamperage and Time Relationships...................................................... 17
Introduction ................................................................................................................ 17
Objective .................................................................................................................... 17
Reference Terms......................................................................................................... 17
Formulas for Time and milliamprage Calculations.................................................... 17
Simulator Exercise ..................................................................................................... 20
Laboratory Exercise ................................................................................................... 21
Lesson Four: Creating an Exposure Chart ......................................................................... 22
Introduction ................................................................................................................ 22
Objective .................................................................................................................... 22
Reference Terms......................................................................................................... 22
Calculations ................................................................................................................ 23
Simulator Exercise ..................................................................................................... 24
Laboratory Exercise ................................................................................................... 27
Lesson Five: Source-to-Film Relationships ....................................................................... 28
Introduction ................................................................................................................ 28
Objective .................................................................................................................... 28
Reference Terms......................................................................................................... 28
Simulator Exercise ..................................................................................................... 29
Calculations for source to film distance change......................................................... 30
Laboratory Exercise ................................................................................................... 32
Lesson Six: Radiographic Equivalency Factors ................................................................. 33
Introduction ................................................................................................................ 33
Objective .................................................................................................................... 33
Reference Terms......................................................................................................... 33
Calculations ................................................................................................................ 35
Simulator Exercise ..................................................................................................... 36
Laboratory Exercise ................................................................................................... 37
Lesson Seven: Defect Content ........................................................................................... 38
Introduction ................................................................................................................ 38
Objective .................................................................................................................... 38
Reference Terms......................................................................................................... 38
Simulator Exercise ..................................................................................................... 39
Laboratory Exercise ................................................................................................... 40
Lesson Eight: Defect Shape, and Relationship to X-ray Source ........................................ 41
Introduction ................................................................................................................ 41
Objective .................................................................................................................... 41
Reference Terms......................................................................................................... 41
Simulator Exercise ..................................................................................................... 43
Laboratory Exercise ................................................................................................... 44
Lesson Nine: Image Magnification, Beam Divergence and Distortion ............................. 45
Introduction ................................................................................................................ 45
Objective .................................................................................................................... 45
Reference Terms......................................................................................................... 45
Geometric Enlargement (Magnification) Calculations .............................................. 46
Geometric Unsharpness Calculations......................................................................... 48
Beam Coverage Calculations ..................................................................................... 50
Simulator Exercise ..................................................................................................... 51
Laboratory Exercise ................................................................................................... 52
Lesson Ten: Developing a Radiographic Technique Card................................................. 53
Introduction ................................................................................................................ 53
Objective .................................................................................................................... 53
Reference Terms......................................................................................................... 53
Simulator Exercise ..................................................................................................... 54
Laboratory Exercise ................................................................................................... 56
Introduction
Successful radiography depends on numerous variables that affect the outcome and quality
of a radiograph. Many of these variables have a substantial effect on the results while
others have only a minor effect. One of the difficulties encountered when learning the
basics of radiography is that there is a relatively long lag time between when an exposure
is made and when the resulting radiograph is ready for viewing. This makes it a time
consuming exercise when the lesson call for multiple exposures to be made in order see
the effects that certain exposure variables have on image quality. These lessons use an Xray inspection simulation program that allows beginning radiographers to experiment with
set-up and exposure variables. Simulated radiographs are produced in a matter of seconds
providing immediate feed on the impact that these variables have on the image quality.
The X-ray simulator (XRSIM) program used for these exercises was developed by
researchers at the Center for NDE at Iowa State University. The XRSIM program allows
physically accurate radiographic inspections to be simulated using a computer aided
design (CAD) model of a part. These lesson plans that make use of the XRSIM program
were developed with funding from the National Science Foundation (NSF).
Contents of this Training Packet
Each of the ten lessons in this packet includes:
· an introduction to the main subject of the lesson
· statement of the objectives
· definition of new terms
· exercises that make use of the X-ray simulation program
· exercises for hand-on lab activities
1
Lesson One:
Film Properties
Introduction
In this lesson, the relationship between film speed and exposure will be evaluated.
Calculations will be made using sensitometric curves to determine the best choice of film
for a given exposure or visa-versa. The manufacturer of the film makes no difference, as
all films will work in the same manner. Review the film manufacturer’s literature
available at your school before beginning this exercise.
Objectives
To develop an understanding of industrial radiographic film properties including the
characteristic curves for various films.
To learn to calculate changes in film speeds while maintaining a constant density of the
radiograph.
Reference Terms
Radiographic sensitivity is the general term used to describe the smallest detail that can
be seen using a radiograph. The term also refers to the ease with which images can be
seen or details can be detected. Radiographic sensitivity, in other words, is the amount of
information that can be found on a radiograph. There are two independent sets of factors
that determine the level of radiographic sensitivity, definition and contrast.
Definition refers to the sharpness of the outline in the image. This sharpness depends on
the type of screens and film used. The sharpness of the outline also depends on the
radiation energy used, the geometry of the radiographic specimen and the spot size of the
radiation source.
Radiographic contrast is the difference between the areas of radiographic density. This
difference in the density depends on two factors, subject contrast and film contrast.
Subject contrast is the ratio of X-ray intensities transmitted through two or more portions
of different thickness in a specimen. The energy of the radiation used and its distribution,
and the intensity of the radiation used have to be taken into account when determining the
subject contrast.
Film contrast refers to the slope of the characteristic curve of the film. This contrast
depends on three factors, the type of film being used, the density of the film, and the way
the film is processed. The process used to expose the film is also important. Of
particularly importance is whether the film has been exposed using lead screens or
fluorescent screens.
2
Film grains are the materials that capture the image, which after development becomes a
radiograph. Film grains are made-up of extremely fine silver bromide crystals. There can
be billions of grains in one square centimeter. The larger the grain size the faster the film.
Industry uses a number of film speeds to produce the desired radiographic image
depending on the quality of the radiograph sought.
Logarithm is the number of the exponent of the power of 10 that a number is raised.
Consider a six-inch scale as a linear form of measurement. If we wanted to represent a
great distance in the physical distance of six inches, we would use a logarithmic
measurement or scale. The logarithmic scale moves by factors of ten, and becomes more
compressed the closer to ten the numbers become. Once ten is reached we began counting
by one hundred, and then by one thousand. In radiography, and ultrasound the logarithmic
scale will be used often.
Sensitometric charts are comprised of a group of curves representing the relative
sensitivity of various X-ray films to exposure. The curves are a plot of the film density
versus the logarithm of the relative exposure they must receive to reach a particular
density. Relative exposure means that one of the curves is used as the standard and all
other curves are related to this curve by a factor. The charts are used to make comparisons
between various films and to make exposure and density calculations when changing from
one film to another.
3
Log Relative Exposure Calculations
Use the sensitometric curves in Figure 1 on page 9 to perform the following calculations:
Example.
A density of 2.0 was produced using Type I film with an exposure time of 3.0 milliampminutes. A density of 3.5 on the same film is desired. Find the 2.0 density on the left of the
chart; move horizontally to film Type I and then move down to the log relative exposure
number at the base of the chart (1.30). Repeat these steps to find the log relative exposure
number for a density of 3.5 (1.65). Subtract 1.30 from 1.65, which leaves 0.35. Take the
inverse log of this number, which is 2.24. Now multiply the original time (3.0) by 2.24 to get
the new exposure setting of 6.72 mA-minutes (4 mA for 1 minute 41 seconds) to achieve a
3.5 density on the same film. If the density were to be decreased, or if a second faster film
were used (further to the left on the chart.), the original exposure time would be divided by
the exposure factor.
1.
If a density of 2.0 is produced using Type I film and an exposure of 25-mA-minutes,
what exposure setting is needed to produce a density of 1.5 using the same film?
_______
2.
If an exposure of 8-mAm produces a density of 2.5 when a Type I film is used, what
exposure is needed to produce the same density using a type 2 film? _______
3.
Using a Type II film, a density of 2.0 is produced with an exposure of 11-mAm. What
exposure is required to increase the density to 3.5 using the same film? _______
4.
If a density of 1.5 is produced using Type II film and an exposure of 8-mAm, what
exposure is necessary to produce a density of 2.5 on type 3 film? _______
5.
If a density of 2.25 is produced using Type III film and an exposure of 21-mAm, what
exposure in necessary to produce the same density on type II film? _______
6.
If an exposure of 5-mAm produces a density of 2.0 using a Type I film is, what exposure
is necessary to produce the same density using a type III film? _______
7.
Using a Type II film, an exposure of 9-mAm produces a density of 2.5. What exposure
is necessary to increase the density to 3.0 on the same film? _______
8.
If an exposure of: 7-mAm density of 3.0 on a Type II film, what exposure is required to
produce a 2.0 density on a type 3 film? _______
9.
Using a Type I film, if an exposure of 14-mAm produces a density of 3.0, what
exposure is needed to reduce the density to 1.5 on the same film? _______
10. If a density of 2.4 is produced on a type III film with an exposure of 26-mAm, what
exposure is required to produce the same density on a type II film? _______
4
Sensitometric Curve Calculations for AGFA Film
Using the film chart Figure 2 on page 10, calculate the exposure times needed to
accommodate the density or film type changes.
Example: An exposure of D-4 film for 1.5 minute produced a radiograph with a density of
1.5. The specification requires a density of 2.5. Use the sensitometric curves to select a new
exposure time. First find the 1.5 density point then move horizontally to the D-4 film. Then
move down the chart to locate the log number (2.51) for that exposure. Next move to the
new density 2.5 and move horizontally to the D-4 film, and then down the chart to locate the
log number (2.75). Now subtract the two log values and take the inverse log of this value
(2.75 - 2.51 = 0.24. Take the inverse log of 0.24 to get 1.7378). Round this number to the
nearest tenth and multiply it by the original exposure time (1.5 X 1.7 = 2.55 minutes) to get
the exposure time needed for a 2.5 density on your radiograph.
1. If a density of 1.5 is produced on D8 film with an exposure of 9-mAm, what exposure is
required to produce a density of 3.0 on D4 film? _______________
2. What exposure is required to change the density on D5 film to 3.5 when an exposure of
12-mAm produces a density of 2.3? _______________
3. If a density of 3.0 is produced with an exposure of 22-mAm when D3 film is used, what
exposure will produce a density of 3.0 when D7 film is used? _______________
4. When D2 film is used, a density of 2.25 is produced with an exposure of 17-mAm. What
exposure is required to produce a density of 3.5 on D4 film? _______________
5. Using D4 film, what exposure is required to increase the density to 3.0 when an exposure
of 7-mAm produces a density of 1.5? ________________
6. If an exposure of 3-mAm produces a density of 3.5 on D7 film, what exposure is
necessary to produce a density of 3.0 on D5 film? _________________
7. If a 24-mAm exposure produces a density of 1.5 on a D4 film, what exposure will
produce a density of 2.5 on D7 film? ________________
8. If a density of 2.0 is produced on D8 film with an exposure of 6-mAm, what exposure is
needed to produce a density of 2.5 on D5 film? _________________
9. Using D4 film, what exposure is required to raise the density to 3.5 when an exposure of
6-mAm produces a density of 2.5? _________________
10. If a 7-mAm exposure produces a density of 3.5 on D5 film, what exposure is needed to
produce a density of 2.0 on D3 film? _________________
5
Simulator Exercise
Use the XRSIM program to evaluate the relationship between film speed and exposure
time by completing the following exercise.
1. Review the AGFA sensitometric curves in Figure 2. This chart shows the speeds and
characteristics of various films. Review Table 1, which shows ratios of film speeds.
Notice in Table 1 that all films are referenced to D-7 film.
2. In the XRSIM program, open the stepwedge11cm CAD file and select 2024Al
(aluminum alloy 2024) as the material. Below your material select the display tab, and
check translucent to allow the defect to be viewed within the part. Using the defect tab
select the sphere and choose air as the material. Locate the defect below the surface on
step five. Select the detector tab and change the film to D-7. Use the top view and
click and drag the film to expand it so the film extends beyond the part (The
stepwedge may need to be moved slightly to reveal the film.) Use the HOMX160
generator with an initial setting of 60 kV, 1 mA, and 7 seconds to produce an image
with a density reasonably close to 2.5 on step five of the stepwedge. Use the
view/slice option to evaluate the density of the stepwedge.
NOTE: Remember to change the name of the XRSIM density image (xyz file)
each time you produce a simulated radiograph or the system will save one file
over the other. To open multiple images for viewing, go to open, change file type
to density image and select the desired file. Open the slice option by left clicking
on the “Imageslice” icon. When the slice window opens, select horizontal and
move your cursor over step six on the stepwedge to measure the density.
3. Using the film characteristic curves, calculate a change of density from 2.5 to 3.5 on
D-7 film. Produce an image using XRSIM to confirm the calculation.
4. Change the detector to D-5 (which has a smaller grain and is a slower film) and use the
appropriate calculations to determine the setting needed to generate a density of 3.5 on
step five. Produce an image to confirm the calculation.
5. Manufacturer’s film speed ratio charts give an overview of the characteristic curve
relationships. On Chart 3, note the speed ratio differences for the films produced by
this company. Notice that the manufacturer has chosen D-7 as the standard or “0”
film. D-7 will be the standard against witch other films will be compared. For
example, if you exposed a D-7 film for 33-milliamp seconds, the chart indicates that a
D-5 film would need to be exposed 1.8 times as long. Note the differences between
the other films. Also note the change of exposure ratios as kilovoltage is increased.
Why is this?
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6. Using the film characteristic curves for AGFA films (Figure 1), compare two films, D4 and D-7. If a density of 2.0 were achieved when D-4 film is exposed for 43 mAs at
100 kV, what would be the correct exposure if D-7 film were
used?__________________________
7. After calculating the time difference look on the "relative exposure factor" chart and
find the ratio between the two films.______________________________
Density
8. Was the time change 3 to 1 as predicted by the exposure factor chart? ____________
Figure 1. Film sensitometric (characteristic) curves for three typical film types.
7
Figure 2. Film sensitometric curves for Agfa Structurix industrial X-ray films.
Radiation 100 KV
200 KV ir 192
Film Type
D-2
D-3
D-4
D-5
D-7
D-8
10.6
4.1
3.1
1.8
1.0
0.7
8.7
4.2
2.6
1.6
1.0
0.7
9.0
5.0
3.0
1.5
1.0
0.7
Figure 3. Approximate Relative Exposure Factors for Agfa Structurix Industrial X-ray films.
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Laboratory Exercise
This exercise requires the use of an X-ray generator. Prior to the operation of this
equipment, the required safety training must have been completed and instructions
on the safe operation of the X-ray equipment must have been received.
1. Produce a film radiograph of a 0.1 to 0.5-inch steel stepwedge using the X-ray system
of your choosing in the laboratory. Select an exposure setting (kV, mA and time) for
any one of the steps from an existing exposure chart for the system. Place a lead letter
on the edge of the step and make the exposure. Did your exposure chart correctly
predict the density you achieved? _________________
If not, what was the difference in density? _____________________________
2. Using the manufacture exposure chart for the film used above, and the density
produced on your first exposure, calculate the correct exposure time for a change of
film (faster or slower). Show your calculations, and new time below.
3. Produce a second radiograph using the calculated change in time to compensate for the
change of film. Allowing for some deviation (+/- 5 percent), did your calculations
produce the density predicted? __________________ If not, identify some of the
possible reasons that for the discrepancy.
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9
LESSON TWO:
KILOVOLTAGE EFFECT ON CONTRAST
Introduction
In this lesson, the relationship between energy of the X-rays and the image contrast will be
evaluated. The energy of the X-rays is controlled by the electrical potential of the X-ray
tube. This potential is generally in the range of thousands of volts. X-ray generators will
have a control that allows the voltage to be adjusted and this is generally labeled in
kilovolts. Therefore, it is common to speak of the energy of X-rays in terms of the voltage
used to produce the X-rays and this value is often referred to as the kilovoltage. The
kilovoltage has an effect on the radiographic image because the energy used to produce
the X-rays is related to the penetrating power of the X-rays.
The first requirement in developing a radiographic procedure is to determine what level of
radiation is necessary to penetrate the object being inspected and produce an image in a
practical exposure time. If too high of kilovoltage is used, image quality deteriorates. A
number of methods have been developed for determining the kilovoltage needed to
radiograph an object of certain thickness and material. The two methods that will be covered
here are the Half-Value Layer Method (HVL) and the Fixed Exposure Method.
Objectives
To evaluate how X-ray energy (kilovoltage) effects radiograph quality.
To investigate how different radiographic films affect image contrast.
To lean to apply several multiple methods of determining the kilovoltage required for an
exposure.
Reference Terms
Kilovoltage is a measure of the electrical potential between the anode and the cathode in the
X-ray tube. The higher the kilovoltage, the shorter the wavelength and the greater the
penetrating power of the X-rays produced. The energy level used for an exposure will be
greatly influenced by the material being radiographed because the X- rays must have enough
energy to penetrate through the material being inspected. The kilovoltage should be chosen
carefully because:
1. scatter increases as the energy increases scatter increases
2. contrast sensitivity decreases as energy increases
Latitude refers to the amount of thickness variation that a particular film will be able to
image in one exposure. As latitude increases contrast will diminish, and vice versa.
Half Value Layer is the thickness of a given material that will reduce the radiation passing
through it by one half. The energy of the ray, and the atomic make-up of the material
determine half value layers. As kilovoltage increases the half value layer will decrease.
10
Calculations
Half-Value Layer Method (HVL)
The HVL Method is a simplification of a very complex calculation and only takes a few
variables into consideration. For example, it is assumed that the energy is a single
wavelength and scatter is not a concern. The HVL Method uses values that have been
previously calculated and can be found in Attenuation Coefficient Tables contained in
various references such as the Nondestructive Testing Handbook, Volume Three on
Radiography and Radiation Testing. Using this method:
· ideally the energy level is selected so that the part thickness to be penetrated is 5
Half-Value Layers.
· satisfactory results can be obtained if the deviation from this rule is no greater than a
factor of 2 half-value layers. Therefore, the target range is 3 to 7 half-value layers,
but at a value of three image contrast is questionable and at a value of 7 exposure
time will be excessive.
· the attenuation coefficients for the material must be located from reference materials
and converted to Half-Value Layers using the following formula.
HVL =
0.693
AttenuationCoefficient
Below are linear attenuation factors to be used with aluminum and steel at a number of
kilovoltage settings. Note from the table below that kilovoltage selection has a great affect
on the HVL.
Kilovoltage
Material
Attenuation coefficient
50
Al
0.964
60
Al
0.729
80
Al
0.540
100
Al
0.456
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50
60
80
100
150
200
St
St
St
St
St
St
15.2
9.52
4.71
2.93
1.54
1.15
Example: A steel part that is 1.27 cm thick must be inspected. Choose a kilovoltage that
should produce a radiograph in a reasonable amount of time. From experience, 150 kV is
know to provide good penetrating power and should produce a radiograph in a relatively
short period. From the table, 1.54 is the value that corresponds to 150 keV for steel. Using
the formula, 0.693 divided by 1.54 equals 0.45 cm. 0.45 cm is the half-value layer for 150
kV. Divided the part thickness by the half-value layer to get the number of half value layers
for the chosen kilovoltage setting. 1.27 divided by .45 equals 2.8 or rounded up 3.0 halfvalue layers. This value is at the lower limit of the range and could result in a radiograph
with questionable contrast sensitivity. The calculation should be repeated using a lower
kilovoltage.
11
Work the calculation at 100kv and determine the number of half value layers.
Half value layers at 100 kV______________________. Which setting is closer to
five half value layers 100 or 150 kV? _______________________
Fixed Exposure Method
In this method, the kilovoltage is adjusted to maintain a constant film density for radiographs
of objects with different material thicknesses and properties. Time, milliamperage, and
source-to-film distance are held constant. This method is not as widely used as the HVL
Method because it requires considerable work experience to develop the knowledge to
produce acceptable radiographs. Without these skills this method requires much trial and
error. As you can imagine, this method would require numerous exposures and added time
without the aid of the simulator.
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Simulator Exercise
Simulator Stepwedge Thickness.
Step
1
0.5 cm
Step
2
1.0 cm
Step
3
1.5 cm
Step
4
2.0 cm
Step
5
2.5 cm
Step
6
3.0 cm
Step
7
3.5 cm
Step
8
4.0 cm
Step
9
4.5 cm
Step
10
5.0 cm
1. Using the simulator, open the stepwedge11cm CAD file and select 2024Al (aluminum
alloy 2024) as the material. Select step nine on the stepwedge and place a void (air)
defect 0.55 cm by 0.45 cm by 0.65 cm. in the center of the step.
2. Using the HVL Method, calculate five half-value layers to get the optimum kilovoltage
for step nine on the stepwedge. Create an image with a density of 2.5 on the step using
D-7 film. Save the image in a file (xy1) for comparison with images you will produce
later. Show your calculations below.
Optimum Kilovoltage for step nine ______________________.
3. Create two more images using D-7 film and maintaining a 2.5 density. Create the first
image with the kilovoltage reduced by 50 percent and the second image with an increase
in kilovoltage 3 times the optimum value calculated above.
Which exposure produced the most easily recognizable defect? ________
4. Using the slice option to evaluate density, record the contrast ratio between the defect and
the stepwedge for each exposure.
Exposure 1. _________________
Exposure 2. _________________
Exposure 3. _________________
Was the exposure with the greatest contrast sensitivity the one where the defect was
easiest to see?_____________
5. Using the slice option to evaluate density of the steps. Which exposure produced the
greatest number of steps within a density range of 1.0 to 4.0?
Exposure 1. _________________
Exposure 2. _________________
Exposure 3. _________________
Did this exposure have the highest or lowest contrast sensitivity? _____________
13
6. Recalculate and repeat your three exposures using D-2 film. Show your calculations
below.
Which exposure produced the most easily recognizable defect? ________
7. Using the slice option to evaluate density, record the contrast ratio between the defect and
the stepwedge for each exposure.
Exposure 1. _________________
Exposure 2. _________________
Exposure 3. _________________
Was the exposure with the greatest contrast sensitivity the one where the defect was
easiest to see?_____________
8. Using the slice option to evaluate density of the steps. Which exposure produced the
greatest number of steps within a density range of 1.0 to 4.0?
Exposure 1. _________________
Exposure 2. _________________
Exposure 3. _________________
Did this exposure have the highest or lowest contrast sensitivity? _____________
9.
Note any differences seen when changing films. Describe the contrast and latitude
differences between the two films.
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Writing Assignment
Describe your observations of this laboratory activity in a two-paragraph summary, and be
prepared to discuss those observations during the next class. In your summary, discuss
which method of determining kilovoltage feel is best, and discuss why. Summarize your
observations on why latitude increases and contrast decreases as kilovoltage increases.
15
Laboratory Exercise
Using the Half-Value Layer method, calculate 3, 5 and 7 half-value layers and note the
corresponding kilovoltage for a steel or aluminum stepwedge. Using an exposure chart
developed for the system, compare the kilovoltage range for your materials. Are the
kilovoltages reasonably close? Write a paragraph that discusses the correlation of the
kilovoltage values produced by the half-value method and those on the exposure chart.
Note any similarities and differences.
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16
LESSON THREE:
MILLIAMPERAGE AND TIME RELATIONSHIPS
Introduction
In this lesson, the relationship between milliamps and the time of an exposure will be
examined. An understanding will be developed of the interaction between the amperage
and time controls, and their relationship to the density of a radiograph. Calculations to
adjust for time or milliamperage to obtain a certain density on the radiograph will be
introduced.
Objective
To develop an understanding of the effects of milliamperage and time changes on the
density of a radiograph.
To learn to calculate the approximate density change on a radiograph when the
milliamperage or time setting of the exposure are changed.
Reference Terms
Milliamperage is a term used to describe the amount of radiation produced by the X-ray
system. The milliamperage is actually the units of the electrical current that is used to
produce the radiation.
Milliamp-minutes (mAm) are the product of the amount of milliamps and the amount of
time used to make the exposure. Since the exposure time is directly tied to the amount of
current used (i.e. the more current used, the less time needed to make an exposure), it is
convenient to note the product of these two value rather that the two individual values.
Formulas for Time and milliamprage Calculations
There is roughly a one-to-one direct relationship between a milliamperage or time change
and the resulting change in image density. If time is held constant and only the
milliamperage is varied, the following equation can be used.
M 1 D1
=
M 2 D2
Where: M1 = Milliamp original
M2 = Milliamp new
D1 = Film density original
D2 = Film density new
17
Example calculation:
With a mA setting of 3.0, a density of 1.0 is produced. What mA setting would be needed to
increase the density to 2.0 with time and Kv remaining constant? 3.0 / x = 1.0 / 2.0. Crossmultiply and divide. 3.0 times 2.0 = 6. Divide 6 by 1.0 = 6.0. Your new mA setting will be
6.0 mA.
Use the previous equation to calculate the missing variable.
1. M1 = 5.0
M2 = ?
D1 = 3.0
D2 = 2.4"
2. M1 = ?
M2 = 3.0
D1 = 2.1
D2 = 1.7
3. M1 = 6.0
M2 = 4.0
D1 = 3.8
D2 = ?
4. M1 = 5.0
M2 = 3.0
D1 = ?
D2 = 3.1
5. M1 = 2.0
M2 = 4.0
D1 =?
D2 = 3.3
Time will now be the variable, and milliamperage will remain constant. The calculation will
be the same as above except that time replaces milliamperage as one of the variables.
T1 D1
=
T2 D2
Where: T1 = Time (in minutes or seconds) original
T2 = Time (in minutes or seconds) new
D1 = Film density original
D2 = Film density new
18
Use the equation above to determine the missing variable.
1. T1 = 2
T2 = 8.0
D1 = 1.1
D2 = ? ______________________
2. T1 = 15.0
T2 =? ____________________
D1 = 2.1
D2 = 1.2
3. T1 = ?____________________
T2 = 9.0
D1 = 2.4
D2 = 1.8
4. T1 = ? ______________________
T2 = 12.0
D1 = 2.6
D2 = 2.1
Now put the two calculations together to address all three variables at the same time. In this
calculation, remember that the milliamps and time are a product and need to be multiplied
before working the calculation.
M 1 ´ T1
D
= 1
M 2 ´ T2 D2
1. M1 = 3.0, T1 = 12.0
M2 = 4.0, T2 = 5.0
D1 = 3.6
D2 =? ___________________
2. M1 = 1.0, T1 = 63.0
M2 = 4.0, T2 = 20.0
D1 = ? ____________________
D2 = 3.7
3. M1 = 4.0, T1 = 40.0
M2 = 4.0, T2 = 27.0
D1 = 3.9
D2 = ? ___________________
4. M1 = 3.0, T1 = 15.0
M2 = 5.0, T2 = ? ____________________
D1 = 2.9
D2 = 1.8
19
Simulator Exercise
After participating in class discussion and viewing demonstrations with the simulator,
complete the calculations for change of density, milliamperage, and time.
Next, complete the following activity using the X-ray simulation program.
1. Use the following settings as a starting point to produce three images:
Part CAD File
Part Material
Source to film distance
Detector
Energy
Current
Time
Stepwedge11cm
Titanium (Ti)
100 cm.
D-5 film
150 kV
1 mA
7 seconds
These settings should generate an image with a density close to 1.7
2. Change the milliamperage by increasing the setting to 2.0. What is the density on step
eight? ________________________________
3. Reduce your milliamps to 1.0 and increase the time to 14 seconds. What is the
density? ________________________
4. Was the resulting density the same for an increase in milliamps as it was for and
increase in time?_____Explain the relationship between time and milliamperage.
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
5. An industry rule-of-thumb is that if the exposure time is doubled, the density will
approximately double. Use the slice option to verify the density results.
6. Continue with the settings used above (1ma and 7 seconds).
a. Calculate the change in time needed to produce a density of 2.5
_________________
b. Calculate the change in time needed to produce a density of 1.0
_________________
7. Write a statement noting the results and conclusions drawn from this lesson.
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
20
Laboratory Exercise
Name:_____________________________________________________
1. Produce two radiographs on any X-ray system in the laboratory using the steel or
aluminum stepwedge. First use an available exposure chart to expose a step near the
center of the stepwedge.
2. Choose any three steps on the processed radiograph and calculate a density change to
raise or lower the density to 2.0 for the steps chosen. Show your work and results
below.
|
3. Once your calculations are complete expose and process the stepwedge and film. Note
the density on the appropriate step. Did you produce a density change as calculated?
Attach your film and explain your findings below.
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
21
Lesson Four:
Creating an Exposure Chart
Introduction
This lesson will explain how to create a radiographic exposure chart. As material
thickness changes exposure times must be adjusted to produce an acceptable density.
Exposure charts provide the proper milliamperage and time settings for a constant
kilovoltage over a range of material thickness. Exposure charts are developed with the
following held constant: kilovoltage, density, film type, film processing, source to film
distance, use of lead screens, and material type. The materials thickness is the variable
and the chart provides a fast and reliable way of determining exposure time that produces
a certain density.
Objective
To learn to interpret radiographic exposure charts to select exposure settings.
To learn to make density conversion calculations.
To create radiographic exposure charts that will be used as guides for establishing
exposure settings for a particular X-ray system, film and film processing parameters.
Reference Terms
Densitometer is an instrument for measuring photographic densities. A number of
different types are available commercially. An important property is reliability; that is, the
densitometer should reproduce readings from day to day.
X-Ray Exposure Chart is a chart that shows the relationship between material thickness,
kilovoltage, and exposure time.
Film Development is the process used to turn a latent image into a viewable radiograph.
Processing variables such as manual or automatic processing, time and temperature will
affect the final radiograph and the outcome of the exposure chart.
Film Speed is a system used to classify the relative exposure times needed to expose
various films. The film speed is dependant on the grain size of the film and larger the film
grain size, the less exposure time required to produce a certain density of the processed
film.
22
Calculations
Density Conversion Calculations
Use the following equation to solve for the missing information.
M 1 ´ T1
D
= 1
M 2 ´ T2 D2
Example:
If 20.0 mAm produces a density of 2.0, what exposure (amperage times time) would be
needed to produce a density of 4.0?
20.0mAm 2 min
=
? mAm
4 min
(20.0 mAm times 4.0 min divided by 2 min = X)
The new amperage would be 40.0 mAm.
1. If 20.0 mAm produces a density of 2.0, what exposure would be necessary to produce a
density of 4.0? _____________________
2. If 15.0 mAm produces a density of 2.3, what exposure would be necessary to produced a
density of 3.6? _____________________
3. If 24.0 mAm produces a density of 3.0, what exposure would be necessary to produced a
density of 2.0? _____________________
4. If 10.0 mAm produces a density of 1.5, what exposure would be necessary to produced a
density of 3.1? _____________________
5. If 15.0 mAm produces a density of 1.3, what exposure would be necessary to produced a
density of 2.6? _____________________
6. If 22.0 mAm produces a density of 1.8, what exposure would be necessary to produced a
density of 2.6? _____________________
7. If 8.0 mAm produces a density of 2.1, what exposure would be necessary to produced a
density of 2.0? _____________________
8. If 18.0 mAm produces a density of 1.3, what exposure would be necessary to produced a
density of 2.6? _____________________
9. If 21.0 mAm produces a density of 1.7, what exposure would be necessary to produced a
density of 2.5 _____________________
10. If 14.0 mAm produces a density of 2.6, what exposure would be necessary to produced a
density of 3.5? _____________________
23
Simulator Exercise
1. Create two exposure charts using the simulator. Review the exposure chart on the
following page before making your exposure chart. Use step eight on the simulator
stepwedge. The step thicknesses are:
Step
1
0.5
cm
Step
2
1.0
cm
Step
3
1.5
cm
Step
4
2.0
cm
Step
5
2.5
cm
Step
6
3.0
cm
Step
7
3.5
cm
Step
8
4.0
cm
Step
9
4.5
cm
Step
10
5.0
cm
1. Place a 0.8 by 0.8 by 0.8 cm defect on the center of step eight for ease of location. To
locate the defect, left click on the defect tab and then “open.” Choose the sphere, and
it will appear on your stepwedge. Under the “Flaw Operation” menu, choose “scale”
enter the dimensions for the flaw. Left click and drag the defect to the position you
choose. To aid in location of the defect use the translucent option. Left click on the
sample tab. At the lower right of the window there is a box marked translucent, left
click. This will let you see the defect as you move it around in the stepwedge.
2. Using the knowledge gained in Lessons 1 and 2, calculate and choose the appropriate
kilovoltage for aluminum and steel material. Choose an appropriate film. Film speed
and type must always be considered when making an exposure chart in order to keep
the exposure time reasonable. Denser materials, such as steel usually require a faster
film than do less dense materials such as aluminum. Industry production demands and
sensitivity requirements will dictate which film should be used. It often is not
practical to x-ray steel with a very fine grain film that takes an extended time to
expose, when a faster film will locate the needed defects.
3. Calculate the kilovoltage for steps one, eight and ten to determine the kilovoltage
range for the span of thicknesses of the stepwedge.
Record the kilovoltage.
Steel
Thickness step one___________ Kilovoltage___________
Thickness step eight__________ Kilovoltage___________
Thickness step ten____________ Kilovoltage___________
Aluminum
Thickness step one___________ Kilovoltage___________
Thickness step eight__________ Kilovoltage___________
Thickness step ten____________ Kilovoltage___________
5. Select the calculated kilovoltage for step number eight of the steel stepwedge and set
the milliamperage and time to produce a density as close to 2.0 as practical on the step
(not on the defect).
24
6. Create the image and use the slice option to record the densities from the steps
beginning with the lightest.
7. Use the density conversion calculations to determine the exposure needed to produce a
density of 2.0 on each of the steps.
8. Plot the exposure versus thickness on log graph paper. On the vertical edge of the log
graph paper, plot the exposure in milliamp-minutes and on the horizontal line of the
graph plot the material thickness. Place a mark at the intersection of these values and
continue until all points for that kilovoltage setting are marked. Now connect the
points to produce a kilovoltage reference line for a range of material thickness and
time settings. The exposure chart on the next page can serve as an example.
9. Next, select the optimum kilovoltage calculated for step one and create another line on
the chart. Repeat the process for step ten of the stepwedge. When complete the chart
should show three kilovoltage lines. Remember to record all information including
film, development method used, screens used, and source-to-film distance (SFD) in an
information box.
10. Repeat the process for the aluminum material and produce a second chart.
11. Once the charts are complete select one thickness (step) for each kilovoltage listed on
the exposure charts and produce an image using the simulator. Using the slice option
record the density of the steps. Theoretically, the densities should all be 2.0 but some
variation is to be expected.
Exposure chart 1
Material ________________________________________
Step thickness: ________________________ Density_________________________
Step thickness: ________________________ Density_________________________
Step thickness: ________________________ Density_________________________
Exposure chart 2
Material ________________________________________
Step thickness: ________________________ Density_________________________
Step thickness: ________________________ Density_________________________
Step thickness: ________________________ Density_________________________
25
Example X-ray Exposure Chart
100 milliamp seconds
90
80
70
60
40
60
80
50
40
100
30
20
10
9
8
120
7
6
5
4
3
2
YX - 5 Film / No screens
Auto Process 85 degrees
Density: 2.0
FFD: 39 inches
Source: X-ray / Model 160
Serial No. RA-293831
Material: Aluminum
1
0
½
1
1½
2
2½
3
3½
Thickness (inch)
26
Laboratory Exercise
Name:_____________________________________________________
Produce an exposure charts for steel or aluminum on one of the laboratory X-ray systems
using a process similar to that used in the simulator exercise. Use a densitometer to
measure the film density that corresponds to each step of the stepwedge on the radiograph.
Generate lines for at least four kilovoltage settings on the chart. Kilovoltage settings
should be in increments of 10 kilovolts or more. Remember to list any variable in the
information box on the chart. When finished, turn in the following documents:
q Calculations used to develop the exposure chart.
q One exposure chart, for aluminum or for steel. Charts will show four
kilovoltage settings over a given thickness range.
q A two paragraph description of your experience developing an exposure chart
27
LESSON FIVE:
SOURCE-TO-FILM RELATIONSHIPS
Introduction
In this lesson, Newton’s inverse square law will be used to calculate the film density when
the source-to-film distance (SFD) has changed. Newton’s inverse square law states that
the intensity of the electromagnetic energy is inversely proportional to the square of the
distance from the source. Therefore, reducing the SFD by one-half will increase the
intensity of the radiation by a factor of four. Since the exposure time is directly related the
radiation intensity, reducing the SFD by one-half would also reduce the exposure time by
a factor of four. Often it is not practical to make exposures at the distance listed on an
exposure chart. Reducing the SFD distance is sometimes necessary to speed the
radiography of extremely thick parts, and increasing the SFD may be necessary when the
physical shape of the part does not permit using distances listed on the exposure chart.
Objective
To develop an understanding of the effects of distance change on the density of a radiograph.
To calculate and maintain a density on a radiograph when the source-to-film distance has been
altered.
Reference Terms
Milliamperage-Distance Relationship is the dependence between the milliamperage
required for a given exposure and the source-to-film distance. This relationship has been
standardized to meet with manufactures’ ratings on the various x-ray tubes.
Time-Distance Relationship is the dependence between the time required for a specific
exposure and the source-to-film distance. The exposure time is indirectly proportional to
the square of source-to-film distance.
Newton’s Inverse Square Law describes the radiation intensity as a function of distance
from the source. The intensity reaching the specimen is inversely proportional to the
square of the distance. Anytime the distance doubles the intensity of the radiation
reaching the film is changed by a factor of four.
Milliamprage, Time, Distance is the relationship between the milliamprage, and time
required for a given exposure and source- to- film distance. This relationship can be
easily calculated for any source- to- film distance change.
Source-To-Film Distance is the measured distance the x-ray tube is from the film to be
exposed. This distance will change for various reasons. Often there is a need to speed up
production, hence the distance will be reduced thereby shorting the exposure time at a
given density.
28
Simulator Exercise
1. After reading and classroom discussion, the following calculations should be completed
and evaluated in class.
2. The following problem should be calculated and the answers confirmed on the number
eight step of the aluminum stepwedge and D-3 film. Place a "void" flaw in the step for
ease of location. Choose a kilovoltage setting appropriate for the thickness you are
exposing (See lesson on kilovoltage selection). Establish a density of 2.5 at the default
setting of 100 cm. This image will be saved in the density file as xyz.xbm. Verify the
density using the slice option. Now change the source to film distance to (35cm),
recalculate the new time setting for the distance change. Using the full and top view note
the change in the radiation cone coverage of your film. Produce an image on the
simulator using your new calculations. Name your image file xy1.xbm. Remember you
must name the file before you produce the simulated image or the image will write over
the xyz.xbm file. Check your density. Did the density remain at 2.5?
____________________________ if not what was the density? ________________ was
it within 10 percent of your calculated change? __________________________
3. Next select the stepwedge choose Fe as your material. Establish a 2.5 density using AA
400 film on step seven. Place a void flaw in the step for ease of location. Calculate a
change of distance to 125 cm while maintaining a 2.5 density. Save this image in a
density file xy2.xbm. Using the full and top views note the change in the radiation cone.
Retrieve the three radiographic image files from the density file and write a short
description of the results. ___________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
4. Using the attached chart for change of distance produce another image with AA 400 film
and a source to film distance of 25 inches (remember to convert cm to inches). The
density on step seven should be near 2.5. Using the chart attached recalculate a change of
distance to 40 inches. Did you maintain the 2.5 density? Write a short description of the
results comparing the calculation method to use of the chart to determine Milliamp and
time settings for a distance change.
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
29
Calculations for source to film distance change
According to Newton’s inverse square law, the intensity of the radiation intensity is inversely
proportional to the square of the distance from the source. This can be represented by the
following equation.
Intensity =
1
D2
Since the exposure of a radiograph is inversely related to the radiation intensity (i.e. as
intensity increases, the exposure must decreases to produce a constant density), it can be
written that the exposure is directly proportional to the square of the source-to-film distance
as represented by this equation.
Exposure º SFD 2
This equation can then be used to make calculations for changes in the source-to-film
distance by setting two equations equal to each other. This equation is
Exposure1
SFD1
2
=
Exposure2
SFD2
2
Example: an exposure for 16mAm with a source to film distance of 20 inches produces a
density of 2.5. It is necessary to move the part closer to the source to reduce the exposure
time but the density must be kept at 2.5. What would the new time be if the distance were
moved to 10 inches from the source and all other factors remained the same? (As before
cross multiply and divide. Four milliamp-minutes would be the new time for the distance
change.)
Use the above equation to solve for the missing variable in order to keep the density constant.
1. If 5.5 mAm at a source-to-film distance of 12 inches produces a density of 3.0, what
exposure is needed to produce the same density if the source is moved to 24 inches?____
2. If 12.0 mAm at a source-to-film distance of 21 inches produces a density of 2.50, what
exposure is needed to produce the same density if the source is moved to 14 inches?____
3. If 16.5 mAm at a source-to-film distance of 18 inches produces a density of 3.3, what
exposure is needed to produce the same density if the source is moved to 12 inches?____
4. If 8.1 mAm at a source-to-film distance of 16 inches produces a density of 3.6, what
exposure is needed to produce the same density if the source is moved to 9 inches?_____
5. If 2.0 mAm at a source-to-film distance of 6 inches produces a density of 2.0, what
exposure is needed to produce the same density if the source is moved to 11 inches?____
6. If 15.5 mAm at a source-to-film distance of 21 inches produces a density of 3.0, what
exposure is needed to produce the same density if the source is moved to 12 inches?____
30
MILLIAMPERAGE-TIME AND DISTANCE RELATIONS
When distances are changed from a given value to another given value on the chart
the original time can be multiplied or divided by the factor given in the chart.
New Dist.
Old Dist.
25"
25"
1.0
30"
1.4
35"
2.0
40"
2.6
45"
3.2
50"
4.0
30"
0.70
1.0
1.4
1.8
2.3
2.8
35"
0.51
0.74
1.0
1.3
1.6
2.0
40"
0.39
0.56
0.77
1.0
1.3
1.6
45"
0.31
0.45
0.60
0.79
1.0
1.2
50"
0.25
0.36
0.49
0.64
0.81
1.0
31
Laboratory Exercise
Name:__________________________________________________________________
1. Produce a radiograph of a stepwedge using the X-ray system, film, and source-to-film
distance of your choice.
2. Change the source-to-film distance and calculate a new exposure setting to produce a
radiograph with densities similar to the first radiograph.
3. Compare the two exposures and write a two paragraph on effects of the source-to-film
distance on exposure density.________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
32
LESSON SIX:
RADIOGRAPHIC EQUIVALENCY FACTORS
Introduction
This lesson addresses the physical properties of materials and how these properties affect
the ability of X-rays to pass through a given amount of material. The material properties
of primary interest in radiography are the density and the atomic number. The higher the
density of a material, the more difficult it is for radiation to penetrate the material. This
concept was studied in Radiation Safety when calculating shielding.
Technique charts and other materials used in industry to control radiographic procedures
usually address only one material. When presented with a new material of a different
density, new exposure times must be determined. This lesson will explain how
radiographic equivalency factors can be used to compensate for changes in materials
properties when exposure parameters for other materials are known.
Objective
To investigate the effect that material properties have on radiographic density.
To learn to compensate for material changes when making exposures by using the exposure
settings at a given kilovoltage for one material to estimate the settings for a second material.
Reference Terms
X-ray Absorption is a term used to describe the ability of a material to stop or absorb xrays. X-ray absorption depends on three factors: the thickness of the material, the density
of the material and the atomic number of the material. The atomic nature of the material
influences the X-ray absorption more than the other two factors combined.
Exposure Factor is a term used to describe the combined effect of milliamprage, time and
source-to-film distance. A change in any of these factors will affect the density of the
radiograph.
Image quality and resolution is affected by the contrast, sensitivity, and definition of the
image.
Equivalence Factor is the value by which the thickness of a material is multiplied to give
the thickness of a "standard" material. Equivalence factors provide a means of relating
material of different densities so that exposure estimates can be made.
33
APPROXIMATE RADIOGRAPHIC EQUIVALENCE FACTORS
Material
50 kV
100 kV
150 kV
220 kV
400 kV
Magnesium
0.6
0.6
0.5
0.08
Aluminum (pure)
1.0
1.0
0.12
0.18
2024 Aluminum
2.2
1.6
0.16
0.22
Titanium
0.45
0.35
Steel
12.0
1.0
1.0
1.0
18-8 Steel
12.0
1.0
1.0
1.0
Copper
18.0
1.6
1.4
1.4
Zinc
1.4
1.3
1.3
Brass
1.4*
1.3*
1.3*
Inconel X
16.0
1.4
1.3
1.3
Zirconium
2.3
Lead
14.0
Uranium
Aluminum is taken as the standard metal at 50kV and 100kV. Steel becomes the
standard at the higher voltages and at gamma ray energy levels. The thickness of the
material of interest is multiplied by the corresponding factor to obtain the approximate
equivalent thickness of the standard metal. The exposure settings that would normally be
used to produce a radiograph of the standard metal at this thickness is used to produce the
radiograph of the material of interest.
*Tin or lead alloyed in the brass will increase these factors.
Example: To radiograph 0.5 inch of copper at 220 kV, multiply 0.5 inch by 1.4 to obtain an
equivalency thickness of 0.7 inch for steel. The exposure settings that would be used to
produce a radiograph of 0.7 inch of steel are; therefore, use to produce the radiograph of 0.5
inch of copper.
34
Calculations
Use the equivalency factors provided in the table on the previous page to answer the
following questions.
What thickness of aluminum is equivalent to two inches of the following materials?
1.
2.
3.
4.
5.
Magnesium ________________
Steel
________________
Copper
________________
Zirconium ________________
2024 Aluminum_____________
Using these values and the exposure chart provided in Lesson Four, estimate the exposure
necessary to radiograph two inches of the following materials if 30 mAm at 100 kV produces
the desired film density for 2 inches of pure aluminum.
6.
7.
Magnesium ________________
2024 Aluminum_____________
If 12 mAm at 150 kV produces the desired film density for 1 inches of steel, what thickness
of the following materials could these generator settings be used to image?
8.
9.
10.
11.
Magnesium _______________
Aluminum _______________
Copper
_______________
Zirconium _______________
If 6-mAm at 100 kV produces the desired film density for 1 inch of aluminum, what
exposure should be used to radiograph 1 inch of the following materials at the same voltage
setting?
12. Magnesium _______________
13. 2024 Aluminum_____________
35
Simulator Exercise
1. Use the X-ray simulation program to produce an image with a density of approximately
2.0 on the sixth step (1 inch thick) of a 2024 aluminum stepwedge. Use D2 film and the
following X-ray generator settings: 100 kV, 1 mA, and 3 seconds.
1. Use the radiographic equivalency factors and the exposure chart in Lesson Four to create
two more images of the stepwedge with its material changed to pure aluminum and
magnesium. Remember that the XRSIM image file must be changed each time a new
image is generated or the program will write over the previous image. Use the slice
option and record the density of the three images. Record your generator settings and
densities for step seven below.
2024 Aluminum kV_________ mAm____________ Step 6 density__________
Pure Aluminum kV_________ mAm____________ Step 6 density__________
Magnesium
kV_________ mAm____________ Step 6 density__________
2. Did the calculations provide an equivalent density on the new material? Was the density
reasonably close +/- 10%?
3. Explain why the radiographic equivalency relationship of steel and copper is 1.6 at 150
kV but changes to 1.4 at 400 kV. Explain why at 400 kV there is no factor listed for
making an exposure with aluminum or
magnesium._____________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
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36
Laboratory Exercise
1. Obtain a steel stepwedge for use in producing a radiograph.
2. Select a film that has an exposure chart that was previously developed for one of the
laboratory X-ray systems and is suitable for the thickness range of the stepwedge,
3. Expose the film using a kilovoltage of 100 or below.
4. Select a stepwedge or a part of aluminum that is the same thickness as the steel part.
Expose another film using the exposure equivalency factors given in this lesson and
the exposure chart to maintain a similar density to the previously produced radiograph.
5. Write two or three paragraphs discussing your project in the space provided below.
6. When complete, record the density and return this paper and your film to the
instructor.
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37
LESSON SEVEN:
DEFECT CONTENT
Introduction
When aluminum products corrode, aluminum oxide or hydroxide is the byproducts of the
reaction. While these corrosion products generally expand in volume when unrestrained and
will be less dense than the aluminum metal. However, if the corrosion products are confined
in an area such as when the corrosion occurs on the faying surfaces of sheets that are fastened
together, the density of the corrosion products will be only slightly less dense than the solid
metal. This lack of variation in density can make corrosion damage difficult to image with
radiography. Conversely, slag or tungsten inclusions in a weld are easier to detect because of
the significant difference in density between these flaws and the matrix material. In this
lesson, an understanding will be developed of how defect substance affects the detection
of a defect. This lesson will also introduce how defect size and shape is also use to
identify the defect type during radiographic interpretation.
Objective
To learn how a defect’s physical properties affect the image on a radiograph.
To learn to recognize defects by their appearance on a radiograph.
Reference Terms
See Appendix A for information on typical welding and casting defects and the appearance
of these defects in radiographs.
38
Simulator Exercise
In this exercise simulated radiographs will be produced that illustrate flaw detectability is
dependant on the density difference between the parent material and the density of the flaw.
Open the simulator program and load the Stepwedge11cm CAD file. Choose aluminum
Create an aluminum (AL 2.702000) for the material and place a 0.5 by 0.5 by 0.5 cm defect
on step nine. Use air for the defect material. Use D-5 film and set the voltage to 80 kV.
Select an exposure that produces a density close to 3.0 on step nine (this should be around 4
mAseconds). Save this image and use the same parameters for the other radiographs
produced in this exercise. Produce radiographs using four other materials for the defects.
One material should be less dense than the aluminum, two denser, and the fourth as close to
the stepwedge material as possible. When choosing defect materials compare the density
numbers listed in the sample and defect windows for the flaw and the parent material to aid
you in your choice of materials. When producing the simulated radiographs, remember to
give each file a new name so that previously generated files will not be overwritten. Use the
slice feature of the program to determine the image density of the flaws and step nine of the
stepwedge.
List the defect materials that were use, their physical densities, and their radiographic
densities below.
Object
Material
Stepwedge
Aluminum
2.702 lbs/in3
___________(S/B Close to 3.0)
Flaw 1
Air
0.00129 lbs/in3
___________
Flaw 2
_________
__________
___________
Flaw 3
_________
__________
___________
Flaw 4
_________
__________
___________
Flaw 5
_________
__________
___________
Physical Density
Image Density
Was it possible to locate all of the defects? _________ Explain how a flaw’s density affects
its detectability in a radiograph. ________________________________________________
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39
Laboratory Exercise
Name:_________________________________________________
1. Contact your instructor for a packet of radiographs to evaluate.
2. Review the radiographs and list below any defects noted in the parts.
3. Return this paper to your instructor when complete.
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40
LESSON EIGHT:
DEFECT SHAPE, AND RELATIONSHIP TO X-RAY
SOURCE
Introduction
This lesson will center on how the size of the flaw and the orientation of the flaw affects
the image produced on a radiograph. Without a loss of material or sufficient foreign
material in the object radiographed, there will be little if any density change in the image.
Also, the defect must be such that the radiation will see a significant change in the amount
of material (or material of a different density) penetrated in order to produce flaw
indication on the radiograph. Cracks, for example are extremely difficult to image when
not oriented perpendicular to the x-ray source.
Objective
To determine what percentage of material loss is detectable with radiography.
To evaluate the effect of defect orientation (in relation to the X-ray source) on flaw
detectability
Reference Terms
X-Ray Intensity is determined by the tube current or the milliamprage. The intensity
refers to the amount of energy that is produced by the x-ray source and directed at the
specimen.
X-ray Absorption depends on three important factors. The first factor is the thickness of
the specimen. The second factor is the specimen’s density. The third, and most
important, factor is the atomic number of the material. The atomic nature of the specimen
is most important since it influences x-ray absorption more than the first two combined.
Inverse Square Law describes the radiation intensity reaching a specimen. The distance
between the source and the specimen governs the intensity of the radiation. The intensity
reaching the specimen is approximately inversely proportional to the square of the
distance.
41
Loss of Material and Crack Defect Calculations
After reading and participating in classroom discussion, work the calculations on defect
size and percent of material loss presented below.
Material Loss Calculations
A material is 0.77 inches thick. What would be the defect thickness if the loss were 4
percent? ___________
A material is 1.23 inches thick. What would be the defect thickness if the loss were 8
percent? ___________
A material is 0.45 inches thick. What would be the defect thickness if the material loss
were 6 percent? ___________
A material is 1.54 inches thick. What would be the defect thickness if the material loss
were 3 percent? ___________
A material is 0.27 inches thick. What would be the defect thickness if the material loss
were 2 percent? ___________
A material is 1.23 inches thick. What would be the defect thickness if the material loss
were 1.7 percent? _________
A material is 0.82 inches thick. What would be the defect thickness if the loss were 2.4
percent? _________
Crack Defect Calculations
Most standards and codes define a crack-like defect or linear defects as one with a length
three times the width. For example, if a defect were 0.009 cm wide, it would need a
length of 3 times this width, or 0.027 cm, to consider it a linear indication.
From the length, width and depth information below, identify each of the flaws as a linear
or nonlinear indication.
1. 0.323 X 0.520 X 0.219 cm
2. 0.213 X 0.620 X 0.419 cm
3. 3.083 X 0.920 X 0.619 cm
4. 2.083 X 1.328 X 1.399 cm
5. 1.283 X 2.10 X 2.819 cm
42
6. 1.323 X 0.520 X 0.219 cm
7. 0.813 X 0.620 X 0.311 cm
8. 0.67 X 0.620 X 0.451 cm
9. 2.033 X 1.328 X 1.399 cm
7. 2.200 X 2.30 X 1.11 cm
Simulator Exercise
1. Using the simulator program, produce a crack like defect with the following dimensions
on the sixth step of the titanium stepwedge X = 0.05, Y = 0.75, Z = 0.35. The defect
should be a void (air). Use the D-5 film and X-ray generator settings of 120 kV, 1ma, 14
seconds. These settings should produce an image with a density near 2.5 on step six.
2. Rotate the defect generated above, 10, degrees from normal using the rotate option in
the defect window. Produce a simulated radiograph. Rotate the defect another 5
degrees so that it is now 15 degrees from normal and produce a third image. Rotate
the defect another 75 degrees so that the defect is now 90 degrees to the one produced
in step one. Produce a fourth image. Save each of the images under a different file
name,
3. Compare each image. Using the slice option, check the densities of each defect.
Explain how flaw detectability was affected by the orientation between the flaw and
the X-ray beam. Explain why any changes seen in the radiographs occur.
_______________________________________
43
Laboratory Exercise
Name:_______________________________________________________________
1. Use a laboratory X-ray system to produce a radiograph of an eddy current aluminum
crack standard with EDM notches of 0.008, 0.020, and 0.040 thousands of an inch
deep. Produce this first image with the flaw depth parallel to the X-ray beam.
2. Make a second exposure with one edge of the standard elevated approximately 5
degrees.
3. Make a third exposure with the standard elevated approximately 15 degrees.
4. Review the radiographs and write a summary of your findings. Were all the flaws
detectable in all three radiographs? If not, explain why they were not.
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44
LESSON NINE:
IMAGE MAGNIFICATION, BEAM DIVERGENCE AND
DISTORTION
Introduction
This lesson is directed at developing an understanding of the physical relationships of the
source spot size, source-to-film distance, part thickness, and part-to-film distance. These
parameters must be managed to produce the desired level of magnification and to limit the
geometric unsharpness of the image. Specifications control the geometric unsharpness to
limit the penumbra or gray area around an image on the radiograph. The cone beam of
radiation produced by the X-ray tube will also be examined. The cone beam varies from
x-ray tube to x-ray tube and if a part and film is placed too close to the X-ray tube, in
some cases, the projection of radiation may not image the entire part on the film.
Objective
To learn how source-to-film distance and part-to-film distance control the magnification in
the image
To learn how the source spot size, part-to-film distance (or part thickness), and source-tofilm distance influence geometric unsharpness of a radiograph.
To learn why it is important to know the radiation beam spread or angle of the cone beam
of a given X-ray generator system and learn how to calculate the size of the projection.
Reference Terms
Source Spot Size refers to the diameter of the area on the X-ray tube target from which
the radiation emanates. The spot size affects the quality of the image with smaller spot
sizes producing sharper images.
Definition refers to the sharpness of a line of transition in a radiograph. Definition is
dependant on the spot size of the radiation source, the energy of the X-rays used, the
geometry of the radiographic setup, and the type of film and screens used.
Beam Spread refers to the cone of radiation produced by a given X-ray generation
system.
Geometric Enlargement is the increase in the size of a feature on a radiograph that
results from locating the part a distance from the film in the exposure setup. Enlargement
or magnification allows the inspector to view feature that would otherwise be too small to
distinguish. Students should be aware that geometric enlargement produces a reduction in
definition in the image.
45
Geometric Unsharpness is the condition in which the width of a line of transition lacks
definition or is fuzzy. Because this condition can affect the quality of a radiographic
image, it becomes necessary to determine and control its magnitude.
Penumbra is a term used to describe the width of a line of transition on a radiograph. The
penumbra or width of the line increase as the geometric unsharpness increases. The
penumbra should be taken into consideration when sizing the defect on a radiograph.
Geometric Enlargement (Magnification) Calculations
The amount of magnification can be calculated using the following formula:
M =
a+b
a
where M = magnification
a = distance from the source to the object
b = distance from the object to the detector
X-ray Source
a
Object
b
Film
Example: What is the magnification if the part is positioned such that its front surface of the
part is 20 inches from the source and 10 inches from the film. Using the given formula
M =
a+b
a
M =
20 + 10
= 1.5 times
20
Calculate the magnification for the following problems. (Show your calculations.)
46
Problems:
1. What is the magnification if the part is positioned 20 inches from the source and 20
inches from the film?
2. What is the magnification if the part is placed 20 inches from the source and 10 inches
from the film?
3. What is the magnification if the source-to-film distance is 36 inches and the part is
placed 10 inches from the source?
4. What is the magnification if the source-to-film distance 100 cm and the part is located
80 cm from the source?
5. What is the magnification is the source-to-part distance is 20 cm and the part-to-film
distance is 80 cm?
6. If the source-to-film distance is 80 inches and a magnification of 1.5 is desired, what
should the distance between the object and the source be?
7. If the source-to-film distance is 36 inches and a magnification of 2.0 is desired, what
should the distance between the object and the film be?
8. What is the magnification if the source-to-film distance is 48 inches and the part is
placed 10 inches from the film?
9. If the source-to-film distance is 120 cm and a magnification of 1.5 is desired, what
should the distance between the object and the source be?
10. If the source-to-film distance is 100 cm and a magnification of 1.0 is desired, what
should the distance between the object and the source be?
47
Geometric Unsharpness Calculations
When the object being radiographed is placed in direct contact with the film, the following
equation can be used to calculate the amount of geometric unsharpness in a radiograph.
t
Ug = f *
d
where f = X-ray source focal-spot size.
t = distance from the source side of part to the film surface.
d = distance from the source to the near surface of the part.
Source Focal Spot (f)
d
t
Object
Film
Penumbra (Ug)
Example: If the source spot size 0.100-inch and a 3-inch thick part is placed 25 inches from
the source, what is the geometric unsharpness?
Using the equation Ug = f *
t
d
Ug = 0.100 *
3 .0
= 0.012 inches
25
48
Problems:
Solve the following problems. (Show your calculations.)
1. If the source spot size is 0.105 inch, and a 1.0-inch thick part is placed 36 inches from
source, what is the geometric unsharpness?
2. If the source-to-object distance is 39 inches and the source spot size is 0.162 inch, how
much geometric unsharpness would there be for a part that is 1.65 inch thick?
3. If an X-ray system with a 0.092 inch source spot size is positioned 25 inches from a
0.75 inch thick part, how much geometric unsharpness with there be?
4. If the source spot size is 0.045 inch and the source-to-film distance is 45 inches, how
much geometric unsharpness will there be for a 2.15inch thick part?
4. If a source with 0.9mm spot size is positioned 33 inches from a 0.25-inch thick part,
what amount of geometric unsharpness would be present in the radiograph?
5. If the maximum amount of geometric unsharpness allowed by a specification is 1mm,
how far must a source with a 3mm spot size be positioned away from the part being
radiographed?
6. If the maximum amount of geometric unsharpness allowed by a specification is 0.040
inch, what is the minimum source-to-film distance that can be used to radiograph a
2.5-inch thick part.
7. If the X-ray source has a 0.088-inch source size and 0.95 inch thick part is placed 32
inches source, what is the geometric unsharpness?
8. If the X-ray source-to-film distance is fixed at 40 inches, what is the largest spot size
that can be used radiograph a 2.5-inch thick part if the geometric unsharpness must be
held to 0.040 inches.
49
Beam Coverage Calculations
The angle of the cone beam produced by an X-ray tube determines the distance of
separation between the tube and the part that is required to image the entire part. Using
basic geometry, the diameter of the projection from the cone can be calculated.
Cone beam angle
Sourceto-part
distance
(d)
½ Cone beam angle (q)
If the cone beam is divided in half to get a right triangle,
basic geometric equation can be used.
a
c
b
Diameter
of area of
coverage
(X)
TanQ =
side _ opposite(b)
side _ adjacent (a)
Therefore:
Tan (1/2 cone beam angle) = side opposite (b)
source-to-part distance (a)
or b = a(Tan q)
Since the side opposite (b) is ½ of the diameter of the x-ray
beam projection, the equation for X becomes:
X =2b or X = 2a(Tan q)
1. Calculate the diameter of the area of coverage for an X-ray tube that produces a 30degree cone beam and is 50 cm from the part.
2. Calculate the diameter of the area of coverage for an X-ray tube that produces a 40degree cone beam and is 20 inches from the part.
3. How far must an X-ray tube with a 20-degree cone beam be away from a 12 inch wide
by 18 inch long part in order to obtain full coverage of the part?
4. How far must an X-ray tube with a 30-degree cone beam be away from a 12 inch wide
by 18 inch long part in order to obtain full coverage of the part?
5. If the source-to-part distance is fixed at 36 inches in the X-ray vault, what is the
smallest diameter cone beam that a source can have in order to image a part that is 30
inches in diameter?
50
Simulator Exercise
1. Using the simulator program, place a 0.8 cm by 0.8 cm by 0.8 cm lead defect in the
eighth step of the aluminum (Al 272000) stepwedge. Use D-2 film and the Homx160
(20 degree cone) generator at a setting of 80 Kv, 1mA and 8 seconds. Generate a
radiograph and save the image as xy1. (Note the cone beam in the full view window.)
2. Change the source to film distance from the default 100 centimeters to 35 centimeters
in the “detector “ window. Generate a second image and label it xy2. Note that the Xray beam does not completely cover the part and the part is so dense that it is not
readable. Reset your time for the change of distance to 2 seconds. Produce an image
labeled xy3. Call up your first images, yx1and xy2, from the density image file and
compare the images. Note how the part is not completely imaged because of the
closeness of the X-ray tube to the part. At this setting, can you clearly see the defect?
_________Why or why not? ______________________________________________
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_____________________________________________________________________
_____________________________________________________________________
3. Select the FXE 200 generator with a 40-degree cone and produce an image of the
stepwedge at 35-cm using the same settings. Note the area covered by the new
generator. Is the entire part covered at 35 cm? __________
4. Write a short explanation of why beam spread must be considered when producing
close exposures, or when exposing a number of parts on a large film.
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5. Now change the source to film distance back to the default of 100 cm. Go to the flaw
tab and change the defect size to 0.3 by 0.4 by 0.4 centimeters. Select “full view” so
that the x-ray tube, part and film can be seen. Using D-5 film with settings of 80 kV,
1ma, and 8 seconds produce an image named xy4. Next, left click and drag the
stepwedge so it is 6.0 centimeters above the film. Run the cad program, and then
produce an image that is labeled xy5. Open the xy4 and xy5 images. Using the slice
option (vertical slice) determine the number of pixels across each defect (use the pixel
count values at the beginning and ending of each defect.) Below, explain the size
difference between the defects in the images and explain why the part is not
completely imaged on the film.
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51
Laboratory Exercise
1. Determine the beam spread (cone beam) of one of the X-ray system in the lab using
the owner’s manual. Record the serial number and beam spread below.
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_____________________________________________________________________
2. Using a source to film distance of 25 inches and an eight by ten inch film cassette,
perform the following task. Use a protractor and some string, locate the edges of the
beam on the film. Will the film be completely covered by the beam? If the distance is
reduced to twelve inches, will the beam still cover the film? Write a short report
describing the project and your observations.
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3. Determine the focal spot size for a given system from the owner’s manual and record
it below. Calculate the minimum source-to-film distance that can be used to
radiograph a one-half inch weld plate and meet a maximum geometric unsharpness
requirement of 0.040 inch.
4. Using three parts with known defect (0.125 inch drilled hole), expose a film with one
part in contact with the film, one part three inches from the film, and one part nine
inches from the film. Calculate the amount of magnification (geometric enlargement)
that should be seen for each of the holes and then determine the enlargement by
measuring the size of the hole on the radiograph. Calculate and subtract any penumbra
change for each of the holes. Show your calculations and results below.
52
LESSON TEN:
DEVELOPING A RADIOGRAPHIC TECHNIQUE CARD
Introduction
This lesson will focus on the development of a radiographic technique card to document
radiographic exposure parameters and the subsequent use of this card to produce
additional radiographs of the same part. Technique cards are used in industry to define the
film, exposure settings on specific equipment, source to film distance, orientation of the
parts, and number of exposures required. Technique cards remove variation in exposures
so that the images produced are consistent and repeatable.
Objective
To develop a radiographic technique card that can be used to document radiographic setup and exposure parameters.
Reference Terms
Radiographic sensitivity is the general term used to describe the smallest detail that can be
seen using a radiograph. The term also refers to the ease in which details can be seen in the
image. In other words, radiographic sensitivity describes the amount of information that can
be found on a radiograph. Two independent factors determine the level of radiographic
sensitivity, definition and contrast.
Definition refers to the sharpness of a line of transition in a radiograph. Definition is
dependant on the spot size of the radiation source, the energy of the X-rays used, the geometry
of the radiographic setup, and the type of film and screens used.
Radiographic contrast is the difference in radiographic density between two areas of
radiograph. This difference in the density depends on two factors, subject contrast and film
contrast.
Subject contrast is the ratio of X-ray intensities transmitted through two or more portions of
different thickness in a specimen. The energy of the radiation used and its distribution, and
the intensity of the radiation used have to be taken into account when determining the subject
contrast.
Film contrast refers to the slope of the characteristic curve of the film. This contrast depends
on three factors, the type of film being used, the density of the film, and the way the film is
processed. The process used to expose the film is also important. Of particularly importance
is whether the film has been exposed using lead screens or fluorescent screens.
X-ray Intensity: the tube current determines x-ray intensity, which is referred to as the
milliamperage. The intensity refers to the amount of energy that is produced by the x-ray
source and directed at the specimen.
53
Simulator Exercise
In this exercise, a technique card will be created for locating a defect in any given area of
the stepwedge CAD File. Produce the technique card to reflect a double loading film
technique to image defects in steps 3 and 8. All information necessary for the exposure
should be included on the technique card. A sketch should be made of each exposure if
more than one exposure is required. The sketch should show positioning of the part and
film in relationship to the x-ray tube.
1. Use the following information on the technique card.
Radiographic procedure: RT-1105.
Acceptance requirements: RT-381, class A.
Films size: 10 inches by 12 inches
Film Processing: Automatic
ASTM pentameters number: 12 and 31
Part name: Stepwedge
Part number: J-1639-L
2. Select the stepwedge from the cad file list, and change the material to Mg_We. Place
two defects in the stepwedge. The defects should be air, and the size in the Z
dimension should be 20 percent of material thickness. The first defect should be
located in step 3, and the second located in step 8. Thickness for step three is 1.5 cm,
and for step eight is 3.0 cm. Calculate the Z dimension of the defect and record it
below
Defect size step 3 ______________Defect size step 8 _____________________
3. Place the appropriate size air defects in steps 3 and 8.
4. To create the double loading effect, the simulator will need to run twice as the system
cannot generate two images in one exposure. One image will be created with a slower
speed film and a second image will be created using the same settings with only the
speed of film increased to image the thicker section. Density range in the area of
interest must be between 2.2 and 3.2 on the simulator images of the stepwedge. Start
by using D-2 film to image the thinner material.
5. Adjust the kilovoltage, milliamperage, and time to produce a density of 2.9 on step 3
using the D-2 film.
6. Change the film to D-7 film (a faster film) to image the thicker material. Do not
change any of the other variables and produce a second image. Did you maintain the
density required for steps 3 and 10 using this technique? __________________
7. If the answer to the above question was yes, complete the technique card on the
following page. Fill in the remarks section of the card with any relevant information
needed by other technicians performing this task. If the answer was no, see your
instructor.
8. Write a two-paragraph description of your project.
54
Customer
Process Specification or
Procedure
Part Name
Date
Accept/ Reject
Part Number
Source Type
Ir-192 Co-60
Source Strength
Material
Material Thickness
Remarks
Source to Film
Distance
kV
mA
VIEW
1
VIEW
2
VIEW
3
Sketch of the Part and Source
VIEW
4
View 1
View 2
View 3
View 4
Time
Penetrameter Size
Screen
Film Manufacturer
Film Processing Information
Automatic____ Manual_____
If Manual Processing Developing Time & Temp.
Film Type & Size
Density
Level III Approval: _________________________________________ Date___________________
Radiographer: _____________________________________________ Date ___________________
55
Laboratory Exercise
1. Contact the instructor for a part to be used for the development of a radiographic
technique card. Using one of the x-ray systems in the laboratory, create a technique
card. Maintain a density range as required by the instructor. The double loading or a
multiple exposure technique should be used if the part thickness exceeds limits of a
single film.
2. When the chart is complete, select a classmate and trade technique cards and parts.
3. Produce an expose of the part as described in the technique card.
4. When complete, evaluate the radiograph and information on the technique.
5. Meet with the student to discuss the quality of the radiograph and note any changes
that are needed to the technique cards.
6. Write a short evaluation on the effectiveness of the technique card reviewed.
7. Attach the evaluation, and film to the technique card.
8. Return the materials to the instructor.
56