This document discusses principles of radiography including interaction of x-rays with matter, film and filmless techniques, and factors that affect radiographic images such as graininess, density, and contrast of films. It also describes Newton's inverse square law that accounts for decrease in radiation intensity with distance from the source. Geometric unsharpness resulting from the size of the radiation source and distances in the setup are explained. Formulas to calculate radiation intensity at different distances and geometric unsharpness are provided.

1. M.KARTHIKEYAN
ASSISTANT PROFESSOR
DEPARTMENT OF MECHANICAL ENGINEERING
AAA COLLEGE OF ENGINEERING & TECHNOLOGY, SIVAKASI
karthikeyan@aaacet.ac.in
ME8097 NON DESTRUCTIVE
TESTING AND EVALUATION

2. UNIT V RADIOGRAPHY (RT)
1. Principle, interaction of X-Ray with matter,
2. imaging, film and film less techniques,
3. types and use of filters and screens,
4. geometric factors, Inverse square, law,
5. characteristics of films - graininess, density, speed, contrast,
6. characteristic curves, Penetrameters,
7. Exposure charts, Radiographic equivalence.
8. Fluoroscopy- Xero-Radiography,
9. Computed Radiography, Computed Tomography

3. RADIOGRAPHIC INSPECTION - FORMULA BASED ON
NEWTON'S INVERSE SQUARE LAW
 In radiographic inspection, the radiation spreads out as it
travels away from the gamma or X-ray source.
 Therefore, the intensity of the radiation follows Newton's
Inverse Square Law.
 As shown in the image, this law accounts for the fact that the
intensity of radiation becomes weaker as it spreads out from the
source since the same about of radiation becomes spread over a
larger area.

4.  The intensity is inversely proportional to the distance from the
source.
 In industrial radiography, the intensity at one distance is
typically known and it is necessary to calculate the intensity at
a second distance.
 Therefore, the equation takes on the form of:
 Where:I1=Intensity 1 at D1I2=Intensity 2 at D2D1=Distance 1
from sourceD2=Distance 2 from source

5.  Note: This is the commonly found form of the equation.
 However, for some it is easier to remember that the intensity
time the distance squared at one location is equal to the
intensity time the distance squared at another location.
 The equation in this form is:
I1 x d1
2 = I2 x d2
2

6. GEOMETRIC UNSHARPNESS
 Geometric unsharpness refers to the loss of definition that is
the result of geometric factors of the radiographic equipment
and setup.
 It occurs because the radiation does not originate from a single
point but rather over an area.
 Consider the images below which show two sources of different
sizes, the paths of the radiation from each edge of the source to
each edge of the feature of the sample, the locations where this
radiation will expose the film and the density profile across the
film.
 In the first image, the radiation originates at a very small
source.

7.  Since all of the radiation originates from basically the same
point, very little geometric unsharpness is produced in the
image.
 In the second image, the source size is larger and the different
paths that the rays of radiation can take from their point of
origin in the source causes the edges of the notch to be less
defined.

8.  The three factors controlling unsharpness are source size,
source to object distance, and object to detector distance.
 The source size is obtained by referencing manufacturers
specifications for a given X-ray or gamma ray source.
 Industrial x-ray tubes often have focal spot sizes of 1.5 mm
squared but microfocus systems have spot sizes in the 30
micron range.
 As the source size decreases, the geometric unsharpness also
decreases.
 For a given size source, the unsharpness can also be decreased
by increasing the source to object distance, but this comes with
a reduction in radiation intensity.


9.  The object to detector distance is usually kept as small as
possible to help minimize unsharpness.
 However, there are situations, such as when using geometric
enlargement, when the object is separated from the detector,
which will reduce the definition.
 The applet below allow the geometric unsharpness to be
visualized as the source size, source to object distance, and
source to detector distance are varied.
 The area of varying density at the edge of a feature that results
due to geometric factors is called the penumbra.
 The penumbra is the gray area seen in the applet.

10. • Codes and standards used in industrial radiography require that
geometric unsharpness be limited.
• In general, the allowable amount is 1/100 of the material
thickness up to a maximum of 0.040 inch.
• These values refer to the degree of penumbra shadow in a
radiographic image.
• Since the penumbra is not nearly as well defined as shown in
the image to the right, it is difficult to measure it in a
radiograph.
• Therefore it is typically calculated.
• The source size must be obtained from the equipment
manufacturer or measured.
• Then the unsharpness can be calculated using measurements
made of the setup.

11. • For the case, such as that shown to the right, where a sample of
significant thickness is placed adjacent to the detector, the
following formula is used to calculate the maximum amount of
unsharpness due to specimen thickness:
• Ug = f * b/a
• f = source focal-spot size
a = distance from the source to front surface of the object
b = the thickness of the object
• For the case when the detector is not placed next to the sample,
such as when geometric magnification is being used, the
calculation becomes:

12. • Ug = f* b/a
• f = source focal-spot size.
a = distance from x-ray source to front surface of
material/object
b = distance from the front surface of the object to the detector