Brief PPT presentation on Y-Ray Radiography. (Gamma Ray Radiography) . Principal of Gamma Radiography X Ray Radiography Presented By Vinal Kumar

1. Presenting by : Vinal Kumar
Branch : Mechanical Engineering(D3)
Roll No. : 1901100400064 (64)
Subject: Non-Destructive Testing
Professor Name :- Prof. Anas Ahmad Siddiqui

2. Gamma radiography is a volumetric non-destructive test
method used to determine internal flaws in castings and
welds. Radiographic testing includes passing of X-Rays or
Gamma rays through the test item form one side and
recording the rays on an imaging media on the other side
giving a permanent visual record of the internal structure
of the test items.
Here, we discuss about Gamma Radiography.

3.  It is Electromagnetic Radiation.(in which electric and magnetic fields vary simultaneously)
 Short Wavelength
 Highest penetration energy (E=hV=hc/lamda). Range : 10^2 to 10^4 GeV called Very
high energy gamma rays and having energy greater than 10^14 eV known as ultra high
energy gamma rays.
 Physical Properties : Charge = 0,Rest Mass = 0
 γ-rays are not deflected by electric and magnetic fields.
 γ-rays travel with the speed of light.
 They can ionize matter and can also expose the film/detector.
 They are not detectable by human senses.
 Get absorbed as well as scattered by matter.
 Gamma waves can be stopped by a thick or dense enough layer material, with high
atomic number materials such as lead or depleted uranium being the most effective form of
shielding.

5.  There are many naturally occurring radioactive materials. For eg. : In the alpha decay of , two
gamma rays of different energies are emitted in addition to the alpha particle.
Reaction :
 But manmade radioactive isotopes or radioisotopes are used for industrial radiography. Man-
made sources are produced by introducing an extra neutron to atoms of the source material.
 For example, Cobalt-60 is produced by bombarding a sample of Cobalt-59 with an excess of
neutrons in a nuclear reactor. The Cobalt-59 atoms absorb some of the neutrons and increase
their atomic weight by one to produce the radioisotope Cobalt-60. .
 This process is known as activation
 As a material rids itself of atomic particles to return to a balance state, energy is released in the
form of Gamma rays and sometimes alpha or beta particles
.

6.  RT uses the ability of gamma rays to penetrate materials.
Gamma rays can even penetrate material that don’t transmit
light.
 Penetration depends upon thickness,the density of material
and size of source being used.
 In passing through the material some of these rays get
absorbed and transmitting the rest of the rays.
 These transmitted rays are recorded on an imaging media
which on further processing gives a radiographic image of the
test object.
 The film/image darkness (density) will vary with the amount
of radiation reaching the film/imaging media through the test
object.
 where darker areas indicate more exposure (higher radiation
intensity) and lighter areas indicate less exposure (lower
radiation intensity).
Schematic Diagram of the
basic principle of Radiographic
Testing

7.  Radiography has sensitivity limitations when detecting cracks.
 X-rays and gamma rays “sees” a crack as thickness variation. Thus larger the variation in
thickness the easier to detect the crack.
 When the path of the gamma ray and x-ray is not parallel to a crack, the thickness variation is
less and the crack may not be visible.
 So the angle between the radiation beam and a crack(linear defect) is so critical,so orientation is
considered and imaging is done at different angles to obtain a accurate view of cracks in the
specimen.
Crack is visible Crack is
not visible

9.  Gamma rays cannot be turned off. Radioisotopes used for gamma radiography are
encapsulated to prevent leakage of the material. The radioactive “capsule” is
attached to a cable to form what is often called a “pigtail.” The pigtail has a special
connector at the other end that attaches to a drive cable.

10.  A device called a “camera” is used to store, transport and expose the pigtail
containing the radioactive material. The camera contains shielding material
which reduces the radiographer’s exposure to radiation during use.
 A hose-like device called a guide tube is connected to a threaded hole called an
“exit port” in the camera.
 The radioactive material will leave and return to the camera through this opening
when performing an exposure!
 A “drive cable” is connected to the other end of the camera. This cable, controlled
by the radiographer, is used to force the radioactive material out into the guide
tube where the gamma rays will pass through the specimen and expose the
recording device.

12.  Both surface and internal discontinuities can be detected.
 Significant variations in composition can be detected.
 It can be used on a variety of materials.
 Can be used for inspecting hidden areas (direct access to surface is not required).
 Very minimal or no part preparation is required.
 Permanent test record is obtained.
 Good portability especially for gamma-ray sources.

13.  Hazardous to operators and other nearby personnel.
 High degree of skill and experience is required for exposure and interpretation.
 The equipment is relatively expensive (especially for x-ray sources).
 The process is generally slow.
 Highly directional (sensitive to flaw orientation).
 Depth of discontinuity is not indicated.
 It requires a two-sided access to the component.
 Difficult to detect small cracks.