When the binding energy is not strong enough to hold the nucleus of an atom together, the atom is said to be unstable. Atoms with unstable nuclei are constantly changing as a result of the imbalance of energy within the nucleus.
Radiogram and its interpolation
B is the image shift of the bar, A is the source shift between exposures, T is the source to film distance, D is the distance of the bar above the film or image plane
When radiographic rays are directed into an object,
some of the photons interact with the particles of
the matter and their energy can be absorbed or
scattered. This absorption and scattering is called
The relationship between the intensity of photons
incident and transmitted is:
I is transmitted photon intensity,
I0is incident photon intensity,
µ is attenuation coefficient,
x is thickness of object
EFFECT OF ATTENUATION
As the radiation passes through the member its intensity
is reduced according to the thickness, density and
absorption characteristics of the materials within the
The quantity of radiation passing through the member is
recorded on a film.
GAMMA RAY RADIOGRAPHY
Gamma rays are types of electromagnetic radiation of
shorter wavelengths than visible light
Shorter wavelengths permit penetration through
High energy levels break chemical bonds
allows “looking” inside structures with photographic
Gamma radiation is the product of radioactive atoms.
Depending upon the ratio of neutrons to protons within its
nucleus, an isotope of a particular element may be stable or
Over time, the nuclei of unstable isotopes spontaneously
disintegrate, or transform, in a process known as “radioactive
decay” and such material is called “radioactive
GAMMA RAY SOURCES USED
Two of the most common industrial gamma-ray sources
for industrial radiography are Iridium-192 and Cobalt-60
Iridium 192 –
Energy : 0.317 to 0.468 MeV
upto 25 to 250 mm thick concrete
Cobalt 60 –
Energy : 1.332 to 1.173 MeV
upto 125 to 500 mm thick concrete
APPLICATION IN STRUCTURAL
Detection of reinforcement location
Detection of Voids and Cracks
Detection of quality of grouted post-tensioned tendons
Measurement of bar depth and flaw depth
The failure of cables
Discontinuities of the ducts
Broken wires or cables in some cases
For materials with uniform thickness and porosity, the
transmitted intensity of gamma rays is dependent only on
the moisture content of the pores.
Find Gamma ray intensity transmitted by that same
material when it is dry.
Reinforcing bars absorb more energy than the
surrounding concrete and show up as light areas on the
DETERMINATION OF CRACKS
Cracks and voids, on the other hand, absorb less
radiation and show up as dark zones on the film.
Crack planes parallel to the radiation direction are
detected more readily than cracks perpendicular to the
QUALITY OF POST TENSIONED
Gammagraphy at 3 different location of bridge,
Observe the marked void in upper duct of Plate 1 (dark band)
In Argentina’s largest bridge complex, Zárate-Brazo Largo,
Depth of bar and depth of flaw can be measured by many
Rigid formula Method
Single Marker Method
Double Marker Method
RIGID BAR METHOD
B D BT
A T D A B
H D K
T - D
IF B2 = 2 B1
FLAW IS AT CENTRE
Three basic requirements must be met to produce X rays,
(a)source of electrons as a heated filament,
(b)means of directing and accelerating the electrons as a
high voltage supply,
(c)target which the electrons can bombard, normally in
the form of heavy metal
The specimen absorbs radiation but where it is thin or,
where there is a void, less absorption takes place. Since
more radiation passes through the specimen in the thin
or void areas, the corresponding areas of the film are
• the X ray tube must be powered by a stable electrical supply. Power
variations in the filament and the high voltage circuit alter the
spectrum and intensity of the generated X ray.
• the target anode and its connecting support structure must be
cooled and be designed to facilitate heat dissipation. A large
rotating anode, which spreads the heat produced over a larger area
of the anode, is often used to extend the serviceable life of the
anode and provide a stable emission of spectra.
• the electron beam emitted from the cathode and the X ray beam
emitted from the anode be focused so that a narrow, high intensity
beam of X rays is produced.
GENERAL CAUTIONS IN
Specifically trained and accredited persons for
implementing the technique
Define a protection area around structure
Move away all the persons during the entire test
No practice involving exposures to radiation should be adopted unless it
produces sufficient benefit to the exposed individuals or to society to
offset the radiation detriment that it causes.
In relation to any particular source, the magnitude of individual doses,
the number of people exposed and the likelihood of incurring exposure
where these are not certain to be received shall be kept as low as
reasonably achievable economic and social factors taken into account
The exposure of individuals resulting from the combination of all the
relevant practices should be subject to dose limits. These are aimed at
ensuring that no individual is exposed to radiation risks that are judged
to be unacceptable in normal circumstance
The most important aspect of radiation protection, assuming that
the practice is justified, is to keep radiation doses as low as
Role of Authorities
Inspection and enforcement
Local rules and supervision
Prevention of access
Both surface and internal discontinuities can be detected.
Significant variations in composition can be detected.
It has a very few material limitations.
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.
Hazardous to operators and other nearby personnel.
High degree of skill and experience is required for
exposure and interpretation.
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.
For application in Bridges with long span, the power
required will be very high
Several hundred metres of area will need to be cleared
so that no possibility of accidental exposure.
Not feasible in densely populated area
Gamma Ray Radiography is a powerful technique as it enables
us to look inside the structure literally
possible to study concrete reinforcements with
unprecedented detail and accuracy
Applications fall outside the scope of the routine inspections
of reinforced concrete beams columns and slabs
Safety issues are there which needs to be taken care of
Guideline on Non Destructive Testing, Ministy of Railway,
Government of India
Non-Destructive Assessment of Concrete Structures: Reliability
and Limits of Single and Combined Techniques - RILEM STATE-
Guidebook on NDT, Department of Atomic Energy
Investigations With Reinforced Concrete Tomography M. A.J.
Mariscotti, P. Thieberger, T. Frigerio, F. Mariscotti And M.