IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research

IGC
Annual Report 2007
IV.A.8. Development of Gamma Ray Backscattering
Facility for Application to Concrete,
Corrosion & Composites
The need for advanced
techniques for detection and
evaluation of embedded
corrosion and a class of subsurface
defects that requires
access only to the one side of
any material or structure to be
inspected has drawn attention
to X-ray or gamma backscatter
as a desirable choice. Among
the techniques using X-ray or
gamma radiation, the
transmission modality is usually
employed. However,
transmission measurements
may not always be possible due
to surrounding space
constraints and for if the object
is too bulky to produce
sufficient radiation penetration.
Transmission provides lineintegrated
information along
the path of radiation from the
source to the detector, which
masks the position of an
anomaly present along the
transmission line. The
Fig.1 Gamma-ray backscattering
scanning facility
scattering modality provides
alternative and in this method
point-wise information can be
obtained by focusing the field
of view of the source and
detector so that they interact
around a point. Since both the
source and detector are
located on one side of the
object, examination of
extended structures becomes
possible. The gamma scattering
method is a viable tool for
inspecting material since it is
an interaction which is strongly
dependent on the electron
density of the scattering
medium, and in turn, its mass
density. Therefore the
information obtained by this
technique is strongly related to
the material density, thus
allowing changes in the
material uniformity to be
monitored.
An indigenous gamma-ray
backscattering scanning facility
has been designed, built and
commissioned. The scanning
system (Fig. 1) consists of four
main modules: the first module
is the source container, second
module houses the detector, the
third is an independent 4-axis
job positioning system and the
Fig. 2 The screen display for easy
operation of complete system
through PC
fourth is the control panel and
PC (Fig. 2). The source and
detector modules are mounted
on a fabricated mild steel
frame and driven by AC
servomotors, linear motion
(LM) guides and ball screws.
The axial travel is 500 mm and
the vertical travel is 400 mm
with an accuracy of ± 0.05
mm. Computer Numerical
Control (CNC) rotary tables of
size 170 mm each are mounted
over the Z-axes of the source
and detector modules and the
source and detector units are
housed over these CNC rotary
tables. Provision is available in
the system to use either
horizontal or streamlined side
looking dipstick HPGe
detectors. The source and
detector modules are designed
to support 450 kg load. The
movement of source and
detector units are programmed
94 FUEL CYCLE