Critical parts in aircraft manufacturing industries such as
stringers are very commonly used in modern aircraft structures
to resist severe compressive loads caused by the aerodynamic
effects. They are generally made-up of thin aluminium (Al) metal
sheets and are one of the key components in the aircraft wings.
Any defects in the stringer components leads to weakening of the
stiffness of the whole aircraft wing structure and consequently,
failure may occur. Hence, there is a need to evaluate the structural
integrity of the stringers using reliable non-destructive testing
(NDT) methods. Due to the complex shaped structure of the
stringer, the one-sided access NDT method such as X-ray back-
scatter technique is more preferable for the non-destructive
imaging.
In difference to conventional transmission X-ray radiography,
the X-ray backscatter technique (XBT) utilizes the scattered radia-
tion caused by the Compton scattering effect [1,2]. As the Compton
À Á
scattering effect depends on electron density ρe in the scattered
object, low-atomic number (Z) materials (e.g. Al, Perspex, compo-
sites and water) exhibit predominant scattered radiations com-
pared to the heavy metals such as Fe, Cu and Pb, respectively