4.2. X-ray backscatter imaging of honeycomb structures
X-ray backscatter technique (XBT) has the significant advantage
(as compared to conventional through-transmission technique) in
detecting low-atomic number (Z) materials (e.g. water, moisture)
in honeycomb structured plates using the unilateral access to the
object. As explained previously, the Compton scattering effect is
predominant for low-Z materials compared to the high-Z materi-
als. Fig. 13 shows the photograph of the 5 cm thick honeycomb
structured plate which is generally used in aerospace industry. The
skin of the honeycomb structured plate is made of 2 mm thick
carbon-fiber-reinforced plastic (CFRP) composite. In order to
validate the applicability of the present XBT to detect low-Z
materials in honeycomb-structured plates, we performed two
different measurements. In the first measurement, we attached
lead (Pb) indicators on the front side of the composite skin plate.
The selected source-to-object distance (SOD) and object-to-slit
distance (OSD) are 65 cm and 35 cm, respectively. The resulted X-