Flaw detection by spatially coded backscatter radiography

Backscatter imaging is suited for the inspection of extended structures like airframes, bridge structures, floors etc., which cannot be inspected with conventional radiography. However indications obtained from backscattering are convoluted and difficult to interpret. The spatial coding technique used in astronomical physics to detect feeble emissions is investigated for the detection of the weak indications produced by the flaw in backscatter imaging. Spatial coding involves the positioning of a mask with open and closed holes (aperture) to selectively permit and block the passage of radiation. The obtained 'coded' indications are then mathematically decoded to detect the presence of anomalies. Monte Carlo simulations were employed to investigate the applicability of this technique. This paper introduces the coded aperture technique, describes how it is applied to scatter radiography, present the results obtained from the simulations and concludes with a discussion on future work. (author)