Detection of glass contamination in horticultural peat with dual-energy X-ray absorptiometry (DXA)

Abstract

The application of dual-energy X-ray absorptiometry (DXA) to the detection of glass contamination in horticultural peat was studied using contaminated peat specimens, imaged with X-ray energies of 40 and 70 kVp and without any physical disruption of the peat samples. The source was an uncollimated beam from an industrial X-ray non-destructive testing system. X-ray transmission characteristics of peat and glass were determined from chemical composition data using XCOM software. The DXA images were analysed for detectivity figure (DF), signal-to-noise ratio (SNR) and contrast. These quantities were compared with those of the unprocessed 40 kVp images. There was >75% detection of glass presence if thicker than 3 mm, but 100% detection of glass fragments thicker than 1 mm. It was not possible to distinguish between glass and stone. DF values were dependent on peat and glass type, and contrast more than doubled with the DXA-derived images compared with their 40 kVp counterparts. Comparison with reported figures for a luggage inspection system shows that this system performs better than expected for commercial security systems. Better DXA results may be possible using simultaneous energy detection, and such a multi-energy sensing system could allow glass/stone detection as part of peat quality assurance, and the determination of peat chemical composition.