An X-ray scanning technique to determine soil macroporosity by chemical mapping

Soil micromorphological studies have used various techniques for pore analy sis, including optical measurements, electron microscopy and computed tomog raphy. This study examined a method based on X-ray photon mapping, in which a scanner obtains the sample's X-ray spectrum, selects those portions whic h have been specified as the elements to map and then only separates that p art of the spectrum to be analysed by the software. With this new technique , the resulting chemical maps are composed of the distribution of selected elements within the sample and the only digitising is to convert the analog ue X-ray signal into a digital signal that can be computer processed. The a pproach provided two-dimensional chemical maps of soil blocks, clearly show ing macropore sizes and distributions and enabling calculation of macroporo sity values. The results showed mean macroporosity values of 17-18%. The ma in benefits of the technique are the precision of data and image processing and the elimination of laborious thin section preparation, as hardened soi l blocks can be scanned automatically. (C) 1999 Elsevier Science B.V. All r ights reserved.