Ž . Powder Technology 101 1999 178–182 X-ray microtomography to characterize the physical properties of soil and particulate systems A. Macedo ) , C.M.P. Vaz, J.M. Naime, P.E. Cruvinel, S. Crestana Embrapa— Agricultural Instrumentation, Sao Carlos, P.O. Box 741, Zip Code 13560-970, Brazil ˜ Accepted 16 July 1998 Abstract Since many of the phenomena occurring in soil are related to grain and pore sizes and their distribution, investigation on a micrometric scale is of great importance. Also, the investigation should be non-invasive in order to avoid disturbing the region of interest of the sample. Many techniques from various areas of science have been adapted to make such investigations, but most of them are invasive or can only analyze global soil properties. Thus an X-ray tomograph was developed at Embrapa—Agricultural Instrumentation, to scan images of soil samples on a micrometric scale. A microtomographic image of a sieved soil sample, presenting aggregates from 212 mm to 250 mm and pores of 100 mm, is shown. Pores of the same size can also be seen in a microtomograph of a sand column, composed of two layers with granulometries of 106 mm to 149 mm and 297 mm to 500 mm. A microtomograph of a column composed of three layers of an orthoclasius powder is also presented. A slight variation in density along the column height can be observed. q 1999 Elsevier Science S.A. All rights reserved. Keywords: X-ray microtomography; Soil; Pore; Porous system; Porous system microtomography 1. Introduction Ž . X- and g-ray computerized tomography CT have been very helpful in medical diagnosis since the first commer- cial tomographs were constructed in 1973. The capacity of this technique to show sample cross-sections in a non-de- structive way also made it useful in other areas. Petrovic et wx wx al. 6 , Hainsworth and Aylmore 3 and Crestana et al. w x 1,2 used CT for the first time in soil science, by measur- ing soil global density and soil water content. Other inves- tigations followed, using CT to measure global parameters or phenomena. However it is necessary to look inside the soil at the level of the pores and aggregates, because most of the transport processes in soil can only be explained if we can observe the topology and geometry of the pores and aggregates. Ž . Nuclear magnetic resonance NMR tomography has also produced good results, but with some restrictions in soil applications due to the presence of paramagnetic material, causing a very low signal to noise ratio, which ) Corresponding author. Fax: q55-016-272-5958; E-mail: alvaro@cnpdia.embrapa.br can make imaging very difficult. The quantification of data in NMR tomography is another difficult task. The need for a tool capable of investigating at the above mentioned level, motivated Embrapa—Agricultural Instru- mentation to construct an X-ray tomograph dedicated to soil application, but which has also been shown to be useful in other fields, such as particulate systems, for instance. 2. Material and methods The equipment developed is a first generation X-ray tomograph with micrometric resolution, and the details of wx its construction can be seen in Macedo et al. 4 . Fig. 1 shows the block diagram of the microtomograph. In order to proceed with the data acquisition, the sample is placed on the position stage, which shows both translational and rotational movements. In each direction, the sample is translated in steps, set by the user. At each stop, the system counts the number of photons that reach the detector. These photons are attenuated by the sample. The attenua- tion depends on the energy used, on the density of the 0032-5910r99r$19.00 q 1999 Elsevier Science S.A. All rights reserved. Ž . PII: S0032-5910 98 00170-3