3-D dual gamma-ray computer axial tomography investigation of polymetallic nodules

Polymetallic nodules (PN) collected from the north-east Pacific Clarion-Clipperton region were investigated with a ¹⁹²Ir dual-energy gamma-ray computer tomograph. Tomographic images depicting density and effective atomic number distribution of the same section were obtained. These images present a linear response for a broad range of sample densities (0.97–6.22 g/cm³), and likewise effective atomic numbers (5.48–29). Sixty-five successive digital sections, each with a thickness of 0.8 mm, reveal the 3-D density as well as the effective atomic number distribution function over the entire nodule volume, allowing one to obtain virtual sections across any desired plane. The tomograms show many details of internal structure of the investigated nodule such as an old nucleus, fissure networks or layer structures. The total concentration of iron and manganese determined by this method was equal to 19.4±1.7%. Gamma-ray computer tomography considerably extends the quantitative analysis capability of classic X-ray computer tomography.