Investigation of the surface topography of rock and ore samples by beta ray backdiffusion radiography using extended area beta ray sources

Since the mapping of heavier elements can be of considerable help to geologists in the determination of structure and texture, as well as in the identification of phases in rock and ore samples, a study has been conducted to evaluate the capabilities and limitations of the method. In the radiographic examination of surface layers using backdiffused beta rays, an electron sensitive radiographic emulsion is pressed against the flat surface of the sample and a homogeneous, extended area beta ray source is put on top of it. Suitable extended area beta ray sources can be either those containing long lived pure beta ray emitting nuclides, like 35S, 147Pr, 204Tl, 32P and 90Sr-90Y, or can simply be neutron irradiated metal foils, for example, of indium or dysprosium. A substantial part of the primary beta radiation which penetrates through the emulsion support and emulsion into the sample and in multiple scattering events is deflected backward from the surface layer of the sample and recorded by a single emulsion coated radiographic film. The surface topography of 60 ore and rock samples, with the elements U, Pb, Hg, W, Sb, Sn, Cu, Zn, Fe, Cr and Al present in various concentrations, was determined. The beta ray diffusion radiographs were compared with optical micrographs and, in the case of the U containing samples, also with alpha track etch autoradiographs. The method offers a quick survey of the surface topography of large areas, with the possibility of identifying different phases where there are large differences in effective atomic number. For quantitative work the method has to first be calibrated with some other method or can be used for inspection of mineral samples with a priori known paragenesis. The spatial resolution is of the order of the range of beta radiation in the sample and, with beta ray sources in the 0.3-1 MeV region, the method can be considered to be macroscopic. 6 refs, 9 figs