Determination of elemental composition in geochemical exploration using a 14-MeV neutron generator

The use of prompt neutron-gamma techniques is well established in the areas of geochemical exploration and environmental monitoring. However, the problems associated with the determination of absolute composition, as compared to elemental identification, can be substantial. For example, in borehole work, the concentration of water can significantly modify the gamma-ray spectrum of the surrounding material. In marine work, the presence of Cl in the water can seriously mask important gamma-ray lines from elements of environmental interest. In order to study these problems, the authors have been using a 14-MeV pulsed neutron generator and a IGe detector system for field measurements where the amount of water in the material has been varied. In addition, they have been doing systematic laboratory measurements of monoelemental samples in water, to determine the detection sensitivity, linearity, and the gamma-ray lines most useful for analysis. These have included elements of environmental interest, e.g. Cd, Ni, Cr and Zn, in the presence of Cl.