Thirteen elements and eleven rare-earth elements (La, Ce, Nd, Sm, Eu, Gd, Tb, Ho, Tm, Yb, and Lu), as well as thorium and uranium, were determined in river sediment samples from the Tigre River, Venezuela, by instrumental neutron activation analysis employing a low-energy photon detector. The analyses were performed on the <63-μm grain size fraction by the following scheme: one irradiation for only 5 h in IVIC's RV-1 nuclear reactor followed by three counting periods, approximately one, three, and seven weeks after the irradiation. This scheme was employed with the purpose of being able to routinely analyze many samples rather than to optimize thirteen different element determinations.
