Neutron Activation Analysis as a Cost Effective Alternative to Wet Chemistry Methods

A neutron activation analysis (NAA) method was developed to analyze soil for Hg, 238U, and 235U as well as, Cr, As, Sb, Se, and Zn. The method was applied to approximately four thousand samples from the flood plain of East Fork Poplar Creek in Oak Ridge Tennessee where significant contamination with mercury is known to have occurred and environmental restoration is under consideration. The objective was to develop a method that could be used with high operating efficiency and thus enable analyses of over 100 samples per day at low analysis cost, while maintaining satisfactory detection limits and measurement errors. Factors contributing to high efficiency and low costs were minimum efforts in sample preparation, and careful choices in neutron irradiation, and gamma-ray counting. Except for efforts to effect homogeneity and select representative aliquots, samples were analyzed as received. Careful selection of neutron irradiation conditions and decay time enabled analyses with only one counting measurement. In principle, the method follows sample handling and quality assurance similar to that of EPA SOW 788. Technical aspects of the method, comparisons of costs with that of \"wet chemistry\" methods, further improvements in efficiency and cost control are presented.