Use of Pu-236 as Tracer for
Neptunium Bioassay Analysis

David J. Fauth and Sherrod L. Maxwell III

Westinghouse Savannah River Company

A new analytical method for neptunium in bioassay samples has been developed by the Analytical Laboratories Department at the Savannah River Site. The method utilizes TEVA Resin™ to selectively co-extract neptunium and plutonium following careful chemical valence adjustment of radionuclides in urine samples. The co-extraction process has been tested using Pu-236 as an internal tracer for neptunium measurement and provides excellent chemical separation from uranium and thorium. The process was tested on 500 samples and compared with the previous process that utilized matrix spikes to establish a batch chemical recovery. The average chemical recovery for plutonium was 72% and 68% for neptunium. A statistical analysis showed strong correlation between the Pu and Np recoveries. Advantages of this method include smaller potential of sample cross contamination, good recoveries, and improved quality assurance from the use of an internal tracer. The method is presently being evaluated to determine if the Pu-236 (with 0.2% Pu-238) tracer can also be used as a tracer for plutonium analyses.