AVS 59th Annual International Symposium and Exhibition
    Applied Surface Science Monday Sessions
       Session AS-MoA

Paper AS-MoA3
ToF-SIMS and NanoSIMS Imaging of Uranium Distributions in the Sediment of Hanford Site

Monday, October 29, 2012, 2:40 pm, Room 20

Session: Quantitative Surface Chemical Analysis, Technique Development, and Data Interpretation - Part 2
Presenter: Z. Zhu, Pacific Northwest National Laboratory
Authors: Z. Zhu, Pacific Northwest National Laboratory
Z. Wang, Pacific Northwest National Laboratory
Correspondent: Click to Email
Nuclear materials processing over the past seventy years has left approximately 55 million gallons of nuclear wastes stored in underground tanks at Hanford site. Some of these wastes are leaking into the ground and the DOE has been working on developing remediation technologies. As a part of these activities, sediment samples have been extensively studied to understand chemical speciation and aqueous mineral chemistry. Although concentrations and distributions of radioactive elements, such as uranium (U), plutonium (Pu), and technetium (Tc) are of great interest, U is the most important one because its concentration in the wastes is significantly higher compared to other radioactive elements. Previous studies show that the sediment samples contain low concentration of U (<10 ppm). However, non-uniform distribution of U is found, and the U appears to be mainly in micron- or sub-micron-size particles. Although an understanding of the chemistry and speciation of these particles is important, it is extremely difficult to obtain the composition of these particles using conventional analytical capabilities such as AES, XPS, and SEM/EDX because of the low concentration of U in the samples. Secondary ion mass spectrometry (SIMS) can be effectively used to discover the chemical components of these U-containing particles with excellent sensitivity and decent spatial resolution. We used ToF-SIMS and Nano-SIMS to image some of these U-containing particles in the sediment samples. Preliminary results indicated that U was present across the sample at lower concentrations, while spots of sub-micron particles with much higher U concentrations were irregularly distributed. The major elements in these “hot” spots appeared to be uranium, sodium, phosphorus, and oxygen.