Year
2011
Abstract
The Environmental Sample Laboratory (ESL) of the IAEA Department of Safeguards has implemented the measurement of Pu in environmental safeguards samples using inductively-coupled plasma mass spectrometry (ICP-MS) since 2008. By virtue of an efficient sample introduction system, optimized measurement conditions, and an improved purification scheme, the Pu detection limit approached the level of attograms (ag) and this capability was verified using Pu standard solutions without chemical separation. In the analysis of real environmental samples, quantities less than 2 femtograms (fg) of Pu were detected in the process and swipe blanks, and many swipe samples showed a concentration of Pu in the range of 1 fg to 10 fg. Approximately 1 fg of Pu originates from reagents, such as HNO3 as well as the matrix of the cotton swipe. Memory effects in the ICP-MS sample introduction system are minimized using two sequential rinsing solutions consisting of 1% HF and 2% HNO3. For the correction of interference effects due to polyatomic ions, the formation ratios for 16 chemical elements were examined and these values were applied in the data evaluation step. The most dominant interfering elements in real swipe samples are U, W, Ir, and Hg, even after the chemical purification of the Pu fraction. Using the current analytical method and measurement system, a practical detectable level of Pu is on the order of a few fg, but it is felt that by using optimized separation methods, ultra-clean reagents, and a multi-collector ICP-MS instrument having improved sensitivity, the detection of Pu at the ag level will be possible in the near future.