Accelerator mass spectrometry of actinides

Summary Accelerator mass spectrometry (AMS) is a sensitive and robust technique typically applied to the quantification of long-lived radioisotopes in samples too small to be decay-counted. AMS is characterized by a high rejection of interferences and a low susceptibility to matrix components, which reduce the demands on sample preparation chemistry. At Lawrence Livermore National Laboratory (LLNL), Center for Accelerator Mass Spectrometry (CAMS), we have developed an AMS capability for the measurement of actinide concentrations and isotopic ratios. To date, this capability has been primarily devoted to the measurement of ²³⁹Pu and ²⁴⁰Pu in bioassay and environmental samples including soils, sediments, waters, and human urine. For these analyses, a known amount of ²⁴²Pu is added to the samples as a reference isotope for normalization. Measurements of standard and intercomparison samples have shown that quantification is accurate and precise from at least 10⁶ to 10¹¹ atoms/sample. Recently, the ratios of ²⁴⁰Pu, ²⁴¹Pu, ²⁴²Pu, and +Pu to intrinsic ²³⁹Pu have been successfully measured in soil samples from nuclear test sites. In addition, initial measurements of U and Np isotopes have yielded results consistent with the Pu measurements with respect to sensitivity, accuracy, precision, and linear range.