Actinide measurements by accelerator mass spectrometry at Lawrence Livermore National Laboratory

摘要

We report on the development of an accelerator mass spectrometry (AMS) system for the measurement of actinides at Lawrence Livermore National Laboratory. This AMS system is centered on a recently completed heavy isotope beam line that was designed particularly for high sensitivity, robust, high throughput measurements of actinide concentrations and isotopic ratios. A fast-isotope switching capability has been incorporated in the system, allowing flexibility in isotope selection and for the quasi-continuous normalization to a reference isotope spike. Initially, our utilization of the heavy isotope system has concentrated on the measurement of Pu isotopes. Under current operating conditions, background levels equivalent to ～ 1 x 10~5 atoms are observed during routine ~(239)Pu and ~(240)Pu measurements. Measurements of samples containing ～10~(13) ~(238)U atoms demonstrate that the system provides a ~(238)U rejection factor during ~(239)Pu measurements of ～10~7. Measurements of known materials, combined with results from an externally organized intercomparison program, indicate that our ~(239)Pu measurements are accurate and precise down to the μBq level (～ 10~6 atoms). Recently, we have investigated the performance of our heavy isotope AMS system in measurements of ~(237)Np and ~(236)U. Results of these investigations are discussed. The sensitivity shown by our Pu measurements, combined with the high throughput and interference rejection capabilities of our AMS system, demonstrate that AMS can provide a rapid and cost-effective measurement technique for actinides in a wide variety of studies.