Detection of Trace Actinide Isotopes in Uranium-Rich Materials via Accelerator Mass Spectrometry

Highly-sensitive detection capabilities of trace actinide isotopes are desired for a wide range of applications from nuclear astrophysics, environmental surveys, nuclear forensics, and nuclear reaction studies. Observing the presence of these isotopes can be difficult. Depending on their half-life, abundance, or decay mode, traditional decay counting may not be practical or even possible. Even commercial mass spectrometers may not be sensitive enough due to the presence of molecular interference. At present, Accelerator Mass Spectrometry (AMS) is the most sensitive technique for such measurements.

Development to establish capabilities of actinide detection was performed at the University of Notre Dame's Nuclear Science Laboratory. This required key developments of the ion source, accelerator yield and transmission, as well as improvements to the detection system. Specifically, a compact ionization chamber was created to improve efficiencies, energy resolution, and longevity of the detection system.

To both establish and characterize these capabilities, several uranium ores and NBS standard materials were measured to demonstrate agreement when compared to other AMS laboratories and provide measurements of ore material that, to our knowledge, have not been measured or reported in literature. Additionally, since this measurement technique may be applicable to a large range of actinide isotopes, we explored other rare isotopes present within the sample material to search for other possible characterizing signatures that may assist providing unique "fingerprints" of these materials. Within this work I will show that we have demonstrated consistency in measured values and established detection capabilities for ²³⁶U/U (10^-10), ²³³U/U (10^-11), ²³¹Pa/²³⁵U (4 x 10^-8) and ²³⁰Th/²³⁴U (8 x 10^-5). Further exploration projected the true ²³⁶U/U limit to down to 1.4 x 10^-11 limited by beam transport, detection efficiency, and sufficiently low-level sample material.