High Efficient Detection of Trace Actinides

New methodologies for detecting trace amounts of actinide elements, such as U, Th and Pu, are being investigated for qualitative and quantitative analysis of unwanted impurities in the materials needed for ultra-low background experiments. An example is the next generation experiment LEGEND for searching neutrinoless double beta decay in ⁷⁶Ge, which must have a half-life sensitivity higher than 10²⁷ years. We have explored Accelerator Mass Spectrometry with negative ions produced with a Cs-sputtering source. However, the typical ionization efficiency for actinides ranges from 0.01% to 0.1%. We report on an alternative method based on laser resonance ionization with elemental selectivity to suppress the interfering and background ions. Efficient three-step ionization schemes for U, Th an Pu have been developed with a resonant ionization laser ion source. Overall ionization efficiencies of about 8% for U, 40% for Th and 51% for Pu have been obtained. We will describe how an analytical compact system using positive ions could be developed based on resonant laser selection for trace detection analysis.