100-fold improvement on Atom Trap Trace Analysis for radiokrypton dating*

Atom Trap Trace Analysis (ATTA) has been used to analyze the rare isotope Kr-81 (half-life = 230 kyrs, I.A.$\sim $ 10$^{-13})$ in environmental samples. Kr-81 analysis can now be used to determine the ages of groundwater samples in the range of 50 -- 1,000 kyrs. The previous instrument (ATTA-2) had an overall counting efficiency of 0.01{\%} and, required a water sample of 1,000 liters. We are developing a new instrument (ATTA-3) to laser-trap and count Kr-81 atoms with the goal of reaching a counting efficiency of 1{\%}, which would reduce the sample size to less than 100 liters of water or ice. Recently we have demonstrated a counting rate of $\sim $ 2000 $^{81}$Kr atoms/hr, which represents a 100-fold improvement over ATTA-2. ATTA-3 will enable a wide range of applications in the earth sciences.