ATTA-3: The Next-Generation Instrument for $^{81}$Kr-Dating

Atom Trap Trace Analysis (ATTA) has been used to analyze two rare isotopes: $^{81}$Kr (isotopic abundance $\sim $ 10$^{-12})$ and $^{85}$Kr ($\sim $10$^{-11})$, in environmental samples. Radiokrypton dating enabled by the ATTA method can now be used to determine the ages of old groundwater in the range of 50,000--1,000,000 years. The present apparatus (ATTA-2) has an overall counting efficiency of 0.01{\%} and, for $^{81}$Kr dating, requires a water sample of at least 1,000 liters. We are developing a new apparatus (ATTA-3) to trap and count $^{81}$Kr atoms with the goal of reaching a counting efficiency of 1{\%}. If successful, the required sample size would be reduced down to 10 liters of water or ice, and a wider range of applications in the earth sciences can be realized. This work is supported by DOE, Nuclear Phys Div, under contract W-31-109-ENG-38, and by a UofC-ANL collaborative seed grant.