Archive Sept. 16 - Prof. Will Williams - Smith College

Trace Analysis, Cold Atom Physics and Smith College

Atom Trap Trace Analysis (ATTA), a MOT-based atom counting method developed in the late 1990s by Zheng-Tian Lu at Argonne National Laboratory, can be used to analyze three noble gas radioisotopes (⁸¹Kr, ⁸⁵Kr, ³⁹Ar) covering a wide range of geological ages and has many important applications including monitoring nuclear proliferation with atmospheric ⁸⁵Kr, monitoring ocean currents with ³⁹Ar (climate change), ultra-pure noble gas detectors with ⁸⁵Kr (dark matter), dating underground water with ⁸¹Kr (replenishment rates for underground aquifers), and measuring the age of ice core samples with ⁸¹Kr (climate history).  Their isotopic abundances are extremely low, in the range of 10^-16 – 10^-11. Yet, ATTA can trap and unmistakably detect these rare isotopes one atom at a time. The system at Argonne National Laboratory is currently limited by the excitation efficiency of the RF discharge that produces the metastable atoms needed for laser cooling and trapping.

The Smith College Atomic Physics Laboratory plans to build the next version of ATTA by replacing the RF discharge with a photon excitation scheme that employs a two-photon transition at 215 nm.  The optical source is a frequency quadrupled Ti-Sapphire laser coupled to a power-build-up optical cavity. The predicted metastable transfer efficiency is 0.75, far larger than current methods that use a discharge source with an efficiency of 10^-3.  The ATTA built at Smith College will be at least 100 times more sensitive than the current best version of ATTA. This highly effective apparatus will be the only ATTA in the world sensitive enough to measure the age of ice core samples and the only United States based ATTA dedicated to monitoring nuclear proliferation.