Synopsis

Clocking the last century

Physics 4, s32
Atom trap analysis has reached new sensitivity limits in measuring the abundance of argon-39, a desirable isotope for dating environmental samples on the time scale of a few hundred years.

With a half-life of 5730 years, carbon- 14 is well suited for radioisotope dating of fossils and other archeological finds. On the other end of the time spectrum, tritium (half-life of 12.3 years) and krypton- 85 (half-life of 10.7 years) are useful for dating ice and water samples over the course of several decades. There are, however, many geological changes that occur on a timescale of 10 500 years. Mixing processes in the ocean and groundwater, for example, have implications for modeling global and regional climate, but a good radioactive “clock” for monitoring these changes is not available.

Argon- 39, which is produced in the atmosphere by cosmic rays and has a half-life of 269 years, would seem an ideal isotope to fill this niche. Unfortunately, the equilibrium isotopic abundance of argon- 39 is only 8×10-16, making it difficult to detect without expensive or time-consuming techniques. Writing in Physical Review Letters, a team of scientists working at Argonne National Laboratory, US, reports they have reached an isotopic sensitivity of 10-16 for argon- 39 using a specialized magneto-optical atom trap that allows them to detect single atoms. In their setup, the team laser-cools and traps argon atoms with a laser tuned to the vicinity of an argon- 39 atomic resonance. Since it takes many cycles of absorption to trap the atoms, there is a nearly complete rejection of the other isotopes from the trap and only the remaining argon- 39 atoms are detected.

Alternative methods to analyze the abundance of argon- 39 exist, such as accelerator mass spectrometry. But with further development, the Argonne group’s technique offers a promising way to perform trace analysis of this important isotope with a table-top apparatus. – Gene Sprouse


Subject Areas

Atomic and Molecular Physics

Related Articles

“Shuttled” Ions Stay Quantum
Quantum Physics

“Shuttled” Ions Stay Quantum

Researchers move an individual Mg+ ion more than 100,000 times between different sites in a trapping array without dropping it or ruining its quantum coherence. Read More »

Quantum Repeater Goes the Distance
Atomic and Molecular Physics

Quantum Repeater Goes the Distance

A quantum repeater based on trapped ions allows the transmission of entangled, telecom-wavelength photons over 50 km. Read More »

Record Precision for Hydrogen Spectroscopy Measurements
Particles and Fields

Record Precision for Hydrogen Spectroscopy Measurements

Measurements of the “hyperfine” splitting of certain electronic levels of hydrogen have broken precision records, potentially enabling precise tests of quantum electrodynamics. Read More »

More Articles