Synopsis: Clocking the last century

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 10500 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


Announcements

More Announcements »

Subject Areas

Atomic and Molecular Physics

Previous Synopsis

Optics

It takes two

Read More »

Next Synopsis

Biological Physics

A tale of two nucleic acids

Read More »

Related Articles

Viewpoint: Lamb Shift Spotted in Cold Gases
Atomic and Molecular Physics

Viewpoint: Lamb Shift Spotted in Cold Gases

Cold atomic gases exhibit a phononic analog of the Lamb shift, in which energy levels shift in the presence of the quantum vacuum. Read More »

Synopsis: Quantum Droplets Swell to a Macrodrop
Atomic and Molecular Physics

Synopsis: Quantum Droplets Swell to a Macrodrop

Experiments with ultracold magnetic atoms reveal liquid-like quantum droplets that are 20 times larger than previously observed droplets.    Read More »

Synopsis: Atomic Line Shape Carries Mark of Quantum Statistics
Atomic and Molecular Physics

Synopsis: Atomic Line Shape Carries Mark of Quantum Statistics

Precision measurements of an atomic transition in cold gases of helium-4 and helium-3 isolate the effects of quantum statistics on the transition’s line shape. Read More »

More Articles