Trapping and Probing Rare Isotopes

We trap and probe atoms of rare isotopes,
and explore related scientific problems in the realm of physics and beyond.

Atom Trap Trace Analysis reaching parts-per-quadrillion sensitivity

Atom Trap Trace Analysis (ATTA), a laser-based atom counting method, has been applied to analyze atmospheric ³⁹Ar (half-life = 269 yr), a cosmogenic isotope with an isotopic abundance of 0.8 parts-per-quadrillion (8x10^-16) in the atmosphere. The possibility of contamination counts due to other atomic or molecular species above the 1x10^-16 level has been excluded. In addition to the superior selectivity demonstrated in this work, both the counting rate and counting efficiency of ATTA have been improved by two orders of magnitude over prior results. Along with the previously demonstrated detection of ⁸¹Kr (229,000 yr) and ⁸⁵Kr (10.8 yr) at the 10^-12 level, ATTA can now be used to analyze all three long-lived noble gas radioisotopes covering a wide range of ages and applications.

 

Testing time-reversal symmetry in atoms and nuclei

We are searching for a permanent electric-dipole moment (EDM) of the Ra-225 (t_1/2 = 15 d) atom. A positive finding would signify the violation of time-reversal symmetry (T). This experiment provides an outstanding opportunity to search for new physics beyond the Standard Model. We have succeeded in realizing laser trapping and cooling of radium atoms (both Ra-226 and Ra-225) for the first time ever. At present, we are developing the techniques and apparatus needed for the EDM measurements with cold Ra-225 atoms.

 

Studying exotic nuclear structure

Helium-8 (He-8) is the most neutron-rich matter that can be synthesized on earth: it consists of two protons and six neutrons, and remains stable for an average of 0.2 seconds. Because of its intriguing properties, He-8 has the potential to reveal new aspects of the fundamental forces among the constituent nucleons. We have recently succeeded in laser trapping and cooling this exotic helium isotope, produced at the GANIL cyclotron facility in northern France, and have performed precision laser spectroscopy on individual trapped atoms. Based on atomic frequency differences measured along the isotope chain He-3 – He-4 – He-6 – He-8, the nuclear charge radius of He-8 has been determined for the first time. The result can now be compared with the values predicted by a number of nuclear structure calculations and is testing their ability to characterize this loosely-bound halo nucleus.

 

Other Research Projects

• Counting Individual Ca-41 Atoms with a Magneto-Optical Trap

• Search for Helium-like Strangelets in the Earth's Atmosphere

 

We acknowledge the support of DOE, Office of Nuclear Physics.