Physicists at Argonne National Laboratory, near Chicago, have
laser-cooled and trapped radium atoms for the first time.
Surprisingly, room temperature blackbody photons -- thermal radiation
over a wide spectrum emitted by the apparatus itself -- were found to
critical role in the laser-trapping of this rare and unstable
element. This represents the heaviest atom ever trapped by laser
Using only 20 nanograms of radium-225 (halflife of 15 days) and
one microgram of radium-226 (halflife of 1,600 years), the Argonne
scientists held tens of radium-225 and hundreds of radium-226 atoms in the
It was particularly challenging to trap radium because
quantities are scarce and the atomic structure is not well studied
Why go through the trouble of trapping radium
atoms? Because it might provide a chance to detect a violation of
time-reversal symmetry (abbreviated with the letter T), which would
manifest itself as an electric dipole moment; that is, even
though the atom as a whole is charge neutral, there might exist a
slight offset between the negative and positive charge within the
atom along its spin axis.
Electric dipole moment searches have been ongoing for over 50
years and continue to yield smaller and smaller limits on the size
of these T-violating interactions. These limits place constraints on
theories beyond the Standard Model of particle physics and
explanations for the matter-antimatter asymmetry in the universe.
Next-generation electric dipole moment searches may take advantage of rare isotopes
such as radium-225, which are expected to be extremely sensitive to
T-violation owing to their non-spherical 'egg'-shaped nucleus. For
the rare and unstable radium atoms, a laser trap offers a promising
path to such a measurement.
Guest et al., Physical Review Letters, upcoming article
See the lab Web site