Studies of atomic properties of francium and rubidium.
Abstract
High precision measurements of atomic properties are excellent probes for elec-
troweak interaction studies at the lowest possible energy range. The extraction of
standard model coupling constants relies on a unique combination of experimen-
tal measurements and theoretical atomic structure calculations. It is only through
stringent comparison between experimental and theoretical values of atomic prop-
erties that a successful experiment can take place. Francium, with its heavy nucleus
and alkali structure that makes it amenable to laser cooling and trapping, stands as
an ideal test bed for such studies.
Our group has successfully created, trapped and cooled several isotopes of
francium, the heaviest of the alkalies, and demonstrated that precision studies of
atomic properties, such as the measurement of the 8S<sub>1/2</sub> excited state lifetime of
<super>210</super>Fr presented here, are feasible. Further work in our program of electroweak studies requires a better control of the electromagnetic environment observed by the sample
of cold atoms as well as a lower background pressure (10<super>-10</super> torr or better). We have designed and adapted to our previous setup a new &ldquo science &rdquo vacuum chamber that fulfills these requirements and the transport system that will transfer the francium
atoms to the new chamber.
We use this new experimental setup as well as a rubidium glass cell to perform
precision studies of atomic and nuclear properties of rubidium. Spectroscopic studies
of the most abundant isotopes of rubidium, <super>87</super>Rb and <super>85</super>Rb, are a vital component in our program. Performing measurements in rubidium allows us to do extensive and rigorous searches of systematics that can be later extrapolated to francium.
We present a precision lifetime measurement of the 5D<sub>3/2</sub> state of <super>87<super>Rb and a measurement of hyperfine splittings of the 6S<sub>1/2</sub> level of <super>87</super>Rb and <super>85</super>Rb. The quality of the data of the latter allows us to observe a hyperfine anomaly attributed to an isotopic difference of the magnetization distribution in the nucleus i.e. the Bohr-Weisskopf effect. The measurements we present in this work complement each other in exploring the behavior of the valence electron at different distances from the nucleus. In addition, they constitute excellent tests for the predictions of ab
initio calculations using many body perturbation theory and bolster our confidence
on the reliability of the experimental and theoretical tools needed for our work.