Francium Trapping Facility

While some francium atoms escape, most stay trapped

While some francium atoms escape, most stay trapped: As reported in the Canadian Journal of Physics (2017), laser-trapped francium atoms were irradiated with blue laser light, causing some of them to be photoionized (lose an electron) and lost from the francium trap. The probability of photoionization was in line with the general trend exhibited by the other alkali atoms. Photoionization losses from the laser trap are one of the most serious limitations for a trap-based tests of atomic parity violation, and the results of this experiment importantly support the feasibility of such experiments.

Electron jumps reveal subtle changes in shape of francium nuclei

Electron jumps reveal subtle changes in shape of francium nuclei: As part of the commissioning process for the Francium Trapping Facility, precise measurements were carried out on the isotopic dependence of the 7s − 7p_1/2 electronic transition in a chain of different francium isotopes. As reported in Physical Review A (2014) these data were combined with previously measured isotope shifts in the 7s - 7p_3/2 transition. Isotope shifts are a sensitive measure of changes in the nuclear charge radius, or size of the nucleus, between isotopes of the same atom. Comparison of the two data sets provides insights into the change of electron behaviour as the number of neutrons in the nucleus varies. The results provide a sensitive gauge of the ability of the atomic many-body calculation to describe the francium atom at a level necessary for the interpretation of the Facility's future atomic-parity violation measurements with francium.    

Key step towards historic measurement of atomic parity violation in francium

Key step towards historic measurement of atomic parity violation in francium: Francium Trapping Facility scientists made the first excitation of the highly forbidden 7s-8s transition on which future atomic-parity violation measurements will be based. As reported in Physical Review A (2018) the researchers scrutinized the accuracy of theoretical predictions of the overlap of the valence electron wavefunction with the nucleus (field shift) and electron-electron correlations (specific mass shift) in francium was carried out, another critical test towards understanding atomic theory in francium.

Seeing francium nuclei as tiny magnets

Seeing francium nuclei as tiny magnets: The ratio of the hyperfine splittings of s and p states is not constant across isotopes due to the isotope-dependent distribution of nuclear magnetization, a phenomenon called the hyperfine anomaly. By carrying out measurements of the hyperfine splitting of the excited electronic 7p_1/2 state at the 100-ppm level, and comparing to previously known ground state 7s splittings, the hyperfine anomaly in six isotopes of francium (Fr) was experimentally determined. As reported in Physical Review Letters (2015) the measured magnetic distributions behave regularly from ²¹³Fr through ²⁰⁷Fr, but ²⁰⁶Fr stops behaving like a spherical nucleus with valence nucleons. The results are valuable input for future calculations of both the anapole moments and the neutron radii needed for small corrections to Francium Trapping Facility measurements of atomic-parity violation for ^207−213Fr.