We use time-correlated single-photon counting techniques on a sample of 210 Fr atoms confined and cooled in a magneto-optical trap to measure the lifetimes of the 9S 1/2 , 8P 3/2 , and 8P 1/2 excited levels. We populate the 9S 1/2 level by two-photon resonant excitation through the 7P 1/2 level. The direct measurement of the 9S 1/2 decay through the 7P 3/2 level at 851 nm gives a lifetime of 107.53± 0.90 ns. We observe the decay of the 9S 1/2 level through the 8P 3/2 level at 423 nm and the 8P 1/2 level at 433 nm down to the 7S 1/2 ground level, and indirectly determine the lifetimes of these to be 83.5± 1.5 ns and 149.3± 3.5 ns, respectively.

We present lifetime measurements of the 7 p 2 P 3/2 and 7p 2 P 1/2 levels of Fr. We use a time-correlated single-photon counting technique on a cold sample of 210 Fr atoms in a magneto-optic trap. We excite the atoms with the trapping and repumping beams of the magneto-optic trap and detect the decay of the atomic fluorescence. The results are a precision experimental test of the atomic many-body perturbation theory applied to the heaviest alkali metal. The lifetime results are 21.02͑11͒ ns and 29.45͑11͒ ns for the 7p 2 P 3/2 and 7p 2 P 1/2 levels, respectively. This gives a line strength ratio S 1/2 /S 3/2 of 0.526͑3͒ for these levels in Fr. To study sources of systematic errors we measure the lifetimes of 5p 2 P 3/2 and 5p 2 P 1/2 in stable 87 Rb and obtain 26.20͑9͒ ns and 27.64͑4͒ ns, respectively.

We report a method to monitor and control laser frequencies with an optical cavity and a digital feedback system. A frequency-stabilized He-Ne laser provides the reference that is transferred to several other lasers using a scanning Fabry-Pérot cavity. A personal computer-based multifunction data acquisition system generates the scan wave form, and reads the detector outputs synchronously with the cavity scan. The computer determines the positions of all of the peaks in the scan, and generates output signals to control the laser frequencies. It also provides a visual display of cavity spectra. We have successfully used the setup to achieve a long-term lock of the lasers for magneto-optical trapping of radioactive francium atoms.

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We measure the hyperfine splitting of the 9S_{1/2} level of 210Fr, and find a magnetic dipole hyperfine constant A=622.25(36) MHz. The theoretical value, obtained using the relativistic all-order method from the electronic wave function at the nucleus, allows us to extract a nuclear magnetic moment of 4.38(5)micro_{N} for this isotope, which represents a factor of 2 improvement in precision over previous measurements. The same method can be applied to other rare isotopes and elements.

We have trapped over 250 000 210 Fr in a new on-line high efficiency magneto-optical trap ͑MOT͒. We describe the new apparatus and present an overview of high-efficiency MOTs for trapping rare isotopes. These traps depend on three critical components: a dry-film coating, a neutralizer, and the optical trap. We have developed a series of independent tests of the effectiveness of these components, and have used the results to construct our trap.

We have measured the hyperfine splitting of the 7P 1/2 state at the 100 ppm level in Fr isotopes ( 206g,206m,207,209,213,221 Fr) near the closed neutron shell (N = 126 in 213 Fr). The measurements in five isotopes and a nuclear isomeric state of francium, combined with previous determinations of the 7S 1/2 splittings, reveal the spatial distribution of the nuclear magnetization, i.e. the Bohr-Weisskopf effect. We compare our results with a simple shell model consisting of unpaired single valence nucleons orbiting a spherical nucleus, and find good agreement over a range of neutron-deficient isotopes ( 207−213 Fr). Also, we find near-constant proton anomalies for several even-N isotopes. This identifies a set of Fr isotopes whose nuclear structure can be understood well enough for the extraction of weak interaction parameters from parity non-conservation studies.PACS numbers: 21.10. Gv,27.80.+w,32.10.Fn Weak interaction studies in heavy atoms require for their interpretation precise knowledge of the atomic and nuclear wavefunctions. To extract nucleon-nucleon weak interaction couplings from the weak interaction induced parityviolating anapole moment [1], nuclei with simple and regular magnetic properties are desirable [2-4]. The nuclear magnetic moment is used to benchmark nuclear structure theories for calculating the anapole moment [3], which is a contact field effect produced inside the finite extent of the nucleus. Here we explore the regularity of the magnetic properties of a chain of Fr isotopes and find that 207−213 Fr in the vicinity of the neutron shell closure mark a range where the nuclear structure is sufficiently tractable for standard model tests and constraints on new physics [5].To lowest order, the atomic hyperfine interaction can be described using a point-like nucleus characterized by the magnetic dipole moment. Deviations from the pointlike approximation of the nucleus, referred to as hyperfine anomalies, come from considering how finite magnetic and charge distributions affect the interaction between the magnetization of the nucleus and the magnetic field created by the electrons. The magnetic contribution is known as the Bohr-Weisskopf (BW) effect [6,7]. The difference in the nuclear charge distribution (Breit-Rosenthal (BR) effect [23][24][25]) produces very small variations between isotopes, leaving the BW effect dominant [26,27]. As a new generation of proposed parity violation experiments in atoms (including Fr) and molecules starts [8][9][10][11][12][13][14], it is important to understand the limiting factors due to the nuclear structure, e.g. the nuclear magnetization, for the interpretation Fr with up to 6 neutron holes, we find near-constant magnetic hyperfine anomalies for the odd-Z, even-N isotopes [15]. The neutron rich odd-even isotope 221 Fr shows a different behavior due to the deformation of the nucleus. The odd-Z, odd-N isotopes have anomaly contributions from both the proton and the valence neutron.BW effect measurements usually require precise knowledge of both, hyper...

We present lifetime measurements of the 7D 3/2 and 7D 5/2 levels of Fr. We use a time-correlated singlephoton counting technique on a sample of 210 Fr atoms confined and cooled in a magneto-optical trap. The upper state of the 7 P 3/2 trapping transition serves as the resonant intermediate level for two-photon excitation of the 7D states. A probe laser provides the second step of the excitation, and we detect the decay of the atomic fluorescence. Our measurements help extend the knowledge of this class of atomic wave functions in which correlation effects are very significant. We measure lifetimes of 73.6Ϯ0.3 ns and 67.7Ϯ2.9 ns for the 7D 3/2 and 7D 5/2 levels, respectively.