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We present a method for measuring the nuclear anapole in a string of francium isotopes. The anapole is a parity non-conserving electromagnetic moment that enables parity-forbidden transitions between ground state hyperfine levels of an atom. The experiment is run by the FrPNC collaboration and relies on a beam of artificially-produced francium from the ISAC facility at TRIUMF.

We observe a hyperfine anomaly in the measurement of the hyperfine splitting of the 6 S 1 / 2 excited level in rubidium. We perform two step spectroscopy using the 5 S 1 / 2 → 5 P 1 / 2 → 6 S 1 / 2 excitation sequence. We measure the splitting of the 6 S 1 / 2 level and obtain for the magnetic dipole constants of 85Rb and 87Rb A = 239.18 ( 4 ) MHz and A = 807.66 ( 8 ) MHz , respectively. The hyperfine anomaly difference of δ 85 87 = − 0.0036 ( 2 ) comes from the Bohr Weisskopf effect: a correction to the point interaction between the finite nuclear magnetization and the electrons, and agrees with that obtained in the 5 S 1 / 2 ground state.

The study of the nuclear polarization of radon is motivated by the expected large enhancement of sensitivity to a CP-violating electric dipole moment (EDM) in isotopes with octupole deformation or vibrational strength. In preparation for EDM measurements, the polarization of radon by spin exchange with laser-polarized alkali metals is studied. The measurement of the alignment of 209Rn using HPGe detectors to observe the resulting anisotropy in the 337 and 745 keV gamma rays emitted following electron-capture decay of 209Rn to 209At is demonstrated. Radon is polarized via spin-exchange collisions with rubidium atoms in an uncoated Pyrex optical pumping cell. Anisotropy measurements at several temperatures are used to study polarization and relaxation.

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 nonconservation studies.

Francium combines a heavy nucleus (Z = 87) with the simple atomic structure of alkalis and is a very promising candidate for precision tests of fundamental symmetries such as atomic parity non-conservation measurements. Fr has no stable isotopes, and the ISAC radioactive beam facility at TRIUMF, equipped with an actinide target, promises to provide record quantities of Fr atoms, up to 1010/s for some isotopes. We discuss our plans for a Fr on-line laser trapping facility at ISAC and experiments with samples of cold Fr atoms. We outline our plans for a measurement of the nuclear anapole moment — a parity non-conserving, time-reversal conserving moment that arises from weak interactions between nucleons — in a chain of Fr isotopes. Its measurement is a unique probe for neutral weak interactions inside the nucleus.

Francium is a candidate for atomic parity non-conservation (PNC) experiments. Its simple atomic structure has been the subject of extensive experimental research facilitated by the ability to trap and cool significant numbers of atoms. The studies include the location of energy levels, their hyperfine splittings and their lifetime. All of these levels are close to the ground state. The results show a remarkable agreement with calculated ab initio properties to a degree that is comparable with other stable alkali atoms. The quantitative understanding of francium has made possible the exploration of avenues for a PNC measurement in the optical and the microwave regimes. These precision experiments have the potential to enhance our understanding of the weak coupling constants between electrons and nucleons, as well as between nucleons.

The processes responsible for the creation of elements more massive than iron are not well understood. Possible production mechanisms involve the rapid capture of protons (rp-process) or the rapid capture of neutrons (r-process), which are thought to occur in explosive astrophysical events such as novae, x-ray bursts, and supernovae. Mass measurements of the nuclides involved with uncertainties on the order of 100 keV or better are critical to determine the process ‘paths’, the energy output of the events, and the resulting nuclide abundances. Particularly important are the masses of ‘waiting-point’ nuclides along the rp-process path where the process stalls until the subsequent β decay of the nuclides. This paper will discuss the precise mass measurements made of isotopes along the rp-process and r-process paths using the Canadian Penning Trap mass spectrometer, including the mass of the critical waiting-point nuclide 68 Se.

The Canadian Penning Trap (CPT) mass spectrometer located at the ATLAS facility of Argonne National Laboratory is an online Penning trap system used for mass measurements of high accuracy on short-lived isotopes. It uses a gas catcher as a novel way to transform radioactive ions efficiently from different sources into cooled beams which are injected into ion traps for further preparation and measurement. The CPT has recently been successfully used to make precise mass measurements on over 40 neutron-rich and neutron-deficient radioactive nuclides related to astrophysical processes.

In order to trap francium atoms in a magneto-optical trap, a beam of singly charged francium ions must be neutralized and reduced to thermal energies. Vacuum requirements prevent the use of a gas-filled charge exchange cell. The simple alternative is to implant the ion beam into a hot catcher foil where the ions neutralize within the foil and then diffuse out. The fraction of ions which neutralize depends upon the work function of the foil and first ionization potential of the ion beam. In order to produce such a neutralizer several suitable materials were tested in a variety of different mechanical designs to determine the most effective and robust system.

The Canadian Penning Trap (CPT) mass spectrometer is designed to make precise mass measurements on a variety of stable and short-lived isotopes. Modifications to the injection system of the CPT have been implemented in recent months, the purpose being to more efficiently collect and transfer weakly-produced reaction products from the target to the Penning trap. These include a magnetic triplet situated after the target chamber to increase the acceptance of the Enge spectrograph, a velocity filter to more effectively separate the beam from the reaction products and the replacement of the Paul trap with a linear trap resulting in more efficient capture and accumulation of ions from the ion cooler. This paper will discuss these recent modifications and how they have increased our ability in making mass measurements on isotopes of low abundance, including those from a 252 Cf fission source.

A new approach to the production of low energy radioactive beams involves the stopping of fast beams produced by fragmentation, in-flight fission or fusion–evaporation reaction into a large gas catcher where the reaction products are thermalized in high-purity helium and extracted as singly charged ions for post-acceleration. This removes the limitation present in standard ISOL technique for species that are difficult to extract from the target/ion source assembly. This approach has been implemented at Argonne since 1998 to inject fusion–evaporation products in an ion trap system. Via a series of improvements since then, we now reach efficiencies for these devices of close to 50% with delay times below 10 ms. In preparation for the RIA project, a larger device for stopping fragmentation products is in preparation. The basic principles behind these devices together with results obtained and experience gained operating these devices will be presented. Preparation for a test of the large gas cell at the full RIA energy at GSI will also be presented.

The Canadian Penning Trap (CPT) mass spectrometer is a device used for high-precision mass measurements on short-lived isotopes. It is located at the ATLAS superconducting heavy-ion linac facility where a novel injection system, the RF gas cooler, allows fast reaction products to be decelerated, thermalized and bunched for rapid and efficient injection into the CPT. The CPT spectrometer and its injection system will be described in detail and its unique capabilities with respect to its initial physics program, concentrating on isotopes around the N=Z line with particular emphasis on isotopes of interest to low-energy tests of the electroweak interaction and the rp-process, will be highlighted.

Au and isotopically enriched Pt targets are discussed for the production of radioactive Fr beams. Target foils, serving also as ionizers, have to be heated in order to enhance the diffusion of atoms to the surface for further extraction and injection into the electrostatic transport system.

We have performed precision measurements in a magneto-optical trap of the 7P1/2 hyperfine structure of the isotopes 209-210Fr. The ratio of these hyperfine constants to the previously measured 7S1/2 ground state values reveals a significant hyperfine anomaly. This anomaly results from the different radial dependence of the electron density in the two atomic levels. The measurements are sensitive to changes in the radial distribution of the neutron magnetism.

Discussion and tests of several designs of sources for continuous vacuum deposition of Au.

We report the spectroscopy of the 8S1/2 energy level in Fr by two-photon excitation of atoms confined and cooled in a magneto-optical trap. The resonant intermediate level is the upper state of either the 7P3/2 trapping transition or the 7P1/2 repumping transition. The center-of-gravity energy difference between the 7S1/2 ground level and the 8S1/2 level is 19 732.52360.004 cm . The hyperfine separation of the 8S1/2 ,F511/2 and F513/2 states is 1

We have performed precision measurements in a magneto-optical trap of the 7P1/2 hyperfine structure of the isotopes 209-210Fr. The ratio of these hyperfine constants to the previously measured 7S1/2 ground state values reveals a significant hyperfine anomaly. This anomaly results from the different radial dependence of the electron density in the two atomic levels. The measurements are sensitive to changes in the radial distribution of the neutron magnetism.

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–Perot 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.

We present the first measurement of an atomic radiative lifetime in Fr. We use a time-correlated single photon counting technique with a cold sample of {sup 210}Fr atoms in a magneto-optic trap. The results are a precision experimental test of the atomic many-body perturbation theory applied to the heaviest alkali. The lifetime for the 7p {sup 2}P{sub 3/2} level of 21.02(16) ns gives a value for the reduced transition matrix element between the levels 7s {sup 2}S{sub 1/2} {r_arrow} 7p {sup 2}P{sub 3/2} of 5.898(22)a{sub {infinity}} atomic units. {copyright} {ital 1997} {ital The American Physical Society}

The techniques of laser cooling and trapping now make it possible to observe large samples of stable atoms in a small volume at low temperature. This capability was recently extended to radioactive isotopes. This opens up new opportunities for the investigation of fundamental symmetries through measurements using radioactive atoms. In this paper we will discuss several fundamental measurements in atomic systems and how the ability to trap radioactive atoms will play an important role in improving the precision of such measurements. Measurements of the effects of the weak interaction are of particular note since they are becoming quite precise. In particular, we will describe in detail the system developed at Stony Brook to trap radioactive alkali atoms and measure weak interaction effects in francium isotopes.

We present the current status of the Francium Trapping Facility at ISAC at TRIUMF. The facility will enable future experiments on the weak interaction with measurements of atomic parity non-conservation laser-cooled samples of artificially produced francium. These experiments require a precisely controlled environment, which the facility is designed to provide. The facility has been constructed and is being prepared for a series of commissioning runs.

The isotope shifts (IS) of 202,203,204 Bi have been measured on the 306.7 nm line using an extremely sensitive gas cell technique of laser spectroscopy. A King plot analysis of this data with other IS measurements in neighbouring isotope chains reveals that the known behaviour of relative changes in mean square nuclear charge radius is only strictly observed above the Z = 82 shell closure.

The FrPNC collaboration has begun the construction of an on-line laser cooling and trapping apparatus at TRIUMF to measure atomic parity non-conservation (PNC) and the nuclear anapole moment in a string of artificially produced francium isotopes. Atomic PNC experiments provide unique high precision tests of the electroweak sector of the Standard Model at very low energies. Furthermore, precision measurements of spin-dependent atomic PNC can determine nuclear anapole moments and probe the weak force within the nucleus. Francium is an excellent candidate for precision measurements of atomic PNC due to its simple electronic structure and enhanced parity violation: both the optical PNC and anapole moment signals are expected to be over an order of magnitude larger than in cesium.

An experimental program is under way to capture neutral francium atoms in a magneto-optic trap. Production and transport of the radioactive Fr atoms near to the trapping region have been tested, with a steady state of 107 atoms. If one hundred atoms are captured from the Maxwell-Boltzmann distribution into a magneto-optic trap, this will be a sufficient number for spectroscopy of the unknown excited states. These measurements would then open the path to investigations of parity-violating transitions in francium.

Performing collinear laser spectroscopy on low intensity radioactive beams requires sensitive detection techniques. We explain our apparatus to detect atomic resonances in neutralized (208-210)Fr ion beams at beam energies of 5 keV and intensities of 10(5) s(-1). Efficient neutralization (or = 80%) is accomplished by passing the beam through a dense Rb vapor. Increased detection efficiency is achieved by amplitude modulating the exciting laser to decrease the scattered light background, allowing fluorescence detection only when the laser is near its minimum in the modulation cycle. Using this technique in a collinear geometry we achieve a background reduction by a factor of 180 and a signal-to-noise increase of 2.2, with the lifetime of the atomic state playing a role in the efficiency of this process. Such laser modulation will also produce sidebands on the atomic spectra which we illustrate.

An apparatus has been developed for on-line studies of the optical spectra of radioactive atoms formed from heavy-ion fusion evaporation reaction products. The unstable nuclei recoil into cell containing a noble gas in which they are neutralized and thermalized by the gas. A laser beam passing through the cell is tuned through an optical resonance of the diffusing atoms, and the resulting fluorescence is detected. The apparatus provides a relatively long laser-atom interaction time and allows the study of atoms too short lived or produced in amounts too small or from elements too refractory to be studied by other means. Isotope shifts of 152,154,156,158Yb have been measured, as well as the shifts between the stable isotopes of the refractory element Hf.

We report on the spectroscopic measurement of the (210)Fr 9S(1/2) energy obtained by two-photon excitation of atoms confined and cooled in a magneto-optic trap. The resonant intermediate level 7P(3/2) is the upper state of the trapping transition. We have measured the energy difference between the 9S(1/2) state and the 7S(1/2) ground state to be 25 671.021 +/- 0.006 cm(-1).

We report here on the measurement of isotope shift and hyperfine splitting of190, 191, 193, 197Pb for the 723 nm atomic optical transition. Detailed analysis of the optical data has been done by combining them with the available muonic and electronicx-ray isotope shift data. The magnetic dipole moments and the electric quadrupole moments of the odd isotopes have been extracted from the hyperfine coupling constants of the atomic states involved in the optical transition used.

Polarization and relaxation of radon isotopes by spin exchange with laser optically pumped rubidium were studied in preparation for electric dipole moment measurements with octupole deformed $^{223}\mathrm{Rn}$. \ensuremath{\gamma}-ray anisotropies provided a measure of nuclear polarization produced by spin exchange with laser polarized rubidium vapor, and the temperature dependence over the range 130 to ${220}^{\ifmmode^\circ\else\textdegree\fi{}}$C was measured to parametrize the spin exchange polarization and the quadrupole-dominated wall relaxation rate. These results provide quantitative data for developing electric dipole moment measurements of octupole-deformed $^{223}\mathrm{Rn}$ and other radon isotopes.

We measure the hyperfine splitting of the $9{S}_{1/2}$ level of $^{210}\mathrm{Fr}$, and find a magnetic dipole hyperfine constant $A=622.25(36)\text{ }\text{ }\mathrm{MHz}$. 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 $4.38(5){\ensuremath{\mu}}_{N}$ 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 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.

Weak interactions within a nucleus generate a nuclear spin dependent, parity-violating electromagnetic moment, the anapole moment. We analyze a method to measure the nuclear anapole moment through the electric dipole transition it induces between hyperfine states of the ground level. The method requires tight confinement of the atoms to position them at the antinode of a standing wave Fabry-Perot cavity driving the anapole-induced microwave $E1$ transition. We explore the necessary limits in the number of atoms, excitation fields, trap type, interrogation method, and systematic tests necessary for such measurements in francium, the heaviest alkali.

A program to study parity nonconservation in francium at TRIUMF is presented. The essential part of the experiment will be a collection of ≈ 106 trapped atoms on-line at the ISAC radioactive beam facility. The atoms can be excited through a parity-forbidden E1 transition either in the microwave or in the optical regime. The rate of excitation gives information on the weak nucleon-nucleon interactions through the anapole moment of the Fr nucleus.

We measure the lifetime of the 8s level on a magneto-optically trapped sample of ^{210}Fr atoms with time-correlated single-photon counting. The 7P_{1/2} state serves as the resonant intermediate level for two-photon excitation of the 8s level completed with a 1300 nm laser. Analysis of the fluorescence decay through the the 7P_{3/2} level gives 53.30 +- 0.44 ns for the 8s level lifetime., Comment: 4 pages, 4 figures

We present a lifetime measurements of the 6s level of rubidium. We use a time-correlated single-photon counting technique on two different samples of rubidium atoms. A vapor cell with variable rubidium density and a sample of atoms confined and cooled in a magneto-optical trap. The 5P_{1/2} level serves as the resonant intermediate step for the two step excitation to the 6s level. We detect the decay of the 6s level through the cascade fluorescence of the 5P_{3/2} level at 780 nm. The two samples have different systematic effects, but we obtain consistent results that averaged give a lifetime of 45.57 +- 0.17 ns., 10 pages, 9 figures

International audience; The Canadian Penning trap (CPT) mass spectrometer at the Argonne National Laboratory makes precise mass measurements of nuclides with short half-lives. Since the previous ENAM conference, many significant modifications to the apparatus were implemented to improve both the precision and efficiency of measurement, and now more than 60 radioactive isotopes have been measured with half-lives as short as one second and with a precision ( Δm/m) approaching 10-8. The CPT mass measurement program has concentrated so far on nuclides of importance to astrophysics. In particular, measurements have been obtained of isotopes along the rp-process path, in which energy is released from a series of rapid proton-capture reactions. An X-ray burst is one possible site for the rp-process mechanism which involves the accretion of hydrogen and helium from one star onto the surface of its neutron star binary companion. Mass measurements are required as key inputs to network calculations used to describe the rp-process in terms of the abundances of the nuclides produced, the light-curve profile of the X-ray bursts, and the energy produced. This paper will present the precise mass measurements made along the rp-process path with particular emphasis on the "waiting-point" nuclides 68Se and 64Ge.

Mass measurements of $^{68}\mathrm{Ge}$, $^{68}\mathrm{As}$, and $^{68}\mathrm{Se}$ have been obtained with the Canadian Penning Trap mass spectrometer. The results determine the mass excess of $^{68}\mathrm{Se}$ as $\ensuremath{-}54\text{ }232(19)\text{ }\text{ }\mathrm{keV}$, the first measurement with a precision and reliability sufficient to address the light-curve and energy output of x-ray bursts as well as the abundances of the elements synthesized. Under typical conditions used for modeling x-ray bursts, $^{68}\mathrm{Se}$ is found to cause a significant delay in the rp process nucleosynthesis.

Mass measurements of 68Ge, 68As, and 68Se have been obtained with the Canadian Penning Trap mass spectrometer. The results determine the mass excess of 68Se as -54 232(19) keV, the first measurement with a precision and reliability sufficient to address the light-curve and energy output of x-ray bursts as well as the abundances of the elements synthesized. Under typical conditions used for modeling x-ray bursts, 68Se is found to cause a significant delay in the rp process nucleosynthesis.

We present lifetime measurements of the ${7p}^{2}{P}_{3/2}$ and ${7p}^{2}{P}_{1/2}$ levels of Fr. We use a time-correlated single-photon counting technique on a cold sample of ${}^{210}\mathrm{Fr}$ 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 21.02(11) ns and 29.45(11) ns for the ${7p}^{2}{P}_{3/2}$ and ${7p}^{2}{P}_{1/2}$ levels, respectively. This gives a line strength ratio ${\mathcal{S}}_{1/2}$/${\mathcal{S}}_{3/2}$ of 0.526(3) 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 ${}^{87}\mathrm{Rb}$ and obtain 26.20(9) ns and 27.64(4) ns, respectively.

Francium is the least studied of the alkali atoms because it has no stable isotopes. We have performed precision spectroscopy on cold Fr atoms in a magneto optical trap. We have determined the location of the first two excited states of the S series by two-photon spectroscopy. We have measured the lifetimes of the 7p levels with a precision better than 0.5%. Our measurements test the many-body perturbation theory ab initio calculations of the dipole matrix element to very high accuracy in this relativistic alkali.

An atomic parity non-conservation measurement can test the predictions of the standard model for the electron-quark coupling constants. The measurements, performed at very low energies compared to the Z0 pole, can be sensitive to physics beyond the standard model. Francium, the heaviest alkali, is a viable candidate for atomic parity violation measurements. The extraction of weak interaction parameters requires a detailed knowledge of the electronic wavefunctions of the atom. Measurements of atomic properties of francium provide data for careful comparisons with ab initio calculations of its atomic structure. The spectroscopy, including energy level location and atomic lifetimes, is carried out using the recently developed techniques of laser cooling and trapping of atoms.

The alkali element francium has no stable isotopes and has eluded extensive study because sufficient quantities have not been available for detailed investigations. More than 1000 {sup 210}Fr atoms have now been contained in a magneto-optic trap. This number is sufficient to allow extensive studies of Fr atomic properties that are necessary input for future tests of fundamental interactions. The {sup 210}Fr ({ital T}{sub 1/2}=3.2 min) were created in the nuclear reaction {sup 197}Au({sup 18}O,5{ital n}){sup 210}Fr and were extracted from the target and injected into the trap. The ratio of the trap loading rate to the production rate in the target was 10{sup {minus}4}, which is 50 times larger than in previous experiments with {sup 79}Rb. {copyright} {ital 1996 The American Physical Society.}

The strong confinement of atoms in six-dimensional phase space in magneto-optic traps makes them a promising tool for work with radioactives. The absence of Doppler broadening and laser-atom interaction more than one thousand times longer compared to atomic beams provide a very good environment for precision measurements. The long term project is to measure parity non-conservation effects in francium. Francium is attractive because the effects are larger than in the other alkalis and francium is trappable. However it does not have stable isotopes. With the Stony Brook linear accelerator we can produce a variety of neutron deficient isotopes. The neutron rich isotopes can come as daughters of radioactive decay in thorium. Since the production rate of radioactive atoms is not high, any experiment with them requires efficient use of the available sample. We have developed an on-line system to capture radioactive atoms from an accelerator.