A. Hatakeyama

Low-energy spin-polarized radioactive beams as a nano-scale probe of matter

Abstract We have commissioned a polarized low-energy 8 Li ion beam line, which together with a high-field β-NMR spectrometer, can act as sensitive new probe of thin films and interfaces. The implantation energy can be continuously adjusted from 1 to 90 keV and the maximum polarization achieved thus far is 80%. This instrument opens up new applications for β-NMR which parallel and complement efforts with low-energy muons. For example, it is possible to probe the magnetic field distribution near the surface of a material by stopping a polarized 8 Li beam in a thin overlayer of Ag. Since the 8 Li adopts a site with cubic symmetry in Ag there is no quadrupolar splitting of the resonance, and the 8 Li acts as a purely magnetic sensor.

Polarized radioactive beam at ISAC

Abstract The polarized beam line at ISAC relies on the well known technique of collinear optical pumping to polarize the nuclear spins of a low energy (10–60 keV) radioactive beam. Alkali-metal beams are longitudinally polarized by optical pumping of a fast atomic beam, which is created by charge exchange of the incident ion beam in a Na vapour cell. At ISAC, the beam is then reionized in a He gas target and directed to the experiments. To date, 30 keV beams of 8Li and 9Li have been polarized, and 11Li and 20Na beams are scheduled immediately following this conference. The polarization of the 8Li beam, using a dual frequency, standing wave Ti:sapphire laser, is up to ∼80%. High polarization is achieved by matching the laser bandwidth to the energy spread in the beam. The status of the facility is reported.

Quadrupolar split 8Li β-NMR in SrTiO3

Abstract We have measured the temperature dependence of the β-NMR resonances of 8 Li + implanted in the top few thousand A of a crystal of SrTiO3 in a magnetic field of 3 T || 〈1 0 0〉 . A well-resolved quadrupolar splitting of the resonance is observed indicating a noncubic Li site with 〈1 0 0〉 symmetry and a quadrupolar frequency ν Q (211 K )=153.2(4) kHz . The cubic-to-tetragonal phase transition is reflected in the linewidths demonstrating that β-NMR is a sensitive probe of the structure near a surface.

Laser frequency locking with 46 GHz offset using an electro-optic modulator for magneto-optical trapping of francium atoms.

We demonstrate frequency offset locking between two laser sources using a waveguide-type electro-optic modulator (EOM) with 10th-order sidebands for magneto-optical trapping of Fr atoms. The frequency locking error signal was successfully obtained by performing delayed self-homodyne detection of the beat signal between the repumping frequency and the 10th-order sideband component of the trapping light. Sweeping the trapping-light and repumping-light frequencies with keeping its frequency difference of 46 GHz was confirmed over 1 GHz by monitoring the Doppler absorption profile of I₂. This technique enables us to search for a resonance frequency of magneto-optical trapping of Fr.

Low energy spin polarized radioactive beams as a probe of thin films and interfaces

Abstract A spectrometer for β-detected nuclear magnetic resonance (β-NMR) has been commissioned at the ISAC facility at TRIUMF. A beam of low energy highly spin polarized 8Li+ can be decelerated and implanted into ultra-thin structures 6–400 nm thick. β-NMR provides local information on the electronic and magnetic properties of materials which is similar to conventional NMR but can be used as a sensitive probe of ultra-thin films, interfaces and other nanostructures. We report here on the status of the spectrometer and preliminary results on a simple metal film.

8Li β-NMR in thin metal films

Abstract We have measured the temperature dependence of the β-NMR resonances of 8 Li implanted in thin films of Au and Ag. At room temperature single narrow resonances are observed. The absence of appreciable quadrupolar splitting or broadening indicates that the Li is isolated and at a site of cubic symmetry. As the temperature is lowered, a second resonance appears which is shifted higher in frequency by ∼100 ppm . We attribute the two lines to two distinct cubic sites with slightly different Knight shifts and discuss the application of this result to study fundamental phenomena exhibited by nano-confined metallic electrons.

Motion-induced magnetic resonance of Rb atoms in a periodic magnetostatic field.

We demonstrate that transitions between Zeeman-split sublevels of Rb atoms are resonantly induced by the motion of the atoms (velocity: approximately 100 m/s) in a periodic magnetostatic field (period: 1 mm) when the Zeeman splitting corresponds to the frequency of the magnetic field experienced by the moving atoms. A circularly polarized laser beam polarizes Rb atoms with a velocity selected using the Doppler effect and detects their magnetic resonance in a thin cell, to which the periodic field is applied with the arrays of parallel current-carrying wires.

Doubly-resonant coherent excitation of HCI planar channeled in a Si crystal

We investigated resonant coherent excitation of H-like Ar17+ and He-like Ar16+ ions planar channeled in a Si crystal under the V-type and ladder-type double resonance conditions. In both cases, we observed distinct enhancement in the ionized fraction of the transmitted ions when the double resonance conditions were satis.ed. In the ladder-type configuration, the enhancement indicates that the doubly-excited 2p2 state of He-like Ar16+was produced through doubly-resonant coherent excitation.

Atomic spin resonance in a rubidium beam obliquely incident to a transmission magnetic grating

We studied atomic spin resonance induced by atomic motion in a spatially periodic magnetostatic field. A rubidium atomic beam, with a velocity of about 400 m s−1, was obliquely incident to a transmission magnetic grating that produced a spatially periodic magnetic field. The magnetic grating was formed by a magnetic thin film on a polyimide substrate that had multiple slits at 150 μm intervals. The atoms experienced field oscillation, depending on their velocity and the field period when passing through the grating, and underwent magnetic resonance. Resonance spectra obtained with a perpendicular magnetization film were in clear contrast to ones obtained with an in-plane magnetization film. The former exhibited resonance peaks at odd multiples of the frequency, determined by the velocity over the period, while the latter had dips at the same frequencies.

Radioactive ion beam transportation for the fundamental symmetry study with laser-trapped atoms

The search for the violation of the fundamental symmetry in a radioactive atom is the promising candidate for precision tests of the standard model and its possible extensions. The subtle signal arising from the symmetry violation is enhanced in heavy atoms, such as a francium (Fr). To realize high precision measurements, a large amount of radioactive isotopes is required. The Fr is produced via a nuclear fusion reaction using a melted gold target with a (18)O primary beam at Cyclotron and Radioisotope Center, Tohoku University. The maximum extraction efficiency of the Fr ion was achieved at approximately 35%. The beam line consists of an electrostatic deflector, three electrostatic quadrupole triplets to the measurement area at 10 m away from the reaction point, and several beam diagnosis systems. We optimized parameters of the beam line.