J. A. Behr

Nuclear Charge Radii of 9,11Li: The Influence of Halo Neutrons

The nuclear charge radius of 11Li has been determined for the first time by high-precision laser spectroscopy. On-line measurements at TRIUMF-ISAC yielded a 7Li-11Li isotope shift (IS) of 25 101.23(13) MHz for the Doppler-free [FORMULA: SEE TEXT]transition. IS accuracy for all other bound Li isotopes was also improved. Differences from calculated mass-based IS yield values for change in charge radius along the isotope chain. The charge radius decreases monotonically from 6Li to 9Li, and then increases from 2.217(35) to 2.467(37) fm for 11Li. This is compared to various models, and it is found that a combination of halo neutron correlation and intrinsic core excitation best reproduces the experimental results.

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.

Efficient transfer in a double magneto-optical trap system

We demonstrate the transfer of potassium atoms from a vapor-cell type magneto-optical trap (MOT) to a second MOT up to 75 cm away with the use of a spatially narrow push laser that generates a 40-m/s atomic beam. By adding two-dimensional MOT’s (atomic funnels) along the transfer path to generate transverse cooling and compression of the beam, we can consistently transfer 78±10% of the atoms.

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.

Tensor interaction constraints from β-decay recoil spin asymmetry of trapped atoms

We have measured the angular distribution of recoiling daughter nuclei emitted from the Gamow-Teller {beta} decay of spin-polarized {sup 80}Rb. The asymmetry of this distribution vanishes to lowest order in the standard model (SM) in pure Gamow-Teller decays, producing an observable very sensitive to new interactions. We measure the non-SM contribution to the asymmetry to be A{sub T}=0.015{+-}0.029 (stat) {+-}0.019 (syst), consistent with the SM prediction. We constrain higher-order SM corrections using the measured momentum dependence of the asymmetry, and their remaining uncertainty dominates the systematic error. Future progress in determining the weak magnetism term theoretically or experimentally would reduce the final errors. We describe the resulting constraints on fundamental four-Fermi tensor interactions.

Quadrupole moments of neutron-deficient 20,21Na

Abstract The electric-quadrupole coupling constant of the ground states of the proton drip line nucleus 20Na ( I π = 2 + , T 1 / 2 = 447.9 ms ) and the neutron-deficient nucleus 21Na ( I π = 3 / 2 + , T 1 / 2 = 22.49 s ) in a hexagonal ZnO single crystal were precisely measured to be | e q Q / h | = 690 ± 12 kHz and 939 ± 14 kHz , respectively, using the multi-frequency β-ray detecting nuclear magnetic resonance technique under presence of an electric-quadrupole interaction. An electric-quadrupole coupling constant of 27Na in the ZnO crystal was also measured to be | e q Q / h | = 48.4 ± 3.8 kHz . The electric-quadrupole moments were extracted as | Q ( Na 20 ) | = 10.3 ± 0.8 e fm 2 and | Q ( Na 21 ) | = 14.0 ± 1.1 e fm 2 , using the electric-coupling constant of 27Na and the known quadrupole moment of this nucleus as references. The present results are well explained by shell-model calculations in the full sd-shell model space.

Coherent population trapping states with cold atoms in a magnetic field

Using potassium atoms cooled with a MOT, ground-state hyperfine coherent population trapped (CPT) states were prepared in a magnetic (B) field, and the behavior of CPT states was experimentally studied. We carefully measured the preparation of the CPT state as a function of time and the CPT signal as a function of laser power. The experimental CPT signal linewidth was approximately proportional to the square root of laser intensity in the range of parameters studied, and limits of this relation were explored theoretically.

Neutral atom traps of radioactives

Abstract Neutral atoms trapped with modern laser cooling techniques offer the promise of improving several broad classes of experiments with radioactive isotopes. In nuclear β decay, neutrino spectroscopy from beta-recoil coincidences, along with highly polarized samples, enable experiments to search for non-Standard Model interactions, test whether parity symmetry is maximally violated, and search for new sources of time reversal violation. Ongoing efforts at TRIUMF, Los Alamos and Berkeley will be highlighted. The traps also offer bright sources for Doppler-free spectroscopy, particularly in high- Z atoms where precision measurements could measure the strength of weak neutral nucleon–nucleon and electron–nucleon interactions. Physics with francium atoms has been vigorously pursued at Stony Brook. Several facilities plan work with radioactive atom traps; concrete plans and efforts at KVI Groningen and Legnaro will be among those summarized. Contributions to the multidisciplinary field of trace analysis will be left up to other presenters.

Measuring isospin mixing in 36Ar using a polarized, neutral atom trap

Abstract Magneto-optical traps provide a cold, compact cloud of radioactive atoms and therefore are an ideal source for use in precision nuclear β decay studies. Optical pumping techniques can add a new dimension to such experiments by efficiently polarizing these samples to ≳99%. T riumf ’s experiment E925 is utilizing these techniques to prepare to measure the isospin mixing between the first two Iπ=2+ excited states of 36Ar with the lowest 2+, T=1 isobaric analog state. The spin-polarized 36K β+ decay observables will be measured using T riumf ’s neutral atom trap at I sac , T riumf ’s isotope separator and accelerator facility. The main purpose is to test isospin mixing models in the s,d-shell needed for determination of the superallowed Fermi strength in 0+xa0→xa00+ decays.

Alignment Correlation Terms In β‐Ray Angular Distributions From Spin Aligned 20F And 20Na

The β‐ray angular distribution from the purely aligned nuclei, 20F(Iπ = 2+, T1/2 = 11.00s) and 20Na(Iπ = 2+, T1/2 = 447.9ms), have been measured to test the G symmetry in the weak nuclear currents. The alignment terms α∓ of mirror pair in the mass number A = 20 system have been obtained as a function of β‐ray energy with the preliminary analysis.