[en] A major theme in Eugene Commins' career has been the use of atomic beam machines on radioactive isotopes, predominantly to study the Weak Interaction

No abstract available

[en] We have limited a CPT-violating correlation in annihilations of polarized ortho-positronium. We searched for an asymmetry in the triple correlation s→·(k→₁xk→₂), where k→₁ and k→₂ are the two largest photon momenta, and s→ is the spin of the positronium. Using the Gammasphere array of Compton-suppressed high-purity germanium detectors, we detected 2.65x10⁷ events of ortho-Ps annihilation. The amplitude of a CPT-violating asymmetry in the data set is found to be 0.0026±0.0031, a factor of 6 smaller than previous experiments

[en] We report a new measurement of parity nonconserving (PNC) optical rotation near the 1.28 μm, 6P_1/2→6P_3/2 magnetic dipole transition in thallium. We find the ratio of the PNC E1 amplitude to the M1 amplitude to be R=(-14.68±0.17)x10^-8, which within the present uncertainty of atomic theory yields the thallium weak charge Q_w(²⁰⁵Tl)=-114.2±3.8 and the electroweak parameter S=-2.2±3.0. Separate measurements on the F=1 and F=0 ground-state hyperfine components of the transition yield R₁-R₀=(0.15±0.20)x10^-8, which limits the size of nuclear spin-dependent PNC in Tl

[en] The beta-neutrino correlation coefficient, a_βν, in Na²¹ is inferred from detecting the β⁺ and low-energy recoil daughter nucleus. Na²¹ is produced at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory and 800 000 atoms are maintained in a magneto-optical trap. From the measured time of flight of recoil ions in the presence of a drift electric field, we find a_βν=0.5243±0.0091. There may be a dependence on the trapped atom population. This and other systematic uncertainties are discussed

[en] We have measured the ground-state hyperfine splitting between the 3S_1/2 F=2,thinspm=0 and 3S_1/2 F=1,thinspm=0 levels of ²¹Na. The measurement was performed with microwave spectroscopy on 40000 radioactive ²¹Na atoms (t_1/2=22 sec) collected in a magneto-optical trap on-line at the 88-in cyclotron at LBNL. The transition was excited with microwaves directed at the atoms and detected with resonant probe fluorescence light. The splitting ν_HFS in a zero magnetic field was determined to be 1906471870±200 Hz. copyright 1999 The American Physical Society

[en] Positronium (Ps) decay to four- and five-photon final states has been measured. From a sample of 3.73x10⁹ detected events of Ps annihilation, the QED-allowed branching ratios of para-Ps to four photons R₄=1.14(33)(21)x10^-6 (stat., sys., 68% C.L.), and ortho-Ps to five photons R₅=1.67(99)(37)x10^-6 (68% C.L.) were measured. No charge-conjugation symmetry violating events were observed, establishing a branching ratio limit for (o-Ps→4γ) of R₄^Ce<3.7x10^-6 (90% C.L.) and a new limit for (p-Ps→5γ) of R₅^Ce<2.7x10^-7 (90% C.L.). The experiment was performed using the Gammasphere array of Compton-suppressed high-purity germanium detectors. Gammasphere's segmentation, high efficiency, and excellent energy resolution allowed event discrimination sufficient to observe the rare decay modes in the presence of substantial backgrounds

[en] We have measured the β-γ directional correlation coefficient A₂₂ in the decay of ²²Na to the 2⁺ 1275 keV excited state of ²²Ne. We find A₂₂=(5.3±2.5)x10^-4. This measurement has higher precision but disagrees with most previous experiments. The value for A₂₂, combined with other experimental inputs, gives recoil-order form factors in disagreement with theoretical estimates. This experiment demonstrates the capabilities of Gammasphere as an instrument for precise β-γ correlation measurements. copyright 1999 The American Physical Society

[en] By confining up to 500,000 radioactive ²¹Na atoms in a magneto-optic trap, we have studied the beta-neutrino correlation. The ²¹Na is produced on-line at the Lawrence Berkeley National Laboratory 88^'' Cyclotron and trapped using common laser cooling techniques. We detect the low-energy recoil ²¹Ne daughter nucleus in coincidence with the decay positron. Using the recoil's time-of-flight, we determine the initial momentum of the recoil nucleus and infer the β-ν correlation. Our current data set has a statistical uncertainty to determine the correlation parameter a to better than 2%, and we are studying potential systematic errors at the few percent level. Other beta decay correlations can be studied using magneto-optically trapped radioactive atoms. Precise measurements of correlation parameters can provide limits on non-Standard Model scalar and tensor interactions, or anomalous induced form factors

[en] The properties of a neutral atom trap are nearly ideal for precise measurements of nuclear β-decay correlation coefficients. Following a radioactive decay, all particles emerge from the trap volume unperturbed and are available for study. However, for measurements online at existing accelerators, sufficient statistics will be difficult to acquire if precision significantly better than 0.01 in the correlation coefficients is desired. We have investigated the feasibility of detecting shake-off electrons in coincidence with the recoiling ions to decrease the statistical uncertainty of some measurements by nearly an order of magnitude