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A radioactive beam of 20Na is stopped in a gas cell filled with Ne gas. The stopped particles are polarized by optical pumping. The degree of polarization that can be achieved is studied. A maximum polarization of 50% was found. The dynamic processes in the cell are described with a phenomenological model.Comment: 16 pages, 6 figure

Background: Lorentz invariance is key in our understanding of nature, yet relatively few experiments have tested Lorentz invariance in weak interactions.Purpose: Obtaining limits on Lorentz-invariance violation in weak interactions, in particular rotational invariance in β-decay. Method:We search for a dependence of the lifetime of 20 Na nuclei on the nuclear spin direction.Such directional dependence would be evidence for Lorentz-invariance violation in weak interactions. A difference in lifetime between nuclei that are polarized in the east and west direction is searched for. This difference is maximally sensitive to the rotation of the Earth, while the sidereal dependence is free from most systematic errors.Results: The experiment sets a limit of 2 × 10 −4 at 90 % C.L. on the amplitude of the sidereal variation of the relative lifetime differences, an improvement by a factor 15 compared to an earlier result.Conclusions: No significant violation of Lorentz invariance is found. The result sets limits on parameters of theories describing Lorentz-invariance violation.

A sensor has been developed for low frequency and DC electric fields E. The device is capable of measuring fields with E = 4 (1) V/cm resolution. It is based on a Y-cut Z-propagation lithium niobate electro-optic crystal. For a particular commercially available bare crystal, we achieved an in air time constant c (air) = 6.4(1.8) h for the decay of the electro-optic signal. This enables field monitoring for several hours. As an application, we demonstrated that a constant electric field E ext = 640 V/cm applied via external electrodes to a particular spherical glass container holding an Xe/He gas mixture decays inside this cell with a time constant glass E = 2.5(5) h. This is sufficient for the needs of experiments searching for a permanent electric dipole moment in 129 Xe. An integrated electric field sensor has been constructed which is coupled to a light source and light detectors via optical fibers. The sensor head does not contain any electrically conducting material.