A gas cell for stopping, storing and polarizing radioactive particles

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

Optimal Road Problem

We consider the problem of paving a path through a mountainous terrain. An optimal path is one that balances the requirement of a route to be both as short as possible and as flat as possible. A new form of Riemannian metric, $tilde{S}$, is proposed to weigh the length of a path, such as to penalize vertical transport more than horizontal, reflecting the cost and difficulty of traffic to change altitude. A geodesic $boldsymbol{gamma}$ of this metric is then a candidate for an optimal path. A number of numerical solution techniques to calculate geodesics are explored, most notably a functional iteration using Christoffel's symbols of the geodesic equation, and geodesic evolution to minimize geodesic curvature. Finally, statistical analyses are done on the resulting geodesics of this weighted metric through a simulated hilly landscape. The metric performs well in balancing horizontal versus vertical travel economically, however it does not prevent a high maximum steepness over the course of the path.

Test of Lorentz invariance in beta decay of polarized Na-20

Background: Lorentz invariance is key in our understanding of nature, yet relatively few experiments have tested Lorentz invariance in weak interactions.Purpose: Our goal is to obtain limits on Lorentz-invariance violation in weak interactions, in particular rotational invariance in beta decay.Method: We search for a dependence of the lifetime of Na-20 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 x 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