Cesium Gettering by Graphite.
Abstract
In cesium (Cs) beam tube (CBT) clocks, only a small fraction of the Cs atoms effusing from the oven travel through the microwave cavity. The remaining fraction is gettered by pieces of graphite and graphite-coated surfaces found at various locations inside the clock. Should the graphite getters cease absorbing Cs, the increasing Cs background would rapidly obscure the true signal, resulting in rapid reduction in the signal-to-noise ratio. Getter failure is then one of the primary life-limiting processes in the Cs beam tubes. We are investigating the gettering properties of graphite in order to be able to characterize the type and the amount of graphite needed to efficiently getter Cs. From a microscopic angle we study the sticking coefficient of Cs on graphite as a function of time; under conditions similar to that encountered in a beam tube. A significant experimental observation is the rapid decrease in the sticking coefficient from an initial value of 1.0 to 0.25-0.30 after several days of exposure of Cs. We are also investigating the bulk gettering properties using various analytical techniques. Of particular interest is the amximum amount of Cs a given graphite can absorb. Preliminary measurements show that graphite can absorb approximately 20% by weight. Keywords: Space-borne clocks; Atomic clocks. (AW)
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 19, 1988
- Accession Number
- ADA195950
Entities
People
- Charles M. Kahla
- Natarajan D. Bhaskar
- Robert A. Cook
- Robert P. Frueholz
Organizations
- The Aerospace Corporation