  Cesium vapor sources.
This can contains a batch of small tubes full of cesium, permanently closed at one end and sealed at the other end with a small plug of indium (see next sample for a close-up of one of them). Their purpose and design is quite interesting.
Various experiments require a source of small amounts of cesium vapor introduced into an otherwise completely evacuated chamber. Cesium is highly reactive: Exposed to air it oxidizes within seconds, so it must be kept in tightly sealed containers. The tricky part is designing a package that can be opened by remote control inside the vacuum chamber, without introducing any contamination.
These cesium sources solve the problem by using a plug of indium, which has a fairly low melting point, to plug one end of the tube. The tube has wire strips leading off both ends of it: When an electric current is applied to these leads the indium melts, exposing the cesium inside. Why indium rather than any number of other substances with low melting points, like wax for example? Two reasons: First, it's completely air-tight, allowing no diffusion of air or moisture, and completely stable in air. And second because nearly all other substances that have a low melting point also have a low boiling point, and/or are fairly volatile at normal temperatures. Wax, plastic, etc, would hopelessly contaminate the vacuum.
These operating instructions and brochure provide more details.
Source: Ethan Currens
Contributor: Theodore Gray
Acquired: 2 December, 2007
Text Updated: 23 December, 2007
Price: Donated
Size: 2.5"
Purity: >99.999%
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