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This exhibit is an early (possible 1910-20) cold cathode X-Ray tube. There are no markings on the glass to give information.
The anode is angled at 45 degrees to send the X-Rays out of the envelope. The concave cathode is a spherical surface that directs the high energy electrons to a single spot on the anode. This is typically less than 1 mm in diameter. This focused beam generates close to a point source of X-Rays and produces the best definition in the resulting radiographs.
The concave cathode on the left and the target (anode) on the right. The electrode supports are sheathed in glass for most of their length. The foil on the anode could be tungsten but research shows that platinum foil is the most likely. The pin-point bombardment has left a hole at the focus of the beam.
The right hand lead is missing. Note the long sealed-off evacuation tube.
The rear of the angled anode with the glass tube behind. In the stem can be seen three points of glass where the inner tube is supported by the outer stem.
A close-up of the foil on the anode.
Here we have an X-Ray of the tube. The concave cathode is clearly defined. In use, X-Rays would emerge directly down towards the bottom of the image.
The balloon envelope is 82 mm in diameter, and including the base pins is 330 mm tall.
Reference: Observation.

 

Updated July 21, 2014.
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