Secret Scotland

If it's secret, and in Scotland…

Hunterian mystery tube

I’d forgotten about this pic taken of a tube, or valve, spotted in the scientific section of the Hunterian’s displays.

Collected along with a number of other views of this collection of objects, this one differed in that it didn’t appear to be an X-Ray source (there’s no target inside the tube).

As noted before, this area suffers from a lack of any plaques describing or identifying the objects on display.

Hunterian Mystery Tube

Hunterian Mystery Tube

In an X-Ray tube, the electrons emitted from the cathode are accelerated by high voltage and strike the target, where they release their energy, causing it to heat, and emit radiation, including X-Rays.

As can be seen from the pic, this tube is ’empty’, apart from four electrodes – assumed to be the cold cathode/emitter and initial acceleration on the left, with an anode on the right to complete the circuit.

There is no heater to boil off electrons to supply the beam, so this is a cold cathode tube that depends on the ionisation of residual gases in the tube to produce free electrons. So, it’s like a Crookes tube (cold cathode tube), but with no target for the electrons to strike and produce X-Rays.

I haven’t been able to dig up a matching example, but it could be a demonstration tube, for use in lectures and intended to show how an electron beam can be bent by a magnetic field.

Electron beams travel in a straight lines, so the beam in the tube seen above would obviously not reach the anode.

However, by applying a magnetic field, it could be made to bend, and be guided by the field so it reached the anode.

With a suitable gas in the tube, which would glow and emit visible when ionised, this tube could be used to show the beam and its path, especially if it was placed between coils, which would allow the magnitude of the magnetic field to be varied.

I’ve seen similar tubes in the past, but they had multiple electrode.

In that case, they just ionise the gas in the tube, and show (via ionised streams) how electrons flow from the cathode to multiple anodes.

I found a couple of related examples online, just described as vacuum tubes, with an interesting sketch showing how the electron flow varied dependent on the degree of vacuum drawn within the tube.

Simple vacuum tube

Simple vacuum tube

With high and low vacuum:

Vacuum Tube

Vacuum Tube

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20/09/2019 - Posted by | Civilian, photography | , , ,

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