Lenard Ray Tube
This is an interesting experiment to demonstrate that electrons can escape from a discharge tube and travel in air. This was first observed by Philipp Lenard using a
discharge tube and a fluorescing screen. Here I have used an old wine bottle as the vacuum tube. A small copper pipe is glued into the base of the bottle. This forms the cathode and
allows the bottle to be out gassed via a vacuum pump. The metal cap is connected to the positive of a high voltage supply and forms the anode. The cap has
a number of holes drilled into it and looks a bit like a pepper pot. So that the bottle can still be evacuated, a piece of tinfoil has been glued over the cap
covering the holes.
With the vacuum pump running 12kv is applied across the bottle. As quite a bit of light is produced from the air discharge it is difficult to notice
light being emitted from a screen at the cap. A mica windowed Geiger counter was placed near the bottle cap. Nothing is detected until the vacuum is good
enough for the glass bottle to start glowing from electron bombardment. At this point increased activity can be heard on the Geiger counter. It is very
directional and being emitted from the top of the bottle cap. Nothing is detected around the neck of the bottle. As the voltage is not higher than 12kV and
the detection is only at the cap it is unlikely to be x-radiation. It behaves like beta radiation so it would appear to be electrons that have
been able to travel through the cap and a distance into the air.
