Shadow cross tube

from Wikipedia, the free encyclopedia

The shadow cross tube is a form of the electron tube . It was invented by the physicist Sir William Crookes in 1879 and is therefore also called the Crookes tube .

It is used to study cathode rays , another name for electron beams.

A shadow cross tube, on the left the radiation-emitting cathode, below the anode and on the right the shadow-throwing cross and the fluorescent screen

construction

The traditional Maltese cross tube consists of an aluminum - cathode , an anode , and a shade in the form of a paw cross or a Maltese cross , often of a fluorescent phosphor screen on which a high upon application of electric voltage , hit by the electric field accelerated electrons generate light based on fluorescence and thus show the shadow of the cross.

All the components just mentioned are located in a partially evacuated glass tube, which has a slightly conical shape. Newer versions are often completely evacuated, have a hot cathode and a Wehnelt cylinder .

The operating voltage of this type of electron tube is around 5–12  kV , similar to that of televisions and CRT monitors .

function

The shadow cross tube was used to research gas discharge and particle beams in a vacuum.

A similar setup led to the discovery of cathode rays . Their properties can be studied on the shadow cross tube , for example their straight-line propagation , which can be deflected by magnetic fields, or the fluorescence they cause on the glass or the fluorescent screen. The straightness of the radiation can be shown by the fact that the rays are sent from the cathode to the anode, but hit the fluorescent screen by their own motion vector past this and image the shadow of the cross. The cross image on the fluorescent screen makes it clear that the source of the excitation must be the cathode.

These properties were originally ascribed to a fourth physical state , the state of radiation . The cathode ray was misinterpreted as an atomic ray.

Designs

There are also slightly modified designs, which, however, have the same functionality as the original. These forms are mostly custom-made by glass blowers. Instead of the cross, any other shape can be made from aluminum and used as an anode.

Gas-filled tubes do not require a heated cathode; they emit electrons due to ion bombardment. If you reverse the polarity, or if the cathode itself is a sheet metal with a hole, you can observe channel rays .

Web links

Commons : Shadow cross tube  - album with pictures, videos and audio files

Individual evidence

  1. Shadow cross tube at Paul's tubes
  2. Carus Sterne: Radiant Matter . In: The Gazebo . Issue 14, 1880, pp. 224–226 ( full text [ Wikisource ]).