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Crookes X-ray tube from around 1910 Another Crookes x-ray tube. The device attached to the neck of the tube (right) is an "osmotic softener". When the voltage applied to a Crookes tube is high enough, around 5,000 volts or greater, [16] it can accelerate the electrons to a high enough velocity to create X-rays when they hit the anode or the glass wall of the tube.
A diagram showing a Crookes tube connected to a high voltage supply. The Maltese cross has no external electrical connection. Cathode rays are so named because they are emitted by the negative electrode, or cathode, in a vacuum tube. To release electrons into the tube, they first must be detached from the atoms of the cathode.
The first-generation cold cathode or Crookes X-ray tubes were used until the 1920s. These tubes work by ionisation of residual gas within the tube. The positive ions bombard the cathode of the tube to release electrons, which are accelerated toward the anode and produce X-rays when they strike it. [2]
Any electron beam would collide with some residual gas atoms within the Crookes tube, thereby ionizing them and producing electrons and ions in the tube (space charge); in previous experiments this space charge electrically screened the externally applied electric field. However, in Thomson's Crookes tube the density of residual atoms was so ...
A CRT in a TV is commonly called a picture tube. CRTs have also been used as memory devices, in which case the screen is not intended to be visible to an observer. The term cathode ray was used to describe electron beams when they were first discovered, before it was understood that what was emitted from the cathode was a beam of electrons.
Crookes tubes created free electrons by ionization of the residual air in the tube by a high DC voltage of anywhere between a few kilovolts and 100 kV. This voltage accelerated the electrons coming from the cathode to a high enough velocity that they created X-rays when they struck the anode or the glass wall of the tube.
Sir William Crookes (/ k r ʊ k s /; 17 June 1832 – 4 April 1919) was an English chemist and physicist who attended the Royal College of Chemistry, [1] now part of Imperial College London, and worked on spectroscopy. He was a pioneer of vacuum tubes, inventing the Crookes tube, which was made in 1875. This was a foundational discovery that ...
Electrons (cathode rays) released from the cathode plate are accelerated down the tube to the left toward the anode, and strike the end wall, which fluoresces. The Maltese cross shaped anode blocks the electrons, casting a shadow on the glowing end wall, demonstrating that the cathode rays travel in straight lines.