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An anode ray (also positive ray or canal ray) is a beam of positive ions that is created by certain types of gas-discharge tubes. They were first observed in Crookes tubes during experiments by the German scientist Eugen Goldstein, in 1886. [1] Later work on anode rays by Wilhelm Wien and J. J. Thomson led to the development of mass spectrometry.
Figure 1. Ives–Stilwell experiment (1938). "Canal rays" (a mixture of mostly H 2 + and H 3 + ions) were accelerated through perforated plates charged from 6,788 to 18,350 volts. The beam and its reflected image were simultaneously observed with the aid of a concave mirror offset 7° from the beam. [1] Figure 2.
The electrons in these tubes moved in a slow diffusion process, never gaining much speed, so these tubes didn't produce cathode rays. Instead, they produced a colorful glow discharge (as in a modern neon light ), caused when the electrons struck gas atoms, exciting their orbital electrons to higher energy levels.
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.
Canal rays, also called anode rays, were observed by Eugen Goldstein, in 1886. Goldstein used a gas discharge tube which had a perforated cathode. The rays are produced in the holes (canals) in the cathode and travels in a direction opposite to the "cathode rays," which are streams of electrons.
Image brightness is also controlled by the current of the electron beam. [235] Higher anode voltages and electron beam currents also mean higher amounts of x-rays and heat generation since the electrons have a higher speed and energy. [155] Leaded glass and special barium-strontium glass are used to block most x-ray emissions.
The kinetic energy of the electrons is converted into heat and radiation (X-ray photons) due to these interactions. Most of the energy carried by the electrons is converted to heat (99%). Only 1% is converted into radiation or X-rays. In order to assist with the dissipation of such high heat, a larger focal spot or focal track is needed.
If the electron and positron have negligible momentum, a positronium atom can form before annihilation results in two or three gamma ray photons totalling 1.022 MeV. [ 119 ] [ 120 ] On the other hand, a high-energy photon can transform into an electron and a positron by a process called pair production , but only in the presence of a nearby ...