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Sunday, September 21, 2008

Fundamentals: Fast electrons

Accelerating electrons to a high speed produces differing results:
1. Accelerating electrons to a few eV (using a few Volts) causes excitation of gas and ionisation of gas molecules. For hydrogen the max voltage is 13.6 V to ionise the atom. The gas will glow with different colours as electron transit from higher to lower energy levels.

2. Accelerating electrons to a few hundred eV (hundreds of volts) causes metal target to produce Xray when electron in the inner shells transit from higher to lower energy levels. Continuous range of Xrays are also emitted due to fast electrons losing their KE upon hitting the metal target.

3. Accelerating electons to a few thousand eV(up to 10000V) produces diffraction pattern when the eletron beam is incident on a crystal . The debroy wavelength of electron is smaller than the atomic separation .