3B Scientific Electron Diffraction Tube D - Manual

3B SCIENTIFIC® PHYSICS
1
Electron Diffraction Tube D 1013885
Instruction sheet
07/13 ALF
1 5 4 7 8 9 11 6 2
R
3 10
1 4-mm sockets for connecting
heater supply
2 2-mm socket for connecting
cathode
3 Internal resistor
4 Filament
5 Cathode
6 Anode
7 4-mm plug for connecting
anode
8 Focussing electrode
9 Polycrystalline graphite
grating
10 Boss
11 Fluorescent screen
1. Safety instructions
Hot cathode tubes are thin-walled, highly
evacuated glass tubes. Treat them carefully as
there is a risk of implosion.
• Do not subject the tube to mechanical
stresses.
• Do not subject the connection leads to any
tension.
• The tube may only be used with tube holder
D (1008507).
If voltage or current is too high or the cathode is
at the wrong temperature, it can lead to the tube
becoming destroyed.
• Do not exceed the stated operating parame-
ters.
• Only change circuit with power supply
equipment switched off.
• Only exchange tubes with power supply
equipment switched off.
When the tube is in operation, the stock of the
tube may get hot.
• If necessary, allow the tube to cool before
dismantling.
The compliance with the EC directive on elec-
tromagnetic compatibility is only guaranteed
when using the recommended power supplies.
2. Description
The electron diffraction tube illustrates the wave
nature of electrons by allowing observation of
interference caused by a beam of electrons
passing through a polycrystalline graphite target
on a fluorescent screen (Debye-Scherrer diffrac-
tion). The wavelength of the electrons can be
calculated for various anode voltages from the
radius of the diffracted rings and the distance
between the crystal layers in the graphite. The
tube also confirms the de Broglie hypothesis.
The electron diffraction tube is a highly evacu-
ated tube with an electron gun consisting of a
pure tungsten heater filament and a cylindrical
anode all contained in a clear glass bulb. The
electrons emitted by the heated cathode are
constrained to a narrow beam by an aperture
and are then focussed by means of an electron-
optical system. The resulting tight, monochro-
matic beam then passes through a micro-mesh
nickel grating situated at the aperture of the gun.
Onto this grid, a thin layer of polycrystalline
graphitised carbon has been deposited by va-
porisation. This layer affects the electrons in the
beam much like a diffraction grating. The result
of this diffraction is seen in the form of an image
comprising two concentric rings that become
visible on the fluorescent screen. A spot result-
ing from the undeflected electron beam contin-
ues to be visible at the centre of the rings.