3—8.
DIFFRACTION OF FAST ELECTRONS ,
57
an extremely thin foil to a photographic plate. With foils of gold,
aluminum, colloidion or platinum he obtained diffraction patterns
on the plate which were similar to those produced by X—rays in the
Debye—Sherrer, powdered crystal method. The arrangement of
his apparatus is shown in gure 3—3. A potential of from 10,000
to 60,000 volts
between electrodes A’ and B in such a
.E
'
D
C
B
A
.
—
"
/|
FIG. 3—3.
The G. P. Thomson experiment.
.
manner that B is the anode or-positive terminal. Electrons are
then accelerated
pass through its small hole and are
collimated by the capillary hole in the metal block'C. The thin '
foil D then diffracts the electrons to the photographic platebr
luminescent screen at E.
'
'
—
There would have been ageneral ’illumination of the screen or '
a blackening of the plateif the foil_ had scattered the electrons in
all directions.
In’stead, severalrings of light appear whenever the
foil is‘ïnade up of minute crystals oriented in a random fashion, as
in gold.
of circles
the screen for such foil
materials as aluminum,
ÇOpper,
in whichthe Small
tals have
at the
-
corners of
triangles, are_ observed when thin micalms
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