introduction-weak-interaction-volume-one

observed were very similar to those produced by 'soft' Laue-Bragg x-rays (13) ,
which was satisfactory, since the electrons' wavelength as predicted by de Broglie' s
relation was very similar to that of these x-rays .
Thomson performed a similar experiment of a more spectacular natur e
using the Debye-Scherrer method2 in x-ray diffraction work . He scattered an
undirectional monochromatic beam of cathode rays with a very thin film containin g
a large number of randomly orientated crystals of white tin . Experiments with
x-rays had shown that the diffracted beam should emerge from the group of
crystals along the surfaces of concentric cones centred about the inciden t
direction . In Thomson's experiment (14) a photographic plate was placed 32 .5 cm
from the group of crystals at a normal to the beam . The image on this plat e
was found to consist of a series of concentric circles similar to those obtaine d
with x-rays . In order to prove that these were caused by the electrons themselve s
and not by secondary electromagnetic radiation, a magnetic field was applied to
the diffracted beam, causing the image to move . Panto (15) developed Thomson' s
technique by using metallic oxides deposited on a thin metal wire instead o f
delicate crystalline films . In 1920 Rupp and Worsnop (16) showed that electron s
were also diffracted by ruled gratings .
Johnson investigated the wave-like nature of hydrogen (17) by reflectin g
the gas from crystal surfaces . His detector was a plate smoked with molybdenu m
trioxide, which becomes blackened when it reacts with hydrogen . Stern, Knauer,
and Eotermann found that the wavelength of molecules in hydrogen were in exac t
agreement with de Broglie's relation (18) . Ellett, Olson and Zahl (19) then
showed that mercury, cadmium and arsenic ion beams could be diffracted b y
crystals, using rock salt as a detector . Some years later Zinn (20) demonstrate d
that neutrons also displayed wave characteristics . Neutrons from a chain-reacting
pile were slowed down by graphite blocks and collimated by a series of cadmiu m
slits . They were reflected from the face of a calcite crystal and detected b y
means of a boron trifluoride counter .