4.
Aston's results
The
beam of charged particles is focussed with magnetic
and electric fields. The position of the focussed spot
depends only on the mass of the ions, not their velocity
(or kinetic energy). These spots all lie on a straight
line, and Aston put photographic paper along this line
to record the masses.
All
the ions of the same mass hit the same point on the
photographic strip, producing a dark spot. The position
of these spots told Aston the masses of all the different
ions within a beam.
Aston's
mass spectra for neon and chlorine, results from the
first mass spectrograph in 1920
Some
ions, such as chlorine, produced more than one spot.
These were due to isotopes of the element, with identical
chemical properties but different masses.
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