9.
Mass Spectrography
Many
scientists were sceptical that the two forms of neon
really existed, as natural neon has a mass of 20.20
on this scale. Francis Aston, a researcher working in
the Cavendish, set out to separate the two forms. His
work was interrupted by the war, but he went on to prove
that neon-20 existed, and was nine times more common
than the more massive neon-22.
In
1919 Aston developed the first Mass Spectrograph to
show different isotopes on strips of photographic film.
He used the Mass Spectrograph to prove the existence
of many dozens of different isotopes for atoms as light
as lithium-7 and as massive as mercury-204. We now know
of several hundreds of isotopes, and high energy physicists
can produce unstable isotopes that break themselves
apart in fractions of a second.
J.J.
Thomson's resigned from the Cavendish in 1918 to become
Master of Trinity College, Cambridge. His discovery
of electrons and natural isotopes were both immensely
important steps towards understanding the nature of
atoms.
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