6.
The second mass spectrograph
Hydrogen
was the exception to the whole number rule, as it has
a mass of 1.008 rather than 1. Aston knew this wasn't
an error in his measurements and wanted to find out
why hydrogen was different. In 1921 he began to build
an improved mass spectrograph.
The
second mass spectrograph used curved plates to produce
its electric field, so that deflected particles would
always be midway between the plates. Aston built the
batteries for these plates himself, and during an experiment
the voltage would be steady to one part in a hundred
thousand. He also created a large, heavy magnet, capable
of producing a powerful magnetic field of 1.6 Tesla,
which is about 30,000 times stronger than the earth's
magnetic field.
When
Aston had investigated the element mercury with his
original mass spectrograph it only produced a blur on
the photographic film. Using his new mass spectrograph
he could separate six isotopes with masses from 198
to 204.
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