4.
Geiger and Marsden
In
1907 Rutherford left McGill University in Canada and
moved to the University of Manchester, where he began
work with Hans Geiger.
They
continued to investigate the scattering of alpha particles.
The particles came from a small sample of radon-222,
a radioactive gas produced when the element radium decays.
These particles were directed through a vacuum and on
to a foil which caused the scattering. The positions
of the scattered particles were seen as scintillations,
or small flashes of light, which were detected using
a microscope that could be rotated around the foil.
The
experiment was quite difficult. Observations could only
be taken in a dark laboratory, and it took about half
an hour for the observer's eyes to adjust to seeing
the traces. Each observer could only count accurately
for about a minute before they needed to swap over.
Geiger later developed the 'Geiger counter', which could
count these pulses automatically in normal light. It
made similar experiments much easier!
The
alpha particle scattering was usually only one or two
degrees. In 1909 Geiger needed an experiment for a research
student, Ernest Marsden. Rutherford suggested that Marsden
look for alpha-particle scattering at large angles.
He didn't think it very likely.
Next
Page
|
