In Rutherford’s experiment he had shot a few alpha particles at a plate of gold (only a few atoms thick) or to test whether atoms are solid, only a few particles bounced off the nuclei of the gold atoms (which are clearly solid ) but why didn’t they bounce off the nuclei of the oxygen atoms in front of and behind the picture?
Answer
Hello,
Good question! The people who carried out this experiment (Hans Geiger and Ernest Marsden in 1909) had also thought of this and decided to vacuum to be carried out. That is, there was no (or at least extremely little) air between the source of the alpha particles, the gold plate and the detector. If that air was there, the alpha particles would indeed be scattered by the atoms in the air (oxygen, but also nitrogen and other elements).
The fact that they used a gold foil is because they just wanted to get a very thin layer of ‘solid’ atoms (as you said, a few atoms thick). Then the diffraction effect on the alpha particles is easier to understand and interpret in the context in which the experiment was performed (namely to see how many alpha particles just bend and how many bounce back). The deflection effect that a layer of air (‘loose’ atoms, a gas) would exert much thicker than the gold foil (eg decimeters instead of a few atoms) would be much more complicated and less obvious.
Hopefully this solves your question about this historical experiment…
Pieter
Answered by
dr. Pieter Gurdebeke
Earth & Nature
http://www.ugent.be
.