# Rutherford's Gold Foil Experiment

Can anybody explain how Rutherford bombarded a 0.0004 cm thick gold foil? How did he put it in a photographic sheet? Wasn't the foil too thin to be held? How did he know that the atoms were deflected at various angles? Did he calculate every alpha particle's angle of deflection?

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## 1 Answer

Gold foil is quite easy to hold you just hang it from a paperclip. The only difficulty is if there is a lot of static electricity in the air which makes it stick to things. (This is the main reason for the cold damp Cambridge's supremacy in early particle physics)

Photographic film at the time wasn't sensitive and so in Marsden and Geiger's experiments they used a tiny target coated with phosphorescent crystals which emitted a spark of light when hist by a particle and viewed them through a microscope. This involved sitting in a dark cupboard for hours straining to see and count rare pinpoints of light while staring down a primitive microscope - this is why the job was given to grad students.

edit: There is a very good book, The fly in the Cathedral which describes this period, the science and the experimental techniques. High vacuum stuff is a pain the ___ even with modern quick connects and Helium leak detectors, doing it with string and sealing wax (literally) was quite a challenge.

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As the older professors say: things are easy for us youngin' grad students. I can go to dinner while I acquire data, unlike poor Marsden and Geiger. –  emarti Jan 13 '13 at 19:55
Might mention how easy it is to manufacture thin foils of gold too: just lay it on a flat, strong surface and hit it with a hammer repeatedly. Jewlers have been doing that for millenia. –  dmckee Jan 13 '13 at 19:59
Are you sure they are using paperclip? The gold foil should hang pretty straight to get scattering results. –  hwlau Jan 14 '13 at 1:55
@hwlau, don't know what they used but you don't need to deposit the gold on a substrate - you can just hold gold foil in a frame. I don't think it has to be all that flat you are only looking for a gross angle not precision crystalography –  Martin Beckett Jan 14 '13 at 2:07