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Geiger-Marsden experiment 2026-10-18
The Geiger-Marsden experiment probes the interior of a chemical atom by counting alpha particles deflected by metal foils. The surprising observation was a small population returning towards the incident side. Hans Geiger and Ernest Marsden performed the experiments under Ernest Rutherford's direction; Ernest Rutherford developed the Rutherford model in 1911. Observation and interpretation were distinct contributions.[ref]
Marsden, Ernest by Ross Galbreath. Dictionary of New Zealand Biography; Biography, paragraphs on the 1909 undergraduate experiment and subsequent interpretation
In 1909, a radon source and its radioactive decay products in a conical glass tube supplied alpha particles through a mica window towards a reflector. Lead shielded a fixed zinc sulfide screen from direct hits; an optical microscope resolved individual particle scintillations. Reflectors occupied the same position. Reflector-out counts tested air scattering; stacked gold foils and bare glass tested thickness and support contributions.[ref]
On a Diffuse Reflection of the Alpha-Particles by Hans Geiger and Ernest Marsden. On a Diffuse Reflection of the α-Particles, printed pp. 495–498, Fig. 1 and experiments I–II
Nearby source geometry blurred incidence angles. Extrapolating platinum counts uniformly over a hemisphere was an assumption, not a universal reflection probability.[ref]
On a Diffuse Reflection of the Alpha-Particles by Hans Geiger and Ernest Marsden. Printed pp. 497, 499–500, angular limitation and experiment III