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
The later angular test used an evacuated chamber with a radon source and scattering foil fixed in place. A diaphragm served as a collimator; a zinc sulfide screen and attached optical microscope rotated about the foil on a graduated platform. Particle scintillation counts sampled successive angles. Foil-out counts supplied background subtraction, with corrections for source radioactive decay and finite beam width. Shielding reduced interfering radiation, but screen glow limited large angles. This tested the Rutherford differential cross-section.[ref]
The Laws of Deflexion of Alpha Particles through Large Angles by Hans Geiger and Ernest Marsden. The Laws of Deflexion of α Particles through Large Angles, transcription PDF pp. 3–7, Variation of Scattering with Angle, Fig. 1 and Tables I–II
Fixed backscattering screen and later rotating angular detector
. Original schematic distinguishing the 1909 shielded reflection arrangement from the 1913 evacuated angular arrangement. Arrows indicate example particle paths, not calculated trajectories; component sizes and distances are schematic. The later screen and microscope rotate together while the source and foil remain fixed. Details.
Articles by others on the same topic
There are currently no matching articles.