Rutherford scattering experiments: Difference between revisions
| Line 12: | Line 12: | ||
ISBN 0387987568, ISBN 9780387987569 |
ISBN 0387987568, ISBN 9780387987569 |
||
</ref>|Ernest Rutherford}} |
</ref>|Ernest Rutherford}} |
||
hahahaha... hi |
|||
==Conclusions== |
==Conclusions== |
||
Revision as of 18:43, 22 October 2009
The Geiger–Marsden experiment (also called the Gold foil experiment or the Rutherford experiment) was an experiment to probe the structure of the atom performed by Hans Geiger and Ernest Marsden in 1909,[1] under the direction of Ernest Rutherford at the Physical Laboratories of the University of Manchester. The unexpected results of the experiment demonstrated for the first time the existence of the atomic nucleus, leading to the downfall of the plum pudding model of the atom, and the development of the Rutherford (or planetary) model.
Experimental procedure and results
Bottom: Observed results: a small portion of the particles were deflected, indicating a small, concentrated positive charge.
A beam of alpha particles, generated by the radioactive decay of radium, was directed normally onto a sheet of very thin gold foil. The gold foil was surrounded by a circular sheet of zinc sulfide (ZnS) which was used as a detector: the ZnS sheet would light up when hit with alpha particles. Under the prevailing plum pudding model, the alpha particles should all have been deflected by, at most, a few degrees; measuring the pattern of scattered particles was expected to provide information about the distribution of charge within the atom. However they observed that a very small percentage of particles were deflected through angles much larger than 90 degrees. According to Rutherford:
It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you. On consideration, I realized that this scattering backward must be the result of a single collision, and when I made calculations I saw that it was impossible to get anything of that order of magnitude unless you took a system in which the greater part of the mass of the atom was concentrated in a minute nucleus. It was then that I had the idea of an atom with a minute massive centre, carrying a charge.[2]
— Ernest Rutherford
hahahaha... hi
Conclusions
Rutherford interpreted the experimental results in a famous 1911/1912 paper.[3] He was able to definitively reject J.J. Thomson's plum pudding model of the atom, since none of Thomson's negative "corpuscles" (i.e. electrons) contained enough charge or mass to deflect alphas strongly, nor did the diffuse positive "pudding" or cloudlike positive charge, in which the electrons were embedded in the plum pudding model. Instead, Rutherford suggested that a large amount of the atom's charge and mass is instead concentrated into a very physically-small (as compared with the size of the atom) region, giving it a very high electric field. Outside of this "central charge" (later termed the nucleus), he proposed that the atom was mostly empty space. Rutherford was unable to say from the experiment whether the nuclear charge was positive or negative, but used the following language for pictorial purposes:
- "For concreteness, consider the passage of a high speed Alpha particle through an atom having a positive central charge Ne, and surrounded by a compensating charge of N electrons."
From energetic considerations of how far alpha particles of known mass and kinetic energy would be able to penetrate toward a central charge of 100 e, Rutherford was able to calculate that the radius of his gold central charge would need to be physically smaller (how much smaller, could not be told) than 3.4 x 10−14 metres (the modern value for the actual radius is only about a fifth of this). This figure applied in a gold atom which was itself known to be much larger: 1.5 x 10−10 metres or so in radius – a very surprising finding, as it implied a strong central charge less than 1/4000th of the diameter of the atom.
Rutherford had used strictly Newtonian methods to analyze the relatively low-energy alpha-scattering of this experiment. Later, when full quantum mechanical methods were available, it was found that they gave the same scattering equation which had been derived by Rutherford by classical means.
Although Rutherford's model of the atom itself had a number of problems with with electron charge placement and motion which were only resolved following the development of quantum mechanics, the central conclusion from the Geiger–Marsden experiment, the existence of the nucleus, still holds.
miley cyrus and caroline reid like turds
See also
- Rutherford backscattering spectroscopy
- Rutherford scattering
- Atomic theory
- List of experiments
- 1909 in science
References
- ^ Geiger H. & Marsden E. (1909). "On a Diffuse Reflection of the α-Particles". Proceedings of the Royal Society, Series A. 82: 495–500. doi:10.1098/rspa.1909.0054.
- ^ David C. Cassidy, Gerald James Holton, Gerald Holton, Floyd James Rutherford, (2002) Understanding Physics Harvard Project Physics Published by Birkhäuser, p. 632 ISBN 0387987568, ISBN 9780387987569
- ^ Rutherford E. (1911). "The Scattering of α and β Particles by Matter and the Structure of the Atom". Philosophical Magazine, Series 6. 21: 669–688.