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# Rutherford's Alpha Particle Scattering Experiment:The discovery of the Nucleus...

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Introduction

Rutherford’s Alpha Particle Scattering Experiment:

The discovery of the Nucleus…

Rutherford was the world leader in alpha-particle physics. In 1906, at McGill, he had been the first to detect slight deflections of alphas on passage through matter. In 1907, he became a professor at the University of Manchester, where he worked with Hans Geiger. This was just a year after Rutherford's old boss, J. J. Thomson, had written a paper on his plum pudding atomic model suggesting that the number of electrons in an atom was about the same as the atomic number. (Not long before, people had speculated that atoms might contain thousands of electrons. They were assuming that the electrons contributed a good fraction of the atom's mass.)

Rutherford's alpha scattering

Middle

Most of the particles went straight through the foil without any deflection – however some of the particles (about 1 in 8000) were deflected by a degree of more than 90 degrees.

This meant that the idea of the “Plum pudding” model (suggested by J.J. Thompson in 1906) was in dispute – a model which Rutherford himself had been a believer in.

Rutherford pondered this problem for some months. He eventually decided there was simply no way it could generate the strength of electric field necessary to deflect the fast moving alphas.

The electric field from a sphere of charge reaches its maximum on the surface. Therefore, for a given charge, assumed spherically distributed, the only way to get a stronger field is to compress it into a smaller sphere.

Conclusion

If an alpha goes through 400 layers of atoms, and in each layer it has a chance of one in ten thousand of getting close enough to the nucleus for a one-degree scatter, this is unlikely to happen twice. It follows that almost certainly only one scattering takes place. It then follows that all ninety or more degrees of scattering must be a single event, so the nucleus must be even smaller than one hundredth the radius of the atom - it must be less than 10-13 meters, as stated above.

This student written piece of work is one of many that can be found in our GCSE Radioactivity section.

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## Here's what a star student thought of this essay

4 star(s)

### Response to the question

Response to the question is done well and outlines the experiment and explains how the different theorys came about from the way the experiment went. To improve the candidate should have included more information on the plum pudding model and ...

### Response to the question

Response to the question is done well and outlines the experiment and explains how the different theorys came about from the way the experiment went. To improve the candidate should have included more information on the plum pudding model and perhaps a diagram so they could explain better how the theory behind that was disproved.

### Level of analysis

No clear introduction is used which would be good to introduce the topic and the concepts of the experiment. The candidate goes into the history behind the experiment well outlining other theories of the time, and how the setup of the experiment worked and the conclusions that could be drawn from it. The sections should be split up a little more clearly so we can follow the experiment a bit better, such as with spaced lining between paragraphs or sub-headings. The diagram included also helps define the experiment well.

### Quality of writing

Good grammar, punctuation and spelling throughout. Sources are not stated which should be done so that the right essays can be given credit, as if not it is plagiarism. The candidate should have used even a base referencing manner.

Reviewed by skatealexia 31/07/2012

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