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RUTHERFORD'S EXPERIMENT
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Now you can present a more advanced exposition of the experiment. Why did Rutherford ask for the experiment to be done? Experiments on the absorption of b particles had also shown that sometimes the b particles were ‘back scattered’. Rutherford suggested that Geiger and Marsden should try looking for similar behaviour with a particles. Rutherford thought it was highly unlikely; because a particles are relatively massive compared with electrons, it was predicted that the as would simply suffer a series of small deflections. They were expected to travel more or less straight through the absorber.However, Rutherford’s main concern was to give Geiger & Marsden something to do that would occupy them and get them some useful hands-on experience, rather than expecting them to get any very exciting results.
Show a diagram of the apparatus. The absorber was a thin gold metal foil. Why use gold? (Thin gold foils, typically 250 atoms thick, were easy to make and readily available.) Why thin? (as are easily absorbed.)
As expected, virtually all the as went straight through, but about 1:8000 were turned through large angles (reflected or back-scattered). An 8 kBq a source gives one large-angle scattering per second.
The chance of a series of small deflections resulting in a reflection is far too small to account for what was observed.
Rutherford was astonished at the result: “It was quite the most incredible event that ever happened to me in my life. It was as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you!” (You may find other versions of this quote, because Rutherford described his experience on many different occasions.)
Show a diagram of the apparatus. The absorber was a thin gold metal foil. Why use gold? (Thin gold foils, typically 250 atoms thick, were easy to make and readily available.) Why thin? (as are easily absorbed.)
As expected, virtually all the as went straight through, but about 1:8000 were turned through large angles (reflected or back-scattered). An 8 kBq a source gives one large-angle scattering per second.
The chance of a series of small deflections resulting in a reflection is far too small to account for what was observed.
Rutherford was astonished at the result: “It was quite the most incredible event that ever happened to me in my life. It was as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you!” (You may find other versions of this quote, because Rutherford described his experience on many different occasions.)
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