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# Ernest Rutherford's Gold Foil Experiment

On conducting this famous experiment Rutherford observed: 1. Some of the alpha rays went through the gold foil normally. 2. Some of them were deflected by severe angles i.e. greater than $$90^\circ$$. 3. A few that is $$\frac{1}{20000}$$ bounced back with an angle of $$180^\circ$$. I can understand that the first two observations were made with the help of a zinc sulphide screen but what about the third observation. How did he observe the bouncing back of alpha rays. Please answer this query. Thanks in advance.

Note by Soham Dibyachintan
3 years, 3 months ago

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It must have been a bit tricky for Rutherford, but he simply placed the detector directly in front of the gold foil, i.e., about where the source of the alpha rays was. Maybe he was not able to measure at exactly 180 degrees back, but close enough to get the idea.

Had he been using light instead of alpha rays, this can be done with a partially silvered mirror. · 3 years, 3 months ago

Thanks a lot sir. · 3 years, 3 months ago

I'm pretty sure if, upon inspection of the zinc sulfide scintillator, you see that at angles very near $$180^o$$ there are a number incident alpha particles, you could assume that some of the alpha particles could have definitely been deflected at $$180^o$$. I see it as being comparable to showing that the limit of a multivariable function at some point in its allowable domain exists using the epsilon-delta definition of a limit. · 3 years, 3 months ago

The zinc sulphide screen was present all around, so even if he could not determine the exact angle, he could speculate that one of 20000 bounced back seeing the glow exactly behind the gold foil · 3 years, 3 months ago

Since the size of the nucleus was very small as compared to that of atom, so only very few particles striked the foil directly straight (which resulted in 180 degree bounce back).........was this your needed answer? · 3 years, 3 months ago