Unit 5 revision - Rutherford's Alpha Scattering Experiment

[jmorris]

What is it? What did it show?

[feedthegoat10]

What is it? What did it show?

An alpha source is placed in a vacuated chamber (so the alpha particles travel futher than they would in air) with a piece of thin metal foil and detectors placed around the chamber, the alpha source releases alpha particles towards the thin metal foil and the detectors pick up where the particle went.
It showed that most of the particles passed through the thin metal foil with only a small number being deflected by over 90 degrees. This shows that the atoms in the thin metal foil are mostly empty space. It also shows that the nucleus is positively charged and makes up most of the atoms mass.

[Joseph Wardley]

What it is:
•An alpha emitting radioactive isotope is placed into an evacuated chamber.
•A thin metal sheet is placed a distance away from the alpha source
•There are alpha detectors around the evacuated chamber.

Why do these things:
•An evacuated chamber is used so alpha partials will not interact with any air molecules, so preventing more than one independent variable in the experiment. Thus the results are more accurate.
•If air partials where to interact with the alpha particles then deflection could be due to this. Also alpha has a short range in air so the metal sheet would have to be a short distance away.
•The alpha source is concentrated so it emits a beam of alpha particle, this is to make sure that all alpha partials pass through or go near the metal plate before hitting the detectors.
•This makes sure that alpha partials have been deflected by the metal plate.
•The metal plate is thin to reduce the number of times the alpha particle is deflected by the nucleuses in the metal sheet.
•This makes it more like a single atom and so makes the results more accurate as we are trying to find out about a single nucleus.

What is observed:
•A high number of counts are exhibited by the detectors that are directly in the line of the alpha sources path. So a high number of alpha particles pass through the atom completely undeflected.
•A small number of counts are exhibited by the detectors that are less than an angle of 90 degrees to the normal path of the alpha particles. So a small number of alpha particles are deflected by angles of less than 90 degrees.
•A very small number of counts are exhibited by the detectors that are more than an angle of 90 degrees to the normal path of the alpha particles. So a very small number of alpha particles are deflected by angles of more than 90 degrees.

What can be deduced from these results:
•The nucleus is small. As most of the alpha particles pass through it
•The nucleus is massive (have most of the mass concentrated in this area). As alpha particles are not deflected when they pass though the empty space of the atom as the mass is small out of the nucleus
• The nucleus is positively charged. As alpha particles are positively charged too and deflection happens as they move into the electric field of the nucleus.

If any of this is wrong i will edit it please tell me if I need to make any changes.

[jmorris]

Thanks for posting this Joe

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