Rutherford Backscattering Experiment

[TauDay]

Homework Statement

In the famous “Rutherford backscattering” experiment, alpha particles (Z=2) of
approximately 7 MeV were used to bombard a Au (Z=79) film. Rutherford derived the
scattering formula by treating an incident alpha particle and a Au target atom as two point
charges with their charge numbers equal to their atomic numbers. This assumption, however,
is not accurate in describing general ion solid interactions. Explain
(a) why was Rutherford’s approach successful in his experiments?
and
(b) under what conditions deviation from Rutherford scattering formula will occur?

Homework Equations

The Attempt at a Solution

a) Rutherford’s approach was successful because he used an extremely thin foil with a target nucleus much heavier than the incident alpha particles.

b) If the foil was thicker and the target nucleus and incident alpha particle were of comparable mass, Rutherford would have observed increased ion-solid reaction types.

 

[mfb]

The thin foil is certainly an important point. The heavy nucleus is something the scattering formula can take into account.

I think the question asks for something that you missed so far. What was the important historic result of the experiment? If you know the result in advance (as we do know) it might look obvious, but at that time it was unclear.
Hint:

Spoiler

What about electrons, for example?

 

[TauDay]

The result was confirmation of the atomic nucleus - most of the foil's mass is concentrated and not evenly distributed.

 

[mfb]

Right.

 

[paranormal]

Additionally, if the target nucleus had a different charge from the incident particle, the scattering pattern would deviate from Rutherford's formula. Other factors that could affect the deviation from Rutherford scattering include the energy and angle of the incident particle, and the composition and thickness of the target material. In general, the closer the target nucleus and incident particle are in mass and charge, the more likely it is for the scattering pattern to deviate from Rutherford's formula.