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Physics · Class 12

Rutherford alpha scattering

Atoms

Most alpha particles pass with small deflection; near passes can turn through large angles. A compact positive nucleus explains rare backward scattering. Larger impact parameter or larger incident energy reduces deflection.

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Rutherford alpha scattering

அணுவின் பெரும்பகுதி காலியாக இருப்பதால் பல ஆல்பா துகள்கள் சிறிதே விலகும். சிறிய நேர்மின் அணுக்கருவிற்கு அருகில் பெரிய விலகல் உண்டாகும்.

Key notes, relationships and model limits

Key relationship

cot(θ/2)=2Eb/(kZzαe²), zα=2; rmin=a+√(a²+b²), a=kZzαe²/(2E).

Remember

Most alpha particles pass with small deflection; near passes can turn through large angles. A compact positive nucleus explains rare backward scattering. Larger impact parameter or larger incident energy reduces deflection.

Common trap

The Bohr-sized electron cloud is not the positive scattering centre.

Model limits

Nonrelativistic alpha; heavy fixed point nucleus; pure repulsive Coulomb field. Electron screening, finite nuclear size and nuclear forces omitted.

What you will learn

Relate scattering angle to impact parameter and nuclear concentration.

Try the experiment

Try both scenarios, change one control, and predict the result before checking the graph and readouts.

Think of it this way

Change one input while keeping the others fixed, as you would in a controlled experiment.

Worked example

For gold Z79 and5 MeV, head-on distance is about45.50 fm.

Why this matters

The model connects rutherford alpha scattering with an observable reading. Check the equation and assumptions before applying it.

Before you start

SI units · algebra · graph reading

Check your understanding

For a head-on Coulomb approach, the alpha scattering angle is?

Read the explanation

Zero impact parameter makes the alpha stop and reverse in the ideal repulsive model.

Course connection: Class XII Chapter 12. Consult the roadmap for CBSE, NEET, JEE Main and Advanced scope.