Nuclear radius

Overview

Distance of closest approach, electron diffraction, R = R₀A^(1/3), and the constancy of nuclear density.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What happens to an alpha particle as it approaches a nucleus, and why?

   Model answer

   The alpha particle decelerates due to Coulomb (electrostatic) repulsion between the positive alpha particle and the positive nucleus.

2. 2

   At the point of closest approach between an alpha particle and a nucleus, what energy transformation has occurred?

   Model answer

   All of the alpha particle's initial kinetic energy has been converted to electric potential energy.

3. 3

   Why does the closest approach method only give an upper limit estimate for nuclear radius?

   Model answer

   Because the alpha particle may not actually reach the nuclear surface; it is repelled before contact, so the measured distance is greater than or equal to the true nuclear radius.

4. 4

   State the Coulomb equation used to find the distance of closest approach in alpha particle scattering.

   Model answer

   Eₖ = kQq/r, or equivalently Eₖ = Qq/(4πε₀r).

5. 5

   In the equation Eₖ = kQq/r for closest approach, what does Q represent?

   Model answer

   Q represents the charge of the nucleus (Ze, where Z is the proton number).

6. 6

   In the equation Eₖ = kQq/r, what does q represent?

   Model answer

   q represents the charge of the alpha particle (2e, since it contains two protons).

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