Nuclei

Geiger-Marsden Experiment (Rutherford Scattering) 
- The experiment measured the number of alpha particles ( ) scattered at different angles ( ). 
- The observed scattering pattern led to significant conclusions about atomic structure. 
Graph: Variation of with  

 Conclusions from the Graph
1. Most alpha particles pass undeflected, meaning the atom is mostly empty space.
2. Few particles are scattered at large angles, implying a small, dense, positively charged nucleus. Expression for Distance of Closest Approach The distance of closest approach ( ) is the minimum separation between the alpha particle and the nucleus before it stops and reverses.
 - At the point of closest approach, the initial kinetic energy of the alpha particle is converted into electrostatic potential energy:  

Solving for : Thus, the distance of closest approach is:  

This represents the minimum distance between the alpha particle and the nucleus before repulsion stops its motion. 
 

Nuclear Fission vs. Nuclear Fusion 

 Thus, nuclear fission and fusion differ in process, energy release, and applications.