1. The problem statement, all variables and given/known data How do 5 protons fill a g9/2 shell in the shell model? There are 10 spots in the g9/2 shell. 2. Relevant equations 3. The attempt at a solution Pauli principle dictates the first four to be in anti-parallel pairs. But the last can be either up or down. Am I missing something or is this really all there is to it?