Matthias Heinz

An electron flying through a heavy nucleus behaves like a tennis ball sent through a picket fence. If the pickets are unevenly spaced (denser here, sparser there) the ball will deflect differently.

The atomic nucleus is not a bag of marbles but an ordered structure where protons and neutrons fill shells, much like electrons in an atom. When a shell is filled, the nucleus becomes especially stable, and the number of particles is called magic. For calcium with 20 protons, the classic magic neutron numbers are 20 and 28.