Interacting boson model

The interacting boson model (IBM) is a model in nuclear physics in which nucleons (protons or neutrons) pair up, essentially acting as a single particle with boson properties, with integral spin of 0, 2 or 4.

The IBM-I treats both types of nucleons the same and considers only pairs of nucleons coupled to total angular momentum 0 and 2, called respectively, s and d bosons. The IBM-II treats protons and neutrons separately.