小中大The spin of composite particles, such as protons, neutrons, and atomic nuclei is usually understood to mean the total angular momentum, which is the sum of the spins and orbital angular momenta of the constituent particles. Such a composite spin is subject to the same quantization condition as any other angular momentum。And we know that both proton and neutron have spin quantum number of 1/2.
Every two of protons and neutrons are paired (means one has +1/2 and the other has -1/2), when they are on the sample energy level. So even number of p, n gives 0 total spin. But if the two p or n are not on the sample energy level (in the excited state), they are not paired, and will give multiple quantum number >=1/2 (this happens in high energy physics).
My suggestion is to think it like the electron orbits of an atom. The nulceons also have levels. Generally, they are paired at each level if they can. If the number is odd, the extra unpaired ones give the spin quantum number of the whole nucleus.
