Answer
There is a Pauli exclusion principle for nucleons as well as electrons. When neutrons pair with neutrons and protons pair with protons, their spins cancel. Even-even nuclei are the only ones with no net spin.
Work Step by Step
There is a Pauli exclusion principle for nucleons as well as electrons. When neutrons pair with neutrons and protons pair with protons, their spins cancel. Even-even nuclei are the only ones with no net spin.