This symmetry reflects similar underlying physics: the pair of neutrons and the pair of protons in helium's nucleus obey the same quantum mechanical rules as do helium's pair of electrons ( although the nuclear particles are subject to a different nuclear binding potential ), so that all these fermions fully occupy 1s orbitals in pairs, none of them possessing orbital angular momentum, and each cancelling the other's intrinsic spin.

This symmetry reflects similar underlying physics: the pair of neutrons and the pair of protons in helium's nucleus obey the same quantum mechanical rules as do helium's pair of electrons ( although the nuclear particles are subject to a different nuclear binding potential ), so that all these fermions fully occupy 1s1s orbitals in pairs, none of them possessing orbital angular momentum, and each canceling the other's intrinsic spin.

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