Whence the odd-even staggering in nuclear binding?
We explore the systematics of odd-even mass staggering with a view to identifying the physical mechanisms responsible. The BCS pairing and mean-field contributions have A - and number parity dependences which can help disentangle the different contributions. This motivates the two-term parametrization c1 + c2/A as a theoretically based alternative to the inverse-power form traditionally used to fit odd-even mass differences. Assuming that the A -dependence of the BCS pairing is weak, we find that mean-field contributions are dominant below mass number A ∼ 40 while BCS pairing dominates in heavier nuclei.