The Nuclear Pairing Gap – How Low Can It Go?

The pairing gap for 53Ca obtained from new experimental data on the masses of 52-54Ca has the smallest value yet observed. This is explained in the framework of the nuclear shell model with schematic and realistic Hamiltonians as being due to shell gaps around the low-j orbital 1p1/2. Minima in the pairing gaps for all nuclei are shown and discussed.