N=16 Magicity Revealed at the Proton Drip Line through the Study of 35Ca

The last proton bound calcium isotope 35Ca has been studied for the first time, using the 37Ca(p; t)35Ca two neutron transfer reaction. The radioactive 37Ca nuclei, produced by the LISE spectrometer at GANIL, interacted with the protons of the liquid hydrogen target CRYPTA, to produce tritons t that were detected in the MUST2 detector array, in coincidence with the heavy residues Ca or Ar. The atomic mass of 35Ca and the energy of its first 3/2+ state are reported. A large N = 16 gap of 4.61(11) MeV is deduced from the mass measurement, which together with other measured properties, makes 36Ca a doubly magic nucleus. The N = 16 shell gaps in 36Ca and 24O are of similar amplitude, at both edges of the valley of stability. This feature is discussed in terms of nuclear forces involved, within state-of-the-art shell model calculations. Even though the global agreement with data is quite convincing, the calculations underestimate the size of the N = 16 gap in 36Ca by 840 keV.