Examining the N = 28 shell closure through high-precision mass measurements of 46, 48Ar

High-precision masses of ⁴⁶Ar and ⁴⁸Ar used to test whether the N=28 shell closure is still a real gap as proton number drops from calcium toward argon.

ISOLTRAP mass spectrometry of argon beams from ISOLDE. Two-neutron separation energies and the N=28 gap are compared with shell-model expectations.

N=28 is a canonical magic number that is already known to weaken in sulphur and silicon. Argon masses are the missing step between the closed calcium chain and that collapse.