Onset of Collectivity for Argon Isotopes Close to N=32

The shell closure at N = 32 has been investigated by a first spectroscopy of the N = 31 nucleus 49Ar at the Radioactive Isotope Beam Factory. Using the 50Ar(p, pn) reaction channel in inverse kinematics, 50Ar projectiles at 217 MeV/nucleon impinged on a 150 mm long liquid hydrogen target, part of the MINOS device. Prompt deexcitation gamma rays were measured with the NaI(Tl) array DALI2+. Reaction products were analyzed with the SAMURAI spectrometer, which allowed the measurement of the momentum distributions and angular momentum transfer. Data were compared to state-of-the-art theoretical predictions, including shell -model, energy -density functional, and ab initio calculations. An onset of collectivity is suggested besides the spherical configuration typical of a closed shell nucleus, such as for 52Ca.