Emergence of the N=16 shell gap in 21O

TL;DR

This study investigates the nuclear structure of 21O, revealing the emergence of the N=16 shell gap through spectroscopy and shell model comparisons, highlighting the evolution of magic numbers in neutron-rich isotopes.

Contribution

The paper provides experimental evidence for the N=16 shell gap in 21O using (d,p) reactions and compares findings with new shell model calculations, advancing understanding of shell evolution.

Findings

Identification of ground and first excited states as Jπ=5/2+ and 1/2+

Observation of two neutron unbound states at 4.76 and 6.16 MeV

Large energy gap indicating the N=16 magic number emergence

Abstract

The spectroscopy of 21O has been investigated using a radioactive 20O beam and the (d,p) reaction in inverse kinematics. The ground and first excited states have been determined to be Jpi=5/2+ and Jpi=1/2+ respectively. Two neutron unbound states were observed at excitation energies of 4.76 +- 0.10 and 6.16 +- 0.11. The spectroscopic factor deduced for the lower of these interpreted as a 3/2+ level, reveals a rather pure 0d3/2 single-particle configuration. The large energy difference between the 3/2+ and 1/2+ states is indicative of the emergence of the N=16 magic number. For the higher lying resonance, which has a character consistent with a spin-parity assignment of 3/2+ or 7/2-, a 71% branching ratio to the first 2+ state in 20O has been observed. The results are compared with new shell model calculations.