How Robust is the N=34 Subshell Closure? First Spectroscopy of ^{52}Ar

Area of Science:

• Nuclear Physics
• Nuclear Spectroscopy
• Exotic Nuclei

Background:

• Understanding nuclear shell structure is fundamental to nuclear physics.
• The N=34 neutron shell closure is known in the doubly magic ^{54}Ca, but its persistence in neutron-rich isotopes is less understood.
• Investigating neutron-rich Argon (Ar) isotopes provides insights into nuclear forces and shell evolution.

Purpose of the Study:

• To perform the first gamma-ray spectroscopy of the neutron-rich isotope ^{52}Ar.
• To investigate the persistence of the N=34 neutron shell closure in ^{52}Ar.
• To explore the evolution of nuclear structure in neutron-rich Ar isotopes.

Main Methods:

• Utilized the ^{53}K(p,2p) one-proton removal reaction at approximately 210 MeV/u.
• Employed gamma-ray spectroscopy to detect emitted photons.
• Conducted shell-model calculations using phenomenological and chiral effective field theory interactions.

Main Results:

• Measured the 2_{1}^{+} excitation energy of ^{52}Ar to be 1656(18) keV.
• This excitation energy is the highest observed among Ar isotopes with N>20.
• Experimental data and theoretical calculations support the existence of an N=34 subshell closure in ^{52}Ar.

Conclusions:

• The results provide the first experimental evidence for the N=34 subshell closure persisting beyond ^{54}Ca, even below the magic proton number Z=20.
• The findings challenge traditional nuclear shell models and highlight the complex evolution of shell structure in exotic nuclei.
• Shell-model calculations successfully reproduce the observed systematics, reinforcing the N=34 subshell closure in ^{52}Ar.