Masses of neutron-rich ${}^{52-54}$Sc and ${}^{54,56}$Ti nuclides: The $N=32$ subshell closure in scandium

Abstract

Isochronous mass spectrometry has been applied in the storage ring CSRe to measure the masses of the neutron-rich ${}^{52-54}$Sc and ${}^{54,56}$Ti nuclei. The new mass excess values $ME$(${}^{52}$Sc) $=$ $-40525(65)$ keV, $ME$(${}^{53}$Sc) $=$ $-38910(80)$ keV, and $ME$(${}^{54}$Sc) $=$ $-34485(360)$ keV, deviate from the Atomic Mass Evaluation 2012 by 2.3$\sigma$, 2.8$\sigma$, and 1.7$\sigma$, respectively. These large deviations significantly change the systematics of the two-neutron separation energies of scandium isotopes. The empirical shell gap extracted from our new experimental results shows a significant subshell closure at $N=32$ in scandium, with a similar magnitude as in calcium. Moreover, we present $ab$ $initio$ calculations using the valence-space in-medium similarity renormalization group based on two- and three-nucleon interactions from chiral effective field theory. The theoretical results confirm the existence of a substantial $N=32$ shell gap in Sc and Ca with a decreasing trend towards lighter isotones, thus providing a consistent picture of the evolution of the $N=32$ magic number from the $pf$ into the $sd$ shell.

6 pages, 5figures, accepted by Physical Review C

References in corpus (8)

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• A nucleus-dependent valence-space approach to nuclear structure
• In-Medium Similarity Renormalization Group for Open-Shell Nuclei
• Probing the N = 32 shell closure below the magic proton number Z = 20: Mass measurements of the exotic isotopes 52,53K
• New precision mass measurements of neutron-rich calcium and potassium isotopes and three-nucleon forces
• Identification of the Lowest $T=2$, $J^{\pi =}{0}^{+}$ Isobaric Analog State in ${}^{52}$Co and Its Impact on the Understanding of $\beta$-Decay Properties of ${}^{52}$Ni
• Structure of 55Sc and development of the N=34 subshell closure
• Spectroscopy of ${}^{50}$Sc and ab initio calculations of $B(M3)$ strengths

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