Dawning of the N=32 shell closure seen through precision mass measurements of neutron-rich titanium isotopes

TL;DR

This study provides precise mass measurements of neutron-rich titanium isotopes near N=32, confirming a weak shell closure and comparing results with advanced shell model calculations, marking the first use of TITAN's MR-TOF-MS for scientific results.

Contribution

First precise mass measurements of $^{51-55}$Ti near N=32 using TITAN's new MR-TOF-MS, confirming a weak shell closure and benchmarking theoretical models.

Findings

Confirmed weak N=32 shell effect in titanium isotopes.

Reduced uncertainties in mass values of $^{52-55}$Ti.

Compared experimental data with shell model predictions, noting overestimation of shell strength.

Abstract

A precision mass investigation of the neutron-rich titanium isotopes $^{51-55}$Ti was performed at TRIUMF's Ion Trap for Atomic and Nuclear science (TITAN). The range of the measurements covers the $N=32$ shell closure and the overall uncertainties of the $^{52-55}$Ti mass values were significantly reduced. Our results confirm the existence of a weak shell effect at $N=32$, establishing the abrupt onset of this shell closure. Our data were compared with state-of-the-art \textit{ab-initio} shell model calculations which, despite very successfully describing where the $N=32$ shell gap is strong, overpredict its strength and extent in titanium and heavier isotones. These measurements also represent the first scientific results of TITAN using the newly commissioned Multiple-Reflection Time-of-Flight Mass Spectrometer (MR-TOF-MS), substantiated by independent measurements from TITAN's Penning trap mass spectrometer.