We present a high-precision mass measurement of the proton-rich nucleus ${}^{23}\mathrm{Si}$, performed with the LEBIT Penning trap at the Facility for Rare Isotope Beams (FRIB) utilizing the time-of-flight ion cyclotron resonance (TOF-ICR) technique. We determined a mass excess of 23362.9(5.8) keV, which agrees with a recent storage-ring measurement from the experimental Cooler-Storage Ring (CSRe) in Lanzhou but has a factor of 20 improved precision. ${}^{23}\mathrm{Si}$ is hence the nucleus with the most precisely known mass among all nuclei with an isospin projection of $T_z=-5/2$. We performed shell-model calculations with the USDC and USDCm Hamiltonians to study binding energy differences and Thomas-Ehrmann shifts in mirror systems with an isospin up to $T=5/2$. Our experimental result and other recently reported masses of neutron-deficient sd-shell nuclei agree well with the theoretical predictions, demonstrating that isospin symmetry breaking in sd-shell nuclei—even at high isospin values—is well described by modern shell-model calculations.

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• Binding energy & masses
• Nuclear astrophysics
• Nuclear forces
• Nuclear structure & decays
• Rare & new isotopes
• 20 ≤ A ≤ 38
• Isospin violation
• Nuclear binding
• Mass spectrometry
• Penning traps
• Precision measurements
• Radioactive beams
• Shell model
• Spectrometers & spectroscopic techniques