Precision mass measurements of magnesium isotopes and implications on the validity of the Isobaric Mass Multiplet Equation

Abstract

If the mass excess of neutron-deficient nuclei and their neutron-rich mirror partners are both known, it can be shown that deviations of the Isobaric Mass Multiplet Equation (IMME) in the form of a cubic term can be probed. Such a cubic term was probed by using the atomic mass of neutron-rich magnesium isotopes measured using the TITAN Penning trap and the recently measured proton-separation energies of ${}^{29}$Cl and ${}^{30}$Ar. The atomic mass of ${}^{27}$Mg was found to be within 1.6$\ddot{I}ƒ$ of the value stated in the Atomic Mass Evaluation. The atomic masses of ${}^{28,29}$Mg were measured to be both within 1$\ddot{I}ƒ$, while being 8 and 34 times more precise, respectively. Using the ${}^{29}$Mg mass excess and previous measurements of ${}^{29}$Cl we uncovered a cubic coefficient of $d$ = 28(7) keV, which is the largest known cubic coefficient of the IMME. This departure, however, could also be caused by experimental data with unknown systematic errors. Hence there is a need to confirm the mass excess of ${}^{28}$S and the one-neutron separation energy of ${}^{29}$Cl, which have both come from a single measurement. Finally, our results were compared to ab initio calculations from the valence-space in-medium similarity renormalization group, resulting in a good agreement.

7 pages, 3 figures