On the masses of A=54 isospin septet and the isobaric multiplet mass equation

Using the ground-state mass of Ni-52 and two-proton decay energy of Zn-54, the ground-state mass excess of( 54)Zn is deduced to be -6504(85) keV. This value is about 2 MeV lower than the prediction of the quadratic form of the isobaric multiplet mass equation (IMME). A cubic fit to the existing mass data of the A = 54, T = 3 isospin multiplet yields a surprisingly large d coefficient of IMME, i.e., d= 18.6(27), being 6.9 sigma deviated from zero, and the resultant vertical bar b/c vertical bar ratio significantly deviates from the systematics. This phenomenon is analyzed in this study, and we conclude that the breakdown of the quadratic form of IMME could be likely due to the mis-assignment of the T = 3 isobaric analog state (IAS) in the T-z = 1 nucleus Fe-54 or extremely strong isospin mixing.