On the Masses of A=54 Isospin Septet and the Isobaric Multiplet Mass Equation

Using the ground-state mass of 52 Ni and two-proton decay energy of 54 Zn,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 6.9σ deviated from zero,and the resultant |b/c| 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 54 Fe or extremely strong isospin mixing.