Evidence for a breakdown of the isobaric multiplet mass equation: A study of the A=35,T=3/2 isospin quartet

Mass measurements on radionuclides along the potassium isotope chain have been performed with the ISOLTRAP Penning trap mass spectrometer. For K-35 (T-1/2=178 ms) to K-46 (T-1/2=105 s) relative mass uncertainties of 2x10(-8) and better have been achieved. The accurate mass determination of K-35 (delta m=0.54 keV) has been exploited to test the isobaric multiplet mass equation for the A=35,T=3/2 isospin quartet. The experimental results indicate a deviation from the generally adopted quadratic form.