Accurate mass measurements of very short-lived nuclei -: Prerequisites for high-accuracy investigations of superallowed β-decays

Mass measurements of Ar-34, Kr73-78, and Rb-74,Rb-76 were performed with the Penning-trap mass spectrometer ISOLTRAP. Very accurate Q(EC)-values are needed for the investigations of the Ft-value of 0(+) --> 0(+) nuclear beta-decays used to test the standard model predictions for weak interactions. The necessary accuracy on the Q(EC)-value requires the mass of mother and daughter nuclei to be measured with deltam/m less than or equal to 3 (.) 10(-8). For most of the measured nuclides presented here this has been reached. The 34Ar mass has been measured with a relative accuracy of 1.1(.)10(-8). The Q(EC)-value of the Ar-34 0(+) --> 0(+) decay can now be determined with an uncertainty of about 0.01%. Furthermore, Rb-74 is the shortest-lived nuclide ever investigated in a Penning trap.