Precise Half-Life Measurement for the Superallowed 0+-->0+ β Emitter 74Rb: First Results from the New Radioactive Beam Facility (ISAC) at TRIUMF

Presently, the world data for superallowed β decay leads to a result in disagreement (at the 98% confidence level) with the predictions of the minimal standard model for the unitarity of the Cabibbo-Kobayashi-Maskawa matrix. Precise data for the superallowed 0⁺-->0⁺ β decay of ⁷⁴Rb would provide a critical test of the nucleus-dependent isospin symmetry-breaking corrections that must be calculated for these superallowed Fermi β decays. The present work reports the first precise measurement of the half-life for ⁷⁴Rb ( t_1/2 = 64.761+/-0.031 ms). The data were obtained at the radioactive beam facility (ISAC) at TRIUMF using a beam of ~4000 ⁷⁴Rb ions s^-1.