B rho-defined isochronous mass spectrometry: An approach for high-precision mass measurements of short-lived nuclei

A technique for broadband high-precision mass measurements of short-lived exotic nuclides is reported. It is based on the isochronous mass spectrometry (IMS) and realizes simultaneous determinations of revolution time and velocity of short-lived stored ions at the cooler storage ring CSRe in Lanzhou. The technique, named the B rho-defined IMS or B rho-IMS, boosts the efficiency, sensitivity, and accuracy of mass measurements, and is applied here to measure masses of neutron-deficient fp-shell nuclides. In a single accelerator setting, masses of 46Cr, 50Fe, and 54Ni are determined with relative uncertainties of (5-6)x10-8, thereby improving the input data for testing the unitarity of the Cabibbo-Kobayashi-Maskawa quark mixing matrix. This is the technique of choice for future high-precision measurements of the most rarely produced shortest-lived nuclides.