$B\rho$-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 ${}^{46}\mathrm{Cr}$, ${}^{50}\mathrm{Fe}$, and ${}^{54}\mathrm{Ni}$ are determined with relative uncertainties of (5–6)$\times {10}^{-8}$, 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.

Figure 1

Schematic view of CSRe with the arrangement of two TOF detectors.

Figure 2

Left: Comparison of the redetermined masses with literature values, where the black symbols are reference nuclides and the red ones are nuclides of interest. The grey shadow represents the mass uncertainties in the AME2020 [30]. Right: Comparison of the newly determined masses with the literature ones (see legend).

Figure 3

Scatter plots of $T_{\exp }$ and $T_{\mathrm{fix}}$ versus $C_{\exp }$ for ${}^{24}\mathrm{Al}^{13+}$ ions (see text for details).

Figure 4

Standard deviations of the TOF peaks (left scale) derived from the original revolution time spectrum (black filled squares), and from the newly constructed spectrum (blue circles). The corresponding absolute accuracies of mass-to-charge ratios are given on the right scale.