Q value of the superallowed decay of 22Mg and the calibration of the 21Na(p, γ) experiment

The masses of the radioactive nuclei {sup 22}Mg and {sup 22}Na have been measured with the Canadian Penning trap on-line mass spectrometer to a precision of 3x10{sup -8} and 1x10{sup -8}, respectively. A Q{sub EC} value of 4124.39(73) keV for the superallowed {beta} decay of {sup 22}Mg is obtained from the difference of these two masses. With this precise Q value, the Ft value for this decay is determined with improved precision and is found to be consistent with the existing precision data set of superallowed Fermi emitters. This provides an important test of the isospin symmetry-breaking corrections. If the mass of {sup 22}Mg determined here is used in the calibration of a recent {sup 21}Na(p,{gamma}){sup 22}Mg measurement, part of the discrepancy observed in that measurement is removed.