Mass measurements and superallowed β decay

A recent Penning-trap measurement of the masses of V46 and Ti46 leads to a QEC value that disagrees significantly with the previously accepted value, and destroys overall consistency among the nine most precisely characterized T=1 superallowed β emitters. This raises the possibility of a systematic discrepancy between Penning-trap measurements and the reaction-based measurements upon which the QEC values depended in the past. We carefully re-analyze (n,γ) and (p,γ) reaction measurements in the 24≤A≤28 mass region, and compare the results to very precise Penning-trap measurements of the stable nuclei Mg24, Mg26 and Si28. We thus determine upper limits to possible systematic effects in the reaction results, and go on to establish limits for the mass of radioactive Al26, to which future on-line Penning-trap measurements can be compared. We stress the urgency of identifying or ruling out possible systematic effects.