High-precision QEC values of superallowed 0+ → 0+β-emitters 46Cr, 50Fe and 54Ni

Short-lived 46Cr, 50Fe and 54Ni were studied by isochronous mass spectrometry at the HIRFL-CSR facility in Lanzhou. The measured precision mass excesses (ME) of 46Cr, 50Fe and 54Ni are −29471(11) keV, −34477(6) keV and −39278(4) keV, respectively. The superallowed 0+→0+β-decay Q values were derived to be QEC(Cr46)=7604(11) keV, QEC(Fe50)=8150(6) keV and QEC(Ni54)=8731(4) keV. The values for 50Fe and 54Ni are by one order of magnitude more precise than the adopted literature values. By combining the existing half-lives and branching ratios, we obtained the corrected Ft values to be Ft(Fe50)=3103(70) s and Ft(Ni54)=3076(50) s. The main contribution to the Ft uncertainties is now due to β-decay branching ratios, still, more high-precision measurements of the half-lives, the masses, and especially the branching ratios are needed in order to satisfy the requirements for a stringent CVC test.