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

Short-lived Cr-46, Fe-50 and Ni-54 were studied by isochronous mass spectrometry at the HIRFL-CSR facility in Lanzhou. The measured precision mass excesses (ME) of Cr-46, Fe-50 and Ni-54 are -29471(11) keV, -34477(6) keV and -39278(4) keV, respectively. The superallowed 0(+) -> 0(+) beta-decay Q values were derived to be Q(EC)(Cr-46) = 7604(11) keV, Q(EC)(Fe-50) = 8150(6) keV and Q(EC)(Ni-54) = 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(Fe-50) = 3103(70) s and Ft(Ni-54) = 3076(50) s. The main contribution to the Ft uncertainties is now due to beta-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. (C) 2017 The Authors. Published by Elsevier B.V.