The precise determination of QEC-value differences between four pairs of superallowed β-emitters: 14O and 26mAl, 26mAl and 42Sc, 42Sc and 54Co; 50Mn and 54Co

The QEC-value differences between four pairs of superallowed 0+ → 0+, T = 1 beta emitters have been precisely determined in order to test calculated charge-dependent corrections to superallowed ft values. The pairs, labelled by the β emitters involved, are: 14O and 26mAl; 26mAl and 42Sc; 42Sc and 54Co; and 50Mn and 54Co. The measured QEC-value differences for the four pairs are: 1401.68 ± 0.13; 2193.5 ± 0.2; 1817.2 ± 0.2 and 610.1 ± 0.5 keV respectively. The results were determined from the measured energy differences between pairs of triton groups produced in two (3He,t) reactions, one on each component of a two-component target. The target assembly could be biased to a potential of up to 150 keV, permitting triton goups to be shifted accordingly along the focal plane of a momentum analyzing Q3D magnetic spectrometer. The energy difference between two observed trition groups was derived from the voltage required to shift the triton group from one target component onto the unshifted position of a triton group from the other target component. This momentum matching technique has the advantage that most experimental uncertainties are common to both reactions and almost cancel in the difference. (orig.)