Variational calculation of the effect of isospin-mixing on superallowed Fermi β decay in the A≃70 mass region

We study the influence of Coulomb-induced isospin-mixing on the superallowed Fermi β decay using the complex EXCITED VAMPIR variational approach for the description of the lowest excited 0+ states in the two isovector triplets of nuclei 70Se, 70Br, 70Kr and 74Kr, 74Rb, 74Sr, respectively. As expected, the effects are small but nevertheless non-negligible. The calculated strength for the 74Rb → 74Kr Fermi β decay to the first excited 0+ state turns out to be very weak, in agreement with the experimentally given upper limit. However, particular non-analog Fermi branches to excited 0+ states with considerable strength are predicted to coexist with the superallowed decay in some of the presently investigated nuclei. This may give some hope for possible experimental detection.