Transitions between the isobaric analogue states in mirror nuclei offer an alternative way to extract the -values  and [40,50]. Those transitions are mixed Fermi and Gamow-Teller, meaning that they are mediated by both the vector and axial-vector currents. Hence, the extraction of requires - in addition to lifetimes and -values - measuring another observable, such as the beta-neutrino correlation coefficient, beta-asymmetry, or neutrino-asymmetry parameter [51,52]. Moreover, the method depends on the radiative and ISB corrections to both the Fermi and Gamow-Teller matrix elements. In spite of these difficulties, current precision of determination of using the mirror-decay approach is similar to that offered by neutron-decay experiments [10,40,50], see also Figs. 8 and 9.
Within our projected-DFT model, we performed systematic calculations of ISB corrections to the Fermi matrix elements, , covering the mirror transitions in all nuclei. Calculations were based on the Slater determinants corresponding to the lowest-energy, unrestricted-symmetry HF solutions. If the unrestricted-symmetry calculations did not converge, the projection was applied to the constrained HF solutions with imposed signature symmetry. These two types of solutions differ, in particular, in relative shape-current orientation, which also varies with depending on the s.p. orbit occupied by an unpaired nucleon. It should be underlined, however, that the HF solutions corresponding to the -decay partners were always characterized by the same orientation of the odd-particle alignment with respect to the body-fixed reference frame. All calculations discussed in this section were performed by using the full basis of HO shells and the SV force.
The obtained values of the ISB corrections to the Fermi transitions,