$A\ge62$ Superallowed Fermi $\beta$-decays and Future Prospects with GRIFFIN

Superallowed Fermi $\beta$ decays of $A\ge62$ nuclei involve relatively large nucleus dependent isospin-symmetry-breaking corrections. The magnitudes of these corrections are of great interest, and the $A\ge62$ decays provide a demanding test of theoretical models. Branching ratio measurements for these decays involve a unique challenge as they have large $Q_{EC}$, and hence a high density of available states in the daughter nucleus, resulting in the Pandemonium effect in which weak feeding is distributed over a large number of states and is difficult to observe. Therefore, high-efficiency detectors are of paramount importance in determining the branching ratio for these decays. The 8$\pi$ spectrometer at TRIUMF's Isotope Separator and Accelerator (ISAC), has been used to establish high-precision branching ratios for $^{62}$Ga and $^{74}$Rb. The newly commissioned GRIFFIN spectrometer at ISAC provides an efficiency 17 times higher than the $8\pi$ for 1 MeV $\gamma$-rays, and larger gains at higher energies which are of particular importance in resolving the Pandemonium effect. The recent branching ratio measurement for the superallowed Fermi $\beta$-decay of $^{74}$Rb will be discussed, as well as the importance of GRIFFIN for future superallowed $\beta$ decay studies at ISAC.