Superallowed Fermi b Decays, CVC and Universality

A review is given of the present status of superallowed Fermi /3 decays including a short discussion of the radiative corrections of order a, Za2, Z2a 3 and of nuclear effects. We also point out that the interaction of the emitted positron with the magneto static field of the spectator nucleons induces additional corrections of about 0·1 % to the ft values. Despite refinements in the calculation of the theoretical corrections, there is a remaining discrepancy between the It values which is even larger than the theoretical uncertainties. This behaviour of the It values is not understood at present.

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