Shell-model picture of virtual detour transitions in 41Ca radiative electron-capture decay.

For the first forbidden unique (1u) radiative electron-capture b decay of Ca, a contribution of the g/b detour transitions via virtual nuclear states to the bremsstrahlung spectrum has been considered in terms of the shell model. Calculations of the matrix elements for the virtual E1 g and allowed Gamow-Teller b transitions have been performed with the use of the Warburton, Becker, Millener, and Brown interactions. For the effective charge, which describes the contribution of the detour transitions, an interval 0.96,eeff,1 has been found. The model predictions are fairly close to the experimental value eeff50.78. A possible origin of the small remaining deviation is discussed.