  It is investigated whether the "X17 puzzle" might be explained by a nuclear
decay chain and a conversion of the two resulting highly energetic $\gamma$s
into an electron-positron pair. It is found that the corresponding kinematics
fits perfectly to the experimental result. Also the conversion rates of this
process are reasonable. However, the assumed nuclear chain reaction is not
favored in the established nuclear models and no explanation for the isospin
structure of the signal can be given. Thus, it has to be concluded that the
process studied in this paper does not give a completely satisfying explanation
of the "X17 puzzle".
