  The presently accepted value of the energy splitting of the Th-229
ground-state doublet has been obtained on the basis of undirect gamma
spectroscopy measurements by Beck et al., Phys. Rev. Lett. 98, 142501 (2007).
Since then, a number of experiments set out to measure the isomer energy
directly, however none of them resulted in an observation of the transition.
Here we perform an analysis to identify the parameter space of isomer energy
and branching ratio that is consistent with the Beck et al. experiment.
