Fig. 2.

Search for delayed coincidences in the ${}^{238}$U (left) and ${}^{232}$Th (right) decay chains. The grey spectrum comprises the not piled-up ${\mathcal{M}}_1$ $\alpha$ events. We tag as daughter (blue) all the events within a $5T_{1/2}$ time-window after a candidate parent event recorded at the ${}^{222}$Rn (left) or ${}^{224}$Ra (right) Q value peak (red). The spectrum of ${}^{224}$Ra daughters (right, in blue) is miscalibrated due to the ${}^{220}$Rn${-}^{216}$Po pile-up. These events are rejected by the pileup rejection cuts, therefore they are not included in the ${\mathcal{M}}_{1\alpha }$ spectrum (grey)