Fig. 9.

Part of the M1 spectrum shown in Fig. 3 with the Bayesian fit of the electron decay at $E_{\text{0}}=255.9$ keV (continuous line). The background fit includes two significant $\gamma$s (dashed lines) at $E_{\gamma ,1}=$238.6 keV ($_{}^{212}$Pb) and $E_{\gamma ,2}=$295.2 keV ($_{}^{214}$Pb), see Table 3