Study of background in CeCl3 crystal and new limits on 0νββ decay in 136Ce and 138Ce isotopes

Three Ce isotopes could decay through double beta processes: 136Ce (Q = 2419(13) keV), 138Ce (Q = 693(10) keV), and 142Ce (Q = 1417(2) keV). No evidences in the spectrum of the CeCl3 crystal indicating the presence of 2β processes in 136Ce and 138Ce have been observed; only limits on the corresponding T1/2 values have been set for some processes. In the plot below you can see the energy region of interest for the considered processes.

New half life limits for different ββ decay processes in 136Ce and in 138Ce were set. In particular, the 2ε captures in 136Ce to various excited levels of 136Ba were considered for the first time. The limits for the resonant neutrinoless transitions to the 2392.1 keV and 2399.9 keV levels of 136Ba have also been derived. The table here summarize all the studied decay modes.

Sensitivity of order of about 1018 y or more can be obtained by using larger and radiopurer CeCl3 crystal working e.g. as scintillator in coincidence with a HP Ge detector.