Performances of a BaF2 detector and its application to the search for ββ decay modes in 130Ba

The potentiality of the coincidence technique to search for ββ decay processes in 130Ba has been studied. A BaF2 crystal scintillator with a mass of 3615 g and two low background NaI(Tl) detectors have been used for this purpose. The performances of the BaF2 detector in the used set-up have preliminarily been investigated, in particular: (i) the α/β light ratio, (ii) the pulse shape discrimination capability between α and β particles, (iii) the main radioactive contaminations of the crystal. As a result, new limits (90% CL) on the lifetimes of the following double beta decay processes in 130Ba have been determined: τ2β+0ν(0+→0+)>1.1×1017 y, τ2β+0ν(0+→21+)>1.5×1017 y, τECβ+0ν(0+→0+)>2.0×1017 y, τECβ+0ν(0+→21+)>1.6×1017 y, τECβ+0ν(0+→22+)>2.0×1017 y and τECβ+0ν(0+→4+)>1.1×1017 y. The new experimental limits obtained for the 0ν(0+→0+) decay modes represent a significant improvement with respect to those previously available for this isotope, while those involving excited levels are set here for the first time.