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 betabeta decay processes in Ba-130 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 alpha/beta light ratio, (ii) the pulse shape discrimination capability between alpha and beta 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 Ba-130 have been determined: tau(2beta+0v(0+-->0+)) > 1.1 x 10(17) y, tau(2beta+0v(0+-->21+)) > 1.5 x 10(17) y, tau(ECbeta+0v(0+-->0+)) > 2.0 x 10(17) y, tau(ECbeta+0v(0+-->21+)) > 1.6 x 10(17) y, tau(ECbeta+0v(0+-->22+)) > 2.0 x 10(17) y and tau(ECbeta+0v(0+-->4+)) > 1.1 x 10(17) y. The new experimental limits obtained for the 0v(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. (C) 2004 Elsevier B.V. All rights reserved.