THE MILANO EXPERIMENT ON DOUBLE BETA-DECAY OF XE-136

An experiment on double beta-decay of Xe-136 has been performed at the Gran Sasso Underground Laboratory (L.N.G.S.). The detector was a multicell proportional counter, built from selected low background materials, which was filled alternatively with natural Xenon, enriched Xenon to 64% in the Xe-136 isotope, and natural Xenon cleaned by ultracentrifugation, and heavily shielded against environmental radioactivity. After 6000 hours of operation half lifetime for the neutrinoless decay mode turns out to be greater than 2 x 10(22) y at 90% C.L. A limit of 6 x 10(19) y, also at 90% C.L., is reported for the 2-nu decay mode.