First search for double-β decay of 184Os and 192Os

A search for double-beta decay of osmium has been realized for the first time with the help of an ultra-low background HPGe gamma detector at the underground Gran Sasso National Laboratories of the INFN (Italy). After 2741 h of data taking with a 173 g ultra-pure osmium sample limits on double-beta processes in Os-184 have been established at the level of T-1/2 similar to 10(14)-10(17) y. Possible resonant double-electron captures in Os-184 were searched for with a sensitivity of T1/2 similar to 10 16 y. A half-life limit T-1/2 >= 5.3x10(19) y was set for the double-beta decay of 192 Os to the first excited level of Pt-192. The radiopurity of the osmium sample has been investigated and radionuclides Cs-137, Os-185 and Bi-207 were detected in the sample, while activities of K-40, Co-60, Ra-226 and Th-232 were limited at the approximate to mBq/kg level.