First search for double- beta decay of platinum by ultra-low background HP Ge gamma spectrometry

A search for double- $ beta$ processes in ¹⁹⁰Pt and ¹⁹⁸Pt was realized with the help of ultra-low background HP Ge 468cm^3 $ gamma$ spectrometer in the underground Gran Sasso National Laboratories of the INFN (Italy). After 1815 h of data taking with 42.5g platinum sample, T _1/2 limits on 2 $ beta$ processes in ¹⁹⁰Pt ( $ varepsilon$ $ beta^{+}_{}$ and 2 $ varepsilon$ have been established on the level of 10¹⁴-10¹⁶y, 3 to 4 orders of magnitude higher than those known previously. In particular, a possible resonant double-electron capture in ¹⁹⁰Pt was restricted on the level of 2.9×10¹⁶ y at 90% C.L. In addition, T _1/2 limit on 2 $ beta^{-}_{}$ decay of ¹⁹⁸Pt (2 $ nu$ +0 $ nu$ ) to the 2⁺ ₁ excited level of ¹⁹⁸Hg has been set at the first time: T _1/2 > 3.5×10¹⁸ y. The radiopurity level of the used platinum sample is reported.