First search for double β decay of platinum by ultra-low background HP Ge γ spectrometry

A search for double β processes in 190Pt and 198Pt was realized with the help of ultralow background HP Ge 468 cm3 spectrometer in the underground Gran Sasso National Laboratories of the INFN (Italy).

Two platinum cups and one lid designed for chemistry purposes with the total mass of 42.53 g were used in the experiment. Taking into account the isotopic composition of the platinum, the sample contains 1.84 x 1019 nuclei of 190Pt and 9.40 x 1021 nuclei of 198Pt. The energy resolution of the spectrometer is FWHM = 2.0 keV for the 1333 keV γ line of 60Co.

The data with the sample were accumulated over 1815.4 h, while the background spectrum was taken over 1045.6 h. The spectra normalized on the time of measurements are presented in Fig. 1. The activity of 137Cs and 192Ir, as well as upper limits on contamination by 40K, 60Co and U/Th daughters are presented in Table 1.
The experiment was used to set limits on double β processes in 190Pt in the range of T1/2 ~ 1014-16 yr, which is 3-4 orders of magnitude higher than the limit on 0νεβ+ (g.s. to g.s.) decay obtained before.