First observation of α decay of 190Pt to the first excited level (Eexc = 137.2 keV) of 186Os
In the spectrum collected with the Pt sample (see figure), the peak at energy (137.1±0.1) keV is observed while it is absent in the background spectrum. The fit of the Pt spectrum in the energy region (120 – 170) keV with a Gaussian peak and linear background gives area of (132 ± 17) counts, inconsistent with zero at about 8σ. The 137.1 keV peak can be explained with the α decay of 190Pt to the first excited level of 186Os. If populated, this level deexcites with the emission of a quantum with energy E=(137.157 ± 0.008) keV which is in nice agreement with that of the observed peak. We did not find alternative processes which could mimic this effect. Thus, the measured T1/2 of the α decay of the 190Pt to the first excited level (Eexc = 137.2 keV) of 186Os decay is: 2.6+0.4-0.3(stat.) ± 0.6(syst.)× 1014 yr. This α decay has been observed for the first time.
Searches for α decays of other Pt isotopes - related with the emission of γ quanta - have also been searched for. Limits of order of 1017-1019 yr have been obtained.