The first ever search for α decays to the first excited state in Yb was performed for six isotopes of hafnium (174, 176, 177, 178, 179, 180) using a high purity Hf-sample of natural isotopic abundance with a mass of 179.8 g. For 179 Hf, also α decay to the ground state of 175 Yb was searched for thanks to the β-instability of the daughter nuclide 175 Yb. The measurements were conducted using an ultra low-background HPGe-detector system located 225 m underground. After 75 d of data taking no decays were detected but lower bounds for the half-lives of the decays were derived on the level of lim T 1/2 ∼ 10 15 − 10 18 a. The decay with the shortest half-life based on theoretical calculation is the decay of 174 Hf to the first 2 + 84.3 keV excited level of 170 Yb. The experimental lower bound was found to be T 1/2 ≥ 3.3 × 10 15 a.
A search for double-beta decay of $$^{190}$$
190
Pt and $$^{198}$$
198
Pt with emission of $$\gamma $$
γ
-ray quanta was realized at the HADES underground laboratory with a 148 g platinum sample measured by two ultralow-background HPGe detectors over 8946 h. The isotopic composition of the platinum sample has been measured with high precision using inductively coupled plasma mass spectrometry. New lower limits for the half-lives of $$^{190}$$
190
Pt relative to different channels and modes of the decays were set on the level of $$\lim T_{1/2}\sim 10^{14}$$
lim
T
1
/
2
∼
10
14
–$$10^{16}$$
10
16
year. A possible exact resonant $$0\nu KN$$
0
ν
K
N
transition to the 1,2 1326.9 keV level of $$^{190}$$
190
Os is limited for the first time as $$T_{1/2} \ge 2.5 \times 10^{16}$$
T
1
/
2
≥
2.5
×
10
16
year. A new lower limit on the double-beta decay of $$^{198}$$
198
Pt to the first excited level of $$^{198}$$
198
Hg was set as $$T_{1/2} \ge 3.2\times 10^{19}$$
T
1
/
2
≥
3.2
×
10
19
year, one order of magnitude higher than the limit obtained in the previous experiment.
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