First search for double β decay of dysprosium
A search for double β decay of dysprosium has been realized for the first time with the help of the ultra low-background HP Ge γ detector DAMA/Ge.
The Dysprosium contains two potentially 2β+ active isotopes: 156Dy with one of the largest releases Q2β = (2012 ± 6) keV (therefore both 2ε and εβ+ channels of decay are possible), and 158Dy ( Q2β = (28.6 ± 2.5) keV, only double electron capture is energetically allowed ).
It should be mentioned the possibility of a resonant enhancement of the neutrinoless double electron capture in 156Dy and 158Dy due to energy degeneracy. Resonant captures are possible on a few excited levels of 156Gd and one level of 158Gd. The properties of the excited levels are listed in table. Because transitions with difference in spin more than 2 are strongly suppressed, only levels of 156Gd with spin <= 2 have been considered in this study.
A Dy2O3 sample with a mass 322 g in a polyethylene bag was placed in the DAMA/Ge detector (GeBer, 244 cm3) and sample was measured over 2512 h; the background of the detector was also measured during 6110 h.