Results on intrinsic radioactivity of Li6Eu(BO3)3 crystal and α decays of Eu

A Li6Eu(BO3)3 monocrystal 14.5 x 5.6 mm (corresponding to a mass about 2.72 g) was inserted in the HP Ge detector (size 408 cm3) located deep underground at LNGS. Measurements of the radioactivity of the crystal has been performed during 1500 h. Considering the measured spectrum and the measured background of the HP Ge detector, the radiation contaminants in the crystal have been derived.

The collected data have also allowed to obtain the first experimental limits on the half lives of two very rare alpha decays: the limit on the half-life of the 151Eu decay to the first excited level of 147Pm and the limit on the half-life of 153Eu decay into 149Pm. They are, respectively: T1/2 > 2.4 x 1016 yr and T1/2 > 1.1 x 1016 yr , at 90% C.L.