Search for double-electron capture in ¹⁵² Gd with GAGG:Ce scintillator

Double-electron capture in 152 Gd was searched for over 1336 h with a 286 g GAGG:Ce crystal scintillator at the Gran Sasso underground laboratory of the INFN (Italy). New, improved by four orders of magnitude, limit on the near-resonant 0 ν 2EC capture in 152 Gd was set as lim T 1 / 2 = 8.1 × 1 0 16 year at 90% C.L. Moreover, for the first time, a laboratory experiment has established a lower limit on the half-life of the allowed 2 ν KL process in the nuclide, with lim T 1 / 2 = 9.2 × 1 0 16 year at 90% C.L.