New limits on 2 ɛ , ɛβ+ and 2 β+ decay of 136Ce and 138Ce with deeply purified cerium sample

Abstract

A search for double electron capture (2 ɛ), electron capture with positron emission (ɛβ+), and double positron emission (2 β+) in 136Ce and 138Ce was realized with a 465 cm3 ultra-low background HP Ge γ spectrometer over 2299 h at the Gran Sasso underground laboratory. A 627 g sample of cerium oxide deeply purified by liquid-liquid extraction method was used as a source of γ quanta expected in double β decay of the cerium isotopes. New improved half-life limits were set on different modes and channels of double β decay of 136Ce and 138Ce at the level of T1 / 2> 10 17- 10 18 yr.