An ultra low background beta-gamma spectrometer

Abstract An ultra low background β-γ spectrometer, ELEGANTS (electron gamma neutrino spectrometer) is developed primarily for studying neutrino-less double β decays (0νββ) of 76 Ge to both 0 + and 2 + states in 76 Se. It consists of a high resolution Ge β detector surrounded by a 4π NaI γ counter. Selection of tru β events by referring to accompanied γ events is shown to be very powerful. It shown extremely high sensitivity to both the 0 + → 0 + and 0 + → 2 + 0 νββ events. It is applied for studying other 0νββ and 2νββ decays, very rare β and / or γ decays and very low radioactivities.