Looking for double beta decay of Nd to excited states of Sm by gamma ray spectroscopy

We have measured the gamma ray activity of a sample of 6189 grams of metallic Neodimium with a germanium detector. From the gamma energy spectrum recorded during almost 6500 hours we extract lower limits for the halflife of the inclusive (0ν + 2ν) ββ decay of ¹⁵⁰Nd to the first excited states of ¹⁵⁰Sm : t_1/2(0⁺ → 0₁⁺ > 1.0·10²⁰, t_1/2(O⁺ → 0₂⁺) > 2.0 · 10²⁾, t_1/2(0⁺ → 2₁⁺) > 9.1 · 10¹⁹.