The more interesting one was the Klapdor-Kleingrothaus claim of observing neutrinoless double beta decay in germanium 76 in the early 2000s. That was a major im

The more interesting one was the Klapdor-Kleingrothaus claim of observing neutrinoless double beta decay in germanium 76 in the early 2000s. That was a major impetus for the generation of double beta decay experiments like this that ran in the 2010s. The MAJORANA experiment used the same isotope and was significantly more sensitive, and pretty thoroughly excluded the half life Klapdor-Kleingrothaus claimed.