Ta180m is the rarest naturally occurring quasistable isotope and the longest lived metastable state which is known. Its possible decay via the β- or the electron capture channel has never been observed. This article presents a search for the decay of Ta180m with an ultralow background Sandwich HPGe γ spectrometry setup in the HADES underground laboratory. No signal is observed and improved lower partial half-life limits are set with a Bayesian analysis to 5.8×1016yr for the β- channel and 2.0×1017yr for the electron capture channel (90 % credibility). The total half-life of Ta180m is longer than 4.5×1016yr. This is more than a factor of two improvement compared to previous searches.

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Persistent URL dx.doi.org/10.1103/PhysRevC.95.044306
Journal Physical Review C
Lehnert, B., Hult, M., Lutter, G., & Zuber, K. (2017). Search for the decay of nature's rarest isotope Ta 180m. Physical Review C, 95(4). doi:10.1103/PhysRevC.95.044306