Ta-180m - longest lived isomer with applications for dark matter detection

Ta-180m is the rarest known quasi-stable isotope and the longest-lived meta-stable state. Its decay has never been observed. The meta-stable state is spin trapped in a 9- configuration, requiring a parity and spin change of 7 units to de-excite to a lower state. It is also the intermediate nucleus in a double-beta-decay-configuration and could decay through beta decay or electron capture requiring 3-fold non-unique transitions. Current half-life limits for these decay modes are between 1e14 and 1e18 yr. This makes Ta-180m an interesting isotope to test nuclear model calculation.

Furthermore, the cosmologically stable nature of Ta-180m can be used to test specific dark matter models. Strongly interacting dark matter can collide with Ta-180m leading to its de-excitation while absorbing the large angular momentum. The energy stored in the meta-stable state is the experimental signature for thermalized dark matter which would otherwise not be detectable in well-shielded underground WIMP experiments.

I will discuss the unique decay scheme of Ta-180m, its application for dark matter searches, and present previous results. I will also discuss different experimental proposals for future searches using tantalum.