Th Isomer

The nucleus of ²²⁹Th has an exceptionally low-energy isomeric transition in the

vacuum-ultraviolet (VUV) spectrum around 8 eV [1]. While a precise measurement of

this transition is difficult with standard nuclear physics techniques, its low

energy provide several new pathways for measuring this laser-accessible nuclear transition.

It has been established that the isomer de-excites primarily via the internal conversion (IC)

channel when neutralized in a solid, with a half-life of 7 μs [2,3]. We will report on an effort

to measure the IC decay of isomeric ²²⁹Th within a superconducting nano-wire single-photon imager (SNSPI).

By leveraging the SNSPI's bias-current-dependent energy responsivity, we aim to measure the

energy released by the isomer into the nano-wire. This in turn will further constrain the

isomer's energy, helping to guide future laser searches.