A link to the preprint. I’ll do the actual math on how many transitions/second it works out to later and edit.

I’ve had an eye on this for like a decade, so I’m hyped.

Edit:

So, because of the structure of the crystal the atoms are in, it actually has 5 resonances. These were expected, although a couple other weak ones showed up as well. They give a what I understand to be a projected undisturbed value of 2,020,407,384,335.(2) KHz.

Then a possible redefinition of the second could be “The time taken for 2,020,407,384,335,200 peaks of the radiation produced by the first nuclear isomerism of an unperturbed ²²⁹Th nucleus to pass a fixed point in space.”