Well there's interesting then.

[LondonManc]

I put 3 teaspoons in my coffee every morning, never done me any harm.

In your opinion....

[xoggoth]

I put 3 teaspoons in my coffee every morning, never done me any harm.

[zeitghost]

Apparently someone's nicked some Iridium 192 in eyerack.

Investigating said Iridium 192 leads to the wiki page

https://en.wikipedia.org/wiki/Isotopes_of_iridium

which informs us that Ir 192 has a half life of 73 days.

But, more interesting is the nuclear isomer page.

https://en.wikipedia.org/wiki/Nuclear_isomer

which describes excited states in nuclei.

There's one in Tantalum which has a half life of 10^15 years, rather longer than the age of the universe.

But Hafnium looks promising:

Another reasonably stable nuclear isomer (with a half-life of 31 years) is 178m2
72Hf, which has the highest excitation energy of any comparably long-lived isomer.

One gram of pure 178m2Hf contains approximately 1.33 gigajoules of energy, the equivalent of exploding about 315 kg (694 lb) of TNT.

Further, in the natural decay of 178m2Hf, the energy is released as gamma rays with a total energy of 2.45 MeV.

You get a fair old bang for your gm of Hafnium.