Metastable nuclei

I was thumbing through Future Spacecraft Propulsion Systems and Integration (2018). It is the smart-person version of Nyrath's Atomic Rockets. As long as Chung is babbling on Twitter and not doing featured-updates, that's what I'm reduced to.

One thing popped out that I hadn't heard of - the Metastable Nucleus. It seems that some heavier-than-steel elements, like Tantalum and Hafnium, have isotopes which can exist in an unbalanced state. They are written Hf-178m or Ta-180m. They are not radioactive; they are just unbalanced. When the nucleus balances itself, it releases the potential energy.

Like, a lot of energy. Not enough to induce any fission to surrounding elements; no neutrons or heliums are ejected in this process, in fact the opposite. But a thousand times more energy than the usual chemical reaction. By the way, this means the shielding only needs deal with the X-rays.

Obviously we don't see much of this in the wild. They're rare-earths to begin with and, well, any such created in the usual process would have gone boom by now. But the authors observed that someone might make some.

Sadly this means, at present, skyscraper-leveling bomb you can carry in a laptop case. Nobody wants this monster on controlling the reaction for anything good, like a Starship with twice the cargo-space and nitrogen or CO₂ for propellant.