Peter Grynch asked:

“Have you heard about the hafnium bomb?”

I have heard of it but need to study it in greater depth. Hafnium is interesting stuff. The folks in the spacecraft thermal protection business were once all a twitter over hafnium diboride. Supposably it was going to revolutionize entry vehicle design. Then they discovered hafnium diboride shatters like glass when subjected to thermal shock (works fine if it’s warmed up slowly). People no longer talk about hafnium diboride (another “good idea” that didn’t work).