This curious info below turns up on Brian Wang's daily blog: in effect, the authors at LLNL claim to created the densest material yet made which is compressed copper.
Of course, they completely overlook ultradense hydrogen clusters, even though Holmlid's evidence seems actually stronger than what is presented here for copper. UDH alone is supposedly far denser than this shock treated copper. https://www.nextbigfuture.com/2020/01/densest-object-on-earth-made-from-compressed-copper.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+blogspot%2Fadvancednano+%28nextbigfuture%29 This is where it gets tricky. Since this research comes from Livermore we can assume there is a military weapons usage, lurking somewhere in the adjacent black ops lab. Possibly an anti-armor (anti-tank) round the size of 30 calibre slug. The end of tanks, so to speak. For that bit of SciFi to be real, one imagines what happens when thorium or uranium hydride is subject to the same shock-wave compression to achieve higher density? DU is already used for this but it is not active. In fact the Lawson criteria would suggest that this research could be important for miniaturized explosive weapons, not simply dense but dense and active - and should include not just dense hydrogen but the hydrides of the heavier metals (that start out being denser than copper). Thorium is available with few restrictions, and an alloy with UDH or UDD would be expected to be very dense even with no residual applied pressure. ThD is not fissile, per se, but who knows what happens with UDD and a proper host which has been densified. Is it adsorbed into an adjacent heavy nucleus to an inner orbital? - which is to ask a scary question: can picochemistry and extreme density convert some fertile isotopes into fissile via a proximity effect?