Collapsium is metal, usually steel, savagely abused using a perverse application of the engineering that allows Abbot Lift-and-Drive units. Such metal is compressed to ridiculous densities. It makes really good radiation shielding. A plating a few atoms thick will stop most radiation cold.
Collapsium allows the true energy supply of the Terro-Human Alliance. Fission. Plutonium, Uranium, Strontium can decay away, as happy as a clam, generating neutrons, alpha particles and whatnot. A thin plating of collapsium around the housing keeps all the evil inside.
It means that objects the size of large jars have to be picked up with industrial sized forklifts, but what the hey.
Radiothermic generators using all sorts of whackjob isotopes are in use in the Terro-Human Alliance. But there's one problem. These produce energy, they can do it consistently for years on end. But the energy generated compared to other means is actually sort of small.
Collapsium plated RTGs have to be combined with Super Batteries to do much good.
Collapsium also makes dandy radiation shielding. Expensive ships are plated all over with the stuff. Ever so slightly thicker layers make military armor.
Cheaper ships coat specific areas or even one safe haven with collapsium to allow the crew to survive the solar wind, and various outbursts and currents in deep space.
Maybe Military grade Collapsium armor can stop a Gamma Burst. No one wwaants to be the first to test the assertion.