We don't really know where we found this stuff, but some engineer once dug it out of a pile of depeleted fuel elements. We can't tell if it is part of a decay chain as we don't even knowit is.
Euphemium seems to negate all forms of kinetic energy, our scientists aren't sure where that energy goes.
You must be thinking "You're men of science, why can't you figure more out?", well there's a simple reason for that: Any machine we use to determine a property either gets compressed into an indistinguishable piece of metal, melts entirely or looses it's warranty anddoes either one of the things mentioned earlier. It's like it does not want to be observed.</p>