Value of Transuranic Elements

Today, I was thinking about what would happen if Earth was to open trade negotiations with an advanced alien race. Specifically, what could the aliens pay us with? Assuming we wanted to keep things covert (thus, no spacecraft or other advanced machines), I wondered if transuranic elements might be just the thing. For instance, we use americium in smoke detectors, but there’s only a few micrograms of it in each one. If we could find an advanced alien race capable of producing large quantities of americium, californium, or other transuranic elements, would this be of great value? If so, what would these elements be used for?

Don’t forget plutonium is a transuranic element. I’m sure quite a few nations in the world would love to get their hands on an unlimited supply of that.

Better armour-piercing shells would be an obvious guess.

Actually, if this situation arose, what I’d immediately be interested in is how they’re stopping the merchandise from decaying - while Americium lasts a fair time once produced, that isn’t really true of anything heavier. Halting radioactive decay would be a neat trick worth knowing.

A more realistic possibility perhaps derives from the speculation that there’s an “island of stability” at higher atomic number, where certain elements will have much longer half lives compared to the other transuranics. People have sometimes suggested that these might live long enough to be more than laboratory curiosities. But I don’t know if any thought has been given to what their physical and chemical properties would be, other than trying to estimate the half lives.