[Straight Vermonter]

The heavier atoms have to be created artificially and are so unstable they don't last long.

Some of the transuranic elements are very unstable but other are relatively stable. Neptunium for example has a halflife of over 2 million years.

[UCANSEE2]

Neptunium is proof that if you take something radioactive and dangerous, like Uranium, and bombard it with extremely high energy, you can make something more radioactive and dangerous.