Question

Has anyone heard of 'anti-helium' or SF6??

Answer 1

I have never heard of it, but was curious enough to search around.

It turns out that SF6 is ~30 times more dense than helium, and both substances are colorless gases. You may have heard of people who briefly inhale helium will speak with a higher-pitched voice than normal. Well, if SF6 is similarly inhaled, the voice will sound lower. Hence, its anti-helium nickname.

A video I found demonstrating the properties of sulfur hexafluoride: http://gprime.net/video.php/jaylenoinhalesantihelium

Answer 2

dam i thought you mean something like
a negative alpha particle from some antimatter decay