Helium 4.
in a sub zero isolated area. then when you want to use it, its all there. but if its not isolated or in a sub zero temperature zone, then it will vanish or be gone or not be there any more.
isotope
Helium 3 has been found on the moon, in the sun, and also where tritium (Hydrogen 3) is concentrated, because Tritium will decay into Helium 3.
The element was first discovered from the spectrum of the sun so it was named after the Sun Helios.