Is joke of course. Was angling for the same joke.
3He is normal helium atom with an extra neutron, hoped to be used in some forms of fusion. It's not considered radioactive. Emitted by the sun it's trapped in lunar rock possibly at concentrations of up to 50 parts per billion but more likely 5-10ppb. The utility of extracting it from the Moon is hotly debated. On Earth isolating it from normal helium involves the same sort of centrifuge used to isolate isotopes of uranium, radium, hydrogen but there is far less of it than in lunar soil.
This is not actually the case in the subject at hand. It's all normal helium. When cooled enough all other gases will precipitate out as they freeze - including Hydrogen - leaving only helium as a gas and so easily isolated. That's actually why it's valuable since it's the only gas that will boil off at temperatures so low that the conductors immersed in the fluid will superconduct supporting the currents necessary for the intense electromagnets used in imaging and such. /Explaining nerd jokes since 1983