jan 1, 1919 - the gaseous element neon produced two positive rays. The ions in the heavier ray had masses about two units, or 10 percent, greater than the ions in the lighter ray. To prove that the lighter neon had a mass very close to 20 and that the heavier ray was indeed neon and not a spurious signal of some kind. Comfirmed isotopes
Added to timeline:
Date:
jan 1, 1919
Now
~ 106 years ago