To be specific, He is a noble gas. A He molecule has an atomic mass of about 4.00 u and S has atomic mass of around 32.066 u. Also, a He molecule is smaller(.94 Angstrom ) in size compares to S ( about 2.08 Angstrom ). Our everyday air molecule ( ~ 79% Nitrogen ) is about 3X the He in size.
*** Disclaimer : I am no horological scientist