It's right there in the article: it mentions welding of aluminum foil seals - for helium.
I have also worked with high vacuum in lab exercises. There's a leak finder apparatus using helium because helium creeps through the smallest leaks - but they have to be leaks! Hydrogen just diffuses through anyway, though not quickly through thick metal (I have that from Wikipedia).
I have also worked with high vacuum in lab exercises. There's a leak finder apparatus using helium because helium creeps through the smallest leaks - but they have to be leaks! Hydrogen just diffuses through anyway, though not quickly through thick metal (I have that from Wikipedia).