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Fascinating - I had expected helium to be a larger molecule than hydrogen.
The given value for hydrogen is for hydrogen gas (i.e. H₂), while helium is just a single atom.
This seems like a terrible use of helium from a sustainability perspective. There are some things that helium is truly essential for, like low temperature cryogenics and neutron detection. Our supply is finite and largely tied to natural gas reserves. When helium leaks out it floats into space and is gone forever. Why does the atmosphere in the drive absolutely have to be helium? Why not any other mix of inert gases…
The amount used in these drives is minuscule, akin to a single party balloon. Given these drives are to be used for many years at a time, I'll go after them after I manage to stop all the birthday balloons.
This seems like a terrible use of helium from a sustainability perspective. There are some things that helium is truly essential for, like low temperature cryogenics and neutron detection. Our supply is finite and largely tied to natural gas reserves. When helium leaks out it floats into space and is gone forever. Why does the atmosphere in the drive absolutely have to be helium? Why not any other mix of inert gases…
my first thought was what happens when it leaks out?
Eventually it will happen and the internal drive atmosphere will be compromised to a point it doesn't work anymore. By then, it should be safe enough to open the drive in a clean Helium-filled room and reseal it.
Or just read the data, store it someplace more durable, and put the drive in a museum.
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Fascinating - I had expected helium to be a larger molecule than hydrogen.
There's a detailed explanation here: https://chemistry.stackexchange.com/questions/115363/is-a-hy... Edit: Oops. Still relevant since it's H2 in play here, but yes, not hyrdrogen vs helium.
There's a free textbook available here [1] that explains that atomic sizes decrease across the periodic table and increase down. In short, it decreases across a horizontal period because more electrons are in the same orbital shell (really a cloud), increasing the negative nuclear charge of the cloud, which is more attractive to the positive atomic nucleus, so the whole cloud is squeezed together, making the whole atom smaller.
[1]: https://chem.libretexts.org/Bookshelves/General_Chemistry/Bo...
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my first thought was what happens when it leaks out?
If the internal pressure in the device is lower than one atm, the leakage is easier to contain because it's not helium wanting to go out, but air pushing to come in. Eventually it will happen and the internal drive atmosphere will be compromised to a point it doesn't work anymore. By then, it should be safe enough to open the drive in a clean Helium-filled room and reseal it. Or just read the data, store it someplace…
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No expert, but it seems to make sense that helium is particularly hard to contain based on molecular diameter: Hydrogen 2.75 Angstroms Helium 2.18 Argon 3.67 Oxygen 3.64 Nitrogen 3.64 “Air” 3.74
Fascinating - I had expected helium to be a larger molecule than hydrogen.
Back then the explanation was that since the He nucleus has twice the positive charge as the Hydrogen one, it'd bring the electrons a bit closer. Both atoms have a single S orbital, He with two electrons.
Also, atomic Hydrogen won't remain atomic for long - it'll quickly connect to another Hydrogen so it's S orbitals share electrons.
Again, from memory of my high-school chemistry classes (30+ years ago).
This seems like a terrible use of helium from a sustainability perspective. There are some things that helium is truly essential for, like low temperature cryogenics and neutron detection. Our supply is finite and largely tied to natural gas reserves. When helium leaks out it floats into space and is gone forever. Why does the atmosphere in the drive absolutely have to be helium? Why not any other mix of inert gases…
Earlier quoted context omitted.
If the internal pressure in the device is lower than one atm, the leakage is easier to contain because it's not helium wanting to go out, but air pushing to come in. Eventually it will happen and the internal drive atmosphere will be compromised to a point it doesn't work anymore. By then, it should be safe enough to open the drive in a clean Helium-filled room and reseal it. Or just read the data, store it someplace…
So it becomes read only when helium leaks out?
Earlier quoted context omitted.
The amount used in these drives is minuscule, akin to a single party balloon. Given these drives are to be used for many years at a time, I'll go after them after I manage to stop all the birthday balloons.
Does anyone have a number on how much Helium is produced in the Earth's crust by radioactive decay?
For those interested in SETI, excessive atmospheric helium might be a detectable techno-signature, a sign that someone is digging into deep crust presumably for hydrocarbons.