"An overview of the different common grades of helium" - https://zephyrsolutions.com/what-are-the-different-grades-of...

Grade 6 (6.0 helium = 99.9999% purity) The closest to 100% pure helium, 6.0 helium is used in the manufacturing of semiconductor chips – Grade 5.5 (5.5 helium = (99.9995% purity) Like 6.0 helium, 5.5 ultra pure helium gas is typically considered “research grade,” also used in chromatography and semiconductor processing

Grade 5 (5.0 helium = 99.999% purity) This high purity grade helium is also widely used for gas chromatography, mass spectrometry, and specific laboratory research when higher purity gases are not necessary, as well as for weather balloons and blimps.

Grade 4.8 (4.8 helium = 99.998% purity) The highest of the “industrial grade” heliums, 4.8 grade helium is often used by the military. The rest is classified...

Grade 4.7 (4.7 helium = 99.997% purity) A “Grade-A” industrial helium, 99.997% helium is mostly used in cryogenic applications and for pressurizing and purging

Grade 4.6 (4.6 helium = 99.996% purity) Grade 4.6 industrial helium is used for weather balloons, blimps, in leak detection

Grade 4.5 (4.5 helium = 99.995% purity) Often the grade most commonly referred to when people say “industrial grade,” 99.995% helium is most commonly used in the balloon industry

Grade 4 (4.0 helium and lower = 99.99% purity) Any helium that is 99.99% and down into the high 80 percents is within the range of purities referred to collectively as “balloon grade helium.”

Helium for diving is going to be a different mix than what's used for balloons. In diving it's used to reduce the partial pressure of oxygen, and also to quickly diffuse back out of tissues when returning to the surface. Very different application!

I wonder if one of you could be going by number of atoms, and the other could be going by weight?

>99.99% pure. Not good enough for MRI

What is the reason that MRI needs grade 6 vs grade 4 helium? I'm imagining that the superconducting wire is within a cryostat filled with liquid helium. Doesn't seem like there would be any appreciably partial pressure of things like nitrogen or oxygen at 4 Kelvin. I imagine the reactivity of oxygen is pretty low at 4 K as well. How much dissolved oxygen or nitrogen can liquid helium support? And how much solidifies out and sinks to the bottom of the cryostat?

Economically I expect it wouldn't be that pure, since it doesn't have to be that pure to provide lift, and party balloons are not trying to maximize lift.

Would you like to offer a rebuttal more well reasoned and thought out than "nuh-uh"?

You have the entire collected knowledge of mankind at your fingertips. You could do 30 seconds of research and find an answer better than "I don't think that sounds right".