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Re: [Phys-l] size controversy



Yes (diffusion). The spectrum tubes have a rather short useful life compared to, say Ar or N.

Sellers recommend a short duty cycle and minimal use. I think they have a short shelf life also (a few years?, an expensive test). There is some discussion as to whether the loss of usefulness is also due (wholly or in part) to out-gassing of the envelope and electrodes and, or absorption by the electrodes. Also there's incomplete thermal expansion matching of the glass metal seals.

bc thinks Van der Waals' radius may not be the "operative" radius, and hasn't yet read the kindly supplied links -- note the cc to tap-l

p.s. note the very good H2 purifier (which I used at Keele) is a hot palladium membrane.

http://www.palladiumcoins.com/hydrogen.html



On 2009, Dec 03, , at 09:26, curtis osterhoudt wrote:

Wikipedia's pages support the claim that He has a smaller radius than H (at least Van der Waals' radius):
http://en.wikipedia.org/wiki/Atomic_radii_of_the_elements_% 28data_page%29
http://en.wikipedia.org/wiki/ Atomic_radius#Empirically_measured_atomic_radii
http://en.wikipedia.org/wiki/Atomic_radius#Calculated_atomic_radii

Is the leakage you refer to an actual physical leakage (i.e. diffusion) of gas into or out of the tubes?

cut