Outgassing of water vapour, and its significance in experiments to determine the Boltzmann constant

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Abstract
The rate of outgassing of water vapour from metal tubing and spheres is estimated and formulae given for the expected amount fraction of water added to otherwise pure gases. The relevance of these estimates to current efforts to redetermine the Boltzmann constant with relative uncertainty of measurement mu(R) (k(B)) approximate to 1 x 10(-6) is supported with experimental results using trace moisture sensors and combined acoustic and microwave resonators. The outgassing does not represent an insuperable obstacle to accurate determinations of the Boltzmann constant in any of the current experiments. However, all workers in this field need to evaluate the extent of outgassing and devise a strategy for estimating and minimizing its effect.