The National Physical Laboratory (NPL) has well-established facilities for radioactivity standardisations of beta emitting gases, e.g.  3H, 85Kr, and more recently 11C, by internal proportional counting.

A Monte Carlo simulation has been developed to determine the corrections for counting losses during the standardisation of 11CO2 in P-10.  It is important to validate this technique. Initially it is necessary to determine the mean energy required to generate a single ion pair (W value) in the gas P-10/CO2 mixture.

The W value of P-10 is well known, 26.0 eV, but values for the three or four part gas mixtures commonly used in the gas counting systems have not been reported.

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