We have made absolute gas gain measurements for proportional counters filled with argon/xenon at various pressure up to ∼ 30 atm (3000 kPa). Our data show that of the various empirical formulae which give gas gain as a function of electric field and gas pressure, the relation proposed by Charles [J. Phys. E5 (1972) 95] gives the best fit over a wide range of pressures for both argon and xenon. The measurements further reveal that gas gain data at low pressures cannot be extrapolated to higher pressures to explain the behaviour of proportional counters filled to such high pressures, because of the changing mobility of positive ions. The details of our measurements and the results obtained are described in this paper.
