Monte Carlo simulations of electron drift velocities in binary inert gas mixtures

Mixtures of inert and molecular gases are commonly employed in the neutron counters used for control and instrumentation in nuclear reactors. These counters are, however, often expected to have long lives under in-core irradiation conditions and this feature could be improved by the use of inert gases alone, provided a mixture with a sufficiently high electron drift velocity could be found. The present paper is concerned with a study, using Monte Carlo simulation techniques, of the electron transport properties of binary mixtures of the inert gases aimed at determining the most suitable filling for a counter. It is shown that He/Ar or He/Kr mixtures would seem to be most suitable for such a purpose.