Drift velocity in n-pentane mixtures and its influence on timing properties of thin gap chambers

We report on the measurements of the electron drift velocity and longitudinal diffusion in n-pentane gas mixtures and on the effect of the drift velocity on the timing properties of Thin Gap Chambers. Gas mixtures of n-pentane-CO2, n-pentane-CO2-CH4, and n-pentane-CO2-CF4 were investigated. rease of the drift velocity has been observed with mixtures containing CF4, while still maintaining the very high, saturated gain, typical for these chambers. The overall improvement of TGC timing properties is such that 99% detection efficiency can be reached within a 20 ns gate. lation of the chamber timing properties using the measured drift velocities, reproduces well the measured data and can be used to predict chamber performance as a function of geometry and gas mixture.