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

Abstract 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-CO 2 , n-pentane-CO 2 -CH 4 , and n-pentane-CO 2 -CF 4 were investigated. An increase of the drift velocity has been observed with mixtures containing CF 4 , 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. A simulation 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.