Influence of oxygen and moisture content on electron life time in helium–isobutane gas mixtures

The presented results refer to 90% helium and 10% isobutane gas mixture. Single electrons have been used to measure the attachment coefficient and drift velocity in homogeneous electric fields in the range from 100 to 1000 Vcm−1. Water vapor and oxygen concentrations varied from 350 ppm up 1.1%, and from 5 to 900 ppm, respectively.