Two determinations of W for electrons in dry air

Two experimental determinations of W, the average energy required to produce an ion pair in dry air, for electrons arising from 60 Co radiation, are presented. One is based on calorimetric and ionometric measurements of absorbed dose in graphite, the other on activity and exposure measurements. The values obtained by using the most recent data for the electron stopping powers are W/e=33.96+or-0.08 and 33.81+or-0.14 J C -1 , respectively. The good agreement with the W values from other authors whose methods do not involve stopping powers gives support to the new stopping-power values.