Absolute Measurement of W for Po 210 Alpha Particles in Air, Nitrogen, and Carbon Dioxide

The average energy expended in producing an ion pair, W alpha , was measured for air, carbon dloxide, and nitrogen ln a twln-chamber system consisting of identical cyllndrical chambers. The values obtalned were 34.97 plus or minus 0.07 for air, 36.38 plus or minus 0.07 for nitrogen, and 34.04 plus or minus 0.1 for carbon dioxide. The calculations were made on the basis of Po/sup 2//sup 1//sup 0/ alpha energy of 5.3054 plus or minus 0.001 Mev and electronic charge of 1.6020 x 10/sup -//sup 1//sup 9/ coulomb. The reason for smaller values than those prevlously obtalned is probably due to improved source preparation techniques, resulting in less self-absorption, and more careful extrapolatlon techniques ln determining saturation currents. (N.W.R.)