The stopping-power of gases for alpha-particles of different velocities

It has long been known that the stopping-power of metal foils relative air depends on the velocity of the alpha-particles traversing the foil. It was also shown by Taylor in 1909 that the stopping-power of hydrogen (relative to air) varied all along the range. Thus the stopping-power of a substance has little meaning, unless a small portion of the range is specified to which the value refers; and if the stopping-power of a gas is measured over the whole or a large part of the range, as has usually been done, the value obtained with be merely an average value. In this paper methods are described of selecting small portions of the range; in this way the stopping-power of gases for alpha-particles of low velocity, of high velocity, and of intermediate velocity has been separately measured. The gases examined were the five monatomic gases, xenon, krypton, argon, neon and helium, and also hydrogen and oxygen.