Precision Measurements of W for Polonium Alpha Particles in Various Gases

Precision measurements of W, the average energy to make an ion pair, have been made with 210 Po alpha particles in a number of commonly used gases. These measurements agree in general with earlier measurements, but the limits of error have been greatly reduced. A particularly good measurement of $W_{\alpha}$ in argon of 26.38 ± 0.04 eV/ion pair has been obtained. If one uses this value in connection with the measured ratio of ionization in air to that in argon under similar beta-particle bombardment, one can determine a value for $W_{\beta \ \text{air}}$ if one assumes the equivalence of $W_{\beta}$ and $W_{\alpha}$ in argon. The value thus obtained of $W_{\beta \ \text{air}}$ = 33.88 ± 0.06 eV/ion pair is believed to be very close to the true value for $W_{\beta \ \text{air}}$. At any rate, it should serve as an upper limit to possible values for $W_{\beta \ \text{air}}$.