Absolute Energy to Produce an Ion Pair by Beta Particles fromS35

The absolute average energy $W_{\beta }$ necessary to form an ion pair in nitrogen, ethylene, and ethane was determined for ${\mathrm{S}}^{35}$ beta particles by the use of a sample assayed in a $4\pi$ counter. The total number of ions produced per second for each gas was determined by a measurement of total ionization in a chamber. The average energy per beta particle was calculated from the known shape of the distribution curve for ${\mathrm{S}}^{35}$. Corrected values of $W_{\beta }$ were found to be 35.3, 26.2, and 24.7 ev/ion pair for ${\mathrm{N}}_2$, ${\mathrm{C}}_2$ ${\mathrm{H}}_4$, and ${\mathrm{C}}_2$ ${\mathrm{H}}_6$, respectively. These values yield a corresponding value for air of 34.1 ev/ion pair. All these are in excellent agreement with values previously predicted from relative beta- and alpha-ray measurements in various gases.