Ionization of Pure Gases and Mixtures of Gases by 5-Mev Alpha Particles

In this experiment the charge produced in a large ionization chamber, by the complete stopping of ${\mathrm{Pu}}^{239}$ alpha particles, was measured using an accurately calibrated capacitor in series with a potentiometer. An electrometer connected across both the capacitor and potentiometer was used as a null indicator. From the charge produced the number of ion pairs $n$ was deduced and $W$, defined by the equation $W=\frac{E}{n}$ where $E$ is the energy used in forming the $n$ ion pairs, was computed.