Ionization in Pure Gases and the Average Energy to Make an Ion Pair for Alpha and Beta Particles

A series of measurements has been made of the relative currents produced in different gases by beta particles from ${\mathrm{Ni}}^{63}$ and from tritium sources in an ionization chamber. In all cases only relative current measurements with argon as a standard gas have as yet been made. The value of $W$, the average energy to make an ion-pair computed relative to argon as a standard, is found to be the same for ${\mathrm{Ni}}^{63}$ and tritium sources. If these relative $W_{\beta }$ values are plotted as abscissas against previously determined $W_{\alpha }$ values for polonium alpha particles as ordinates, a marked difference is observed in the gases investigated. For hydrogen and the noble gases the plotted points lie closely on a 45 degree straight line through the origin. Thus for these gases the ratio $\frac{W_{\alpha }}{W_{\beta }}$ is constant. This constant may well be unity, but this is not proved as yet by these results. For all other gases so far investigated, the plotted points lie above the 45 degree line, indicating a higher efficiency of ionization (and a lower $W$) for the beta particles than for the polonium alpha particles. These results are in accord with the findings of Gray and Gurney. Gurney's results have been extended here to include a greater variety of gases for reduced alpha particles of approximately 1-Mev energy. Two postulates are advanced to explain the behavior of $W_{\alpha }$ and $W_{\beta }$ here found.