Ionization of Gases by Neutrons

The ionization currents produced in hydrogen, helium, nitrogen, methane, ethylene and argon by the neutrons from beryllium have been measured for gas pressures from 5 to 80 atmospheres. The relative diameters of the atomic nuclei have been calculated from the relative ionizations. Assuming that the radius of the neutron is small compared to the radii of the atomic nuclei, the relative radii of the nuclei are found to be $r_{\mathrm{H}}=1.0\mathrm{}$, $r_{\mathrm{He}}=1.4\mathrm{}$, $r_{\mathrm{N}}=1.9\mathrm{}$, $r_{\mathrm{C}}=2.8\mathrm{}$, and $r_{\mathrm{A}}=4.1\mathrm{}$. The target areas of the nuclei $a_{\mathrm{H}}=1.0\mathrm{}$, $a_{\mathrm{He}}=2.0\mathrm{}$, $a_{\mathrm{N}}=3.5\mathrm{}$, $a_{\mathrm{C}}=8.0\mathrm{}$, and $a_{\mathrm{A}}=17\mathrm{}$, vary roughly as their atomic numbers. The pressure-ionization curves for neutrons are found to differ from the $\gamma$-ray curves in the same gases.