Ionization Chamber Study of the Disintegration ofHe3andN14by Thermal Neutrons

Abstract

The total ionization produced by the reactions ${\mathrm{He}}^3\mathrm{}(n,p)\mathrm{}$ and ${\mathrm{N}}^{14}\mathrm{}(n,p)\mathrm{}$ in a gas mixture consisting mainly of argon was measured by means of a cylindrical ionization chamber operated under conditions of electron collection. High resolution was achieved by suitable choice of chamber geometry and by use of a low noise level amplifier. The total ionization charges collected from polonium alpha-particles, from the disintegration products of ${\mathrm{He}}^3\mathrm{}(n,p)\mathrm{}$ and from those of ${\mathrm{N}}^{14}\mathrm{}(n,p)\mathrm{}$ are found to be in the ratio 1:0.145±0.002:0.119±0.001, respectively. Comparison with polonium alpha-particles on the assumption of a constant average energy per ion pair in argon then yields reaction energies of 766±10 kev for ${\mathrm{He}}^3\mathrm{}(n,p)\mathrm{}$ and 630±6 kev for ${\mathrm{N}}^{14}\mathrm{}(n,p)\mathrm{}$. The difference between these energies agrees well with the difference between the end points of the beta-ray spectra of ${\mathrm{C}}^{14}$ and ${\mathrm{H}}^3$. This agreement supports the assumption of a proportionality between energy and ionization in argon independent of particle type. A value of 785±6 kev is computed for the neutron-hydrogen mass difference from these data.