Accurate differential cross sections have been measured for the reactions $^{2}\mathrm{H}{(d,^{3}\mathrm{He})}_{n}$ at 12.305 MeV, for $^{3}\mathrm{H}{(p,^{3}\mathrm{He})}_{n}$ at 13.600 MeV, and $^{2}\mathrm{H}{(t,^{4}\mathrm{He})}_{n}$ at 20.000 MeV. The relative error for most of the data is on the order of 1% and the scale error is less than 1%. The data are used to give absolute normalizations to the measured neutron spectra from these reactions and will be useful in the analysis of mass-4 and mass-5 systems.[NUCLEAR REACTIONS $^{2}\mathrm{H}(d,^{3}\mathrm{He})$, $E=12.305$ MeV, $\ensuremath{\theta}(\mathrm{c}.\mathrm{m}.)=24\ensuremath{-}{96}^{\ensuremath{\circ}}$; $^{3}\mathrm{H}(p,^{3}\mathrm{He})$, $E=13.600$ MeV, $\ensuremath{\theta}(\mathrm{c}.\mathrm{m}.)=25\ensuremath{-}{103}^{\ensuremath{\circ}}$; $^{2}\mathrm{H}(t,^{4}\mathrm{He})$, $E=20.000$ MeV, $\ensuremath{\theta}(\mathrm{c}.\mathrm{m}.)=36\ensuremath{-}{104}^{\ensuremath{\circ}}$; $\ensuremath{\Delta}\ensuremath{\theta}=\ifmmode\pm\else\textpm\fi{}{0.03}^{\ensuremath{\circ}}$, measured differential cross sections $\ensuremath{\sigma}(\ensuremath{\theta})$; $\ensuremath{\Delta}\ensuremath{\sigma}=1%$.]