Reaction ${}_{}{}^3{}_{}{}^{}\mathrm{H}\mathrm{}(d,n)\mathrm{}{}_{}{}^4{}_{}{}^{}\mathrm{He}$ as a Calibrated Polarized Neutron Source and the Analyzing Power of ${}_{}{}^4{}_{}{}^{}\mathrm{He}\mathrm{}(n,n)\mathrm{}{}_{}{}^4{}_{}{}^{}\mathrm{He}$ from 20 to 30 MeV

Results are reported for the zero-degree analyzing power and longitudinal vector polarization transfer coefficient values of the reaction ${}_{}{}^3{}_{}{}^{}\mathrm{H}\mathrm{}(d,n)\mathrm{}{}_{}{}^4{}_{}{}^{}\mathrm{He}$. These data allowed a calibration of the neutron polarization to an absolute accuracy of ± 2%. The analyzing power of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ was measured using the calibrated neutron beam for $E_n$ in the range 20 to 30 MeV. The results of the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ analyzing power measurements are compared to phase-shift predictions as well as other data for ${}_{}{}^4{}_{}{}^{}\mathrm{He}\mathrm{}(n,n)\mathrm{}{}_{}{}^4{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}\mathrm{}(p,p)\mathrm{}{}_{}{}^4{}_{}{}^{}\mathrm{He}$ in the same energy region.