Analyzing power forHe4(n→, n)He4elastic scattering at 50.4 MeV

The analyzing power $A_y\left(\theta \right)$ for elastic scattering of neutrons by ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ has been measured for eight angles in the range $80°<{\theta }_{\mathrm{lab}}<150\mathrm{}°$ at 50.4 MeV. A polarized neutron beam ($p_n=0.50\mathrm{}$) was produced through bombardment of a high-pressure deuterium target by a 50 MeV polarized deuteron beam ($p_d=0.55\mathrm{}$) and by collimation of the neutrons in the 0° direction. A liquid-helium polarimeter placed in the neutron beam was used to measure asymmetries for left and right elastic scattering, with cyclic beam polarization reversal. Multiparameter methods of data acquisition and analysis were used to discriminate against backgrounds from ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ breakup reactions and from interactions with the target-cell walls. The extracted $A_y$ values exhibit the large positive maximum at backward angles and the smaller negative minimum at more forward angles typical of $n$-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ scattering at lower energies. The $n$-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ $A_y$ values are compared with $p$-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ results at a nearby energy by means of a phase-shift analysis and are found to be in good agreement (except perhaps in the negative minimum) when Coulomb corrections to the phase shifts are taken into account.