Spin-Orbit and Target Spin Effects in Helion Elastic Scattering

The well depth of the spin-orbit term for the helion-nucleus optical-model potential was determined by performing parameter searches for elastic scattering data at successive fixed values of $V_s$. Resulting plots of $\frac{{\chi }^2}{N}$ vs $V_s$ show consistent minima for the 13 data sets used. Elastic angular distributions studied were for ${}_{}{}^{60}{}_{}{}^{}\mathrm{Ni}$ at four energies between 35 and 71 MeV and for three groups of neighboring even- and odd-mass targets at energies between 60 and 71 MeV. The $\frac{{\chi }^2}{N}$ vs $V_s$ plots for all the even-mass ($I=0\mathrm{}$) targets have minima at values of $V_s$ between 2.0 and 3.0 MeV, while the plots for all the odd-mass ($I\ne 0$) targets have minima about 1 MeV greater (3.0 to 4.0 MeV). This difference in the best-fit values of $V_s$ is consistent over a wide range of target mass and of scattering energy, and suggests the presence of a detectable target spin interaction in helion elastic scattering.