Analyzing Power of 3
He Between 1.60 and 5.54 MeV
We report the measurements of the analyzing power Ay(θ) of n-3He elastic scattering with unprecedented accuracy and angular coverage at five incident neutron energies between 1.60 and 5.54 MeV. To this end, we employed the polarization-transfer reactions 3H(p, n)3He and 2H(d, n)3He at 0° for neutron generation and a recently developed high-pressure 3He gas scintillator as an active target, enabling neutron-time-of-flight and 3He recoil-energy determinations. We obtained simultaneously the neutron polarization with a 4He-based polarimeter, capitalizing on the well-known n-4He Ay(θ). Our n-3He Ay(θ) data are compared to rigorous four-nucleon calculations using high-precision nucleon-nucleon potential models. The agreement between data and calculations is fair at the lower energies and becomes less satisfactory with increasing neutron energy. However, in comparison to the pure isotriplet p-3He system in the same energy region, the agreement between measured and calculated Ay is much better for the mixed (isotriplet and isosinglet) n-3He system, indicating large and somewhat counterintuitive isospin effects. We note that the incorporation of a Δ-mediated three-nucleon force in calculations of n-3He scattering was found to affect A y(θ) negligibly, suggesting the need for the reconsideration of fundamental interactions in resolving the four-nucleon analyzing power puzzle first established about a decade ago in p-3He scattering. © 2013 Springer-Verlag Wien.
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