Measurement of the polarized 3He neutron absorption cross section

A three-body force is a force that is not present in a system of two objects but manifests in a three-body system, that is to say the two body forces are insufficient to describe the system. For neutron-rich (exotic) nuclei the stability becomes increasing critical to the three-body nuclear (3N) forces. Also calculations of the deuteron-tritium fusion reaction, intensively studied for power generation, require 3N forces. Although models for the 3N forces exist and give a rough estimate of the relative sizes and spin dependence of three- and higher-body effects compared to two-nucleon forces, more precise experimental data on systems with few nucleons is needed to determine the relative strengths of these forces. To better constrain the spin-dependent parts of the 3N force, data are required on the spin-dependent scattering of three- and four-body systems with precision at the sub-percent level. We have been working to determine the n-3He incoherent scattering cross section in experiments at FRM2 and upcoming at SNS. These values however are dependent on the polarized 3He neutron absorption cross section, σp, which has only been weakly experimentally or theoretically bound, further knowledge of this cross section in itself adds to the experimental constraints on theory of three-body forces. In order to determine σp absolutely we propose to measure the transmission of a polarized 3He cell while performing a precision NMR measurement of absolute 3He polarization.