Neutron-Deuteron Scattering and Three-Body Interactions

University dissertation from Uppsala : Acta Universitatis Upsaliensis

Abstract: High-precision differential cross section data of the neutron-deuteron elastic scattering reaction at 95 MeV are presented. The neutron-proton scattering differential cross section was also measured and used as a reference to allow an accurate absolute normalization of the neutron-deuteron data.Two multi-detector arrays were used, MEDLEY and SCANDAL, at the neutron beam facility at The Svedberg Laboratory in Uppsala. Three different configurations of the detectors allowed to perform three independent measurements. The first experiment involved detecting recoil deuterons from thin deuterated polyethylene targets with the MEDLEY setup and allowed a large angular coverage. In the second experiment, high-precision data were obtained at neutron backward angles, using the SCANDAL setup with the same technique. For the third experiment, data were obtained in the forward angular range using the SCANDAL setup with a technique where neutrons scattered on heavy water were detected by neutron-proton conversion in plastic scintillators and tracking the protons through the detectors. Events from elastic neutron-deuteron scattering were identified in the data analysis, and differential cross sections were obtained after applying corrections and evaluating systematic uncertainties due to effects which could affect the shape or the absolute normalization of the data.The results are compared with modern Faddeev calculations using realistic nucleon-nucleon potentials combined with three-nucleon interactions. The effects of three-nucleon forces are expected to increase the differential cross section by about 30% in the region of the minimum. The data agree with this prediction, thus providing evidence for three-nucleon force effects.