Neutron standard cross sections for 1H and 6Li from R-matrix analyses and microscopic calculations for the N-N and 7Li systems

We present work on the N-N and 7Li systems that is relevant to the international effort to re-evaluate the neutron standard cross sections. The R-matrix analysis of the N-N system also determined the n-p capture cross section for use in BBN modeling of light-element abundances in the early universe with an uncertainty of less than 2.5%. The R-matrix results for the 6Li(n,t)4He cross section agree qualitatively with a microscopic RRGM calculation that uses semi-realistic N-N potentials. However, they disagree with some cross-section measurements for the reaction, and with another evaluation. As part of the IAEA-sponsored Coordinated Research Project to improve the standard neutron cross sections, we have undertaken a study of the A = 2, 4, 7, and 11 systems, using phenomenological R-matrix fitting of experimental data, and theoretical calculations of these systems with realistic and semi-realistic nuclear forces (both two-nucleon and three-nucleon), using the Refined Resonating Group Model (RRGM). The R-matrix calculations have been performed using the Los Alamos Energy Dependent Analysis code, EDA. Results will be given here only for the R-matrix analysis of the N-N system, and for both approaches to the 7Li system. Results for the 4He system are given by HMH in another presentation at this conference, and those from the 11B R-matrix analysis were not available at the time of the conference.