Measurements of the Neutron-Proton and Neutron-Carbon Total Cross Section from 150 to 800 keV
There have been very few measurements of the total cross section for np scattering below 500 keV. In order to differentiate among NN potential models, improved cross section data between 20 and 600 keV are required. We measured the np and nC total cross sections in this energy region by transmission; a collimated neutron beam was passed through CH2 and C samples and transmitted neutrons were detected by a BC-501A liquid scintillator. Cross sections were obtained with a precision of 1.1-2.0% between 150 and 800 keV using ratios of normalized neutron yields measured with and without the scattering samples in the beam. In energy regions where they overlap, the present results are consistent with existing precision measurements, and fill in a significant gap in the data between En = 150 and 500 keV.
Semilocal momentum-space regularized chiral two-nucleon potentials up to fifth order
Abstract.We introduce new semilocal two-nucleon potentials up to fifth order in the chiral expansion. We employ a simple regularization approach for the pion exchange contributions which i) maintains the long-range part of the interaction, ii) is implemented in momentum space and iii) can be straightforwardly applied to regularize many-body forces and current operators. We discuss in detail the two-nucleon contact interactions at fourth order and demonstrate that three terms out of fifteen used in previous calculations can be eliminated via suitably chosen unitary transformations. The removal of the redundant contact terms results in a drastic simplification of the fits to scattering data and leads to interactions which are much softer (i.e., more perturbative) than our recent semilocal coordinate-space regularized potentials. Using the pion-nucleon low-energy constants from matching pion-nucleon Roy-Steiner equations to chiral perturbation theory, we perform a comprehensive analysis of nucleon-nucleon scattering and the deuteron properties up to fifth chiral order and study the impact of the leading F-wave two-nucleon contact interactions which appear at sixth order. The resulting chiral potentials at fifth order lead to an outstanding description of the proton-proton and neutron-proton scattering data from the self-consistent Granada-2013 database below the pion production threshold, which is significantly better than for any other chiral potential. For the first time, the chiral potentials match in precision and even outperform the available high-precision phenomenological potentials, while the number of adjustable parameters is, at the same time, reduced by about $ \sim 40$∼40%%. Last but not least, we perform a detailed error analysis and, in particular, quantify for the first time the statistical uncertainties of the fourth- and the considered sixth-order contact interactions.
Total Neutron Yields from Light Elements under Proton and Alpha Bombardment
Total neutron production cross sections have been measured for targets of D, T, Li/sup 7/, Be/sup 9/, B/sup 11/, C/sup 13/, C/sup 14/, and F/sup 19/ under proton bombardment and of Li/sup 7/, Be/sup 9/, B/sup 10/, and Si/sup 29/ under alpha-particle bombardment. Energy ranges covered differ, but were contained between threshold and 5 Mev for protons and between threshold and 9 Mev for alphas. In several cases cross sections for the inverse reactions, (n,p) and (n, alpha ), have been computed and compared, where available, with direct measurements. (auth)