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. 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 E_n=150 and 500 keV.