Progress on Precision Cross Section Measurements with the NIST Alpha-Gamma Device

The Alpha-Gamma device at the National Institute of Standards and Technology utilizes the interaction of neutrons with a totally absorbing $^{10}$B target to precisely measure the flux of a monochromatic neutron beam. This measurement provides a calibration of the $^{6}$Li(n,$alpha$)$^{3}$H based flux monitor used in the NIST neutron lifetime experiment to better than 0.1,\% and is also being utilized in novel, 0.2,\% level, measurements of the $^{235}$U neutron-induced fission and $^6$Li neutron capture cross sections in an effort to provide systematically independent determinations of these important quantities. Each of these measurements requires ancillary efforts to characterize, for example, device solid angles, target characteristics, and alpha counting efficiencies. The results of recent and ongoing characterization measurements will be presented.