Precision measurements of cold neutron flux using the Alpha-Gamma device

The Alpha-Gamma device at the National Institute of Standards and Technology utilizes the interaction of neutrons with a totally absorbing ¹⁰B target to precisely measure the flux of a monochromatic neutron beam. This apparatus has been used to calibrate the ⁶Li(n,α)³H based flux monitor which the NIST neutron beam lifetime experiment BL2 used in its measurement of the most precise in-beam neutron lifetime to date. The unique geometry and measurement technique of Alpha-Gamma allows for a competitive measurement of neutron interaction cross sections, such as the uranium-235 fission cross section (n,f). A description of Alpha-Gamma design, recent improvements in the measurement of systematic effects, and further applications of this technique will be discussed.