Precision neutron flux measurements and applications using the Alpha Gamma device

The Alpha Gamma device [1] is a totally-absorbing ${}^{10}B$ neutron detector designed to measure the absolute detection efficiency of a thin-film lithium neutron monitor on a monoenergetic neutron beam. The detector has been shown to measure neutron fluence with an absolute accuracy of 0.06%. [2] This capability has been used to perform the first direct, absolute measurement of the ${}^6Li(n,t){}^4He$ cross section at sub-thermal energy, improve the neutron fluence determination in a past beam neutron lifetime measurement by a factor of five, and is being used to calibrate the neutron monitors for use in the upcoming beam neutron lifetime measurement BL2 (NIST Beam Lifetime 2) [3]. The principle of the measurement method will be presented and the applications will be discussed. Particular focus will be given to the proposed measurement of the ${}^{235}U(n,f)$ cross section for thermal neutrons. [1] D. M. Gilliam, G. L. Greene, and G. P. Lamaze, Nucl. Instrum. Methods A 284, 220 (1989) [2] A.T. Yue et al, Phys. Rev. Lett. 111, 222501 (2013) [3] http://arxiv.org/abs/1410.5311