MEASUREMENT OF THE 19F(a,n)22Na REACTION CROSS SECTION FOR NUCLEAR SAFEGUARDS SCIENCE

Year
2016
Author(s)
M.S. Smith - Oak Ridge National Laboratory
W.A. Peters - Oak Ridge National Laboratory
S.T. Pittman - Oak Ridge National Laboratory
S.J. Thompson - Idaho National Laboratory
R.R.C. Clement - Patrick Air Force Base
Abstract
Alpha particles emitted from the decay of uranium in a UF6 matrix can interact with fluorine and generate neutrons via the 19F + a –> 22Na + n reaction. These neutrons can subsequently be used to determine the uranium content in the UF6 matrix. The accuracy of this non-destructive assay (NDA) technique is limited by the large uncertainty of the reaction cross section. We have made complementary measurements of this reaction with both 4He and 19F beams to determine the cross section to an average precision of 7.6% over the alpha energy range of 3.9 – 6.7 MeV. Our new absolute cross section enables improved interpretations of NDAs of containers of arbitrary size and configuration. As an illustration of this, the new cross section changes the neutron emission rate in a 100 g spherical UF6 assembly by approximately 10-12%, and reduces the uncertainty from 51% to 14%, compared to simulations using the old cross section.