The use of the Associated Particle Imaging technique for high-precision nuclear data measurements with 14 MeV neutrons

We developed a high-precision technique to measure absolute cross sections for non-elastic gamma-ray production with 14 MeV neutrons by integrating HPGe detectors with good time resolution into our setup. We make use of a Deuterium-Tritium (DT) neutron generator equipped with an Associated Particle Imaging (API) system to tag individual neutrons with their associated 𝛼 particles resulting from the reaction D + T → n + 𝛼. These tagged neutrons interact with a desired sample resulting in the prompt emission of a gamma ray, mostly due to non-elastic reaction channels. The coincident detection of gamma rays and their associated 𝛼 particles result in significant background suppression in terms of both "room return" as well as delayed activation in the target. Additionally, this technique removes most uncertainties associated with neutron flux measurements without the need for activation foils or secondary detectors. Using this approach, systematic uncertainties are greatly reduced, and we project 1-sigma errors in the cross section below 5% for most isotopes. We recently achieved the integration of an array of High-Purity Germanium (HPGe) detectors with the API system and demonstrated excellent time resolution with the best performing detector achieving approximately 5 ns Full Width at Half Maximum (FWHM). We will present results from the commissioning of this setup in preparation for the Berkeley Atlas measurement campaign, which will be a database of non-elastic scattering cross sections at 14 MeV for nearly two dozen isotopes relevant to active interrogation applications on Earth and in space.