Neutron Yields for Antiproton Microfission Experiments

Neutrons that are produced following antiproton annihilation on uranium nuclei are transported through compressed targets by the SCATTER Monte Carlo code in support of antiproton microfission experiments. The SCATTER code and necessary input data are described. Results show that the high-energy (>20 MeV) component of the source is responsible for the majority of the neutron yield. Results for a wide range of uniformly compressed targets are presented for moderation levels of hydrogen-to-uranium ratios of 0:1, 3:1, and 9:1 in ²³⁵U targets and ²³⁸U. Moderation is found to increase neutron yields at a given Uniformly compressed unmoderated ²³⁸U targets demonstrate 9 to 16% lower yields than ²³⁵U. Four targets under different, nonuniform compression conditions are considered. The average yield in these cases is ∼21.8 ± 0.2 neutrons per source antiproton, an increase of 34% over the 16.3 primary neutrons per antiproton. The average yield of the nonuniform compression cases agrees within error with uniformly compressed targets.