Measuring neutron yield and ρ R anisotropies with activation foils at the National Ignition Facility

Summary form only given. Neutron yields at the National Ignition Facility (NIF) are measured with a suite of diagnostics, including activation of ~20-200g samples of materials undergoing a variety of energy-dependent neutron reactions. Samples of indium were mounted on the end of a Diagnostic Instrument Manipulator (DIM), 25-50 cm from the implosion, to measure 2.45 MeV D-D fusion neutron yield. The 336.2 keV gamma rays from the 4.5 hour isomer of In-115m produced by (n,n´) reactions are counted in High-Purity Germanium detectors. For capsules producing D-T fusion reactions, zirconium and copper are activated via (n,2n) reactions at various locations around the target chamber and bay, measuring the 14.1 MeV neutron yield to accuracies better than 5%. By mounting zirconium samples on ports at nine locations around the NIF chamber, anisotropies in the primary neutron emission due to asymmetries in the fuel areal density can be measured to a relative precision of 3%. Efforts are underway to deduce neutron spectral information, particularly the magnitude of T-T fusion neutron production, using multiple collocated materials with varying activation thresholds.