Measuring neutron yield and ρR anisotropies with activation foils at the National Ignition Facility
1 Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
2 University of New Mexico, Albuquerque, NM 87131, USA
3 Sandia National Laboratory, Albuquerque, NM 87185, USA
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Published online: 15 November 2013
Neutron yields at the National Ignition Facility (NIF) are measured with a suite of diagnostics, including activation of ∼20–200 g samples of materials undergoing a variety of energy-dependent neutron reactions. Indium samples 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 115mIn 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 MeV neutron yield to accuracies on order of 7%. By mounting zirconium samples on ports at nine locations around the NIF chamber, anisotropies in the primary neutron emission due to fuel areal density asymmetries can be measured to a relative precision of 3%.
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