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15 September 2014 Measurement of reaction-in-flight neutrons using thulium activation at the National Ignition Facility
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We report on the first observation of tertiary reaction-in-flight (RIF) neutrons produced in compressed deuterium and tritium filled capsules using the National Ignition Facility at Lawrence Livermore National Laboratory, Livermore, CA. RIF neutrons are produced by third-order, out of equilibrium (“in-flight”) fusion reactions, initiated by primary fusion products. The rate of RIF reactions is dependent upon the range of the elastically scattered fuel ions and therefore a diagnostic of Coulomb physics within the plasma. At plasma temperatures of ∼5 keV, the presence of neutrons with kinetic energies greater than 15 MeV is a unique signature for RIF neutron production. The reaction 169Tm(n,3n)167Tm has a threshold of 15.0 MeV, and a unique decay scheme making it a suitable diagnostic for observing RIF neutrons. RIF neutron production is quantified by the ratio of 167Tm/168Tm observed in a 169Tm foil, where the reaction 169Tm(n,2n)168Tm samples the primary neutron fluence. Averaged over 4 implosions1–4 at the NIF, the 167Tm/168Tm ratio is measured to be 1.5 ± 0.3 x 10−5, leading to an average ratio of RIF to primary neutron ratio of 1.0 ± 0.2 x 10−4. These ratios are consistent with the predictions for charged particle stopping in a quantum degenerate plasma.
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G. P. Grim, R. Rundberg, M. M. Fowler, A. C. Hayes, G. Jungman, M. Boswell, A. Klein, J. Wilhelmy, A. Tonchev, and C. B. Yeamans "Measurement of reaction-in-flight neutrons using thulium activation at the National Ignition Facility", Proc. SPIE 9211, Target Diagnostics Physics and Engineering for Inertial Confinement Fusion III, 921108 (15 September 2014);

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