Measurement of reaction-in-flight neutrons using thulium activation at the National Ignition Facility

G. P. Grim; R. Rundberg; M. M. Fowler; A. C. Hayes; G. Jungman; M. Boswell; A. Klein; J. Wilhelmy; A. Tonchev; C. B. Yeamans

doi:10.1117/12.2066249

15 September 2014 Measurement of reaction-in-flight neutrons using thulium activation at the National Ignition Facility

G. P. Grim, R. Rundberg, M. M. Fowler, A. C. Hayes, G. Jungman, M. Boswell, A. Klein, J. Wilhelmy, A. Tonchev, C. B. Yeamans

Author Affiliations +

Proceedings Volume 9211, Target Diagnostics Physics and Engineering for Inertial Confinement Fusion III; 921108 (2014) https://doi.org/10.1117/12.2066249
Event: SPIE Optical Engineering + Applications, 2014, San Diego, California, United States

Abstract

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); https://doi.org/10.1117/12.2066249

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